COMBUSTION CHARACTERISTICS OF THERMALLY STRESSED
HYDROCARBON FUELS
by
COLIN WILLIAM CURTIS
B.S., University of Colorado Colorado Springs, 2014
A thesis submitted to the Graduate Faculty of the
University of Colorado Colorado Springs
in partial fulfillment of the
requirements for the degree of
Master of Science
Department of Mechanical and Aerospace Engineering
2016
© 2016
Colin William Curtis
ALL RIGHTS RESERVED
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This thesis for Master of Science degree by Colin William Curtis has been approved for the Department of Mechanical and Aerospace Engineering by
Dr. Bret Windom, Chair
Dr. John Adams
Dr. Janel Owens
______
Date iii
Curtis, Colin William (M.S., Mechanical Engineering)
Combustion Characteristics of Thermally Stressed Hydrocarbon Fuels
Thesis directed by Assistant Professor Bret C. Windom
ABSTRACT
Liquid propelled propulsion systems, which range from rocket systems to hypersonic scramjet and ramjet engines, require active cooling in order to prevent additional payload requirements. In these systems, the liquid fuel is used as a coolant and is delivered through micro- channels that surround the combustion chambers, nozzles, as well as the exterior surfaces in order to extract heat from these affected areas. During this process, heat exchange occurs through phase change, sensible heat extraction, and endothermic reactions experienced by the liquid fuel. Previous research has demonstrated the significant modifications in fuel composition and changes to the fuel’s physical properties that can result from these endothermic reactions. As a next step, we are experimentally investigating the effect that endothermic reactions have on fundamental flame behavior for real hydrocarbon fuels that are used as rocket and jet propellants. To achieve this goal, we have developed a counter-flow flame burner to measure extinction limits of the thermally stressed fuels. The counter-flow flame system is to be coupled with a high pressure reactor, capable of subjecting the fuel to 170 atm and 873 K, effectively simulating the extreme environment that cause the liquid fuel to experience endothermic reactions. The fundamental flame properties of the reacted fuels will be compared to those of unreacted fuels, allowing us to determine the role of endothermic reactions on the combustion behavior of current hydrocarbon jet and rocket propellants. To quantify the change in transport properties and chemical kinetics of the reacting mixture, simultaneous numerical simulations of the reactor portion of the experiment coupled with a counterflow flame simulation are performed using n-heptane and n-dodecane.
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For my parents and to the memory of John B. Curtis.
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ACKNOWLEDGEMENTS
The author wishes to sincerely thank the following individuals:
Dr. Tom Bruno, for all of his help regarding the high pressure laboratory bench, words cannot express how grateful I am.
Dr. Janel Owens, for all of her help with the GC/FID and GC/MS measurements. I would also like to sincerely thank her for agreeing to be on my thesis committee.
Dr. John Adams for serving on my thesis committee when he didn’t have to.
Dr. Bret Windom for his patience and guidance for the past two years.
Brandon Patz, for his friendship and assistance throughout this study. Without your help I would have had a much more difficult time conducting this study.
Steve Burke, for being a scientific soundboard and for being there for me when the times were difficult.
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TABLE OF CONTENTS
CHAPTER
I. INTRODUCTION ...... 1
II. THEORY ...... 11
III. EXPERIMENTAL METHODS...... 25
IV. NUMERICAL METHODOLOGY ...... 40
V. RESULTS ...... 45
VI. CONCLUSION...... 86
REFERENCES …………………………………………………………………………. 89
APPENDIX A ...... 94
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LIST OF TABLES TABLE 5.1: This table contains the recorded mass and volume change of reacted n-heptane at a variety of pressures at a constant temperature of 873 K and reactor residence time of 1 minute...... 52
5.2: The recorded mass and volume change of reacted n-dodecane at a variety of reactor pressures at a constant temperature of 873 K and reactor residence time of 1 minute...... 55
5.3: The recorded mass and volume change of reacted Jet A at a variety of reactor pressures at a constant temperature of 873 K and reactor residence time of 1 minute...... 58
5.4: Experimentally measured thermal decomposition of n-heptane at 170 atm...... 60
5.5: Summarized version of the actual species predicted to form during n-heptane pyrolysis at a reactor temperature of 873 K, reactor residence time of 1 minute, and a reactor pressure of 170 atm...... 62
5.6: Normalized composition resulting from n-heptane pyrolysis at a reactor temperature of 873 K, reactor residence time of 1 minute, and a reactor pressure of 170 atm. This composition was used for all reacted n-heptane PREMIX and OPPDIF simulations...... 62
5.7: Experimentally measured liquid composition following the thermal decomposition of n-dodecane at 170 atm...... 65
5.8: Summarized version of the actual species predicted to form during n-dodecane pyrolysis at a reactor temperature of 873 K, reactor residence time of 1 minute, and a reactor pressure of 170 atm...... 67
5.9: Normalized composition resulting from n-dodecane pyrolysis at a reactor temperature of 873 K, reactor residence time of 1 minute, and a reactor pressure of 170 atm. This composition was used for all reacted n-heptane PREMIX and OPPDIF simulations...... 68
5.10: Experimentally measured composition of the liquid Jet A following the thermal decomposition at 100 atm, 873 K and 1 min residence time...... 72
A.1: GC/FID results for thermally stressed n-heptane at a reactor pressure of 10 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 96
A.2: GC/FID results for thermally stressed n-heptane at a reactor pressure of 30 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 96
A.3: GC/FID results for thermally stressed n-heptane at a reactor pressure of 50 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 96 viii
A.4: GC/FID results for thermally stressed n-heptane at a reactor pressure of 70 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 97
A.5: GC/FID results for thermally stressed n-heptane at a reactor pressure of 100 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 97
A.6: Predicted n-heptane decomposition for the reactor pressures 10 atm, 30 atm, 50 atm, 70 atm, 100 atm, and 170 atm...... 98
A.7: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 10 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 99
A.8: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 30 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 99
A.9: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 50 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 100
A.10: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 70 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 101
A.11: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 100 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 102
A.12: Predicted n-dodecane decomposition for the reactor pressures 10 atm, 30 atm, 50 atm, 70 atm, 100 atm, and 170 atm ...... 103
A.13: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 10 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 104
A.14: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 30 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 105
A.15: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 50 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 107
A.16: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 70 atm, a reactor temperature of 873 K, and a residence time of 1 minute...... 109
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LIST OF FIGURES
FIGURE
1.1: The resulting hydrocarbon family types for thermally stressed and unstressed RP-1 rocket propellant kerosene at two temperatures, 475 °C (TS-475) and 510 °C (TS- 510) [3]...... 2
2.1: Laminar flame structure for temperature of an arbitrary species within a flame [30]. ……....………………………………………………………………………...... 13
2.2: Laminar flame structure for reactant and product mass fractions of an arbitrary species within a flame [30]. ………………………………...…….………………………...13
2.3: Stationary one-dimensional flame in a tube containing a combustible gaseous mixture. ………...…………………………………………………………………………….15
2.4: General schematic of a counterflow diffusion flame created by opposing oxidizer and fuel jet streams. ……………….…………………………………………………….16
2.5: An arbitrary isotherm surface used for defining stretch [40]. ………………………18
3.1: Cross-sectional schematic of the fuel delivering counterflow burner. Note, the oxidizer delivering burner has an identical geometry. ……….………………………………27
3.2: SOLIDWORKS assembly of constructed framing apparatus……………………….27
3.4: Counterflow flame burner configuration used in liquid fuel experiments. ..……...….31
3.5: Schematic of the fuel vaporization system used for all liquid fuel experiments. …...32
3.6: High pressure laboratory bench schematic. ………………………………………….34
3.7: Cross-sectional schematic of the constructed high temperature reactor. …………….34
3.8: Schematic of the coupled high pressure reactor and counterflow flame burner. ……39
5.1: Shown above is the extinction strain of methane at 400 K plotted against the fuel mole fraction, where it is being diluted with nitrogen. ………...…………………………46
5.2: The experimentally measured extinction strain of n-heptane at 0.8 atm is compared to the predicted extinction strain rate curve. Additionally, the experimental and numerical extinction strain rate curves at 1.0 atm reported by Princeton are compared [22]. ……………………...…………………………………………………………47
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5.3: Experimentally measured extinction strain rate for unreacted n-dodecane compared to the numerically simulated extinction strain rate for unreacted n-dodecane. ………….……………………………………………………………………...……49
5.4: Experimentally measured and numerically predicted decomposition of n-heptane in liquid phase as a function of pressure at a reactor temperature of 873 K and a reactor residence time of 1 minute. ………...………………………………….……………51
5.5: Formation of 1-hexene during n-heptane pyrolysis as a function of pressure at a reactor temperature of 873 K and a reactor residence time of 1 minute. …...…….…………53
5.6: Experimentally measured and numerically predicted decomposition of n-heptane in liquid phase as a function of pressure at a reactor temperature of 873 K and a reactor residence time of 1 minute. ………...……………………………………….………54
5.7: Formation of n-heptane and 1-octene during n-dodecane pyrolysis as a function of pressure at a reactor temperature of 873 K and a reactor residence time of 1 minute. ………………………………………………………………………………………56
5.8: Experimentally measured decomposition of n-dodecane and tridecane within Jet A as a function of pressure. The reactor temperature and reactor residence time were held constant at 873 K and 1 minute. ……………………….……………………………58
5.9: Chromatogram resulting from the GC-FID analysis of the collected n-heptane liquid sample from the reactor experiments at 873 K, a 1 min residence time, and a reactor pressure of 170 atm. …………...………………….………………………………...61
5.10: Chromatogram resulting from the GC/FID analysis of the collected n-dodecane liquid sample from the reactor experiments at 873 K, a 1 min residence time, and a reactor pressure of 170 atm. ………………………………………………………………..66
5.11: Chromatogram resulting from the GC/FID analysis of neat Jet A. ……………….70
5.12: GC-FID analysis of the collected Jet A liquid sample from the reactor experiments at 873 K, a 1 min residence time, and a reactor pressure of 100 atm. ………………....71
5.13: Numerical and experimental global extinction strain rate plotted against the fuel mole fraction. ...……………………………...……………………….………………….75
5.14: Comparison between the extinction strain rates of unreacted n-heptane and reacted liquid n-heptane at a reactor pressure of 170 atm, a rector temperature of 873 K, and a reactor residence time of 1 minute. ..…...………………………………………...76
5.15: Numerical and experimental global extinction strain rate for n-dodecane plotted against the fuel mole fraction. 78 xi
5.16: Experimentally measured global extinction strain rate for Jet A plotted as a function of fuel mole fraction. ……...……………………….……………………………...80
5.17: Adiabatic flame temperature for reacted and unreacted n-heptane at a reactor pressure of 170 atm, a reactor temperature of 873 K, and a reactor residence time of 1 minute. ……….…………………………………………………………………………….82
5.18: Flame speed of unreacted and reacted n-heptane at a reactor pressure of 170 atm, a reactor temperature of 873 K, and a reactor residence time of 1 minute. …………83
5.19: Adiabatic flame temperature for reacted and unreacted n-dodecane at a reactor pressure of 170 atm, a reactor temperature of 873 K, and a reactor residence time of 1 minute….………………………………………………………………………...85
5.20: Flame speed of unreacted and reacted n-dodecane at a reactor pressure of 170 atm, a reactor temperature of 873 K, and a reactor residence time of 1 minute. ………….85
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NOMENCLATURE
SL Laminar flame speed
ρb Density of burned gas vx Flow velocity in the x direction vr Flow velocity in the radial direction
δ Flame thickness u Axial flow velocity
Ka Karlovitz number
S Flame surface
V Radial component of the flow velocity of a flame surface v Fluid velocity entering flame surface
K Flame stretch
A Infinitesimal element on flame surface or the cross sectional area of the flow
(PLUG) r Radial coordinate
Vox Velocity of the oxidizer jet stream
Vf Velocity of the oxidizer jet stream
ρox Oxidizer density
ρf Fuel density
L Distance between the fuel nozzle and oxidizer nozzle of a counterflow flame
burner ag Global flame strain rate
ρ Fluid density xiii u Axial velocity of the gas a Surface area of the internal surface of the PLUG reactor
Wk Molecular weight of species k
Kg Number of species
k Molar production rate of species k due to surface reactions
Q ̇ e Heat flux from the outer tube and the accumulation of energy in the bulk solid
(PLUG)
Qi Heat flux from either the interior tube wall or the reacting gas (PLUG) hk Specific enthalpy of species k
Mean heat capacity per unit mass of the gas
̅ a�e Surface area per unit length of the outer tube wall
P Absolute pressure within PLUG reactor
F Drag force of the interior tube surface
Φ equivalence ratio
Xf Fuel mole fraction
Yf Fuel mass fraction
CHAPTER 1 INTRODUCTION
1.1 Motivation
To prevent additional payload requirements, liquid fuels may be used to cool combustion chambers to extend material limits and increase performance prior to being combusted. These applications can range from liquid fuel propelled rocket systems to hypersonic scramjet and ramjet vehicles. In these systems, the fuel is delivered through micro-channels surrounding the combustion chambers, nozzles, and underneath exterior surfaces at high pressures to draw heat away from these affected areas [1]–[5]. Heat extraction occurs as a result of sensible and latent heat exchange and by way of endothermic reactions which occur during the fuel pyrolysis. As an example of the effectiveness that endothermic fuels have in regards to cooling, 1 kmol of decane can absorb 82 MJ/kmol of energy (combining the latent, sensible, and chemical heat extraction). In order to achieve the same cooling capability through the sensible heating of
1 kmol of air, a temperature difference of ~2800 K would be needed.
When a hydrocarbon fuel is used as a coolant, the extreme environment can have a significant impact on the fuel composition. Many have investigated the effect that endothermic reactions have on the fuel structure and subsequent fuel properties for a wide variety of propellants [3], [6]–[13]. These findings have demonstrated that when a hydrocarbon fuel is thermally stressed, the endothermic reactions cause significant changes to important thermophysical properties, most notably, the volatility, density, viscosity, and speed of sound [3], [6]–[13]. Studies have also shown that endothermic reactions significantly alter the fuel composition, decreasing the molecular weight and creating a 2 significant amount of hydrogen gas, smaller hydrocarbons, and a suite of hydrocarbons with increased an C/H ratio as indicated by Figure 1.1, which shows the resulting hydrocarbon family types for thermally stressed (reacted at two reactor temperatures, 450 and 510 °C) and unstressed of RP-1 rocket propellant kerosene [3].
Figure 1.1: The resulting hydrocarbon family types for thermally stressed and unstressed
RP-1 rocket propellant kerosene at two temperatures, 475 °C (TS-475) and 510 °C (TS-
510) [3].
The change in fuel composition/structure may have a significant impact on the heat release, flame propagation, and mass burning rates in these highly turbulent combustion systems stemming from modifications to fuel chemistry and molecular/thermal diffusivity.
To date, however, the effect of the endothermic reactions on the subsequent combustion behavior of the reacting mixture has not been experimentally examined. This study will investigate: 1) the degree of thermal decomposition that a fuel can experience when used 3 in a typical regenerative cooling system at high pressure and temperature; and 2) the impact that this thermal decomposition has on fundamental combustion properties for three hydrocarbon fuels, n-heptane, n-dodecane, and Jet A.
1.2 Background
Numerous studies have been performed that evaluate n-heptane pyrolysis [14]–[17].
In the work presented by Garner et al., the pyrolysis of both saturated and unsaturated n- heptane was evaluated via shock tube over a pressure range of 25 – 50 atm and a temperature range of 1000 – 1350 K [14]. Their studies revealed the formation of several species that include acetylene, ethane, ethene, propene, allene, propyne, 1-butene, 1- pentene, and 1-hexene due to the thermal decomposition of n-heptane [14]. Additionally, it was observed that there was no pressure dependence for the decomposition of n-heptane and formation of acetylene at the reflected shock pressures of 25 atm and 50 atm [14]. This was determined to be because the reacting species were at the high-pressure limit [14].
Another notable study conducted in regards to n-heptane pyrolysis was by Fridlyand et al., which reported oxidation and pyrolysis measurements for n-heptane at a nominal pressure of 3.95 atm over a temperature range of 900 – 1500 K [15]. When evaluating a gaseous sample of the reacted n-heptane, Fridlyand et al. observed a similar species formation to that measured by Garner. Their results indicated that n-heptane pyrolysis led to the formation of methane, ethylene, acetylene, and propylene [15]. It is important to note that the reported species formations from both Garner et al. and Fridlyand et al. are representative of the hydrocarbon species that would be burned within a hypersonic combustion chamber [15]. Fridlyand et al. also studied the ignition delay of reacted n- heptane through the use of a single pulse shock tube, where they assumed that the ignition 4
delay was positively correlated to the temperature at which CO2 is formed (above 1000 K)
[15]. It is important to note that the ignition delay measurements performed by Fridlyand et al. used n-heptane/ethylene mixtures in order to simulate the pyrolytic and oxidative decomposition of n-heptane [15]. Fridlyand et al. concluded that the thermal decomposition of hydrocarbon fuels, such as n-heptane, experienced shorter ignition delays than neat hydrocarbon fuels [15].
When compared to n-heptane, there are few experimental and numerical studies involving n-dodecane pyrolysis and combustion. n-dodecane is major component in many widely used jet fuels and rocket propellants [18]. n-Dodecane is commonly used in the formation of jet fuel surrogate mixtures and represents the normal paraffin class of hydrocarbons that are present within jet fuels, such as Jet A [19]. In the work presented by
Malewicki and Brezinsky, the oxidation and pyrolysis of n-dodecane was investigated through the use of a heated high pressure single pulse shock tube over a temperature range of 867 – 1739 K, pressures ranging from 19 – 74 atm, reaction times that ranged from 1.15
– 3.47 ms, and equivalence ratios from 0.46 to 2.05, and ∞ (i.e. 100% fuel to study the pyrolysis) [19]. Similar to the n-heptane pyrolysis and oxidation study performed by
Garner et al., the decomposition of n-dodecane and formation of intermediary species demonstrated no pressure dependence from 25 – 50 atm [19]. It was determined, however, that the rate of fuel decomposition for n-dodecane begins to increase within 1030 – 1050
K [19]. The composition of the thermally stressed fuel resulting from pyrolysis and oxidation was measured using gas chromatography flame ionization detection (GC/FID) and gas chromatography mass spectrometry (GC/MS). Some of the major hydrocarbon species formed from the endothermic reactions were, ethylene, methane, propylene, 1, 3- 5 butadiene, ethane, 1-butene, acetylene, 1-hexene, and 1-pentene [19]. A recent study conducted by Banerjee et al. experimentally and numerically investigated the pyrolysis, as well as oxidation, of n-dodecane for a temperature range of 1000 – 1300 K over a span of
1 – 40 ms residence time at atmospheric pressure (1 atm) [20]. In their study, 63% of n- dodecane decomposed within 40 ms and the largest intermediate species were ethylene, propene, methane, and 1-butene [20]. These species resulting from the thermal decomposition of n-dodecane are consistent with those reported by Malewicki and
Brezinsky [19].
Jet A is a kerosene based aviation fuel used by commercial airports in North America and is a complex mixture that contains hundreds of hydrocarbon species that vary in concentrations [21]. Many studies have been performed that investigated the thermal decomposition of kerosene based fuels but few have evaluated the decomposition of Jet A specifically [1], [2], [7]. In the work presented by Widegren and Bruno, the thermal decomposition of Jet A was evaluated using an ampule reactor at a reactor pressure of
340.49 atm, reactor temperatures ranging from 648 K to 724 K, and reactor residence times that were varied between 30 minutes to less than 1 minute [1]. The liquid phase and vapor phase of the reacting fuel was separated and collected. Using GC/FID and GC/MS, the compositions of the collected samples were analyzed [1]. The largest percent area of species measured in the liquid phase were, n-dodecane, n-tridecane, n-undecane, n- tetradecane, n-pentadecane, n-decane, and 1-ethyl-2,3-dimethyl benzene [1]. For the vapor phase samples, some of the primary species detected of the thermally stressed samples were butane, pentane, propane, 2-methylpropane, 2-methylbutane, ethane, and hexane [1]. 6
Numerous studies have documented the combustion behaviors of large hydrocarbon fuels [22]-[30]. Work presented by Won et al. investigated the thermal and mass transport effects resulting from chemical kinetics that lead to the extinction of diffusion flames for larger hydrocarbon fuels [22]. One of the fuels studied by Won et al. was n-heptane. In their body of work, Won et al. performed a scaling analysis that led to the conclusion that the extinction limits of diffusion flames are proportional to the enthalpy of combustion and binary diffusion coefficient of hydrocarbon fuels [22]. In the same study, it was also determined that the binary diffusion coefficient was inversely proportional to the square root of the fuels’ molecular weight [22].
Laminar flame speeds and extinction limits of n-dodecane have been the focus of several studies [23], [24]. The laminar flame speed and extinction limits of n- dodecane/O2/N2 mixtures were experimentally measured and numerically predicted by
Kumar and Sung [23]. It was determined that the chemical kinetic mechanism used to predict the flame speed and extinction strain rate for n-dodecane, the Utah Surrogate
Mechanism Version 3 beta [25], overpredicted the experimentally measured data [23].
Holley et al. also analyzed the flame speed and extinction limits of n-dodecane [26]. In their presented work, it was determined that the flame speed and the extinction strain rates of large premixed hydrocarbon fuels were insensitive to the diffusivity of the fuel [26]. For large non-premixed fuels, however, the extinction strain rates were highly sensitive to the fuel diffusivity, which led to the conclusion that larger fuel diffusivities cause flames to be more resistant to extinction [26].
Lastly, the extinction strain rates and laminar flames speeds for Jet A have also been studied [23], [27]–[29]. In the study perfumed by Dooley et al., the extinction strain rate 7 and ignition delay time for Jet A was compared to a surrogate mixture composed of n- decane, iso-octane, and toluene [29]. It is important to note that these three hydrocarbons were chosen in order to represent the hydrogen/carbon ratio of Jet A. A counterflow flame burner was used to measure the extinction strain rate of both the surrogate and commercial
Jet A [29]. A counterflow flame burner consists of two opposing Bunsen burners that can be operated in a premixed mode or more commonly in a non-premixed mode where one burner supplies the fuel stream and the other an oxidizer stream. A counterflow flame burner creates a flat circular flame that can be approximated as one-dimensional and allows for measurements, such as flame extinction limits, to be measured [30]. The formulated surrogate mixture was determined to be in good agreement with the measured extinction strain rate for Jet A for a fuel stream temperature of 500 ± 5 K and a oxidizer flow temperature of 298 ± 5 K [29]. Additionally, ignition delay measurements over a temperature range of 500-1000 K at a pressure of 12.5 atm for the composed surrogate was in good agreement with that of Jet A [29]. Dooley et al. ultimately concluded that their composed jet fuel surrogate was an accurate representation of Jet A in practical combustion systems [29]. Other studies that have also investigated combustion properties such as, extinction strain rate, ignition delay times, and laminar flame speeds, include Holley et al.,
Law et al. and Kumar et al. [23], [27]. Additional studies have also investigated how accurate formulated surrogates were at representing the combustion behavior of neat Jet A
[23], [27], [31]. Clearly, there is a number of works related to the development of jet fuel surrogates, but none of the work to date has included a fuel’s ability to match combustion properties after the fuel has been used in a endothermic cooling system.
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1.3 Research Goals
To elucidate the combustion behavior of thermally stressed large hydrocarbon fuels, the present study will investigate the thermal decomposition and flame behavior of n- heptane, n-dodecane, and Jet A. This will be achieved through the use of a high pressure laboratory bench to induce thermal decomposition of n-heptane, n-dodecane, and Jet A. A counterflow flame burner will be used to evaluate and compare the extinction strain rates of neat and thermally stressed fuels. The objectives of this study include:
1. Construction and validation of a transportable counterflow flame burner that
will be used to measure the extinction strain of liquid and gaseous fuels.
2. High pressure reactor characterization for n-heptane, n-dodecane, and Jet A.
The thermal decomposition of these hydrocarbons will be evaluated for the
following pressures: 10 atm, 30 atm, 50 atm, 70 atm, 100 atm, and 170 atm.
The reactor temperature and reactor residence time for each pressure evaluated
will be held constant at 873 K and 1 minute. A reactor pressure of 170 atm and
a reactor temperature of 873 K will provide the best representation of a
hypersonic or rocket active cooling system [3]. The reacted fuels will be
collected in the liquid phase and the species resulting from endothermic
reactions will be determined through the use of GC/FID and GC/MS.
3. Numerical simulations using the plug flow simulator, PLUG, available within
the CHEMKIN® will be used to predict the thermal decomposition of n-
heptane and n-dodecane for the same pressures evaluated experimentally. The
resulting predicted species compositions will then be compared to the 9
experimental data and will then be used as fuel input compositions for laminar
flame speed and counterflow flame simulations.
4. The resulting reacted fuel compositions for n-heptane and n-dodecane will be
used as inputs within the counterflow flame simulator, OPPDIF, available
within CHEMKIN®. The extinction strain rates of the reacted fuels will then
be predicted and compared to the predicted extinction strain rates for neat n-
heptane and n-dodecane.
5. The developed counterflow flame burner will be used to investigate the
extinction strain rates of neat n-heptane, n-dodecane, and Jet A.
6. To experimentally measure the extinction strain rate of reacted n-heptane, n-
dodecane, and Jet A, the counterflow flame burner will be coupled directly to
the high pressure reactor. The extinction strain rates of the reacted fuels will be
measured using the GC/FID and GC/MS results to determine the molecular
weight and density of the reacted fuels.
7. The extinction strain rates of reacted and unreacted n-heptane, n-dodecane, and
Jet A will be compared to the extinction strain rates of their neat compositions.
The experimental data for n-heptane and n-dodecane will then be compared to
the predicted reacted and unreacted extinction strain rates of n-heptane and n-
dodecane.
8. The laminar flame speeds of neat and thermally stressed n-heptane and n-
dodecane will be predicted using the PREMIX program within CHEMKIN®.
In order to provide insight into how fuel lean and fuel rich flames are affected
by the decomposition of neat species, the flame speeds will be evaluated for 10
equivalence ratios from 0.4 – 1.6. The predicted flame speeds for both reacted
n-heptane and n-dodecane will be investigated using the predicted thermally
stressed compositions at a reactor pressure of 170 atm and a residence time of
1 minute.
9. The adiabatic flame temperatures of thermally stressed n-heptane and n-
dodecane will also be investigated using the predicted reacted fuel compositions
at a reactor pressure of 170 atm and a reactor residence time of 1 minute. The
adiabatic flame temperatures will be predicted using the PREMIX program
within CHEMKIN®.
CHAPTER 2
THEORY
This chapter describes the fundamental concepts that are used throughout the duration of this study. Laminar flames, laminar flame speeds, flame stretch, and flame extinction are discussed in detail. This study measures the global extinction strain rate of neat and thermally stressed hydrocarbon fuels. Subsequently, the fundamental theory behind counterflow flames and various derivations of the global strain rate equation are elaborated on. Lastly, the numerical programs used to predict the laminar flame speed
(PREMIX), thermal decomposition through a plug flow reactor (PLUG), and counterflow flames (OPPDIF) are also described.
2.1 Laminar Flames
A flame is a self-sustaining propagation of a localized combustion zone that is at subsonic velocities. For the flame to be localized it must occupy only a small portion of the combustible mixture at any point in time, otherwise the flame will no longer be able to be sustained and will extinguish [30]. A laminar flame exists as a thin region where there are large gradients in species concentrations and temperature [32]. A flame can be divided into two regions, the preheat zone and the reaction zone. In the preheat zone, little heat is released and the unburned gases nearing the flame front are heated by the reaction zone.
The reaction zone is the primary region where chemical energy is released. Figure 2.1 and
Figure 2.2 provide graphical representations of how flame temperature and species concentrations behave within the preheat zone and reaction zone. As shown in Figure 2.1, the flame temperature is lower in value in the preheat zone and reaches larger temperatures in the reaction zone [30]. Figure 2.2 shows the reactant species mass fraction (Yr) and 12
product species mass fraction (Yp) profiles across both the preheat zone and reaction zone of a laminar flame. The formation of product species and consequently the destruction of reactant species begins within the preheat zone. This trend continues into the reaction zone until 100% of all reactant species react to form all product species [30]. It is important to note that the reaction zone can be further dived into more regions, a thin region where fast chemistry occurs (i.e. fast chemistry region), and a wider region where slow chemistry occurs (i.e. post-flame region). The fast chemistry region is dominated by bimolecular reactions where the destruction of fuel molecules and the creation of new intermediate species occurs [30]. A biomolecular reaction occurs when two molecules collide and react to form two different molecules [30]. An example of a biomolecular reaction is the combustion of hydrogen and oxygen is shown below.
(2.1)
When at atmospheric pressure, Hthe + fast O chemistry → OH + Oregion is usually less than 1 mm. In the post flame region, the chemistry consists mainly of radical recombination reactions, which are significantly slower than radical generation or chain branching reactions [30].
Subsequently, this region can extend several millimeters for a flame at atmospheric pressure. Note that a recombination reaction, often a termolecure reaction, correspond to the reverse of a unimolecular reaction (reaction where a single species is rearranged) [30].
An example of a termolecure reaction is shown in Eq. 2.2, where hydrogen, oxygen, and an arbitrary species, M, react to form a hydroperoxyl radical. This reaction is very important at high pressures and is considered a chain terminating reaction as the hydroperoxyl radical is much less reactive than the H radical.
(2.2)
H + O + M ↔ HO + M 13
Figure 2.1: Laminar flame structure for temperature of an arbitrary species within a flame
[30].
Figure 2.2: Laminar flame structure for reactant and product mass fractions of an arbitrary species within a flame [30].
14
2.1.2 Laminar flame speed
Laminar flame speed, SL, is defined as the velocity that unburned gases move through a stationary flame in the direction normal to the flame surface (i.e. flame front)
[33]. It is important to note that the laminar flame speed is also referred to as the laminar burning velocity, flame velocity, or normal combustion velocity. Figure 2.3 depicts a stationary one-dimensional flame in a tube containing a combustible gaseous mixture. The unburned reactants enter the flame in a direction normal to the flame sheet at a velocity equal to the flame propagation velocity, SL [30]. The burned gas velocity is greater than the unburned gas since the flame heats the reactants thus causing the density of the products to be less than that of the recants (i.e. the velocity of the burned gas is increased in order to conserve mass). The laminar flame speed can be expressed in Eq. 2.3, where the density of the burned gas is represented as, ρb, the velocity of the burned gas is expressed as, b, and the density of the unburned gas is, ρu [30].
(2.3) � = ��
Figure 2.3: Stationary one-dimensional flame in a tube containing a combustible gaseous mixture. 15
2.3 Counterflow Flames
A counterflow flame burner consists of two opposing concentric Bunsen burners, where one burner supplies a jet of fuel and the other supplies a jet of an oxidizer, as demonstrated in Figure 2.4. Details of the experimental setup used in this study will be provided in Chapter 3. The opposing jets create a planar counterflow diffusion flame between the two potential flows. The resulting diffusion flame can be approximated as one- dimensional (x-direction dependent) along the center-line which in turn greatly simplifies the complexities of both experiments and calculations [30]. Because of their simplicity, counterflow flames are an important experimental benchmarks when developing chemical kinetic mechanisms [34]–[37]. In the development of chemical mechanisms, experimental data which are often used as validation metrics include, temperature profiles, species profiles, flame speeds, and flame extinction strain rates [34]–[37]. Laminar counterflow flames also serve as a fundamental element in the complex non-premixed turbulent flames, where the flame structure can be composed by a distribution of laminar diffusion flames
[30], [38]. 16
Figure 2.4: General schematic of a counterflow diffusion flame created by opposing oxidizer and fuel jet streams.
The two opposing jets of fuel and oxidizer create a stagnation plane where the velocity in the x direction, vx, is equal to zero. The location of the resulting stagnation plane is dependent of the momentum of both the oxidizer and fuel jet. If the momentum of both jets are equal, the stagnation plane would be positioned at the midpoint between the two burners. However, if the momentum of one of the supplying streams is larger than the other, the stagnation plane will be closer to the opposing stream outlet. The location of the diffusion flame is dependent on the position where the mixture is nominally stoichiometric
[30]. If the reactant mixture requires more oxidizer than fuel to be stoichiometric, then the flame will be established closer to the nozzle which is supplying the fuel. The opposite occurs when the fuel mixture requires more fuel to be stoichiometric.
2.3.1 Flame stretch
The concept of flame stretch was first introduced by Karlovitz in 1953 to describe flame extinction under the influence of velocity gradients [39], [40]. His work resulted in 17 the Karlovitz number, which is defined as the ratio of the convective timescale to the chemical timescale and is expressed in Eq. 2.4, where δ represents the flame thickness and u is the axial flow velocity [38].
(2.4) � = � Karlovitz’s definition of flame stretch was used�� by Lewis and von Elbe to quantify and explain the phenomenon of flame stabilization for one-dimensional flames as seen in a CF burner [40].
A generalized definition of flame stretch was developed by Forman Williams and is displayed as Eq. 2.5 [40], [41]. Figure 2.5 depicts an arbitrary surface and has been included to assist in describing flame stretch [40], [41]. When defining flame stretch, it is important to first define an arbitrary surface (isotherm), S, which has a velocity V and where the fluid has a velocity v [40], [41]. The general definition of stretch, K, of an infinitesimal element, A, on S is given by its Lagrangian time derivative of the area [39], [40].
Alternatively, stretch can be defined as the rate of change of any differential surface element that is scaled by its value [40]. It is important to note that the boundary of the surface element A is assumed to move tangentially to the fluid velocity [39], [40]. It is important to note that the units for K are inverse seconds, s-1. This allows for K to be viewed as time scale associated with rate of area reduction or increase [40].
2.5 �� = � � 18
Figure 2.5: An arbitrary isotherm surface used for defining stretch [40].
Williams expression for flame stretch Eq. 2.5 can be reduced for a planar flame in stagnation as shown in Eq. 2.6 where V represents the radial component of the flow velocity and r is the radial coordinate [32].
2.6 � = 2.3.2 Flame Extinction �
There are two factors that can lead to extinction of a laminar counterflow flame.
The first cause for extinction is if the rate of thermal diffusion from the flame exceeds the rate of heat generation [32]. The second possible reason for extinction occurs when the chemical reaction timescales required to sustain combustion exceeds the available reaction time [32]. For counterflow flames, an increase in flame stretch will reduce the available reaction time and can result in an increase in the amount of heat loss from the flame front 19
[32]. Both effects can cause the flame to extinguish. Knowing the extinction limits of fuels is important in both aviation (e.g. hypersonic engines) and commercial settings (e.g. gas turbines) when sustaining a flame is of the utmost importance.
There are two expressions that correspond to different assumptions regarding the flow geometry of the oxidizer and fuel streams that can be used to calculate the extinction strain rate of a counterflow flame. It is important to note that the strain rate of a flame is another way of discussing the stretch of a flame. Both expressions neglect the effects of chemistry and temperature gradients and are therefore referred to as, “global strains” [42].
A parabolic flow geometry will result if the counterflow burner consists of jets that are formed by long straight tubes [42]. For this case, the jet streams are modeled using a potential flow solution as the boundary condition [42]. The resulting global strain rate equation for the parabolic flow field is shown in Eq. 2.7 [42], [43].
2.7 � �� � = + The second flow geometry is a plug flow (which � is� radially � uniform across the nozzle exit) and results from solving the potential flow solution for a plug flow geometry [41]. The expression for the global strain rate for a plug flow design is provided in Eq. 2.8 [42], [43].
2.8 � � � = + � � � -1 Within both of these expressions, Eq. 2.7 and Eq. 2.8, ag is the global strain rate (s ), Vox is the velocity of the oxidizer jet stream, Vf is the velocity of the fuel jet stream, ρox represents the density of the oxidizer, ρf is the density of the fuel, and L represents the distance between the two nozzles [42], [43]. It is important to note that the global strain 20 rate is essentially the amount stretch (strain) that the flame experiences just before extinction. A lager ag value indicates that the flame is more resilient to experiencing extinction than if a lower ag value was recorded for a given fuel. The presented study will use the global strain rate equation for plug flow, Eq. 2.8, due to the design of the counterflow flame burner which supplies a uniform plug flow. The constructed counterflow flame burner will be thoroughly discussed in Chapter 3.
2.4.1 PREMIX Program
The PREMIX program is able to predict the flame speeds, temperature profiles, and species profiles for two laminar premixed flame configurations. The present study will use the PREMIX program to predict the laminar flame speed and adiabatic flame temperature of both neat and thermally stressed n-heptane and n-dodecane. The first configuration that
PREMIX is able to evaluate is the burner-stabilized flame with a known mass flow rate.
When solving this configuration, the conservation and species transport equations are solved. The second flame configuration is the freely propagating flame. For this case there are no heat losses and thus the temperature profile is determined through the energy equation. In order to solve either of these cases, a Gas-Phase Kinetics pre-processor, reads user-supplied data regarding the species and chemical reactions for a particular reaction mechanism where it is then able to extract more information from a thermodynamic property data base. The resulting calculations are saved and are used as a linking file for both the Transport Pre-Processor, and the PREMIX program. The pre-processor determines polynomial representations of the temperature dependent parts of the individual species viscosities, thermal conductivities, and the binary diffusion coefficients of the mixture. Again, the results are saved and used as a linking file for the PREMIX program. 21
PREMIX uses these files to initialize the species- and reaction-specific information that allows for a particular flame and other parameters to be defined.
When solving for temperature and species distribution, PREMIX employs equations that govern steady, isobaric, quasi-one-dimensional flame propagation. These equations are, the continuity equation, conservation of energy, species concentration, and equation of state. It is important to note that it is assumed that each proceeds according to the law of mass action and that the forward rate coefficients used by PREMIX are in the modified Arrhenius form. The numerical solution first makes finite difference approximations in order to reduce the boundary value problem to a system of algebraic equations. A very coarse mesh is used for the initial approximation. After obtaining a solution for the coarse mesh, new mesh points are added in regions where the solution or its gradients change rapidly. The mesh continues to become finer until the solution converges to a predetermined degree of tolerance. After discretizing the governing conservation equations, the resulting system of nonlinear algebraic equations is solved through the damped modified Newton algorithm.
2.4.2 OPPDIF Program
The OPPDIF program within CHEMKIN computes a numerical model of a planar diffusion flame between two opposing nozzles, where one nozzle supplies a fuel stream and the other an oxidizer stream. The two- or three-dimensional flow field is reduced to a one-dimensional problem through a similarity transformation. The similarity transformation employed assumes that the radial velocity of the flow field varies linearly in the radial direction [44], [45]. The resulting fluid property functions are solely dependent on the axial distance. Neglecting edge effects, the resulting one-dimensional model 22 predicts the temperature, species, and velocity profiles within the flow between the two nozzles. When performing OPPDIF extinction strain rate calculations, the fuel stream and oxidizer stream velocities are predetermined through a momentum balance and are increased proportionally (to maintain equal momentum) until flame extinction occurs.
Once extinction has been achieved, the resulting fuel and oxidizer velocities are applied to the global extinction strain rate equation (Eq. 2.8).
The OPPDIF program follows the same time-dependent and steady state methods as the PREMIX program to solve the continuity equation, perpendicular momentum equation, and the energy and species conservation [32]. It is important to note that since the radial velocity varies linearly in the radial direction, plug flow boundary conditions at the nozzle exits were assumed [32]. Similar to the PREMIX program, OPPDIF uses Gas-
Phase Kinetics and Transport libraries to determine the chemical reaction rates, thermodynamic properties, and transport properties.
2.4.3 PLUG Program
PLUG is a program within the CHEMKIN package that numerically models an ideal, steady state, non-dispersive, plug-flow chemical reactor. An ideal plug-flow reactor assumes that there is no mixing in the axial (flow) direction but has perfect mixing in the transverse direction(s). This allows for the achievable reactant conversion to be maximized
[46]. Furthermore, since there is no mixing in the axial direction and there are no transverse gradients, this in turn results in no diffusive mass-transfer limitations. Ultimately the PLUG program will be used to predict the decomposition of n-heptane and n-dodecane for a range of pressures. The resulting compositions for thermally stressed n-heptane and n-dodecane will be used as inputs into the PREMIX and OPPDIF simulations. This will provide a 23 means to numerically investigate the effect of thermally stressing a fuel on the combustion properties such as flame speed, adiabatic flame temperature, and compare to experimental data. The numerical methodology will be discussed in greater detail in Chapter 4.
The PLUG program is modeled using first-order ordinary differential equations and requires no chemical transport properties (e.g. mass or thermal diffusivities). The governing differential equations for the plug-flow reactor are simplified variations of the conservation of mass (Eq. 2.9), energy (Eq. 2.10), and momentum (Eq. 2.11), which are displayed below. The presented expression for the conservation of mass states that the mass flow rate of the gas can change as a result of the generation or consumption by surface reactions. In this expression ρ represents the density, u is the axial velocity of the gas, A is the cross sectional area of the flow, ai is the surface area of the internal surface of the reactor, Wk is the molecular weight of species k, Kg is the number of species, and k represents the molar production rate of species k due to surface reactions. It is important ̇to note that this study neglected surface reactions for all PLUG simulations and thus the righthand side of the equation was equal to zero.
� (2.9) �� � �� � + �� + � = �� ∑ ̇� � �� �� �� �=
The expression for the conservation of energy states that the total energy of the flowing gas changes due to the heat flux Qe from the outer tube and the accumulation of energy in the bulk solid. Within this expression, Qi represents the heat flux from either the interior tube wall or the reacting gas, hk is the specific enthalpy of species k, is the mean heat
� ̅ 24
capacity per unit mass of the gas, and ae represents the surface area per unit length of the outer tube wall.
� �ℎ � � � � ∑ ℎ� + � ̅ + ⋯ �= �� �� �� (2.10) � � � + ∑ ℎ��� + �� ∑ ̇� � = � − � �� ∑ ̇� �ℎ� �= �= �=
The momentum equation represents the balance between the pressure forces, inertia, viscous drag, and the momentum caused by surface reactions. In this expression, P represents the absolute pressure and F is the drag force of the interior tube surface.
� (2.11) � � �� � + � � + + �� ∑ ̇� � = �� �� �� �=
These one-dimensional governing differential equations and species’ bimolecular reaction equations are solved using the implicit numerical software DASSL. DASSL provides a numerical solution to implicit systems of differential/algebraic equations [46]. Similar to the programs, OPPDIF and PREMIX, the PLUG application implements surface kinetics and gas-phase kinetics pre-processors to obtain kinetic and thermodynamic transport parameters from thermodynamic and chemical kinetic databases.
CHAPTER 3
EXPERIMENTAL METHODS
The experimental methodology section describes the various apparatus and experimental techniques employed in this study. The functionality and experimental parameters of both the counterflow flame burner and high pressure reactor systems are described in great detail. Furthermore, the experimental techniques for flame extinction measurements (global strain rate) and thermal decomposition are discussed. Lastly, the methodology of measuring the global strain rate of thermally stressed fuels by coupling the reactor and counterflow burner together is described.
3.1 Experimental Apparatus
3.1.1 Counterflow burner
A counterflow burner was constructed to perform experimental extinction strain rate calculations. The cross-sectional schematic of a single burner is shown in Figure 3.1.
It is important to note that the oxidizer and fuel burners are identical. The counterflow flame burner was constructed out of three separate pieces of aluminum and consists of six sections. At the bottom of the burner there are two inlets for either a heated fuel/nitrogen flow or an oxidizer. The fuel mixture or oxidizer then enters the main flow channel which is 30 mm in diameter and 85 mm in length. The temperature of the gas is then measured by a type K thermocouple. Details of the heating system are discussed later for each individual experiment. A steel mesh screen was used as a flow straightener and was placed between the burner base and the converging nozzle section 30 mm upstream of the nozzle exits thus ensuring uniform velocity profiles. Two Teflon O-rings were used with one being placed between burner base and nozzle, and the other between nozzle and top section of 26 the burner. The top section of the burner consisted of four inlets for the heated nitrogen co- flow that surrounds the main flow from the burner nozzle. The heated nitrogen co-flow limits the severity of flow shear and creates an inert curtain around the counterflow flame which shields the flame from the environment. The diameter of the nozzle exit is 10 mm and the diameter of the co-flow outlet is 14 mm.
In addition to the construction of the counterflow burners, a framing system was developed that would allow for the burners to be mounted in opposing directions. The framing system constructed needed to be able move horizontally and vertically in order properly align the burners as well as to investigate various separation distances between the two burners. Figure 3.2 shows a SOLIDWORKS assembly of the constructed framing apparatus. The downward facing burner supplies the fuel/nitrogen mixture and the upwards facing burner supplies the oxidizer jet. The framing system was constructed using aluminum t-slotted rails and two ¼” thick aluminum plates. The developed rectangular frame has a height of 18” and a width/length of 12”. The burners were mounted to the aluminum plates which were in turn mounted to t-slotted frames via bolts and brackets.
The upward facing burner is only able to move in the horizontal direction and the downward facing burner is able to move both vertically and horizontally. To achieve various separation distances between the two burners, sheets of acrylic were measured and placed between both nozzles. The downward facing burner was moved vertically until both nozzles were pressing against the acrylic sheets. It is important to note that a level was used to ensure that the aluminum plates were not slanted. In order to ensure that the burners were concentric, a counterflow flame was generated using methane and air as the oxidizer where the burners were continually adjusted horizontally until a stable flat stagnate flame 27 was achieved. A separation distance of 9 mm was determined to provide consistent results and was used for all measurements.
Figure 3.1: Cross-sectional schematic of the fuel delivering counterflow burner. Note the oxidizer delivering burner has an identical geometry.
Figure 3.2: SOLIDWORKS assembly of constructed framing apparatus. 28
3.1.2 Counterflow burner – Gaseous flow
Before conducting experiments using liquid fuels, it was important that the counterflow flame burner be tested and validated against numerical models and previous experimental data. To achieve this, methane (CH4) was chosen due to its gaseous state at room temperature and the amount of previous research that has been carried out for methane in a counterflow flame configurations and kinetic model development [36], [42],
[47]. Figure 3.3 depicts the counterflow burner configuration used for gaseous fuels.
OMEGA® T-Type inline heaters were used to heat the nitrogen and methane flows of the downward facing burner. A TEMPCO® Duraband model MBH01003 band heater was used to heat the downward facing burner to minimize heat loss. Lastly, the nitrogen co- flow of the downward facing burner was heated using electrical heating tape. The temperatures of electric heaters were monitored by K-type thermocouples and were controlled through a proportional-integral-derivative (PID) controller so that the temperature of gaseous mixture exiting the downward facing nozzle (fuel flow) was maintained at 400 ± 5 K. A fuel temperature of 400 K was chosen to match previous experiments to allow for a comparison. The oxidizer stream (air) and the N2 co-flow of the upward facing nozzle were not heated and remained at 298 K. The inline heaters for the methane and nitrogen flow as well as the band heater on the downward facing burner were maintained at 403.15 ± 5 K in order to ensure the desired exit temperature of the methane/nitrogen mixture was kept at 400 ± 5 K.
The volumetric flow rates for all gaseous flows was controlled by using sonic nozzles. Sonic nozzles choke the flow of the gaseous fluid which allows for the mass flow rate to be adjusted by changing the upstream pressure of the flow. Digital pressure gauges 29 were used to monitor the pressure of all gaseous fluids for all experiments conducted. All sonic nozzles were obtained from O’Keefe Controls CO®. The orifice diameter of the sonic nozzles ranged from 0.0039” to 0.02”. A SUPELCO® bubble meter, model 20428-U, was used to calibrate the volumetric flow rate of each sonic nozzle versus an upstream pressure set point.
Figure 3.3 Counterflow flame burner configuration for gaseous fuels.
3.1.3 Counterflow burner – Liquid fuels
Figure 3.4 shows the schematic for the counterflow flame burner configuration when liquid fuels are tested. The downward facing nozzle delivers a heated fuel/N2 stream, where the fuel is delivered and controlled by a syringe pump into an atomizer (discussed in detail below) where it interacts with high temperature low flow rate N2 stream and is 30 then vaporized within a heated sampling cylinder. The liquid fuels evaluated in this study include, n-heptane, n-dodecane, and Jet A. The vaporized fuel/N2 mixture is then introduced into a cross flow of heated N2 and carried out of the nozzle exit and into the flame. The upward facing nozzle supplies the oxidizer flow (i.e. air). Both reactant streams were heated and protected from the environment with a heated N2 jacketing co-flow.
Electrical heating tape was used for both atomizer and N2 co-flow, OMEGA® T-Type inline heaters, model APH-3741, were used to heat the N2 entering the atomizer as well as the adjacent inlet at the base of the burner, and a TEMPCO® Duraband model MBH01003 band heater was attached to the downward facing burner to reduce the heat loss from the chamber and to avoid fuel condensation prior to delivery into the flame. The temperatures of electric heaters were monitored by K-type thermocouples and were PID controlled so that the temperature of gaseous mixture exiting the downward facing nozzle was maintained at 500 ± 5 K. The oxidizer stream (air) and the N2 co-flow of the upward facing nozzle were not heated and remained at 298 K. The flow rates of the oxidizer, nitrogen carrier gas, and nitrogen co-flow were controlled by calibrated sonic nozzles. The volumetric flow rate of gaseous fuels (e.g. methane) was controlled via sonic nozzle connected to a pressure gauge valve. The volumetric flow rates of the liquid fuels, however, were controlled using either a Syringe Pump® model, NE-1000, or an ISCO® Model 260D high pressure syringe pump.
31
Figure 3.4: Counterflow flame burner configuration used in liquid fuel experiments.
To achieve a counterflow flame for the various liquid fuels evaluated, a liquid fuel vaporization system (i.e. atomizer) was constructed and its schematic is shown below in
Figure 3.5. Liquid fuel was delivered and controlled by a syringe pump (Syringe Pump® model, NE-1000) into 304 stainless steel micro tube with an inner diameter (ID) of 0.016” and an outer diameter (OD). Nitrogen is supplied and heated by an inline heater where the temperature is monitored by a type K thermocouple. For all experiments the nitrogen flow stream was heated to 100 °C and was maintained through the use of a PID controller. The heated nitrogen flow then enters a type 304 stainless steel micro tube with an ID of 0.069” and an OD of 1/8” that encases the micro tube used for liquid fuel delivery. Both tubes then 32 enter a sampling cylinder (2” ID, 4” long) that is heated via electrical heating tape. The nitrogen and fuel stream then interact resulting a fuel/N2 spray mixture that is then vaporized in the sampling cylinder. It is important to note the fuel/N2 mixture exiting the sampling cylinder was heated and maintained at 463 ± 5 K for all n-heptane experiments.
For all n-dodecane experiments, the sampling cylinder was held 498 ± 5 K.
Figure 3.5: Schematic of the fuel vaporization system used for all liquid fuel experiments.
3.1.4 High pressure reactor
The reactor schematic used to thermally stress the rocket propellants is depicted in Figure
3.6. This device consists of a high pressure syringe pump (ISCO® Model 260D) capable of generating 55 MPa (543 atm), at constant flow rates that are specified on the pump controller. The pressurized fluid is delivered into a high temperature reactor consisting of a 25 cm length of 1.6 mm (1/16 in.) 316 L stainless steel capillary tubing with an ID of 0.5 mm. This length of tubing is tightly wrapped around a stainless steel mandrel that contains a 300 W cartridge heater. It is important to note that the cartridge heater is coated with titanium nitride in order to ensure efficient heat transfer and to increase the life span of the 33 cartridge heater [3], [5]. The coiled tubing and mandrel is then coated with a high thermal conductive ceramic and aluminum powder compound which was then fitted into a stainless steel heat shield with a 1” OD and a 0.93” ID. A type K thermocouple capable of reaching temperatures of 1300 K was potted in contact with the reactor tubing. Figure 3.7 shows the cross-sectional schematic of the constructed high pressure reactor. The reactor is placed within a stainless steel chassis and is surrounded by Pyrex wool insulation. Furthermore, the reactor is capable of generating a controlled temperature of up to 600 °C, with uncertainties of less than 1 °C at temperatures below 475 °C and uncertainties of approximately 5 °C at temperatures between 500 and 600 °C [3]. After the fluid passes through the reactor, it is directed via a stainless steel capillary tube into a NESLAB® chilled water bath heat exchanger, model RTE-140, set to -5 °C in order to quench the reaction and cool the thermally stressed fluid prior to entering the back pressure regulator.
Downstream from the back pressure regulator, the fluid is collected for chemical analysis
(described later). The residence time is controlled through specifying a volumetric flow rate of the high pressure syringe pump. The pressure is then set to the desired set point by adjustment of the back pressure regulator. 34
Figure 3.6: High pressure laboratory bench schematic.
Figure 3.7: Cross-sectional schematic of the constructed high temperature reactor.
3.2 Flame extinction methodology
Extinction strain rates were experimentally measured following the methodology of previous work [28], [48], [49]. The flow velocities of both the fuel and oxidizer are gradually increased for a fixed fuel fraction while maintaining equivalent momentums of fuel and oxidizer streams until flame extinction is observed. Once extinction was achieved, 35 the flow velocities and flow densities were applied to the global strain rate equation for plug flow burner setup (Eq. 2.8). Furthermore, mixtures and flow conditions which resulted in flames positioned near either burner exit were not considered to avoid influence from heat loss to the nozzle exits [28], [48], [49]. In addition, extinction was also induced by increasing the fuel dilution by slowly decreasing the flow rate of the fuel for a fixed strain rate while maintaining a momentum balance [28], [47]. The momentum of the flame was determined using the fluid velocity and density of the fuel mixture. For n-heptane and n-dodecane, the liquid and gaseous densities were obtained from experimental data recorded by NIST. For Jet A, the molecular weight and ideal gas law were used to approximate the density of Jet A at 500 K.
3.3 Thermal decomposition
3.3.1 n-Heptane
This study evaluated the effect that endothermic reactions had on n-heptane at a constant reactor temperature of 873 K, a constant reactor residence time of 1 minute, and for a variety of pressures (10, 39, 50, 70, and 170 atm). Note that a residence time of 1 minute was chosen in order to ensure that the fluid had enough time to react. The mass and volume change for each pressure was also recorded in order quantify the amount of n- heptane, n-dodecane, and Jet A decomposed. This was achieved by first collecting 5 mL of unreacted fuel that had passed through the unheated system and recording its mass and its atmospheric volume. This sample was used as a comparison to evaluate changes in mass/volume of the reacted (i.e. heated reactor) samples. For each pressure, once steady state was reached, the high pressure pump was run continuously for 5 mL, and the reacted fuel was then collected and the resulting mass and volume change was recorded. It is 36 important to note that the recorded mass and volume changes were used in order to properly determine the amount a thermal decomposition of the reacted fuel into gaseous species which were not quantifiable with the available analytical equipment. The composition of the collected liquid samples were analyzed by detector GC/FID and GC/MS.
All GC-MS analyses reported in this study were performed using a 30 m x 0.25 mm x 0.25 µm film thickness capillary column, model DB-5MS. GC-FID measurements employed a 30 m x 0.53 m x 0.32 µm film thickness column, model DB-624. Helium was used as the carrier gas for both the GC-MS and GC-FID analyses. The method that was applied to the GC-MS required the following; injector temperature of 250 °C, initial oven temperature at 50 °C followed by a 10 °C/min ramp to a final temperature of 270 °C. The
GC-FID analyses applied following program; injector temperature of 250 °C and an isothermal oven temperature at 50 °C. Differences in the GC oven programs were a result of different columns and their respective affinity to separating hydrocarbons.
3.3.2 n-Dodecane
Another fuel that was analyzed was n-dodecane. It is a larger hydrocarbon than n- heptane and subsequently has weaker atomic bond energies than a smaller hydrocarbon, such as n-heptane. As a result, it is expected that compounds generated through endothermic reactions will be more significant. Additionally, research has been done regarding the development of chemical kinetic mechanisms for n-dodecane, and therefore, pyrolysis, counterflow flames, and flame speeds can all be numerically modeled [37], [50].
In order to characterize the reactor for n-dodecane, measurements were performed at a variety of pressures (10 atm, 30 atm, 50 atm, 70 atm, 100 atm, and 170 atm) at a constant reactor temperature of 600 °C and a residence time of 1 min. For each of these 37 measurements, samples were collected for analysis via GC/FID and GC/MS. Additional measurements were performed at various residence times 0.5 min, 0.75 min, and 1 min at a reactor temperature of 600 °C and a pressure of 170 atm. It is important to note that a reactor temperature of 600 °C and a pressure of 170 atm was chosen in order to ensure maximum thermal decomposition of the fuel. The mass and volume change was recorded for each measurement using the same method employed in the n-heptane decomposition measurements. All GC/MS measurements were performed using a 30 m x 0.25 mm x 0.25
µm film thickness capillary column, model DB-5MS, and all GC/FID measurements were performed using a 30 m x 0.53 m x 0.32 µm film thickness column, model DB-624. The methods employed by both the GC/FID and GC/MS were identical; the injector temperature of the oven was 250 °C, with an initial oven temperature of 50 °C that was held for 10 min, the oven temperature was than increased by 16.667 °C/min to an oven temperature of 250 °C held isothermally for 15 min.
3.3.3 Jet-A
The last liquid fuel analyzed was commercial grade Jet-A. Jet-A is a common hydrocarbon fuel primarily used in turbofan engines which power the majority of the commercial airliner fleet [21]. Jet-A is composed of hundreds of hydrocarbon compounds and subsequently cannot be numerically modeled due to its kinetic complexity. The measurements performed on thermally stressed Jet-A were very similar to those of n- dodecane. The thermal decomposition of Jet-A was measured at several reactor pressures
(10 atm, 30 atm, 50 atm, 70 atm, and 100 atm) at a constant temperature of 600 °C and a residence time of 1 min. It is important to note that measurements were not performed at a reactor pressure of 170 atm because thermal decomposition was too severe and resulted in 38 coking that clogged the reactor thus making it unusable. Measurements were also performed at various residence times; 0.5 min, 0.75 min, and 1 min. The mass and volume change of each measurement was recorded in the same manner as both n-heptane and n- dodecane. Samples were collected for each experimental condition and were analyzed through GC/FID and GC/MS. The columns used in these measurements were the same as those used for the n-dodecane measurements. The methods used by both the GC/FID and
GC/MS were identical; the injector temperature of the oven was 250 °C, with an initial oven temperature of 50 °C that was held for 10 min, the oven temperature was than increased by 12 °C/min to an oven temperature of 290 °C held isothermally for 20 min.
3.4 Combustion behavior of thermally stressed fuels
The objective of this body of work is to determine how the thermal decomposition of hydrocarbon fuels affects the combustion behavior of the fuel. As a primary step, thermally stressed n-heptane at a reactor pressure of 170 atm, a reactor temperature of 873
K, and a 1-minute reactor residence in the liquid phase was collected via reservoir. Using the same experimental conditions implemented for neat n-heptane, the extinction strain curve was evaluated for the thermally stressed liquid sample. By evaluating the flame behavior of thermally stressed n-heptane exclusively in the liquid phase, we are negating the effect of gaseous species that may be formed during pyrolysis. These gaseous species may alter the extinction strain curve in a different manner than the observed extinction curve for thermally stressed n-heptane in the liquid phase. Subsequently, future work will include investigating this relationship by coupling the counterflow flame burner to the high pressure reactor used for thermal stressing of fuels. Figure 3.8 shows the schematic for the coupling of the counterflow burners and the high pressure reactor. 39
Figure 3.8: Schematic of the coupled high pressure reactor and counterflow flame burner.
CHAPTER 4
NUMERICAL METHODOLOGY
The numerical methodology section describes the various numerical models developed in order to simulate the plug flow reactor used for thermal decomposition of n- dodecane and n-heptane, laminar flame speed, as well as counterflow flames for reacted and unreacted n-heptane and n-dodecane. Each model developed was designed to match its respected experimental configuration, excluding the laminar flame models since experimental flame speeds and adiabatic flame temperatures were not measured. The unreacted PREMIX and OPPDIF simulations evaluated the combustion behavior of neat n-heptane and neat n-dodecane. The reacted PREMIX and OPPDIF simulations, however, used the resulting composition formed during both n-heptane pyrolysis and n-dodecane pyrolysis. Additionally, the chemical mechanisms employed in the developed models are also discussed in detail.
4.1 Plug Flow Reactor
The thermal decomposition of both n-heptane and n-dodecane was numerically modeled using the PLUG program within CHEMKIN® [51]. The chemical reaction mechanism used for both fuels was the detailed C8-C16 n-Alkane mechanism developed by Lawrence Livermore National Laboratory (LLNL) [50]. It is important to note that the detailed n-heptane mechanism [35], also developed by LLNL, was not used because the predicted decompositions of thermally stressed n-heptane exhibited a non-physical trend with pressure, which opposed experimental observations. The C8-C16 mechanism contains 1282 species with 5030 elementary reversible reactions and was validated by comparing computed results to several different experimental apparatuses such as shock 41 tube, flow reactors, and jet stirred reactors [50]. These comparisons were performed over a wide range of pressure values, 1 to 80 atm, temperatures from 650 to 1600 K, and equivalence ratios from 0.2 to 1.5 [50].
The variables used within each model were based on the dimensions of the reactor used for experimentation; the inner diameter of the reactor was set to 0.05 cm, with a length of 25 cm, and a fluid velocity of 0.833 cm/s (1 min residence time). A numerical model was developed for each of the pressures that were experimentally evaluated; 10 atm, 30 atm, 50 atm, 70 atm, 100 atm, and 170 atm. These simulations will be compared to the experimentally measured decomposition of both n-heptane and n-dodecane in the following chapter. The resulting predicted n-heptane and n-dodecane compositions will then serve as fuel input parameters for both OPPDIF and PREMIX simulations. The numerical models developed were ideal reactors, meaning that they were isothermal, experienced no surface chemistry, and diffusion in the axial direction was neglected.
Furthermore, the reacting fuel experienced no gradients in velocity, temperature, and composition in the radial direction. Subsequently to account for non-ideal behaviors actually experienced in the experiments, the reactor temperature of the numerical models was varied in value until the predicted n-heptane (or n-dodecane) concentration matched that of the measured n-heptane (or n-dodecane) concentration. An example PLUG input file for n-dodecane has been included in the appendix, section A.1.
4.2 Laminar Flame Speed and Adiabatic Flame Temperature
Although flame speed measurements were not experimentally conducted, numerical models were developed in order to assist in future work. The PREMIX program within CHEMKIN® was used to numerically simulate both the flame speed and adiabatic 42 flame temperature of reacted and unreacted fuels (n-heptane and n-dodecane). The laminar flame speed and adiabatic flame temperature were simulated for a variety of equivalence ratios, which vary from 0.4 to 1.6. This range of equivalence ratios was chosen to provide insight into how the flame behavior is affected for fuel lean and fuel rich mixtures. Due to computational limitations, reduced chemical reaction mechanisms for n-heptane and n- dodecane were used. The reduced n-heptane mechanism developed by LLNL was used for the n-heptane models. The reduced n-heptane mechanism was developed based on the detailed LLNL n-heptane mechanism and contains 159 species with 770 reversible elementary reactions [49]. The reduced mechanism was validated through comparisons to experimentally measured extinction strain rates and autoignition of n-heptane in strained laminar flows [49]. The laminar flame speeds and adiabatic flame temperatures for dodecane were numerically simulated using the 106 species n-dodecane skeletal mechanism developed by Luo [37]. The n-dodecane skeletal mechanism was developed from the LLNL mechanism for 2-methyl alkanes which consists of 2,755 species and
11,173 reactions [37]. The reduced mechanism contains 105 species with 420 reactions and was validated through 0-D and 1-D combustion systems, that include autoignition, jet stirred reactor, laminar premixed flame, and counterflow diffusion flame [36].
The laminar flame speed and adiabatic flame temperature was simulated for reacted and unreacted n-heptane and n-dodecane. It is important to note that these simulations maintained consistent fuel concentrations (i.e. equivalence ratio) so that proper comparisons could be made. For the reacted n-heptane and n-dodecane simulations, the resulting mixture of the PLUG simulations at a pressure of 170 atm, a temperature of 600
°C, and a residence time of 1 min were used as an input for an equilibrium calculation to 43 determine the final composition at local ambient conditions (atmospheric pressure at
Colorado Springs, 0.8 atm, 300 K). The reduced mechanisms, however, do not include all the species that resulted from predicted thermal decomposition of the detailed LLNL n-
Alkane mechanisms from the plug flow reactor simulation. As such, subsequent flame calculations were executed using the reduced mechanism required a renormalization of the predicted product composition from the plug flow reactor calculations (predicted with the detailed mechanism) to include only the species present in the reduced mechanism.
4.3 Counterflow Flames
The OPPDIF program within CHEMKIN® was used in the modeling of counterflow flames for unreacted and reacted n-heptane and n-dodecane. The reduced mechanisms for n-heptane and n-dodecane used for modeling of laminar flame speeds were also used for the counterflow flame models. The UCSD chemical reaction mechanism was used for the CH4 counterflow flame modeling consists of 50 species with 235 reactions
[36]. The numerical counterflow flame models were designed to match the experimental configurations. The separation distance, L, oxidizer temperature, and atmospheric pressure for all models was 9 mm, 298 K, and 0.8 atm. The fuel stream temperature for the CH4 counterflow flame simulation was the same as the experimental configuration at a temperature of 400 K. Likewise, the fuel stream temperature for the n-heptane and n- dodecane models was the same as the experimental fuel stream temperature, 500 K.
The extinction strain rate of the numerical counterflow flame models followed a similar procedure to that of the experimental methodology. This was achieved by first establishing a flame and the gradually increasing the fuel and oxidizer stream velocities until extinction occurred. The point of extinction was able to be determined by evaluating 44 the gaseous temperature between the two burners, when the 1-D temperature failed to exceed the boundary temperature of both nozzles, extinction had occurred. The resulting fuel and oxidizer velocities were then used to determine the global extinction strain rate through Eq. 2.8. For prediction of extinction strain rates for the thermally stressed samples, the composition of the PLUG solution for a pressure of 170 atm, temperature of 873 K, and a residence time of 1 min for both n-heptane and n-dodecane was used as an input for the counterflow flame models. Similar to the laminar flame speed models, the input required renormalization of the predicted product composition to include only the species of the respected reduced mechanism. The global extinction strain was determined in the same manner as the unreacted fuels. An OPPDIF input file for thermally stressed n-heptane at reactor pressure of 170 atm, a reactor temperature of 873 K, and reactor residence time of 1 minute is shown in the appendix A.2.
CHAPTER 5
RESULTS
This chapter discusses the validation of the developed counterflow flame burner by comparing experimentally measured extinction strain rates to the extinction strain rates determined through counterflow flame simulations for methane and n-heptane. The high pressure reactor is then characterized by evaluating the thermal decomposition of n- heptane, n-dodecane, and Jet A over a range of reactor pressures at a constant reactor temperature of 873 K and reactor residence time of 1 minute. Next, the GC/FID and
GC/MS results for thermally stressed n-heptane, n-dodecane, and Jet A at a reactor pressure of 170 atm were analyzed and compared to the simulated thermal decomposition using the
PLUG program. The predicted extinction strain rate curves of reacted and unreacted n- heptane and n-dodecane were then compared where it was observed that reacted fuels experience lower extinction strain rates. The extinction strain curve for Jet A is then presented and the methodology for estimating its molecular weight and density is elaborated. Lastly the predicted adiabatic flame temperature and laminar flame speed profiles for unreacted and reacted n-heptane and n-dodecane are presented.
5.1 Counterflow flame validation The first step in our experimental procedure was to first validate the constructed counterflow flame burner for both gaseous fuels and liquid fuels. The gaseous fuel analyzed was methane and the liquid fuel chosen was n-heptane. For methane, both the fuel stream was heated to 400 K and the oxidizer steam was not heated and thus had a temperature of 298 K. The extinction strain rates for methane was measured and numerically predicted as a function of fuel mole fraction (i.e. fuel dilution with N2). The 46 resulting extinction strain rates can be seen in Figure 5.1. The extinction strain rate of methane was evaluated between a fuel mole fraction (Xf) of 0.3 and a fuel mole fraction of
1 (a mole fraction of 1 is undiluted with nitrogen and is completely composed of methane).
The experimentally measured and numerically simulated extinction strain rates for methane were in good agreement with one another. The next stage of the validation process was to numerically simulate and experimentally measure the extinction strain rate for a liquid fuel, n-heptane.
400 350 300 250 200 Experimental 150 Numerical 100
50 Extinction Strain Rate Strain(1/s) Rate Extinction 0 0.2 0.4 0.6 0.8 1 1.2 Xf (mol/mol)
Figure 5.1: Shown above is the extinction strain of methane at 400 K plotted against the fuel mole fraction, where it is being diluted with nitrogen.
The validation process for n-heptane was identical to the procedure used for methane, however, the fuel was heated and vaporized as described in Chapter 3. The temperature of the fuel stream entering the flame was maintained at 500 K and the oxidizer was kept at an ambient temperature of approximately 298 K. The experimentally measured 47 and numerically predicted n-heptane flame extinction strain rates as a function of fuel mole fraction (i.e. fuel dilution) results are shown in Figure 5.2. It is important to note that the extinction strain rate was only measured and calculated up to a mole fraction (Xf) of 0.15 owing to non-ideal flow dynamics caused by high flow velocities, which in turn was observed to create an unstable/bouncing flame. In addition, data and numerical simulations taken by researchers from Princeton University [22] are also included for reference.
450
400
350
300 Unreacted n-Heptane
) 250
-1 Unreacted n-Heptane (s
g g [1]
a 200 Unreacted n-Heptane 150 (Numerical)
100 Unreacted n-Hetpane (Numerical) [1] 50
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16
Xf (mol/mol)
Figure 5.2: The experimentally measured extinction strain of n-heptane at 0.8 atm is compared to the predicted extinction strain rate curve. Additionally, the experimental and numerical extinction strain rate curves at 1.0 atm reported by Princeton are compared [22].
The differences in the n-heptane extinction strain rates between those taken here and previously recorded values by researchers at Princeton are expected as a result of the differences in the experimental ambient pressure with the results from Princeton collected at a nominal pressure of 1 atm and those reported herein were collected at a nominal 48 pressure of 0.8 atm [52]. For lower pressures the extinction strain rate of n-heptane experiences a decreases in value and slight shift in the direction of larger fuel mole ratios when compared to the extinction strain rate at higher pressures [52]. There was good agreement between the numerically determined and experimentally measured global extinction strain rate thus indicating the kinetic mechanism used was effective for predicting the strain rates of n-heptane. Given the consistency between the numerical predictions and experimental results we had confidence that our experimental and numerical techniques were correctly measuring extinction strain rates and could be applied to more complex fuel systems.
Lastly, the counterflow flame validation for n-dodecane followed the same procedure used for n-heptane. The fuel stream was heated and maintained at 500 K while the oxidizer stream was maintained at 298 K. Similar to the extinction curves for n-heptane, the experimentally measured and predicted extinction curves were evaluated up to an Xf value of 0.15 due to non-ideal flow conditions that occur at larger fuel mole fractions. The resulting extinction strain rate curves are presented below in Figure 5.3. The numerical results are in good agreement with the experimental extinction strain rate curve at lower Xf values ranging from 0.6 through 0.8. However, as the fuel mole fraction increases in value, the prediction extinction strain rate underestimates the experimental extinction strain rate curve by up to 50 s-1. This observed behavior is most likely due to the oversimplification of the reduced n-dodecane mechanism. Subsequently, a sensitivity analysis of the reaction pathways contained in the reduced n-dodecane mechanism will need to be performed in order to elucidated the exact cause. 49
400
350
300
250 )
-1 Unreacted n-dodecane
(s 200
g g a 150 Unreacted n-dodecane (Numerical) 100
50
0 0.04 0.06 0.08 0.1 0.12 0.14 0.16 X (mol/mol) f
Figure 5.3: Experimentally measured extinction strain rate for unreacted n-dodecane compared to the numerically simulated extinction strain rate for unreacted n-dodecane.
5.2 Reactor Characterization
5.2.1 n-Heptane
As previously stated, GC/FID and GC/MS were used to determine the effect of endothermic reactions on the composition of n-heptane, n-dodecane and Jet A after being reacted for a range of pressures, at a constant temperature of 873 K and at 1 min reactor residence time. Using the results of the GC-analysis and measured mass change, the mole fraction (Xf) of n-heptane, n-dodecane, and select components of Jet A exiting the reactor was determined for each pressure. These results, excluding Jet A, were then compared to the plug flow reactor simulations.
The first fuel evaluated was n-heptane. Figure 5.3 compares the experimentally determined liquid mole fraction of n-heptane to the predictions from the numerically 50 simulated plug flow reactor as a function of pressure. Figure 5.3 contains both the shifted and non-shifted predicted n-heptane mole fraction. The non-shifted n-heptane mole fraction mimicked the experimental conditions and thus required a reactor temperature of
873 K and a reactor residence time of 1 min. The resulting n-heptane mole fraction, however, severely over predicted the amount thermal decomposition actually experienced by the fuel following the experiments. As discussed in Chapters 3 and 4, the plug flow simulation assumed that the reactor was ideal. Subsequently, to account for non-ideal behaviors in the experiment, this required that the model reactor temperature at each pressured be adjusted until a n-heptane mole fraction similar in value to the experimentally measured data was achieved. The required reactor temperatures for the reactor pressures,
10 atm, 30 atm, and 50 atm were all 848 K. As the reactor pressure increased the reactor temperature also increased. For the reactor pressures, 70 atm, 100 atm, and 170 atm, the required reactor temperatures were determined to be, 853 K, 857 K, and 860 K. As can be seen in Figure 5.4, there was good agreement between the shifted predicted n-heptane mole fraction and the experimentally measured n-heptane mole fraction. 51
0.70
0.60
0.50 Experimental n- heptane, 873 K, 1 min res. 0.40
(mol/mol) Shifted numerical 0.30 n-heptane, 1 min
res. n-c7h16
X 0.20 Unshifted numerical n- 0.10 heptane, 873 K, 1 min res. 0.00 0 20 40 60 80 100 120 140 160 180 P (atm)
Figure 5.4: Experimentally measured and numerically predicted decomposition of n- heptane in liquid phase as a function of pressure at a reactor temperature of 873 K and a reactor residence time of 1 minute.
When evaluating the n-heptane decomposition data, it was determined that as pressure increases, the n-heptane mole fraction decreases, as can be seen in Figure 5.3. This is a result of thermally stressing the fuel, which induces endothermic reactions that break the fuel molecules, n-heptane, into other hydrocarbon compounds. The species formed owing to endothermic reactions that will be discussed in detail in a later section of this chapter. At a reactor pressure of 10 atm, n-heptane experienced moderate decomposition with a mole fraction of approximately 0.65. As the reactor pressure increased, the amount of n-heptane decomposition increased. At a reactor pressure of 30 atm, the liquid n-heptane mole fraction was ~ 0.58, for a reactor pressure of 70 atm the resulting n-heptane mole 52 fraction was ~ 0.48, and for a reactor pressure of 170 atm, the measured liquid n-heptane mole fraction was ~ 0.37.
At each of these pressures, 5 mL of unreacted fuel (no heat, reactor temperature of
298 K) and reacted fuel (at a reactor temperature of 873 K) was delivered through the reactor following the mass and volume change was also recorded, the results of which are shown in Table 5.1. The unreacted n-heptane that has not been thermally stressed, had a recorded mass of 4.45 g for measured volume of 5.2 mL after being collected from the non- heated and non-pressurized reactor. As can be seen in Table 5.1, the n-heptane fuel experiences severe changes in mass and volume, thus indicating that a large portion of the fuel is being decomposed into gaseous species.
Table 5.1: This table contains the recorded mass and volume change of reacted n-heptane at a variety of pressures at a constant temperature of 873 K and reactor residence time of
1 minute.
Pressure (atm) Mass C7H16 (g) Vol. (mL) 10 3.04 4.8 30 2.75 4.2 50 2.55 4.0 70 2.36 3.9 100 2.15 3.4 170 1.30 2.6
In addition to comparing the experimentally measured mole fraction of n-heptane in liquid phase to predicted n-heptane decomposition, it was important to compare the numerical predictions after the temperature shift for other species that are present in the liquid phase. In order to elucidate how accurate the simulated plug flow reactor is when predicting the formation and or decomposition of other species, 1-hexene was chosen. The 53 temperature shifted 1-hexene mole fraction comparison is shown below in Figure 5.4 as function of pressure. As indicated by Figure 5.5, the predicted mole fraction of 1-hexene follows the same trend but underestimates the experimentally measured data.
0.006
0.005
0.004
Temperature shifted 0.003 numerical, 1-hexene
(mol/mol) formation f f X 0.002 Experimental, 1- hexene formation 0.001
0.000 0 50 100 150 200 P (atm)
Figure 5.5: Formation of 1-hexene during n-heptane pyrolysis as a function of pressure at a reactor temperature of 873 K and a reactor residence time of 1 minute.
The next fuel that was analyzed was n-dodecane. Figure 5.5 compares the experimentally measured and predicted liquid mole fraction of n-dodecane as a function of pressure. Similar to the decomposition of n-heptane, Figure 5.5 shows both the shifted and unshifted numerical predictions of n-dodecane decomposition. For the unshifted simulation, the reactor temperature was held at a constant temperature of 873 K and a reactor residence time of 1 minute. The resulting n-dodecane mole fraction predictions grossly overestimated the amount of n-dodecane decomposition. The temperature shifted plug flow simulations used the following temperatures for the reactor pressures, 10 atm, 54
30 atm, 50 atm, 70 atm, 100 atm, and 170 atm: 818 K, 823 K, 834 K, 842 K, 851 K, and
865 K. As depicted in Figure 5.6, the resulting predicted n-dodecane mole fractions were in good agreement with the experimentally measured n-dodecane liquid phase mole fractions.
0.80
0.70
0.60 Experimental n- dodecane, 873 K, 1 0.50 min res.
0.40 Shifted numerical, n- dodecane, 1 min res.
(mol/mol) 0.30
0.20 Unshifted numerical,
n-c12h26 n-dodecane, 873 K, 1 X 0.10 min res.
0.00 0 20 40 60 80 100 120 140 160 180 P (atm)
Figure 5.6: Experimentally measured and numerically predicted decomposition of n- heptane in liquid phase as a function of pressure at a reactor temperature of 873 K and a reactor residence time of 1 minute.
When thermally stressing n-dodecane, it was observed that the fuel experienced more decomposition as the reactor pressure increased. When the reactor pressure was maintained at 10 atm, the resulting n-dodecane mole fraction was ~ 0.70. For a higher reactor pressure, 70 atm, the liquid phase n-dodecane mole fraction was nearly half that at
10 atm with a measured value of ~ 0.38. Lastly, the n-dodecane mole fraction at a reactor pressure of 170 atm was ~ 0.13, thus indicating that a large majority of n-dodecane is being lost to the formation of other species. This presumption is further validated through 55 the recorded mass and volume change of liquid n-dodecane for each reactor pressure, as shown in Table 5.2. The measured unreacted n-dodecane mass and volume were 3.58 g and 5 mL. At reactor pressure of 170 atm, the measured mass was 2.14 g, which is a 40
% decrease from the unreacted mass. Furthermore, the recorded volume also decreased by 40 % to 3.0 mL. The decrease in mass and volume indicates that approximately 40 % of the reacted n-dodecane is forming gaseous species.
Table 5.2: The recorded mass and volume change of reacted n-dodecane at a variety of reactor pressures at a constant temperature of 873 K and reactor residence time of 1 minute.
Pressure (atm) Mass C12H26 (g) Vol. (mL) 10 3.11 4.4 30 2.83 4.0 50 2.59 3.8 70 2.48 3.6 100 2.34 3.4 170 2.14 3.0
Lastly, it was important to evaluate how well the n-dodecane mechanism [50] predicted the formation and or decomposition of various species during n-dodecane pyrolysis. Figure 5.7 shows the measured and temperature shifted predicted mole fractions for n-heptane and 1-octene. For both species, the n-dodecane mechanism under-predicts the experimentally measured mole fractions. However, the observed trends for both 1- octene and n-heptane are similar in behavior. For n-heptane, the numerical model exhibits the experimental data by gradually increasing in value in a parabolic manner. Additionally, the predicted mole fraction of 1-octene increases in value at first but begins to plateau at roughly 100 atm. The experimentally measured liquid phase mole fraction for 1-octene was 56 observed to have a similar trend by first increasing in value until 50 atm where the mole fraction begins to remain at a relatively consistent mole fraction value of 0.39.
0.06
0.05
0.04 Experimental, n- heptane formation Experimetnal, 1- 0.03
octene formation (mol/mol)
f f Numerical, n- X 0.02 heptane formation Numerical, 1- 0.01 octene formation
0.00 0 20 40 60 80 100 120 140 160 180 P (atm)
Figure 5.7: Formation of n-heptane and 1-octene during n-dodecane pyrolysis as a function of pressure at a reactor temperature of 873 K and a reactor residence time of 1 minute.
5.2.3 Jet A
The last fuel evaluated was aviation kerosene (Jet A). Jet A is a very complex mixture that contains hundreds of hydrocarbon species that vary in amounts depending on factors such as crude oil, the refinement process, and even the time of year that it is manufactured [21]. Subsequently, this causes difficulty when trying to evaluate the decomposition of the fuel when thermally stressed and ultimately determine the extinction strain rate. Due to its complexity, the thermal decomposition of Jet A could not be compared to any numerical plug flow simulations. Instead, select species, n-dodecane and 57 tridecane, were chosen to assist in the characterization of the reactor for Jet A. A sample of neat Jet A, meaning unreacted, was collected and its composition was evaluated through the use of GC/FID and GC/MS. The mass of the unreacted was 3.9 g. The exact procedure followed was discussed in Chapter 3. For neat Jet A, 12.21% of the mixture was composed of n-dodecane and 2.51% was tridecane. Figure 5.8 shown below shows how the liquid phase mole fraction of n-dodecane and tridecane behaves as a function of temperature. It is important to remind the reader that the reactor temperature was maintained at 873 K and the fuel experienced a reactor residence time of 1 minute. As the reactor pressure was increased, it was observed that the liquid phase mole fractions of both n-dodecane and tridecane decreased, thus implying that they are both forming new species due to endothermic reactions. The mass and volume of reacted Jet A for each pressure was recorded and is displayed below in Table 5.3. Similar to the mole fractions of n-dodecane and tridecane, the mass and volume of Jet A both decrease as the reactor pressure increases, thus further validating the previous statement.
58
0.12
0.1
0.08 n-dodecane mass fraction, 873 K, 1 min
0.06 res.
(mol/mol) f f
X 0.04 Tridecane mass fraction, 873 K, 1 min res. 0.02
0 0 50 100 150 P (atm)
Figure 5.8: Experimentally measured decomposition of n-dodecane and tridecane within
Jet A as a function of pressure. The reactor temperature and reactor residence time were held constant at 873 K and 1 minute.
Table 5.3: The recorded mass and volume change of reacted Jet A at a variety of reactor pressures at a constant temperature of 873 K and reactor residence time of 1 minute.
Pressure Mass Jet A (g) Vol. (mL) 10 3.8886 5.0 30 3.2118 4.4 50 3.1837 4.2 70 3.1724 4.0 100 2.94038 3.8
5.3 Thermal Decomposition
This section includes the results from the GC/FID and GC/MS measurements of all samples for n-heptane, n-dodecane, and Jet A. It will also include the resulting numerical decomposition of n-heptane and n-dodecane for all pressures. Furthermore, it will include 59
the resulting GC/FID signals, the correlation between Xf and the integration of the GC/FID signals will be discussed.
5.3.1 n-Heptane Thermal Decomposition The composition of the cracked n-heptane was determined by extracting ~10 µL from a sample that was generated by the method described in Chapter 3. The sampled fluid was then injected into ~1 mL of solvent (methylene chloride), which was weighed before and after sample introduction so that the concentrations of all the detected species could be quantified. Gas chromatography analysis was then performed by taking only peaks with areas which made up more than 0.75 % of the total chromatogram area. Figure 5.8 depicts the corresponding chromatogram and Table 5.4 lists the species formed by endothermic reactions of n-heptane for a reactor temperature of 873 K, a residence time of 1 min, and a reactor pressure of 170 atm. Table 5.4 and Figure 5.9 indicates that a majority of the cracked heptane is being decomposed into pentane, cyclopropane-1-2-dimethyl, 1-pentene,
(Z)-2-heptene, and octane. The total number of species predicted to be formed during n- heptane pyrolysis at a 170 atm was 1266, all of which are shown in Table A.1-A.5. When performing flame speed and counterflow simulations, the species that made up the majority of the composition were used, however, a portion of the predicted species were not included within the reduced chemical mechanisms needed to compute the flame extinction and flame speed of the thermally stressed samples and therefore required normalization to form 100% mole fraction of reacted fuel. A summarized version of the predicted composition for a reactor pressure of 170 atm is shown below in Table 5.5 and the normalized composition can be seen is Table 5.6.
60
Table 5.4: Experimentally measured thermal decomposition of n-heptane at 170 atm.
Peak Time Compound Area %Area 2 1.07 1-Pentene 317366 1.192% 4 1.24 Pentane 898891.8125 3.375% 5 1.27 Pentane (isomer) 260389.25 0.978% 9 1.61 2-Pentene, (Z)- 540220.75 2.028% 10 1.63 Cyclopropane, 1,2-dimethyl-, cis- 900495.8125 3.381% 11 1.70 Cyclopropane, 1,2-dimethyl-, cis- (isomer) 293865.0625 1.103% 12 1.77 Cyclopropane, 1,2-dimethyl-, cis- (isomer) 363513.8125 1.365% 19 4.08 1-Hexene 300666.5625 1.129% 23 4.86 1-Heptene 295072.0313 1.108% 24 5.08 Heptane 20765158 77.969% 25 5.38 (Z)-2-Heptene 483770.4688 1.816% 27 6.15 Cyclohexane, methyl- 240183.2813 0.902% 36 8.78 Heptane, 3-methyl- 262226 0.985% 38 9.56 1-Heptene, 2-methyl- 251481.5156 0.944% 41 10.69 Octane 459414.5 1.725% 61
Figure 5.9: Chromatogram resulting from the GC-FID analysis of the collected n-heptane liquid sample from the reactor experiments at 873 K, a 1 min residence time, and a reactor pressure of 170 atm.
62
Table 5.5: Summarized version of the actual species predicted to form during n-heptane pyrolysis at a reactor temperature of 873 K, reactor residence time of 1 minute, and a reactor pressure of 170 atm.
Species Xf Species Xf Species Xf
nC7H16 3.72E-01 H2 3.87E-03 C15H30-7 1.68E-03
C2H6 1.94E-01 C8H16-1 3.34E-03 C15H30-5 1.67E-03
CH4 8.53E-02 C4H10 3.26E-03 C15H30-6 1.67E-03
C3H6 7.79E-02 C16H32-8 2.27E-03 C15H30-4 1.66E-03
C2H4 7.04E-02 C16H32-7 2.26E-03 C15H30-3 1.66E-03
C4H8-1 4.50E-02 C16H32-5 2.26E-03 C15H30-2 1.66E-03
C5H10-1 4.49E-02 C16H32-6 2.25E-03 C15H30-1 1.64E-03
C6H12-1 2.49E-02 C16H32-4 2.25E-03 nC8H18 1.43E-03
C3H8 1.35E-02 C16H32-2 2.25E-03 C10H20-1 1.33E-03
C7H14-1 8.01E-03 C16H32-3 2.25E-03 nC9H20 1.20E-03
nC5H12 5.48E-03 C16H32-1 2.24E-03 C7H14-2 9.79E-04
nC6H14 4.07E-03 C9H18-1 1.96E-03 C7H14-3 9.11E-04
Table 5.6: Normalized composition resulting from n-heptane pyrolysis at a reactor temperature of 873 K, reactor residence time of 1 minute, and a reactor pressure of 170 atm. This composition was used for all reacted n-heptane PREMIX and OPPDIF simulations.
Species Xf
nC7H16 4.11E-01
C2H6 2.14E-01
CH4 9.43E-02
C3H6 8.61E-02
C2H4 7.78E-02
C4H8-1 5.00E-02
C5H10-1 4.99E-02
C4H6 8.19E-04
H2 4.27E-03
C7H14-2 9.94E-03
C7H14-3 1.01E-03
C4H6 6.45E-04
63
When evaluating the liquid fraction compositions measured through GC/FID and
GC/MS for n-heptane over the range of reactor pressures, it was observed that as the reactor pressure increased the generation of unsaturated higher C/H ratio species, such as 1- hexene, 1-pentene, were formed. Additionally, as the reactor pressure increased, the liquid fraction of larger hydrocarbons, such as octane, increased. The same observations were made within the predicted compositions for thermally stressed n-heptane, where the Xf for species such as 1-butene, pentadecene, and 1-pentene increased with pressure.
5.3.2 n-Dodecane Thermal Decomposition When determining the liquid composition for thermally stressed n-dodecane, chromatography analysis was performed and only peaks with areas which made up more than 1.0 % of the total chromatogram area were identified. The corresponding chromatogram is shown in Figure 5.10 and Table 5.7 lists the species percent area of the species identified for a reactor temperature of 873 K, a residence time of 1 min, and a reactor pressure of 170 atm. The identified liquid fractions of thermally stressed n- dodecane for all other reactor pressures are located in the appendix and are labeled as Table
A.7-11. Similar to n-heptane pyrolysis, the formation of unsaturated higher C/H ratio species and large hydrocarbons increased with reactor pressure. The percent area of n- dodecane decreased dramatically as the reactor pressure increased. At a reactor pressure of
170 atm, the recorded percent area for n-dodecane was 22.37 %. Referring to the mass and volume change reported in Table 5.2 for a reactor pressure of 170 atm, an approximate
40% decrease in mass and volume indicates that a large portion of n-dodecane was lost to the formation of gaseous species. The composition of the gaseous species formed at this time was not able to be determined and will subsequently be examined in future work.
When evaluating the liquid composition of n-dodecane at a 170 atm, the most prominent 64 species other than n-dodecane were butane, pentane, hexane, heptane, 1-octene, octane, nonane, decane, 1-decene, and toluene.
Table 5.8 contains the actual molar fractions of the predicted species that compose the majority of the thermally stressed n-dodecane at 170 atm. The behavior of the species formation and decomposition was consistent with that of the experimentally measured liquid fractions. As the reactor pressure increased, the formation of unsaturated higher C/H ratio species and large hydrocarbons also increased. A portion of the species that have the largest mole fractions besides n-dodecane are the following: ethane, ethylene, 1-hexene, methane, propene, 1-pentene, 2-heptene, 1-octene, and 1-decene. At a reactor pressure of
170 atm, the species with the highest mole fraction was ethane, C2H6, which has a boiling point at temperature of 184 K at 1 atm and is therefore in a gaseous state. When performing
PREMIX and OPPDIF simulations a reduced n-dodecane mechanism was used and did not contain all of the species predicted by the detailed mechanism used for PLUG simulations.
This required that the composition be renormalized to 100% mole fraction to account for any rejected species that were not present in the reduced mechanism. The resulting normalized composition is shown in Table 5.9. It is important to note that the non- normalized gaseous species will be used in conjunction with the experimentally measured liquid mass fractions for n-dodecane to determine a molecular weight and density of the thermally stressed fuels when performing extinction limit measurements of the thermally stressed fuels.
65
Table 5.7: Experimentally measured liquid composition following the thermal decomposition of n-dodecane at 170 atm.
Peak Time Compound Area % Area 3 1.06 Propene 436314 1.1929% 5 1.23 Butane 1133502 3.0990% 6 1.27 Butane (isomer) 308226 0.8427% 7 1.32 1-Butene 256236 0.7006% 9 1.50 Butane 2-methyl 188947 0.5166% 10 1.63 Pentane 2891257 7.9048% 11 1.69 2-Pentene 509193 1.3922% 12 1.75 2-Pentene (isomer) 539774 1.4758% 14 2.53 Hexane 1774261 4.8509% 22 4.46 Benzene 575861 1.5744% 24 4.83 1-Heptene 1783193 4.8753% 25 5.02 Heptane 3022820 8.2645% 37 9.50 Toluene 970093 2.6523% 38 10.19 1-Octene 1478481 4.0422% 39 10.59 Octane 2471113 6.7561% 55 14.40 p-Xylene 674176 1.8432% 56 14.59 1-Nonene 1000203 2.7346% 57 14.75 Nonane 2229094 6.0944% 75 17.10 1-Decene 926252 2.5324% 76 17.21 Decane 1017735 2.7825% 93 19.04 1-Undecene 549231 1.5016% 94 19.13 Undecane 479037 1.3097% 110 20.81 Dodecane 11360884 22.3702% 66
5000000
4500000
4000000 Methylene Chloride (Solvent) 3500000
3000000 n-Dodecane
2500000
2000000 Intesity (A.U.) Intesity
1500000
1000000
500000
0 0 5 10 15 20 25 Retention time (min.)
Figure 5.10: Chromatogram resulting from the GC/FID analysis of the collected n- dodecane liquid sample from the reactor experiments at 873 K, a 1 min residence time, and a reactor pressure of 170 atm.
67
Table 5.8: Summarized version of the actual species predicted to form during n-dodecane pyrolysis at a reactor temperature of 873 K, reactor residence time of 1 minute, and a reactor pressure of 170 atm.
Species Xf Species Xf Species Xf
C2H6 2.32E-01 nC8H18 7.70E-03 C15H30-4 3.51E-03
nC12H26 1.31E-01 C11H22-1 7.63E-03 C15H30-1 3.49E-03
C2H4 9.80E-02 nC7H16 6.39E-03 C15H30-2 3.47E-03
C6H12-1 7.41E-02 C4H10 5.52E-03 C15H30-3 3.47E-03
C3H6 6.69E-02 C16H32-8 4.51E-03 nC10H22 3.04E-03
CH4 5.51E-02 C16H32-5 4.47E-03 H2 2.48E-03
C5H10-1 4.43E-02 C16H32-7 4.46E-03 nC11H24 2.20E-03
C7H14-1 4.42E-02 C16H32-6 4.45E-03 C13H26-1 1.84E-03
C8H16-1 2.85E-02 C16H32-4 4.42E-03 C4H6 1.42E-03
C4H8-1 2.75E-02 C16H32-3 4.41E-03 C12H24-2 1.19E-03
C10H20-1 2.32E-02 C16H32-2 4.40E-03 C14H28-1 1.12E-03
C9H18-1 1.53E-02 C16H32-1 4.36E-03 C12H24-5 1.03E-03
nC6H14 1.23E-02 C12H24-1 4.00E-03 C9H18-4 1.01E-03
C3H8 1.11E-02 C15H30-5 3.57E-03 nC13H28 8.60E-04
nC5H12 1.06E-02 C15H30-7 3.56E-03 C12H24-4 7.75E-04
nC9H20 7.74E-03 C15H30-6 3.53E-03 nC14H30 6.86E-04
68
Table 5.9: Normalized composition resulting from n-dodecane pyrolysis at a reactor temperature of 873 K, reactor residence time of 1 minute, and a reactor pressure of 170 atm. This composition was used for all reacted n-heptane PREMIX and OPPDIF simulations.
Species Xf
C2H6 2.81E-01
nC12H26 1.58E-01
C2H4 1.19E-01
C6H12-1 8.98E-02
C3H6 8.11E-02
CH4 6.67E-02
C7H14-1 5.39E-02
C8H16-1 3.45E-02
C4H8-1 3.33E-02
C10H20-1 2.91E-02
C9H18-1 2.04E-02
C3H8 1.35E-02
C4H10 6.69E-03
C12H24-5 8.48E-03
H2 3.00E-03
C4H6 1.72E-03
5.3.3 Jet A Thermal Decomposition
Jet A is a complex mixture that contains hundreds of species. Figure 5.10 is the chromatogram resulting from the GC/FID analysis of Jet A. To get a sense of the complexity of the composition selected peaks are identified (i.e. nC6, nC8, nC9, nC10, nC12, and nC13). The method used for the GC/FID and GC/MS analysis of unreacted and reacted
Jet A was discussed in Chapter 3. As can indicated by Figure 5.11, numerous compounds were detected with a total of 187 peaks being measured. The majority of the liquid neat sample was composed of large hydrocarbons with the tallest and highest frequency of peaks occurring within the nC9 and nC16 subsections. For neat Jet A, some of the species with the 69 largest percent areas (liquid mass fractions) were n-dodecane with 12.21 % area, hexadecane with 7.79 % area, nonadecane with a 5.26 % area, and heptadecane with a 5.24
% area. The same behavior that was noted for the thermal decomposition of both n-heptane and n-dodecane was observed when evaluating the gas chromatography results for Jet A.
As the reactor pressure increased the generation of unsaturated higher C/H ratio species also increased. The percent area of the larger hydrocarbons decreased and the formation smaller hydrocarbons increased in percent area. This can be seen in Figure 5.12 that shows the chromatogram of thermally stressed Jet A at a reactor pressure of 100 atm, a reactor temperature of 873 K. In Figure 5.11, the number of recorded peaks increased to a value of 207, with the relative intensity of the peaks occurring within the nC9 and nC16 subsections decreasing in value, and the relative intensity for smaller hydrocarbons
4 (subsections nC through nC9) increased.
Table 5.10 lists all the identified species that make up over 0.25% of the fuel composition for thermally stressed Jet A at a rector pressure of 100 atm. The GC/FID and
GC/MS results for all other Jet A measurements can be found in the appendix in Tables
A.13 - A.15. Table 5.10 consists of fifty four identified species, all of which sum to just
69.11% percent of the measured sample. As shown in Figure 5.8, the percent area of n- dodecane decreased to 5.0 %. The percent areas of other notable species, such as hexadecane, nonadecane, and heptadecane were, 5.3 %, 3.0 %, and 3.4 %. 70
Figure 5.11: Chromatogram resulting from the GC/FID analysis of neat Jet A. 71
Figure 5.12: GC-FID analysis of the collected Jet A liquid sample from the reactor experiments at 873 K, a 1 min residence time, and a reactor pressure of 100 atm.
72
Table 10: Experimentally measured composition of the liquid Jet A following the thermal decomposition at 100 atm, 873 K and 1 min residence time.
Peak Time (min.) Compound Area % Area 17 3.79 2-Chloroethanol 1015022 2.08% 18 4.02 Heptane 1010247 2.07% 19 4.27 Heptane (isomer) 299288 0.61% 20 4.46 Heptane (isomer) 645298 1.32% 21 4.64 Cyclohexane, methyl- 688424 1.41% 22 4.82 Cyclohexane, methyl- (isomer) 1304943 2.68% 23 5.02 Cyclohexane, methyl- (isomer) 1182953 2.43% 24 5.32 2-Pentene, 2,3-dimethyl- 665503 1.37% 26 6.11 Heptane, 2-methyl- 866320 1.78% 27 9.50 Octane, 2-methyl- 1072593 2.20% 28 14.40 Benzene, 1-ethyl-3-methyl- 1427147 2.93% 29 14.58 Nonane 80782 0.17% 30 14.74 Decane, 2,5,6-trimethyl- 215319 0.44% 33 16.84 Benzene, 2-ethyl-1,4-dimethyl- 531081 1.09% 34 16.99 Benzene, 4-ethyl-1,2-dimethyl- 477227 0.98% 35 17.10 1-Deacane 165031 0.34% 36 17.22 Nonane, 3-methyl- 1455687 2.99% 37 17.59 Benzene, 2-ethyl-1,3-dimethyl- 1026545 2.11% 38 17.70 Cyclodecene, 1-methyl- 382311 0.78% 40 18.03 Nonane, 3-methyl- 531165 1.09% 41 18.24 Cyclohexane, 1,2,4-trimethyl- 383622 0.79% 42 18.36 Cyclohexane, hexyl- 290907 0.60% 44 18.50 Dodecane, 2-methyl- 247372 0.51% 45 18.63 Dodecane, 4-methyl- 1007496 2.07% Naphthalene, 1,2,3,4-tetrahydro-5- 46 18.78 methyl- 581620 1.19% Naphthalene, 1,2,3,4-tetrahydro-5- 214349 0.44% 47 19.02 methyl- (isomer) 49 19.14 Decane, 3,8-dimethyl- 2033338 4.17% 50 19.23 Decane, 3,8-dimethyl- (isomer) 332819 0.68% 51 19.34 Cyclohexane, pentyl- 384268 0.79% 52 19.44 Cyclohexane, pentyl- (isomer) 279656 0.57% 53 19.57 Cyclohexane, pentyl- (isomer) 131387 0.27% 54 19.65 Dodecane, 4,6-dimethyl- 598853 1.23% 55 19.76 Dodecane, 4,6-dimethyl- (isomer) 47903 0.10% 56 19.94 Tridecane 927142 1.90% 57 20.07 Naphthalene, 1-ethyl- 188590 0.39% 73
Peak Time (min.) Compound Area % Area 59 20.21 Naphthalene, 1-ethyl- (isomer) 201618 0.64% 60 20.33 Naphthalene, 1,6-dimethyl- 346433 0.71% 61 20.59 Dodecane 557376 1.14% 62 20.67 Dodecane (isomer) 134707 0.28% 63 20.79 Dodecane (isomer) 2172267 4.46% 64 21 Dodecane (isomer) 356804 0.73% 70 21.42 Hexadecane 660140 1.36% 71 21.56 Hexadecane (isomer) 679774 1.40% 72 21.68 Hexadecane (isomer) 54074 0.11% 73 21.74 Nonadecane 397885 0.82% 74 21.87 Nonadecane (isomer) 632259 1.30% 75 22.1 Nonadecane (isomer) 180246 0.37% 76 22.26 Hexadecane 1245209 2.56% 77 22.36 Hexadecane (isomer) 763939 1.57% 78 22.52 Naphthalene, 2,6-dimethyl- 512996 1.05% 79 22.62 Naphthalene, 2,6-dimethyl- (isomer) 78821 0.16% 91 23.07 Heptadecane 1342060 2.75% 93 23.33 Heptadecane (isomer) 835116 1.71% 97 23.62 Nonadecane (isomer) 728464 1.50%
5.4 Extinction Strain Rate of Reacted Fuels
5.4.1 Thermally Stressed n-Heptane
As previously stated, the reduced kinetic mechanism used does not contain several species that the fuel decomposed into (namely, propane, butane, cyclohexane, and butane) as computed using the detailed mechanism. To account for the missing species, the fuel compositions used for numerical evaluation of extinction strain rates were re-normalized to include only the species present in the reduced mechanism as shown in Table 5.6. For all numerical counterflow flame simulations, only the predicted fuel compositions resulting from a reactor temperature of 873 K, a 1 min residence, and a reactor pressure of 170 atm were used as input fuel parameters. This is because a reactor pressure of 170 atm and a reactor temperature of 873 K provides an accurate representation of hypersonic or rocket 74 active cooling systems [3]. The PLUG simulation of n-heptane at a reactor pressure of 170 atm and a reactor temperature of 873 K experiences approximately 43% change in the mass, and the computed extinction strain rate is predicted to decrease as shown in Figure
5.13. The severity at which the predicted extinction strain rate decreases when compared to the unreacted extinction curve increases as the fuel mixture becomes more diluted with nitrogen. At a Xf value of 0.15, the reacted extinction strain is predicted to decrease by 3.54
%, for a Xf value of 0.1 the reacted extinction strain is 18.3 % percent lower, and at a Xf of
0.06, the reacted extinction strain rate is 37.5 % lower than the unreacted extinction strain rate. It is important to note that the decrease in extinction strain rate for thermally stressed n-heptane is counterintuitive. Through thermal decomposition a large majority of n- heptane lost to the formation of smaller hydrocarbons. It has been documented that a decrease in a fuel’s molecular weight and or molecular size leads to an increased resilience to experiencing extinction [26]. Subsequently, an increase in extinction strain rate was expected for thermally stressed n-heptane. In order to fully understand the effect that these species have on the extinction strain rate of the thermally stressed n-heptane, reactor coupled flame experiments and a sensitivity analysis will be performed. 75
400
350 Unreacted n- Heptane 300
250
Unreacted n- )
-1 200 heptane (s
g g (Numerical) a 150 Reacted n- 100 heptane 873 K, 1 min 50 (Numerical) 0 0.04 0.06 0.08 0.1 0.12 0.14 0.16 X f Figure 5.13: Numerical and experimental global extinction strain rate plotted against the fuel mole fraction.
As a preliminary step towards determining the extinction strain rate of thermally stress n-heptane, n-heptane was stressed at a reactor pressure of 170 atm, a reactor temperature of 873 K, and a reactor residence time of 1 minute. The reacted n-heptane was collected in a reservoir and the resulting liquid was than supplied to the counterflow flame burner via syringe pump at the same experimental conditions as the unreacted n-heptane.
These conditions were discussed in Chapter 3, however, it is important to note that the exit temperature of the fuel sided burner was maintained at temperature of 500 K. Using the results obtained from GC/FID and GC/MS analyses, the molecular weight and density of the reacted n-heptane in liquid phase was able to be estimated. The molecular weight and density of neat n-heptane is 100.21 g/mol and 679.59 kg/m3 (at 0.8 atm). For reacted n- heptane at reactor pressure of 170 atm, reactor temperature of 873 K, a reactor residence time of 1 minute, the molecular weight of the resulting liquid was estimated to be 97.58 76 g/mol and the measured density was 538.40 kg/m3. The resulting extinction curve is shown in Figure 5.14 and it can be seen that the extinction strain for reacted n-heptane in the liquid phase has slightly increased. This is opposite of what was predicted by the counterflow flame burner simulations but it is important to note that gaseous species formed during n- heptane pyrolysis were not present in the supplied flow. As a result, the full effect that the thermally decomposition has on the extinction curve has yet to be evaluated.
450
400
350
300 Unreacted n-
) heptane
-1 250
(s g g
a 200 Reacted n-heptane, 150 873 K, 1 min (Liquid) 100
50
0 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 X (mol/mol) f Figure 5.14: Comparison between the extinction strain rates of unreacted n-heptane and reacted liquid n-heptane at a reactor pressure of 170 atm, a rector temperature of 873 K, and a reactor residence time of 1 minute.
5.4.2 Thermally Stressed n-Dodecane
Figure 5.15 shows the numerically predicted extinction strain for unreacted and reacted n-dodecane at reactor pressure of 170 atm, a reactor temperature of 873 K, and a reactor residence time of 1 minute. The extinction strain rate curve for reacted n-dodecane 77 exhibits the same behavior observed for reacted n-heptane, in that it is lower in value when compared to unreacted n-dodecane. As the fuel Xf decreases, the difference between the reacted and unreacted n-dodecane extinction strain increases. At an Xf of 0.15, the extinction strain rate of reacted n-dodecane is 10.79 % lower than unreacted n-dodecane.
When the fuel Xf decreases to 0.10, the extinction strain rate for reacted n-dodecane is
26.59 % lower than the predicted unreacted n-dodecane. At a fuel Xf value of 0.06, the extinction strain rate of reacted n-dodecane is 50.64 % lower than that of unreacted n- dodecane at the same Xf value. The decrease experienced by thermally stressed n- dodecane, like the extinction curve of thermally stressed n-heptane, is opposite of the trend that what was expected to occur. Instead, an increase in the extinction strain rate for thermally stressed n-dodecane due to the production of smaller hydrocarbon species was the expected result. 78
450
400
350
300 Unreacted n-
) 250 dodecane -1
(s (Numerical) g g
a 200 Reacted n- 150 dodecane, 873 K, 1 min res. 100 (Numerical) 50
0 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
Xf
Figure 5.15: Numerical and experimental global extinction strain rate for n-dodecane plotted against the fuel mole fraction.
The differences between the reacted and unreacted n-dodecane extinctions strain rates are much larger than those observed for n-heptane. This can be explained by the larger mass change experienced by n-dodecane, which is approximately 87 %. The larger mass change indicates that n-dodecane experiences more thermal decomposition than n-heptane, which had a 43 % mass change. The larger production of other species, such as ethane, which is almost twice the percent composition of n-dodecane at 28.10 %, could be the reason for the decreases in extinction strain rates for reacted n-dodecane. In order to elucidate the decrease in the predicted extinction rate curve for reacted n-dodecane, as sensitivity analysis will be conducted in future work. Furthermore, experimentally measured extinction strain rates for reacted n-dodecane will be performed and the validity of the predicted results will be determined. 79
5.4.3 Jet A Extinction Strain Rate
Figure 5.15 contains the experimentally measured extinction strain for commercial
Jet A and previously measured extinction strain rate for research grade Jet A (POSF
404658) measured by Princeton [22]. The molecular weight of the neat Jet A needed to calculate the momentum balance for the extinction strain rate experiments was taken to be
158.28 g/mol corresponding to an average single surrogate compound of C11H21, [21]. The ideal gas law was used to determine the density of gaseous Jet A at 500 K, which was also needed to calculate the fuel stream momentum for the extinction strain rate measurements.
The POSF 404658 measurements were taken at 1.0 atm and the atmospheric pressure of the Jet A extinction strain rates that were measured here were at 0.8 atm. As can be seen in
Figure 5.16, the extinction strain rate that we measured is lower in value and intersects the extinction curve measured by Princeton at approximately 0.68 Xf. As previously discussed, at lower pressures the extinction strain rate decreases in value and experiences a slight shift in the direction of larger fuel mole ratios when compared to the extinction strain rate at higher pressures [52]. The intersection of the two extinction curves may be due to differences in fuel composition. The composition of aviation kerosene fuels, such as Jet A, can be highly variable and dependent on may factors such as on the crude oil and refinement process used in the manufacturing process [21]. The composition inconsistency of Jet A and the effect it can have on the thermal-fluid properties has been well documented
[53].
When evaluating the thermal decomposition of Jet A, it was observed that there was a shift in composition to smaller molecular weights as Jet A was thermally stressed.
In order to determine the molecular weight and density of reacted Jet A, all the liquid and 80 gaseous fractions and corresponding molecular weights of each species will need to be determined for the liquid samples analyzed through gas chromatography. Future work will investigate a means to do these experiments by separating the gas and liquid product streams and analyzing the two separately.
350
300
250
200 Jet-A @ 0.8 atm 150 POSF 404658 @ 1.0
100 atm [1] Extinction Strain Rate (1/s) Rate Strain Extinction 50
0 0.04 0.06 0.08 0.10 0.12 0.14 0.16 XF
Figure 5.16: Experimentally measured global extinction strain rate for Jet A plotted as a function of fuel mole fraction.
5.5 Numerical Flame Speed and Adiabatic Flame Temperature
5.5.1 Unreacted and Reacted n-Heptane
In addition to measuring and computing the extinction strain rates of reacted and unreacted n-heptane. Numerical models were developed that investigated the effect of the endothermic reactions on the adiabatic flame temperature and flame speed of the fuel. It is important to note that the reactant temperature for all PREMIX simulations was 298 K.
Each model contained the decomposed n-heptane composition determined from the plug 81 flow reactor using the detailed mechanism. Like the extinction strain rate computations, the reduced n-heptane kinetic mechanism was used requiring the composition to be normalized to account for the missing species. Figure 5.17 contains the resulting adiabatic flame temperature computations for equivalence ratios ranging from 0.4 to 1.6 of reacted and unreacted n-heptane. The maximum adiabatic flame temperature for unreacted n- heptane is 2381 K at an equivalence ratio is 1.1. The characteristic rich shifting of the maximum adiabatic flame temperature from stoichiometric hydrocarbon/air mixtures has been determined to be caused by product dissociation, which reduces the amount of heat released [54]. This dissociation is greater for fuel lean mixtures and is why the maximum adiabatic flame temperature occurs when the mixture is slightly fuel rich [54]. When subjected to a higher reactor temperature and longer residence time of 873 K and 1 min, the adiabatic flame temperature profile is approximately the same the unreacted profile.
The maximum adiabatic temperature of the reacted n-heptane is slightly larger than that of the unreacted n-heptane and again occurs for an equivalence ratio of 1.1 at a value of 2392
K. 82
2600
2400
2200
2000 Unreacted n- heptane 1800 Reacted n- heptane, 873 K, 1600 170 atm, 1 min res.
Adiabatic Flame Temp. (K) Temp. Flame Adiabatic 1400
1200 0 0.5 1 1.5 2 phi
Figure 5.17: Adiabatic flame temperature for reacted and unreacted n-heptane at a reactor pressure of 170 atm, a reactor temperature of 873 K, and a reactor residence time of 1 minute.
Figure 5.18 shows the flame speed of reacted and unreacted n-heptane for the same range of equivalence ratios as the adiabatic flame temperature computations. The resulting simulations experience a similar trend as the adiabatic flame temperature. The maximum flame speed of the unreacted n-heptane simulation was 96.13 cm/s and occurred at the same equivalence ratio, 1.1, corresponding to the maximum adiabatic flame temperature. When n-heptane experienced more decomposition (873 K and a 1 min residence time) the flame speed profile experiences a slight increase in value. This is expected owing to an increase in production of hydrogen, alkenes, and alkynes. Like the adiabatic flame temperature of reacted n-heptane, the maximum flame speed is predicted marginally increase. The 83 maximum flame speed of reacted n-heptane occurs at an equivalence ratio of 1.1 and has a value of 100.0 cm/s.
120
100
80 Unreacted n- heptane 60
Reacted n- 40 heptane, 873
Flame (cm/s) Speed Flame K, 170 atm, 1 min res. 20
0 0 0.5 1 1.5 2 phi
Figure 5.18: Flame speed of unreacted and reacted n-heptane at a reactor pressure of 170 atm, a reactor temperature of 873 K, and a reactor residence time of 1 minute.
5.5.1 Unreacted and Reacted n-dodecane
The adiabatic flame temperature and flame speed for both unreacted and reacted n- dodecane was also numerically simulated. Similar to the n-heptane simulations, the reactant temperature for all PREMIX simulations was 298 K and each reacted model contained the decomposed n-dodecane composition determined from the plug flow reactor simulations. The predict flame speed of reacted and unreacted n-dodecane is shown below in Figure 5.19 for equivalence ratios ranging from 0.4 – 1.6. The maximum adiabatic flame temperature of neat n-dodecane was 2383 K at an equivalence ratio of 1.1. At a reactor 84 temperature of 873 K, a reactor pressure of 170 atm, and a residence time of 1 minute, the adiabatic flame temperature experiences a slight increase in value. The profile shift for reacted n-dodecane is more drastic than the profile shift experienced by reacted n-heptane.
This may be due to the larger production of production of hydrogen, alkenes, and alkynes.
The maximum adiabatic flame temperature for reacted n-dodecane, however, only slightly increases to a temperature of 2385 K. In order to determine why the adiabatic flame temperature profile shifts a sensitivity analysis will be conducted as part of future work.
2600
2400
2200
2000 Unreacted n- dodecane 1800
Reacted n- 1600 dodecane, 873 K, 170 atm, 1
Adiabatic Flame Temp. (K) Temp. Flame Adiabatic min res. 1400
1200 0 0.5 1 1.5 2 phi Figure 5.19: Adiabatic flame temperature for reacted and unreacted n-dodecane at a reactor pressure of 170 atm, a reactor temperature of 873 K, and a reactor residence time of 1 minute.
The laminar flame speed as a function of equivalence ratio for reacted and unreacted n-dodecane is shown below in Figure 5.20. The maximum flame speed for the unreacted n-dodecane simulation occurred at the same equivalence ratio as the maximum 85 adiabatic flame temperature (ϕ = 1.1) and was 84.10 cm/s. The maximum laminar flame speed of reacted n-dodecane occurs at the same equivalence ratio as unreacted n-dodecane
(ϕ = 1.1) and is 88.53 cm/s. In order to elucidate the cause for the slight increases in both adiabatic flame temperature and laminar flame speed of reacted n-dodecane, sensitivity analyses that investigate the various reaction pathways that occur during the combustion process will need to be performed.
100.0
90.0
80.0
70.0
60.0
50.0 Unreacted n- dodecane 40.0
Flame Speed (cm/s) FlameSpeed 30.0
20.0
10.0
0.0 0 0.5 1 1.5 2 phi
Figure 5.20: Flame speed of unreacted and reacted n-dodecane at a reactor pressure of 170 atm, a reactor temperature of 873 K, and a reactor residence time of 1 minute.
CHAPTER 6
CONCLUSION
The presented study investigated the thermal decomposition of n-heptane, n- dodecane, and Jet A using a high pressure reactor at constant reactor temperature of 873
K, a constant reactor residence time of 1 minute, and for pressures ranging from 10 – 170 atm. The composition of the reacted fuels was then analyzed using GC/FID and GC/MS.
The thermal decomposition of n-heptane and n-dodecane was predicted over the same pressure range and the resulting compositions for a reactor pressure of 170 atm were used as inputs for flame speed and counterflow flame simulations. The ultimate goal of the presented work was to elucidate how change in thermophysical properties due to endothermic reactions of thermally stressed fuel affected the extinction strain rates and laminar flame speeds of a large hydrocarbon fuel. Below are the conclusions made from this study:
1. The constructed counterflow flame burner was validated for gaseous fuels
(methane) and liquid fuels (n-heptane) through comparison of previous work and
predicted extinction strain rates. The good agreement between the experimental
data and simulated data indicated that the developed counterflow flame burner was
valid method for measuring the extinction strain rate of hydrocarbon fuels.
2. The detailed n-dodecane chemical mechanism underpredicted the decomposition
of both n-heptane and n-dodecane for all reactor pressures. To closely simulate the
experimental data, the reactor temperature for the numerical models had to be
altered from that of the experimental reactor temperature, 873 K. A lower reactor
temperature was required for low reactor pressures but this requirement gradually 87
increased as the reactor pressure increased. For both n-heptane and n-dodecane, the
formulated species due to endothermic reactions did not predict that of the
experimental data as well as the decomposition of the main fuel species. However,
the observed trends exhibited the same behavior as the experimental data.
3. For all fuels investigated, as the reactor pressure increased, the fuel experienced
more decomposition. This was observed in both the experimental data and
predicted reacted fuel compositions. Additionally, the C/H ratios of the thermally
stressed fuels also increased with pressure as did the formation of unsaturated
hydrocarbons.
4. The predicted extinction strain rates of thermally stressed n-heptane and n-
dodecane at a reactor pressure of 170 atm was lower in value when compared to
the extinction strain rates of their neat counterparts. These observed trends are the
opposite of what was expected. Previous work has shown that the decrease in a
fuel’s molecular weight and or molecular size leads to increase in restance to
extinction [26].
5. Thermally stressed n-heptane was collected in the liquid phase for a reactor
pressure of 170 atm. The extinction strain rate of the collected fuel was then
evaluated using the constructed counterflow flame burner. There was a slight
increase in the extinction strain rates of n-heptane, however, the measured fuel did
not contain the gaseous species that are formed during the pyrolysis of n-heptane.
6. The flame speed and adiabatic flame temperature of unreacted and reacted n-
heptane and n-dodecane was numerically simulated through the PREMIX program
available within CHEMKIN®. The adiabatic flame temperature of unreacted and 88
reacted n-heptane was approximately the same in value, however, the predicted
laminar flame speed of reacted n-heptane was slightly larger than the flame speed
of unreacted n-heptane. For reacted n-dodecane, both the laminar flame speed and
adiabatic flame temperature were marginally larger in value when compared to
those predicted by unreacted n-dodecane.
Future Work
There are multiple steps that will be taken to improve upon the presented work. In regards to the predicted extinction strain rates and laminar flame speeds for both unreacted and reacted n-dodecane, sensitivity analyses will be performed to determine the reaction pathways and chemical transport phenomenon that lead to the predicted results. Next,
GC/FID for thermally stressed gaseous n-heptane will be performed in order to determine the actual combined liquid and gaseous fuel composition. Most importantly, the high pressure reactor will be coupled directly to the counterflow flame burner and experimental measurements of the extinction strain rates of thermally stressed n-heptane, n-dodecane, and Jet A will be performed.
89
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APPENDIX A
A.1: PLUG input for n-dodecane at a reactor pressure of 170 atm, a reactor temperature of 862 K, and a reactor residence time of 1 minute.
XEND 25 DIAM .05 ISO TEMP 862 PRES 170 VDOT 0.00833333 REAC nc12h26 1 DX 1. ATOL 1.0E-14 RTOL 1.0E-14 END
A.2: OPPDIF input for thermally stressed n-heptane at a reactor pressure of 170 atm.
/RSTR /USEV MIX PCAD 0.5 RGTC 1.0 ENRG PLAT AFUE 0 AOXI 0 VFUE 55 VOXI 50.63 TFUE 500 TOXI 298 TMAX 2500 NTOT 800 NPTS 100 XEND .889 XCEN 0.45 WMIX 1.5 PRES 0.8 IRET 50 UFAC 2. SFLR -1.E-4 PRNT 11 TIME 200 1.E-6 TIM2 200 1.E-6 GRAD .1 95
CURV .1 FUEL n2 0.85 FUEL nc7h16 0.0616551 FUEL c2h6 0.03213 FUEL ch4 0.0141440 FUEL c3h6 0.0129132 FUEL c2h4 0.011676 FUEL c4h8-1 0.0074928 FUEL c5h10-1 0.0074864 FUEL c4h6 0.00012291 FUEL h2 0.00064110 FUEL c7h14-2 0.00149115 FUEL c7h14-3 0.00015111 FUEL c4h6 9.6787E-05 OXID n2 0.789916 OXID o2 0.210084 PROD co2 0.22 PROD h2o 0.34 PROD n2 0.44 KOUT h2 o2 h2o oh RTOL 1.E-4 ATOL 1.E-10 ATIM 1.E-10 RTIM 1.E-4 ASEN HSEN END
96
Table A.1: GC/FID results for thermally stressed n-heptane at a reactor pressure of 10 atm,
a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time Compound Area %Area 40 0.99 1-Pentene 199144 0.14% 1- 41 1.06 880577 0.63% Pentene(isomer) 42 1.22 Pentane 2021187 1.44% 46 1.59 2-Pentene, (Z)- 1952697 1.39% 63 5.18 Heptane 1.34E+08 95.52%
Table A.2: GC/FID results for thermally stressed n-heptane at a reactor pressure of 30 atm,
a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time Compound Area %Area 18 0.99 1-Pentene 151670 0.09% 19 1.06 1-Pentene (isomer) 1078340 0.65% 20 1.22 Pentane 2978140 1.80% 23 1.32 Pentane (isomer) 188856 0.11% 23 1.59 2-Pentene, (Z)- 3230203 1.95% 118 5.20 Heptane 153465584 92.86% 123 5.75 Cyclohexane, methyl- 509336 0.31%
Table A.3: GC/FID results for thermally stressed n-heptane at a reactor pressure of 50 atm,
a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time Compound Area %Area 35 1.06 1-Pentene 773270 0.78% 36 1.23 Pentane 2349865 2.37% 37 1.32 Pentane (isomer) 196495 0.20% 40 1.59 2-Pentene, (Z)- 2673756 2.70% 41 1.69 Cyclopropane, 1,2-dimethyl-, cis- 179454 0.18% 42 1.77 Cyclopropane, 1,2-dimethyl-, cis- (isomer) 227271 0.23% 48 4.02 1-Hexene 230859 0.23% 51 5.14 Heptane 90969856 91.90% 52 5.75 Cyclohexane, methyl- 501761 0.51% 53 6.12 Cyclohexane, methyl- (isomer) 167209 0.17%
97
Table A.4: GC/FID results for thermally stressed n-heptane at a reactor pressure of 70 atm, a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time Compound Area %Area 15 1.06 1-Pentene 794566 0.89% 16 1.23 Pentane 2488229 2.79% 17 1.32 Pentane (isomer) 244494 0.27% 20 1.60 2-Pentene, (Z)- 2918849 3.27% 21 1.69 Cyclopropane, 1,2-dimethyl-, cis- 254845 0.29% Cyclopropane, 1,2-dimethyl-, cis- 22 1.77 (isomer) 276507 0.31% 28 4.04 1-Hexene 281974 0.32% 29 4.27 1-Hexene 212342 0.24% 32 5.13 Heptane 80295664 89.89% 33 5.75 Cyclohexane, methyl- 562903 0.63% 34 6.12 Cyclohexane, methyl- (isomer) 186031 0.21%
Table A.5: GC/FID results for thermally stressed n-heptane at a reactor pressure of 100 atm, a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time Compound Area %Area 20 1.06 1-Pentene 764218 0.86% 22 1.23 Pentane 2626627 2.95% 23 1.32 Pentane (isomer) 292095 0.33% 26 1.59 2-Pentene, (Z)- 3294770 3.70% 27 1.69 Cyclopropane, 1,2-dimethyl-, cis- 375247 0.42% Cyclopropane, 1,2-dimethyl-, cis- 28 1.74 (isomer) 384365 0.43% 34 3.79 1-Hexene 190583 0.21% 35 4.05 1-Hexene (isomer) 231980 0.26% 36 4.06 1-Hexene (isomer) 198109 0.22% 37 4.27 1-Hexene (isomer) 286547 0.32% 39 4.65 1-Heptene 235714 0.26% 40 5.12 Heptane 77257552 86.81% 41 5.36 (Z)-2-Heptene 1307353 1.47% 42 5.75 Cyclohexane, methyl- 568252 0.64% 43 6.12 Cyclohexane, methyl- (isomer) 255620 0.29%
98
Table A.6: Predicted n-heptane decomposition for the reactor pressures 10 atm, 30 atm, 50 atm, 70 atm, 100 atm, and 170 atm.
10 atm 30 atm 50 atm 70 atm 100 atm 170 atm
nC7H16 0.6773 nC7H16 0.5536 nC7H16 0.5366 nC7H16 0.4654 nC7H16 0.4106 nC7H16 0.3717
C2H4 0.08837 C2H6 0.1067 C2H6 0.1168 C2H6 0.1431 C2H6 0.1681 C2H6 0.1937
C2H6 0.06188 C2H4 0.1049 C2H4 0.1005 C2H4 0.1021 C2H4 0.0938 CH4 0.08527
C3H6 0.04609 CH4 0.06586 CH4 0.0654 CH4 0.07463 CH4 0.08154 C3H6 0.07785
CH4 0.04495 C3H6 0.06002 C3H6 0.06385 C3H6 0.07276 C3H6 0.07805 C2H4 0.07039
C4H8-1 0.02923 C4H8-1 0.03973 C4H8-1 0.04062 C4H8-1 0.04417 C4H8-1 0.04563 C4H8-1 0.04504
C5H10-1 0.02509 C5H10-1 0.03384 C5H10-1 0.03551 C5H10-1 0.04055 C5H10-1 0.04382 C5H10-1 0.04485
C6H12-1 0.01058 C6H12-1 0.01355 C6H12-1 0.01501 C6H12-1 0.01824 C6H12-1 0.0214 C6H12-1 0.02491
H2 0.009237 H2 0.004607 H2 0.004302 C3H8 0.005525 C3H8 0.008564 C3H8 0.01349
C3H8 0.002157 C3H8 0.002031 C3H8 0.003263 H2 0.004568 C7H14-1 0.0053 C7H14-1 0.008011
C4H6 0.00144 C7H14-1 0.001612 C7H14-1 0.00215 C7H14-1 0.003488 H2 0.00445 nC5H12 0.005476
C4H10 0.001069 C8H16-1 0.000696 C8H16-1 0.000819 nC5H12 0.001333 nC5H12 0.002619 nC6H14 0.004066
C7H14-2 0.000728 C4H6 0.000694 C4H10 0.00062 C8H16-1 0.00131 C8H16-1 0.00204 H2 0.003865
C7H14-1 0.000603 C10H20-1 0.00058 C16H32-7 0.000617 C4H10 0.001145 C4H10 0.001932 C8H16-1 0.003341
C7H14-3 0.00054 C9H18-1 0.000561 C16H32-8 0.000616 C16H32-8 0.001027 nC6H14 0.001782 C4H10 0.003256
C6H12-2 0.000163 C7H14-2 0.000524 C16H32-5 0.000614 C16H32-7 0.001026 C16H32-8 0.001553 C16H32-8 0.002274
C3H4-A 9.39E-05 C11H22-1 0.000506 C16H32-3 0.000613 C16H32-5 0.001021 C16H32-7 0.001548 C16H32-7 0.002262
C5H81-3 7.99E-05 C12H24-1 0.000502 C16H32-6 0.000613 C16H32-2 0.00102 C16H32-5 0.001542 C16H32-5 0.002255
C5H10-2 5.63E-05 C13H26-1 0.000496 C16H32-4 0.000613 C16H32-3 0.00102 C16H32-2 0.00154 C16H32-6 0.002252
C4H8-2 4.71E-05 C16H32-7 0.000477 C16H32-2 0.000613 C16H32-6 0.00102 C16H32-3 0.00154 C16H32-4 0.002252
C6H101-5 4.65E-05 C16H32-8 0.000476 nC5H12 0.000613 C16H32-4 0.00102 C16H32-6 0.00154 c16h32-2 0.002251
C3H4-P 4.63E-05 C16H32-5 0.000474 C16H32-1 0.000612 C16H32-1 0.001016 C16H32-4 0.00154 C16H32-3 0.002251
nC5H12 3.45E-05 C16H32-4 0.000474 C4H6 0.000562 nC6H14 0.000815 C16H32-1 0.001532 C16H32-1 0.002237
C5H81-4 3.4E-05 C16H32-2 0.000474 C7H14-2 0.00056 C15H30-7 0.000789 C9H18-1 0.001192 C9H18-1 0.001956
iC4H8 3.4E-05 C16H32-3 0.000474 C9H18-1 0.000535 C15H30-6 0.000786 C15H30-7 0.001176 C15H30-7 0.001677
C3H3 2.17E-05 C16H32-6 0.000474 C10H20-1 0.000534 C15H30-5 0.000785 C15H30-6 0.001169 C15H30-5 0.001667
C6H101-4 1.86E-05 C16H32-1 0.000473 C7H14-3 0.000502 C9H18-1 0.000784 C15H30-5 0.001169 C15H30-6 0.001666
C6H101-3 1.27E-05 C4H10 0.000468 C15H30-7 0.000479 C15H30-4 0.000784 C15H30-4 0.001167 C15H30-4 0.001663
nC6H14 1.15E-05 C7H14-3 0.000462 C15H30-6 0.000477 C15H30-3 0.000784 C15H30-3 0.001166 C15H30-3 0.001662
C2H2 1.14E-05 C15H30-7 0.000373 C15H30-5 0.000476 C15H30-2 0.000784 C15H30-2 0.001166 C15H30-2 0.001662
C6H12-3 9.41E-06 C15H30-6 0.000373 C15H30-4 0.000476 C15H30-1 0.000778 C15H30-1 0.001156 C15H30-1 0.001644
C3H5-A 1.41E-06 C15H30-5 0.000371 C15H30-3 0.000476 C7H14-2 0.000694 C10H20-1 0.0009 nC8H18 0.001431
iC4H10 4.33E-07 C15H30-4 0.000371 C15H30-2 0.000476 C10H20-1 0.00069 C7H14-2 0.000827 C10H20-1 0.001329
C4H71-3 2.28E-07 C15H30-3 0.000371 C15H30-1 0.000473 C4H6 0.000664 C7H14-3 0.000759 nC9H20 0.001201
C2H5 1.32E-07 C15H30-2 0.000371 C11H22-1 0.000394 C7H14-3 0.000629 C4H6 0.000701 C7H14-2 0.000979
C7H132-4 2.8E-08 C15H30-1 0.000369 C12H24-1 0.000392 C11H22-1 0.000443 nC8H18 0.000556 C7H14-3 0.000911 C7H133-5 2.43E-08 C14H28-1 0.000295 C13H26-1 0.000387 C12H24-1 0.000434 C11H22-1 0.00049 C4H6 0.000584
99
Table A.7: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 10 atm, a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time Compound Area % Area 2 1.06 Propene 431898 0.48% 3 1.23 Butane 735860 1.06% 7 1.60 Pentane 1144848 2.00% 19 4.84 1-Heptene 558556 2.65% 20 5.01 Heptane 115435 0.55% 35 10.21 1-Octene 367507 2.58% 36 10.58 Octane 72487 0.55% 54 14.60 1-Nonene 851248 2.38% 55 14.75 Nonane 188763 0.56% 68 17.11 1-Decene 1030806 2.36% 69 17.21 Decane 73347 0.16% 95 20.93 Dodecane 21893208 81.22%
Table A.8: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 30 atm, a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time Compound Area % Area 2 1.06 Propene 857737 0.46% 3 1.23 Butene 2305586 1.24% 7 1.60 Pentane 4893307 2.63% 11 2.49 Hexane 4569778 2.46% 20 4.84 1-Heptene 6417867 3.45% 21 5.02 Heptane 2140961 1.15% Heptane 22 5.36 459076 0.25% (isomer) 34 10.22 1-Octene 6142723 3.30% 35 10.59 Octane 2031193 1.09% 46 14.60 1-Nonene 5555037 2.99% 47 14.75 Nonane 2111052 1.14% 56 17.11 1-Decene 5490630 2.95% 57 17.22 Decane 609002 0.33% 68 19.05 1-Undecene 2293710 1.23% 69 19.13 Undecane 223893 0.12% 81 20.93 Dodecane 133733040 71.91%
100
Table A.9: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 50 atm, a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time (min.) Compound Area % Area 2 1.06 Propene 475733 0.55% 4 1.23 Butane 1335078 1.54% 8 1.60 Pentane 1621961 1.87% 9 1.62 Pentane (isomer) 1328449 1.54% 10 1.69 2-Pentene 244153 0.28% 2-Pentene 11 1.75 279999 0.32% (isomer) 21 4.84 1-Heptene 3643596 4.21% 22 5.02 Heptane 1814320 2.10% 23 5.36 Heptane (isomer) 399574 0.46% 33 9.51 Toluene 38561 0.04% 34 10.20 1-Octene 3429483 3.96% 35 10.58 Octane 1666226 1.93% 47 14.59 1-Nonene 3067210 3.55% 48 14.75 Nonane 1716931 1.98% 60 17.11 1-Decene 3031338 3.50% 61 17.21 1-Decene (isomer) 562096 0.65% 72 19.05 1-Undecane 1244087 1.44% 73 19.13 Undecane 210104 0.24% 84 20.87 Dodecane 56023236 64.76%
101
Table A.10: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 70 atm, a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time (min.) Compound Area % Area 2 1.06 Propene 636347 0.69% 4 1.23 Butane 1787795 1.93% 5 1.32 1-Butene 213770 0.23% 8 1.60 Butane 2-methyl 1675266 1.80% 9 1.62 Pentane 2023575 2.18% 10 1.69 2-Pentene 366495 0.39% 11 1.75 2-Pentene (isomer) 370045 0.40% 13 2.49 Hexane 2300173 2.48% 23 4.84 1-Heptene 3896031 4.20% 24 5.02 Heptane 2545876 2.74% 38 10.20 Toluene 3647702 3.93% 39 10.59 1-Octene 2359389 2.54% 54 14.41 Octane 217683 0.23% 55 14.59 p-Xylene 3134771 3.38% 56 14.75 1-Nonane 2382258 2.57% 73 17.11 1-Decene 3077353 3.31% 74 17.21 Decane 849323 0.91% 89 19.05 1-Undecene 1306498 1.41% 90 19.13 Undecene 365171 0.39% 102 20.87 Dodecane 50218968 54.08%
102
Table A.11: GC/FID results for thermally stressed n-dodecane at a reactor pressure of 100 atm, a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time (min) Compound Area % Area 2 1.06 Propene 524972 0.79% 4 1.23 Butane 1565754 2.37% 5 1.32 1-Butene 239433 0.36% 7 1.50 Butane 2-methyl 117730 0.18% 8 1.63 Pentane 3286814 4.98% 9 1.69 2-Pentene 435267 0.66% 10 1.75 2-Pentene (isomer) 432745 0.66% 14 2.50 Hexane 1872778 2.83% 24 4.84 1-Heptene 2945574 4.46% 25 5.02 Heptane 2830212 4.28% 37 9.51 Toluene 332676 0.50% 38 10.20 1-Octene 2546109 3.85% 39 10.59 Octane 2457815 3.72% 53 14.59 p-Xylene 2077949 3.15% 54 14.75 1-Nonane 2378649 3.60% 71 17.11 1-Decene 2007348 3.04% 72 17.21 Decane 915388 1.39% 85 19.05 1-Undecene 896377 1.36% 86 19.13 Undecene 409525 0.62% 99 20.84 Dodecane 27956616 42.32%
103
Table A.12: Predicted n-dodecane decomposition for the reactor pressures 10 atm, 30 atm,
50 atm, 70 atm, 100 atm, and 170 atm
10 atm 30 atm 50 atm 70 atm 100 atm 170 atm nC12H26 0.7046 nC12H26 0.565 nC12H26 0.4633 nC12H26 0.3702 nC12H26 0.2737 C2H6 0.2318
C2H4 0.0952 C2H4 0.1315 C2H4 0.1488 C2H4 0.1553 C2H4 0.1809 nC12H26 0.1305
C2H6 0.06159 C2H6 0.09613 C2H6 0.1238 C2H6 0.1505 c2h4 0.1449 C2H4 0.09798
C6H12-1 0.02747 C6H12-1 0.04082 C6H12-1 0.05101 C6H12-1 0.06043 C6H12-1 0.06975 C6H12-1 0.07412
C3H6 0.02144 C3H6 0.03476 C3H6 0.04532 C3H6 0.0547 C3H6 0.06362 C3H6 0.06694
CH4 0.02101 CH4 0.02718 CH4 0.0307 CH4 0.03467 CH4 0.04011 CH4 0.05507
C5H10-1 0.01298 C5H10-1 0.01972 C5H10-1 0.02512 C5H10-1 0.03046 C5H10-1 0.03627 C5H10-1 0.04425
C4H8-1 0.01295 C4H8-1 0.01883 C4H8-1 0.0228 C7H14-1 0.02811 C7H14-1 0.03486 C7H14-1 0.0442
C7H14-1 0.01204 C7H14-1 0.01786 C4H8-1 0.02277 C4H8-1 0.02588 C4H8-1 0.02815 C8H16-1 0.02848
C10H20-1 0.009902 C10H20-1 0.01419 C8H16-1 0.01775 C8H16-1 0.02123 C8H16-1 0.02505 C4H8-1 0.02752
C8H16-1 0.0097 C8H16-1 0.01419 C10H20-1 0.01721 C10H20-1 0.01982 C10H20-1 0.02221 C10H20-1 0.02318
C9H18-1 0.002964 C9H18-1 0.004427 C9H18-1 0.005924 C9H18-1 0.007843 C9H18-1 0.01077 C9H18-1 0.01532
H2 0.002851 H2 0.003865 H2 0.004613 H2 0.005025 C11H22-1 0.005292 nC6H14 0.0123
C11H22-1 0.001564 C11H22-1 0.002307 C11H22-1 0.003048 C11H22-1 0.003958 C3H8 0.00507 C3H8 0.01113
C12H24-1 0.000433 C3H8 0.000818 C3H8 0.001735 C3H8 0.002962 H2 0.004683 nC5H12 0.01064
C4H6 0.000349 C12H24-1 0.000642 C12H24-1 0.000963 nC5H12 0.002013 nC6H14 0.004611 nC9H20 0.007741
C13H26-1 0.000313 C12H24-2 0.000368 nC5H12 0.000945 nC6H14 0.001971 nC5H12 0.004173 nC8H18 0.0077
C12H24-2 0.000232 C4H6 0.00036 nC9H20 0.000922 nC9H20 0.001807 nC9H20 0.003478 C11H22-1 0.007633
C12H24-5 0.000171 nC9H20 0.000358 nC6H14 0.000806 nC8H18 0.001488 nC8H18 0.003134 nC7H16 0.006385
C9H18-4 0.000166 C13H26-1 0.000354 nC8H18 0.000699 C12H24-1 0.001442 nC7H16 0.002535 C4H10 0.005521
C14H28-1 0.000166 nC5H12 0.000324 nC7H16 0.000581 nC7H16 0.00122 C4H10 0.002298 C16H32-8 0.004507
C3H8 0.000157 C12H24-5 0.000272 C4H10 0.000552 C4H10 0.001141 C12H24-1 0.002244 C16H32-5 0.004472
C12H24-4 0.000128 C9H18-4 0.000268 C12H24-2 0.000494 C16H32-5 0.000784 C16H32-8 0.001505 C16H32-7 0.004462
C12H24-3 0.000118 nC8H18 0.000253 C4H6 0.000458 C16H32-8 0.000784 C16H32-5 0.0015 C16H32-6 0.004447
C12H24-6 8.58E-05 nC6H14 0.000242 C16H32-5 0.000437 C16H32-7 0.000781 C16H32-7 0.001496 C16H32-4 0.004417
C4H10 8.41E-05 C4H10 0.000226 C16H32-8 0.000435 C16H32-6 0.000777 C16H32-6 0.001488 C16H32-3 0.004405
C8H16-4 6.38E-05 C16H32-5 0.000223 C16H32-7 0.000435 C16H32-4 0.00077 C16H32-4 0.001477 C16H32-2 0.004403
C16H32-5 6.04E-05 C16H32-7 0.000221 C13H26-1 0.000433 C16H32-3 0.000769 C16H32-3 0.001473 C16H32-1 0.004364
C16H32-7 5.95E-05 C16H32-8 0.000221 C16H32-6 0.000432 C16H32-2 0.000768 C16H32-2 0.001472 C12H24-1 0.003998
C16H32-8 5.88E-05 C16H32-6 0.000219 C16H32-4 0.000428 C16H32-1 0.000766 C16H32-1 0.001465 C15H30-5 0.003571
C16H32-6 5.85E-05 C16H32-4 0.000217 C16H32-3 0.000427 C15H30-5 0.000696 C15H30-5 0.001294 C15H30-7 0.003564
C16H32-4 5.7E-05 C16H32-2 0.000216 C16H32-2 0.000427 C15H30-7 0.000693 C15H30-7 0.001291 C15H30-6 0.003525
C16H32-2 5.69E-05 C16H32-3 0.000216 C16H32-1 0.000426 C15H30-6 0.000685 C15H30-6 0.001275 C15H30-4 0.003511
C16H32-3 5.69E-05 C16H32-1 0.000216 C15H30-5 0.000392 C15H30-1 0.000685 C15H30-1 0.001272 C15H30-1 0.003489 C16H32-1 5.69E-05 nC7H16 0.00021 C15H30-7 0.00039 C15H30-4 0.000684 C15H30-4 0.001271 C15H30-2 0.00347
104
Table A.13: GC/FID results for thermally stressed Jet A at a reactor pressure of 10 atm, a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time (min.) Compound Area % Area 41 4.6 Cyclohexane, methyl- 292063 0.22% 42 4.8 Cyclohexane, methyl- (isomer) 899522 0.69% 43 5.02 Cyclohexane, methyl- (isomer) 300698 0.23% 74 13.62 Decane 525014 0.40% 75 13.87 Decane (isomer) 469876 0.36% 76 14.13 Decane (isomer) 520252 0.40% 77 14.40 Benzene, 1-ethyl-3-methyl- 1230214 0.95% 78 14.58 Nonane 644016 0.50% 79 14.75 Decane, 2,5,6-trimethyl- 1204251 0.93% 80 15.07 Nonane, 3-methyl- 436716 0.34% 81 15.17 Nonane, 3-methyl- (isomer) 728529 0.56% 82 15.46 Nonane, 3-methyl- (isomer) 566208 0.44% 83 15.70 Cyclopentane, (2-methylpropyl)- 1365184 1.05% 84 15.92 Cycloheptane, methyl- 945416 0.73% 85 16.23 Benzene, 1,2,3-trimethyl 700537 0.54% 86 16.43 Benzene, 2-ethyl-1,4-dimethyl- 2030879 1.56% Benzene, 2-ethyl-1,4-dimethyl- 87 16.59 874795 0.67% (isomer) 88 16.84 Undecane, 5-methyl- 1402245 1.08% 89 16.99 Benzene, 4-ethyl-1,2-dimethyl- 1402028 1.08% 90 17.10 1-Deacane 772010 0.59% 91 17.22 Nonane, 3-methyl- 3629362 2.79% 92 17.37 Nonane, 3-methyl- (isomer) 383386 0.29% 93 17.59 Benzene, 2-ethyl-1,3-dimethyl- 2187993 1.68% 94 17.70 Cyclodecene, 1-methyl- 1684501 1.30% 95 17.82 Undecane 855196 0.66% 96 17.94 Undecane, 2,6-dimethyl- 930491 0.72% 97 18.03 Nonane, 3-methyl- 2494550 1.92% 98 18.25 Cyclohexane, 1,2,4-trimethyl- 1246673 0.96% 99 18.37 Cyclohexane, hexyl- 1578013 1.21% 100 18.43 Cyclohexane, hexyl- (isomer) 717407 0.55% 101 18.49 Dodecane, 2-methyl- 1332290 1.02% 102 18.63 Dodecane, 4-methyl- 2578100 1.98% Naphthalene, 1,2,3,4-tetrahydro-5- 103 18.79 1576519 1.21% methyl- Naphthalene, 1,2,3,4-tetrahydro-5- 104 19.01 2510465 1.93% methyl- 105
Table A.14: GC/FID results for thermally stressed Jet A at a reactor pressure of 30 atm, a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time (min.) Compound Area % Area 86 13.39 Decane 137099 0.12% 87 13.62 Decane (isomer) 420276 0.37% 88 13.87 Decane (isomer) 381202 0.33% 89 14.12 Decane (isomer) 502315 0.44% 91 14.40 Benzene, 1-ethyl-3-methyl- 1363655 1.20% 92 14.58 Nonane 747086 0.66% 93 14.75 Decane, 2,5,6-trimethyl- 1103951 0.97% 94 15.07 Nonane, 3-methyl- 345105 0.30% 95 15.17 Nonane, 3-methyl- (isomer) 763520 0.67% 96 15.45 Nonane, 3-methyl- 448114 0.39% 97 15.70 Cyclopentane, (2-methylpropyl)- 1172148 1.03% 98 15.92 Cycloheptane, methyl- 683148 0.60% 99 16.06 Cycloheptane, methyl- 100350 0.09% 100 16.23 Benzene, 1,2,3-trimethyl 646595 0.57% 101 16.43 Benzene, 2-ethyl-1,4-dimethyl- 1792777 1.57% 102 16.59 Benzene, 2-ethyl-1,4-dimethyl- (isomer) 741603 0.65% 103 16.83 Undecane, 5-methyl- 1329571 1.17% 104 17.00 Benzene, 4-ethyl-1,2-dimethyl- 1252794 1.10% 105 17.10 1-Deacane 850744 0.75% 106 17.22 Nonane, 3-methyl- 3270229 2.87% 107 17.37 Nonane, 3-methyl- (isomer) 319530 0.28% 108 17.59 Benzene, 2-ethyl-1,3-dimethyl- 2150104 1.89% 109 17.70 Cyclodecene, 1-methyl- 1497019 1.31% 110 17.81 Undecane 755679 0.66% 111 17.94 Undecane, 2,6-dimethyl- 782216 0.69% 112 18.03 Nonane, 3-methyl- 2201487 1.93% 113 18.24 Cyclohexane, 1,2,4-trimethyl- 1172810 1.03% 114 18.30 Cyclohexane, hexyl- 71160 0.06% 115 18.37 Cyclohexane, hexyl- (isomer) 1283667 1.13% 116 18.43 Dodecane, 2-methyl- 659975 0.58% 117 18.50 Dodecane, 4-methyl- 1115836 0.98% Naphthalene, 1,2,3,4-tetrahydro-5- 118 18.63 methyl- 2357725 2.07% Naphthalene, 1,2,3,4-tetrahydro-5- 119 18.79 1518837 1.33% methyl- (isomer) 120 19.02 Decane, 3,8-dimethyl- 2284693 2.01% 121 19.15 Decane, 3,8-dimethyl- (isomer) 4757786 4.18% 106
Peak Time (min.) Compound Area % Area 122 19.24 Cyclohexane, pentyl- 936919 0.82% 123 19.33 Cyclohexane, pentyl- (isomer) 1159187 1.02% 124 19.44 Cyclohexane, pentyl- (isomer) 1383720 1.21% 125 19.57 Dodecane, 4,6-dimethyl- 848352 0.74% 126 19.65 Dodecane, 4,6-dimethyl- (isomer) 1816407 1.59% 127 19.75 Tridecane 951240 0.83% 128 19.94 Tridecane (isomer) 1423999 1.25% 129 19.94 Naphthalene, 1-ethyl- 1462868 1.28% 130 20.08 Naphthalene, 1-ethyl- (isomer) 1190513 1.05% 131 20.16 Naphthalene, 1-ethyl- (isomer) 702397 0.62% 132 20.22 Naphthalene, 1,6-dimethyl- 1100127 0.97% 133 20.33 Naphthalene, 1,6-dimethyl- (isomer) 1550639 1.36% 134 20.44 Dodecane (isomer) 744603 0.65% 135 20.59 Dodecane (isomer) 1779367 1.56% 136 20.79 Dodecane 5937344 5.21% 137 21.01 Dodecane (isomer) 2554968 2.24% 138 21.12 Dodecane (isomer) 1259843 1.11% 139 21.25 Dodecane (isomer) 660208 0.58% 140 21.31 Hexadecane 589568 0.52% 141 21.42 Hexadecane (isomer) 1248784 1.10% 142 21.56 Hexadecane (isomer) 2018324 1.77% 143 21.69 Hexadecane (isomer) 429717 0.38% 144 21.74 Nonadecane 1209456 1.06% 145 21.87 Nonadecane (isomer) 1838417 1.61% 146 21.98 Nonadecane (isomer) 629839 0.55% 147 22.1 Hexadecane 684433 0.60% 148 22.26 Hexadecane (isomer) 3283781 2.88% 149 22.36 Naphthalene, 2,6-dimethyl- 1062656 0.93% 150 22.43 Naphthalene, 2,6-dimethyl- (isomer) 568110 0.50% 151 22.53 Naphthalene, 2,6-dimethyl- (isomer) 997620 0.88% 154 22.62 Heptadecane 205899 0.18% 165 23.07 Heptadecane (isomer) 2248760 1.97% 167 23.33 Heptadecane (isomer) 1365398 1.20% 170 23.62 Nonadecane 1973087 1.73% 107
Table A.15: GC/FID results for thermally stressed Jet A at a reactor pressure of 50 atm, a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time (min.) Compound Area % Area 90 13.61 Decane 478417 0.48% 91 13.87 Decane (isomer) 458381 0.46% 92 14.12 Decane (isomer) 632326 0.63% 93 14.39 Benzene, 1-ethyl-3-methyl- 1424225 1.42% 94 14.58 Nonane 698512 0.70% 95 14.74 Decane, 2,5,6-trimethyl- 1051218 1.05% 96 15.06 Nonane, 3-methyl- 398454 0.40% 97 15.16 Nonane, 3-methyl- (isomer) 886996 0.89% 98 15.45 Nonane, 3-methyl- (isomer) 448486 0.45% 99 15.69 Cyclopentane, (2-methylpropyl)- 1055272 1.05% 100 15.91 Cycloheptane, methyl- 701893 0.70% 101 16.06 Cycloheptane, methyl- (isomer) 107935 0.11% 102 16.23 Benzene, 1,2,3-trimethyl 621095 0.62% 103 16.42 Benzene, 2-ethyl-1,4-dimethyl- 1481735 1.48% 104 16.59 Benzene, 2-ethyl-1,4-dimethyl- (isomer) 673617 0.67% 105 16.83 Undecane, 5-methyl- 1250144 1.25% 106 16.99 Benzene, 4-ethyl-1,2-dimethyl- 1045458 1.04% 107 17.10 1-Deacane 734005 0.73% 108 17.21 Nonane, 3-methyl- 2484142 2.48% 109 17.36 Nonane, 3-methyl- (isomer) 325807 0.33% 110 17.59 Benzene, 2-ethyl-1,3-dimethyl- 1891361 1.89% 111 17.69 Cyclodecene, 1-methyl- 1117574 1.12% 112 17.81 Undecane 639476 0.64% 113 17.93 Undecane, 2,6-dimethyl- 390131 0.39% 114 17.94 Undecane, 2,6-dimethyl- (isomer) 242583 0.24% 115 18.02 Nonane, 3-methyl- 1734745 1.73% 116 18.24 Cyclohexane, 1,2,4-trimethyl- 995664 0.99% 118 18.36 Cyclohexane, hexyl- 931343 0.93% 119 18.42 Cyclohexane, hexyl- (isomer) 497989 0.50% 120 18.49 Dodecane, 2-methyl- 862690 0.86% 121 18.62 Dodecane, 4-methyl- 1863518 1.86% Naphthalene, 1,2,3,4-tetrahydro-5- 122 18.78 1329989 1.33% methyl- Naphthalene, 1,2,3,4-tetrahydro-5- 123 19.02 1802788 1.80% methyl- (isomer) 124 19.13 Decane, 3,8-dimethyl- 3297860 3.29% 125 19.22 Decane, 3,8-dimethyl- (isomer) 823671 0.82% 108
Peak Time (min.) Compound Area % Area 126 19.33 Cyclohexane, pentyl- 910291 0.91% 127 19.44 Cyclohexane, pentyl- (isomer) 1118944 1.12% 128 19.57 Cyclohexane, pentyl- (isomer) 629670 0.63% 129 19.64 Dodecane, 4,6-dimethyl- 1426571 1.42% 130 19.75 Dodecane, 4,6-dimethyl- (isomer) 791539 0.79% 131 19.93 Tridecane 2270046 2.27% 132 20.07 Naphthalene, 1-ethyl- 880262 0.88% 133 20.16 Naphthalene, 1-ethyl- (isomer) 525884 0.52% 134 20.21 Naphthalene, 1-ethyl- (isomer) 821310 0.82% 135 20.33 Naphthalene, 1,6-dimethyl- 1222612 1.22% 136 20.43 Naphthalene, 1,6-dimethyl- (isomer) 617501 0.62% 137 20.59 Dodecane (isomer) 1473726 1.47% 138 20.78 Dodecane 4349263 4.34% 139 21 Dodecane (isomer) 1835101 1.83% 140 21.1 Dodecane (isomer) 1000531 1.00% 141 21.24 Dodecane (isomer) 556929 0.56% 142 21.3 Dodecane (isomer) 497098 0.50% 143 21.42 Hexadecane 1069399 1.07% 144 21.55 Hexadecane (isomer) 1510569 1.51% 145 21.68 Hexadecane (isomer) 302707 0.30% 147 21.73 Nonadecane 924876 0.92% 148 21.87 Nonadecane (isomer) 1294469 1.29% 151 21.97 Nonadecane (isomer) 396155 0.40% 152 22.09 Nonadecane (isomer) 597180 0.60% 153 22.25 Hexadecane 2267195 2.26% 154 22.36 Hexadecane (isomer) 906491 0.90% 155 22.42 Naphthalene, 2,6-dimethyl- 393334 0.39% 156 22.52 Naphthalene, 2,6-dimethyl- (isomer) 876046 0.87% 159 22.62 Naphthalene, 2,6-dimethyl- (isomer) 267048 0.27% 168 23.07 Heptadecane 2258298 2.25% 170 23.324 Heptadecane (isomer) 1102549 1.10% 175 23.61 Nonadecane 1402858 1.40%
109
Table A.16: GC/FID results for thermally stressed Jet A at a reactor pressure of 70 atm, a reactor temperature of 873 K, and a residence time of 1 minute.
Peak Time (min.) Compound Area % Area 24 4.03 Heptane 1135252 0.77% 25 4.28 Heptane (isomer) 326675 0.22% 26 4.46 Heptane (isomer) 657050 0.45% 27 4.64 Cyclohexane, methyl- 826154 0.56% 28 4.82 Cyclohexane, methyl- (isomer) 1799034 1.22% 29 5.02 Cyclohexane, methyl- (isomer) 1265253 0.86% 30 5.32 2-Pentene, 2,3-dimethyl- 968807 0.66% 33 6.11 Heptane, 2-methyl- 1382045 0.94% 43 9.50 Octane, 2-methyl- 1745932 1.19% 65 13.61 Decane 783491 0.53% 66 13.87 Decane (isomer) 774863 0.53% 67 14.12 Decane (isomer) 1091492 0.74% 68 14.40 Benzene, 1-ethyl-3-methyl- 2453007 1.67% 69 14.58 Nonane 1028738 0.70% 70 14.75 Decane, 2,5,6-trimethyl- 1624532 1.10% 71 15.07 Nonane, 3-methyl- 629169 0.43% 72 15.17 Nonane, 3-methyl- (isomer) 1507321 1.02% 73 15.45 Nonane, 3-methyl- (isomer) 663538 0.45% 74 15.70 Cyclopentane, (2-methylpropyl)- 1567223 1.07% 75 15.92 Cycloheptane, methyl- 1108464 0.75% 77 16.23 Benzene, 1,2,3-trimethyl 913986 0.62% 78 16.43 Benzene, 2-ethyl-1,4-dimethyl- 2097070 1.43% 79 16.60 Benzene, 2-ethyl-1,4-dimethyl- (isomer) 995928 0.68% 80 16.84 Undecane, 5-methyl- 1966226 1.34% 81 17.00 Benzene, 4-ethyl-1,2-dimethyl- 1569550 1.07% 82 17.10 1-Deacane 995794 0.68% 83 17.22 Nonane, 3-methyl- 3447227 2.34% 84 17.37 Nonane, 3-methyl- (isomer) 484488 0.33% 85 17.59 Benzene, 2-ethyl-1,3-dimethyl- 2853705 1.94% 86 17.70 Cyclodecene, 1-methyl- 1487555 1.01% 87 17.81 Undecane 930809 0.63% 88 17.94 Undecane, 2,6-dimethyl- 843190 0.57% 89 18.03 Nonane, 3-methyl- 1999043 1.36% 91 18.24 Cyclohexane, 1,2,4-trimethyl- 1571523 1.07% 92 18.37 Cyclohexane, hexyl- 1261633 0.86% 93 18.43 Cyclohexane, hexyl- (isomer) 653096 0.44% 94 18.50 Dodecane, 2-methyl- 1201478 0.82% 110
Peak Time (min.) Compound Area % Area 95 18.63 Dodecane, 2-methyl- (isomer) 2637250 1.79% Naphthalene, 1,2,3,4-tetrahydro-5- 96 18.79 1992554 1.35% methyl- Naphthalene, 1,2,3,4-tetrahydro-5- 97 19.01 1513660 1.03% methyl- (isomer) 100 19.14 Decane, 3,8-dimethyl- 4351607 2.96% 101 19.23 Decane, 3,8-dimethyl- (isomer) 1066489 0.73% 102 19.34 Cyclohexane, pentyl- 1369587 0.93% 103 19.44 Cyclohexane, pentyl- (isomer) 1574647 1.07% 104 19.57 Cyclohexane, pentyl- (isomer) 802259 0.55% 105 19.65 Dodecane, 4,6-dimethyl- 2061663 1.40% 106 19.76 Dodecane, 4,6-dimethyl- (isomer) 1089593 0.74% 107 19.94 Tridecane 3212282 2.18% 108 20.08 Naphthalene, 1-ethyl- 1129250 0.77% 109 20.16 Naphthalene, 1-ethyl- (isomer) 651444 0.44% 110 20.21 Naphthalene, 1-ethyl- (isomer) 1185925 0.81% 111 20.33 Naphthalene, 1,6-dimethyl- 1727817 1.17% 112 20.43 Naphthalene, 1,6-dimethyl- (isomer) 832751 0.57% 113 20.59 Dodecane (isomer) 2160947 1.47% 114 20.79 Dodecane 5893231 4.01% 115 21.01 Dodecane (isomer) 2361665 1.61% 116 21.11 Dodecane (isomer) 1425338 0.97% 117 21.25 Dodecane (isomer) 744337 0.51% 118 21.28 Dodecane (isomer) 55188 0.04% 119 21.31 Dodecane (isomer) 657265 0.45% 120 21.42 Hexadecane 1570411 1.07% 121 21.56 Hexadecane (isomer) 2080431 1.41% 122 21.69 Hexadecane (isomer) 377116 0.26% 123 21.74 Nonadecane 1321010 0.90% 124 21.87 Nonadecane (isomer) 1659276 1.13% 125 21.95 Nonadecane (isomer) 44498 0.03% 128 21.98 Nonadecane (isomer) 494898 0.34% 129 22.1 Nonadecane (isomer) 816603 0.56% 130 22.26 Hexadecane 2915325 1.98% 131 22.36 Hexadecane (isomer) 1206175 0.82% 133 22.43 Naphthalene, 2,6-dimethyl- 423252 0.29% 134 22.53 Naphthalene, 2,6-dimethyl- (isomer) 1219099 0.83% 137 22.63 Naphthalene, 2,6-dimethyl- (isomer) 378412 0.26% 147 23.07 Heptadecane 2561393 1.74%