AN EXPERIMENTAL INVESTIGATION INTO CHEMICAL ADDITIVE EFFECTS ON IGNITION DELAY OF METH.4NE INJECTED INTO AIR
Brad Bretecher
A thesis submitted in conformity with the requirernents for the degree of Master of Applied Science Graduate Department of Mechanicd and Industrial Engineering University of Toronto
O Copyright by Brad Bretecher. 2000 National Library Bibliothèque nationale IM .,,ad, du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. rue Wellington OttawaON K1AON4 Ottawa ON KIA ON4 Canada Canada
The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or seil reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la fome de rnicrofiche/nlm, de reproduction sur papier ou sur format électronique.
The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts from it Ni la thèse ni des extraits substantiels may be printed or othemise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. An Experimental Investigation into Chernical Additive Effecu on Ignition Delay of Methane Injected into Air M. A. Sc., 2000 Brad Bretecher Department of Mechanical and Industrial Engineering University of Toronto
Abstract
Experiments were performed to investigate if possible synergy exists between two additives introduced to methane that would result in a shorter ignition delay than that for natural gas or methane containing only one additive. Testing was conducted in both a compression- ignition engine and a combustion bomb that afford optical access into the combustion chamber.
Initial engine tests showed the importance of minimizing the injector sac volume of injectors for gaseous fuels. In combustion bomb tests with no power supplied to the glowplug, the methane mixtures reduced the ignition delay value by a factor of three compared to natural gas. Even with the additives. however, the ignition delay times achieved under the conditions tested are too long for practical use in an engine (C 2 rns). For the two lower glowplug temperatures used
(1350 and 1375 K), practical ignition delays cm only be achieved at the highest intake system pressure tested. At the highest glowplug temperature, additives in the methane can provide significant reductions (20-308) in injection delay times. The substantial sensitivity to operating conditions displayed by the results is indicative of the underlying complexity of the processes uivolved. Additional investigation will be required to fully understand the ignition processes. Acknowledgements
I would like to thank Professor Wallace for providing me with a guidance and lrarning atmosphere 1 will forever appreciate. Besides teaching me a lot. Hannu Jaiiskelzinen and Paul
Salanki serve as great role models and friends. Richard Ancimer and Haifeng Liu were also very iieipful ana patient when asked countless questions. Appreciation is expressed to al1 of the machinists at UTMIE who taught me more about design and manufactunng rhan an entire undergraduate degree did. I would like to thank June. Rachelle, Vito, and all of my friends in
Toronto and Winnipeg for brightening my life. Most importantly. 1 would like CO thmk my parents. Ed and Stella, and my sister. Rhonda, who 1 love very much and can always count on for support.
..- III Table of Contents
Abstract
Acknowledgernents
Table of Contents 1v
List of Tables vii
List of Figures X
List of Appendices xii
Nomenclature xiii
1. Introduction 1
1.1 Natural Gas Use in intemal Combustion Engines 1
1.2 Thesis Objective 3
2. Theory and Past Research 4
2.1 Combustion Phases in a Compression4gnition Engine 4
2.2 Factors Affecting Ignition Delay 7
2.2.1 hcylinder Temperature and Pressure 7
2.2.2 Engine Operating Parameters 9
2.2.3 Fuel Composition 11
2.3 Crtane Improvement of Natural Gas 13
2.3.1 Dimethyi Ether 17
2.3.2 Nitromethane 20
3. Experimental Apparatus 22
3.1 Optical Engine 22 3.2 Combustion Bomb
3.3 Fueling Systern
3.3.1 Fuel Mixtures
3.3.2 Fuel Injector
3.3.3 Fuel System Apparatus
3.4 lntake Air Heating
3.5 Combustion Chamber Pressure Measurement
3 -6 Data Acquisition
3 6.1 Bornb Combustion hdges
4. Test Procedures
4.1 Lister-Ricardo Optical Engine
4.1.1 Operating Procedure
4.1.2 Analysis of Optical Engine Data
4.2 Combustion Bomb
4.2.1 Operating Procedure
4.2.2 Analysis of Bomb Data
5. Discussion of Results
5.1 Testing in the Lister-Ricardo Opticai Engine
5.2 Combustion Bomb Experiments
5.2.1 Tesùng without a Glowplug
5.2.2 Combustion Images of Glowplug-Assisted Ignition
5.2.3 Testing with a Glowplug Temperature of 1400 K
5.2.4 Testing with a Glowplug Temperature of 1350 K 52.5 Testing with a Glowpluj Temperature of 1375 K
6, Conclusions and Recommendations
6.1 Optical Engine
6.2 Combustion Bomb
References
Appendices List of Tables
Table 2.1: Properties of Dimethyl Ether (DME) and Diesel-fuel
Table 3.1 : Optical Engine Specifications
Table 3.2: Fuel Mixture Matrix
Table 3.3: Composition of Natural Gas Used for Testing
Table 4.1: Operating Conditions for Optical Engine
Table 4.2: Combustion Bomb Test Conditions
Table 5.1: Latest Start of Injection BTDC for which Ignition Occurs [CADI. intake temp.=340°C
Table 5.2: Average Bomb Openting Temperatures
Table 5.3: Bomb Operating Temperatures, lntake Boost Pressure=O psi
Table 5.4: Bomb Operating Temperatures, Intake Boost Pressure=lO psi
Table 5.5: Bomb Operating Temperatures, Intûke Boost Pressure=20 psi
Table 5.6: Bomb Operating Temperatures, Intake Boost Pressure=30 psi
Table 5.7: Absolute Intake Pressures [kPa]
Table A. 1: Cdibration Data for Glowplug A
Table A.2: Cdibration Data for Glowplug B
Table A.3: Cdibration Data for Washer Load Ce11
Table C. 1: Ignition Delay, no glowplug, nat. gas, int. P=20
Table C.2: Ignition Delay, no glowplug, nar. gas, int. P=25
Table C.3: Ignition Delay, no gIowpIug, nat. gas, int. P=29.5
Table C.4: Ignition Delay. m glowplug, DMVrneth. int. P=20
Table CS: Ignition Delay, no glowplug, DiMYmeth. int. P=25
vii Table C.6: Ignition Delay. no gfowplug,nitrolDMUmet h. int. P=20
Table C.7: Ignition Delay. no glowplug,nitro/DMUmeth, int. P=25
Table C.8: Ignition Delay and Bomb Temperatures. no glowplug. dme/methane, int P=20
Table C.9: Ignition Delay and Bomb Temperatures, no giowplug, nit/dme/methane, int P=20
Tables C. 10: Summary oi ignition Delay Times, Glowplug T=1400 K 1O0
Tables C. 1 1: Summary of Ignition Delay Times, Glowplug T= 1350 K LOO
Tables C. 12: Summary of Ignition Delay Times. Glowplug T= 1375 K 1O0
Table C. 13: Bomb Test Data, nat. gas, GP Temp=1400 K, int P=O psig 101
Table C. 14: Bomb Test Data. nat. gas, GP Terne= 1400 K, int P=10 psig 102
Table C. 15: Bomb Test Data, nat. gas. GP Temp=1400 K, int P=20 psig 1 O3
Table C. 16: Bomb Test Data. nat. gas, GP Temp=LJOO K. int P=30 psig 1O4
Table C. 17: Bomb Test Data. DMEheth. GP Temp=1400 K. int Pdpsig 105
Table C.18: Bomb Test Data, DMUmeth, GP Temp=1400 K. int P=IO psig L O6
Tabie C. 19: Bomb Test Data, DMUmeth, GP Temp= 1400 K, int P=20 psig 1O7
Table C.20: Bomb Test Data, DMUmeth, GP Temp=1400 K, int P=30 psig 108
Table C.21: Bomb Test Data, nitrolDWmeth, GP Temp= 1400 K. int P=O psig 109
Table C.22: Bomb Test Data, nitrolDMUmeth, GP Temp=1400 K. int P=lO psig 110
Table C.23: Bomb Test Data, nitro/DMUmeth, GP Temp=140 K. int P=20 psig 111
Table C.24: Bomb Test Data, nitro/DME/meth, GP Temp=1400 K, int P=30 psig 112
Table C.25: Bornb Test Data, nat. gas. GP Temp=L350 K, int P=û psig 113
Table C.26: Bomb Test Data, nat. gas, GP Temp= 1350 K, int P=10 psig 114
Table C.27: Bomb Test Data. nat. gas, GP Temp=i350 K. int P=20 psig 115
viii Table C.28: Bomb Test Data. DMUmrth.. GP Temp=1330 K. int P=O psig
Table C.29: Bomb Test Data. DMUmeth.. GP Temp= 1350 K, int P= 10 psig
Table C.30: Bomb Test Data, DMUrneth.. GP Temp=l350 K, int P=20 psig
Table C.3 1: Bomb Test Data, nitro/DME/meth., GP Temp=1350 K. int P=O psig
Table C.32: Bomb Test Data, nitro/DME/meth., GP Temp=1350 K, int P=10 psig
Table C.33: Bomb Test Data, nitrolDWmeth., GP Temp=1350 K. int P=20 psig
Table C.34: Bomb Test Data, nat. gas, GP Ternp= 1375 K, int Pdpsig
Table C.35: Bomb Test Data, nat. gas, GP Temp= 1375 K, int P= 10 psig
Table C.36: Bomb Test Data, nat. gas, GP Temp=1375 K. int P=20 psig
Table C.37: Bomb Test Data, DMUmeth.,GP Temp=1375 K. int P=û psig
Table C.38: Bomb Test Data, DMUmeth., GP Temp=1375 K. int P= 1 O psig
Table C.39: Bomb Test Data, DMUmeth.. GP Temp=1375 K. int P=20 psig
Table C.40: Bomb Test Data, nitrolDMUmeth.. GP Temp= 1375 K, int P=O psig
Table C.4 1: Bomb Test Data. nitrolDMUmeth.. GP Temp=L375 K. int P=10 psig
Table C.42: Bomb Test Data, nitro/DME/meth., GP Temp=l375 K. int P=20 psig List of Figures
Figure 2.1: Heat-Release Diagram Showing Phases in Compression-Ignition
Figure 2.2: Ignition Delay vs. Temperature for Different Pressures (fuel mixture is 89.4% methane- 10.6% Ethane)
Figure 2.3: Limited Effectiveness of Cetane hprover (Dodecyl niuate) on the Cetane Number as Concentration is Increased
Figure 2.4: Ignition Delay Time vs. Temperature for Methane Mixtures Containing DME and H202(P=40 bar, $=1.0 methane-air)
Figure 2.5: Major Pathways in the Decornposition of Gaseous Nitromethane
Figure 3.1 : Bowditch Piston
Figure 3.2: Combustion Bomb Mated to CFR Engine
Figure 3.3: Bomb Chamber Geometry
Figure 3.4: Injector Logic Pulse and Fibre Optic Lift Trace During Start of Injection
Figure 3.5: Fueling Apparatus
Figure 3.6: Intake Heating System for Optical Engine
Figure 3.7: Washer-type Load Ce11
Figure 3.8: Optical Engine Data Acquisition System
Figure 3.9: Combustion Bornb Data Acquisition System
Figure 5.1 : In-cylinder Pressure and injector Pulse for Skipfire= 1
Figure 5.2: Injection Cycle
Figure 5.3: Combustion Cycle
Figure 5.4: Original Injector Nozzle for Optical Engine
Figure 5.5: The 0ngin:il and New Pintles
Figure 5.6: New Nozzle with Lenethened Pintle Figure 5.7 Current Injector Nozzle with Tip Removed
Figure 5.8: Peak Bomb Temperature vs. Inrake Pressure
Figure 5.9: Ignition Delay [ms],injection duration = 5 CAD
Figure 5.10: ICCD Combustion Images [CADI BTDC, intake pressure=O psig
Figure 5.1 1 : lCCD Combustion Images [CADI BTDC,intake pressure=lO psig
Figure 5.12: ICCD Combustion Images [CADI BTDC, intake pressure=20 psig
Figure 5.13: Ignition Delay vs. Intake Pressure, glowplug temps=1400 K
Figure 5.14: Ignition Delay vs. Intake Pressure, glowplug temp.= 1350 K
Figure S. 15: Ignition Delay vs. Intake Pressure, glowplug temp.=1375 K
Figure 5.16: Ignition Delay vs. Peak Bomb Pressure, Natural Gas
Figure 5.17: Ignition Delay vs. Peak Bomb Pressure, DMUmethane
Figure 5. L 8: [gnition Delay vs. Peak Bomb Pressure. nitro./DME/methane
Figure A. 1: GLowplug Temp. vs. Resistmce, Glowplug A
Figure A.2: Glowplug Temp. vs. Resistance, Glowplug B
Figure A.3: Load Ce11 Voltage vs. Force
Figure B.1: Chromatograph for 0.1%,5% DME, Methane Mixture
Figure 8.2: Chromatograph of 99.999% Methane
Figure B.3: Chromatograph of Pure Nitromethane List of Appendices
Appendix A: Calibrations
A. 1 Glowplug Calibrations
A.2 Washer Load Ce11 Calibration
Appendk B: Gas Analysis
Appendix C: Bomb Data
C. 1 No Glowplug
C.2 With Glowplug
C.2.1 Glowplug Temperature = 1400 K
C.2.2 Glowplug Temperature = 1350 K
C.2.3 Glowplug Temperature = 1375 K
xii Nomenclature
Abbreviations
ATDC after top dead centre
CAD crank angle degrees
CARB California Air Resources Board
CFC chlorofluorocarbon
Coopentive Fuel Research
me thane
nitromethane
dimethyl eiher
CDM crank degree markers
compression-ignition
dimethyl ether
EGR exhaust gas recirculation
Engine Research and Developrnent Laboratory
flame ionization detector
intensified charge coupled device int P intake pressure
MAP manifold absolute pressure ng natural gas
NGV natural gas vehicte NI-DAQ National Instniments Data Acquisition Sysrem nitro nitromethane
NOx oxides of niuogen rpm revolutions per minute
SOI start of injection
TDC top aead cenue
UTME University of Toronto. Mechanical and Industrid Engineering
VI virtual instrument
xiv compression ratio specific heat ratio 1 Introduction
1.1 Natural Gas Use in Internal Combustion Engines
There are a number of reasons to explore the use of alternative fuels today.
Implementing sorne of these fuels reduces the reliance on foreign cmde oil supply since thev are not typically derived from cmde oil and are more domestically accessible. More impomntly. however, is the reality that the air quality in many urban centres has been in decline, and most alternative furls produce less atmosphenc-altenng emissions. Law stipulating mandatory vehicle emissions testing are becoming more common, and automotive manuhcturers are constantly working to adhere CO demanding guidelines stipulated by the government.
Recently, naturai gas has gained much attention and popularity. especially for vehicle
Reets and transit buses. Research has shown that reductions in hydrocarbon and NOx emissions are possible in natural gas-fueled spark ignition (SI) engines [Il. Carbon dioxide prodüction cm aiso be expected to be Iower since naturai gas is composed of 80-99% methane [2], a gas which contains less carbon per unit energy than any other fossil fuel [3]. An additional benet3 of using
naturai gas in SI engines is reaiized during cold-starting conditions. Unlike gasoline, natural gas
does not bave to be vapourized before mixing with air, therefore fuel enrichment is not
necessary, reducing fuel consumption and hydrocarbon production.
These advantagrs have been reÿlized by many auto companies and engine manufacturrrs
who have developed naturai gas vehicle technology. In fact, Chrysler's naturai gas-fuelled B350
van and minivan were the first vehicles using any fuel to satisfy the California Air Resources
Board's (CARB) low emission vehicle (LEV) and ultra low emission vehicle (ULEV) rcquirements [2]. Currently. there is estimated to be over 800.000 naiural gas vehicles (NGVS) in use worldwide, with 40.000 in the United States alone [-Cl.
Presently, the majority of NGV's are powered by spark ignition engines. Given the substantial emissions reductions accomplished switching from gasoline to natural jas, Furling diesel engines with natural gas appears promising, especially considering that compression ignition (Coengines have higher fuel and mechanical erficiencies. and lower fuel consumption than SI engines.
Despite the apparent advantages of the gaseous fuel. there are problems associated with using it in a diesel engine. Natural gas has a very high research octane number of approxirnately
130 [l]. This fact proves advantageous in an SI engine since a higher compression ratioan be used. thereby increasing the efficiency and power output. Unfortunately. a high octane number implicitly requires a fuel to have a low cetane number. and such is the crise for naturül sas.
Having a low cetane number, naturd gas does not ignite easily in a CI cnginr. This results in a long ignition delay, the time between the start of injection of fuel to the time when ignition occurs. A long ignition delay is undesinble since it results in a high in-cylinder pressure nse and excessive peak pressures. increasing mechanical engine stresses, noise. and emissions. Studies show that methane requires an in-cylinder temperature of approxirnately 1200 K to achieve the acceptable ignition delay standard of 2 ms [5,6]. Such high compression tempcntures required for compression ignition necessitates an ignition assist. One type of ignition assist involves using fuel additives that decrease the autoignition temperature of the hiel. The intention of this thesis is to investigate certain ignition improving additives and t heir effect on ignition dehy . 1.2 Thesis Objective
The objective of this research is CO investisate possible synergy berween isnition improving additives that may be used to reduce the ignition delay of methane injected into compression-heated air. It is intended to establish that ignition delay times cm be reduced by employing additives in economical quantities, rnaking this method of ignition assist attractive for enabling the use of methane or natural gas as a viable diesel fuel. 2 Theory and Past Research
2.1 Combustion Phases in a Compression-Ignition Engine
Use of compression-ignition engines provides numerous advantages, as evidenced by widespread use in trucking and fleet vehiclc applications. These benefits. such as hioh toque and low fuel consumption. result from the combustion process in a diesel engine. Unlike sp&- ignition engines, which require a spark to ignite a homogeneous fuel-air mixture, a compression- ignition engine relies on the tendency of certain fuels to spontüneously ignite, or autoignite. when injected into a high pressure and temperature environment. Since autoignition is actudly . desired, the compression ratio can be higher compared to an SI engine. thus raising the fuel conversion efficiency. Higher fuel conversion efficiencies and lower fuel consumption also result frorn the lean fuel-air ratios (typicdly more than 20% lean of stoichiometric) that are charücteristic of compression-igni tion. Volume tric and mechanicd e fficiencies at pan load are
also greaeater in a CI engine because the intake air is unthrottled, thereby allowing the maximum
amount of air into the cylinders and reducing pumping work [7].
There are a number of stages in the combustion process in a CI engine. They are shown
in Figure 2.1. Premixed combustion phase
O Mixing-controfled combustion phase i
Cmnk angle, deg
Figure 2.1 : Heat-Relese Diagram Showing Phases in Compression-Ignition [7]
Characteristics of the heat-release. defined as the rate of chernical energy relelise of the fuel during cornbust ion. di fferentiate he stages. Of signi ficant importance in this resrarch is the ignition delay penod, bepinning from point (a) , the start of injection (SOI).to point (b), the start of combustion, and can be recognized as having no detectable heat-release. Two separate phenomena occur during this ignition delay. When first injected, the fuel must atomize, vapourize. and mix with air: a process termed physical delay. Time is also required for the oxidation of the fuel and chemical reactions preceding ignition. This rvenr is referred to as chemical delay. and usually occurs simultaneously to the physical delliy. Ir is desirable to hiive short total delay times (less rhan 2 ms). Longer delays allow more fuel and air to mix, so when combustion begins, the pressure increases rnuch more rapidly and is greater in magnitude. This uncontrolled. inefficient combustion cm cause high mechanical stresses. engine vibration and noise. and increüsed NO, cmissions dur io higher prak in-cylinder teniper;ttiires. For rxperimsntütion. pressure transducers lire implrmentrd to detenninr in-cy lindcr pressures. therrby allowinj the heai rctleiise ro be cülculatrd. Howrver. soiiietinirs it is possible to find the ignition point simply by examining the pressure data for ii sharp increase in slopc.
Flame luminosity detectors may also detemine the beginning of ignition by detecting the onset of a flarne, however, typically such methods are not as accurate [7]. Fraser et. al [SI found that t'or natural gas, the luminous delay urne and the delay time found from the pressure were quite simila. Only for delay times less than 0.2 rns were luminous drlays found to be less thiin the pressure delay. One proposed explanation for the difference is that ür higher cylinder trrnperatures. a flame may be visible before enough fuel and air have mixed and combusted to sufficirntly raise the combustion pressure to noticeable levrls.
The second phase of the diesel combustion process, referred to as the premixed combustion phase (b to c). consists of rapid buming of the fuel-air mixtiire thüt mixed to combustible proportions during the ignition delay period. As previously describrd, longer delay times produce larger peak pressures and temperatures during this period. and thus. can be detrimental to engine life and operation.
Following the premixed combustion is the mixing controlled combustion phase (c to d).
During this period, the combustion rate is controlled by the rate at which the fuel and air are able to mix. Typically another peak in heat releasr toms, but is smaller than that of the premixed phase.
The Iast stage is the lare combustion stage (d to e),which is charactenzed by the burning of the last rernaining portions of fuel and combustion products, such as soot. As mentionrd. of the four stages of diesel cornb~istion.the focus of rhis research is on ihr.
ignition dehy pa-iod in ü direct injection, natuml gas fuelcd enginr. There are ri niimbe; of
hctors thar üffecr the delay and will be discussed in the nrxt section.
2.2 Factors Affecting Ignition Delay
2.2. L In-cylinder Temperature and Pressure
For ignition to occur in a diesel enpine, the in-cylinder temperature and pressure have to
be higher thün the autoignition point of the fuel. Therefore, temperature and pressrire have a
large effect on ignition delay. In fact, some research involving fuel injection into constant
temperature and pressure environrnents has shown that temperature and pressure are the mosr
significant factors in the length of the ignition delay for a given fuel [7]. But whereas
temperature effecrs on ignition delüy are very pronounced and estüblished in r he l i terature.
pressure effects seem to be fuel dependent. Siebers and Edwards. as stated by Friiscr et al. [5].
discovered that isooctane and cetane had a significant sensitivity to pressure. but delay times for
rthanol and methanol had little or no dependence on pressure. Fraser et al. however. found that
when igniting natural gas in a constant volume combustion bomb and varying the pressure
between 5 and 55 atm., the pressure affected the delay very little compared to temperature.
These expenmental findings corroborate earlier models thüt arnved üt the samc conclusion. The
strong dependence of ignition delay on temperature and the relative inefkcrivensss of varying
pressure found by Fraser et. al. is shown in Figure 2.2. Figure 2.2: Ignition Delay vs. Temperature for Different Pressures (fuel mixture is 89.4% rnethane- 10.6% Ethane) [SI
More recent studirs discovered that increasing vesse1 pressures resulted in an approximatc tirst order reduction in ignition delay. however. tempenture effects were still much more signifiant WI.
Refemng again to Figure 2.2, it is useful to note that to achieve a desinble ignition delay of less than 2 rns using natural gas, the tempenture in the bomb must be greater than 1200-1250
K. Naber et al. [8] found slighrly lower temperatures (1 100-1 130 K) are required for a delay time of 2 ms. Fraser et al. [5] concluded that the high autoignition temperature of natural gas imposes the need for an ignition assist, such as an ignition source or fuel additives.
Aesoy and Valland [IO] studied the use of a glow plug as an ignition assist and discovered that for optimum fuel jet-glow plug geometries, a glow plug temperature of greater than 1250 K was still required. Other research involving direct injection into a large-bore diesel engine discovered that a glow plus temperature as high as 1350 K was vital For autoignition of natuml gas [II]. Ot'concern for this ignition approüch is the duriibility of the glow plug. Glow plug erosion. corrosion and fatigue are ihr adverse rt'fecis resiiliii~gIi.oiii upwaiioii ai siiçli elevated temperatures [ 101.
A more durüble ignition assist that is becoming popular for natiirül _iüs Cl engines is pilot fuel injection. It entails injecting a small amount of diesel fuel into the cylinder, which ignites rapidly, providing an ignition source for a subsequent injection of natural gas. The combustion of the diesel fuel not only increases in-cylinder temperature, but can also provide free radicals that aid oxidization of the natural gas. Ignition delay times of as low as 1 ms have been observed
[Il]. One dnwback for this ignition method is the complexity of the injector design nectssary for the injection of two separate fuels. Nevertheless, it is still a promishg alternative. sincc even with the addition of the diesel pilot, a reduction in NO, emissions of 50% has been observed
[Dl.
2-22 Engine Operating Parameters
Engine operating parameten, such as load, speed, injection timing, as well as nozzle design can have varied effects on ignition delay times. Most of these factors are secondary since they influence ignition delay by affecring in-cylinder temperatures üt the time of injection. For instance, an engine at higher loüds requires more fuel. The increased amount of fuel itself does not affect ignition delay, since only enough is needed to provide an approximately stoichiometric region to initiate combustion. Rüther the reason why more fuel produces a smdler delay time is because bumîng more fuel per cycle resulü in higher combustion temperatures, and hence increased residual jas and cylinder wall temperatures. Consequently, in-cylinder tempentures are greater during the compression stroke when the fuel is injected. A lincar decrerise in iznition delay with increase in engine load has been observed for various htels [7]. Injection duration affects the delay by altering the ümount of fuel resident in the cylinder for different engine loads. The time when the injection begins üIso has a significant effect.
When injection starts too early in the compression stroke, cylinder temperatures are not high enough for autoignition. Cylinder temperatures are typicdly highest near top-dead-centre
(TDC),however, injection beginning at TDC does not produce the shortest delays. If fuel injection commences at TDC, the pressure and temperature are starting to decrease as a resuit of the piston moving downward in the expansion stroke. To allow for the finite time involved in fuel jet penetration and mixing, the injection should begin before TDC. Minimum ignition delay times occur when the start of injection is 10- 15" BTDC [7]
The ignition delay time can also be decreased by heating the intake air or increüsing the compression ratio, according to the polytropic expression,
T1= T,(~J~-', where T2is the compression temperature, TI is the intake air tempenture, r, is the compression ratio, and n is the polytropic exponent. Heywood (71 explains that empirically. ignition drlay has a strong dependence on intake air temperature when the in-cylinder temperature during injection is below 1000 K, but the influence dirninishes when in-cylinder temperatures are greater than
1000 K.
[ntuitiveiy, higher engine speeds should also result in increased in-cylinder temperatures due to less tirne king available for heat transfer to the cylinder walis. Surprisingly, Heywood notes that a speed increase results in only a slight decrease in ignition delay when rxpressed in milliseconds, and with respect to crank angle degrees, the decrease is approximately linear.
Additionally, under warm engine oprating conditions, the swiri rate that increases wi th engine speed has little effect on delay. In contrast. Sun's [13] simulations of glowplug assisted ignition of nütural gas in ü combustion bomb, higher swirl rates increased the ignition delay substantiülly. The swirl wiis believed to reduce the residrnce time of the fuel jet near the glow pluj. and increse hrüt dissipation in the ignition region, consequently slowing the pre-combustion reactions. Sun
hypothesized that since swirl rate is proportional to engine speed. ignition delay would be very
sensitive to speed variations.
Swirl can also affect the rate of fuel-air niixing. However, factors in fuel-air mixing such
as fuel delivery rate, drop size. and injection velocity were found to have very little effect on the
ignition delay. In some studies. it has been observed that increasing the diameter of the nozzle
orifice by four times had no effect. As well, altering the length-to-diameter ratio of the orifice,
or using multi-hole nozzles changed the delay very little [7]. Although the design of the nozzle
has little effect on ignition delay, the composition of the fuel exiting it is very significant and is
discussrd in the following section.
2.2.3 Fuel Composition
The chernical composition of a fuel affects the autoignition tempenture of a fuel, and
therefore affects the ignition delay for a given set of engine operating conditions. In contrast to
the octane nurnber specification for fuels used in spark-ignition engine, the cetane number for
compression-ignition fuels is higher for fuels that have a greater tendency to autoignite. The
higher the cetane number, the shoner the ignition delay. Normal, straight-chained alkanes obtain
the highest ignition quality, with the ignition quality increasing as the chain length increases.
Adding normal alkanes to a fuel elevares the cetane number, thereby dccreasing delay timrs [ 141. A number of studies have found that the concentration of non-niethme rilkrines in naturr~l
;as makr a significant differencc in drlay times and autoienition temprriitures. Fmer et al. [5] found a slight decrease in delay tirnes for natural jas with higher ethane concentrations. To achieve a delay time of 2 ms for methane-ethane mixtures contciining 0. 5.13 and 10.6 % (by vol.) ethane, temperatures of i250, 1225 and 1200 K, respectively, were required.
As mentioned previously, Naber et al. [8] found that lower temperatures were required for autoignition of methane. Their autoignition temperature for a delay the of 2 n~swas 1 L30
K. cornpared to 1250 K found by Fraser et al.. Deçpite this differencr Naber et al. found the same trend in concentration of ethane versus delay times. Additionally. the nütural gas mixtures with more higher hydrocûrbons like n-butane and propane produced even shorter deliiy tinies.
Since both their experimental and kinetic models showed the same trends. the study concludrd that the srnalier delay times of fuels with increased concentrations of higher hydrocarbons is due
to chernicd kinerics and not ph ysical propenies of the composition. Higher hydrocarbons oxidize more readily, producing OH, H, and O radicals that eventually initiate oxidizrition of the
methane. Without these radicais, methane oxidation would rely solely on O2 [14]. Additional
studies corroborate the sensitivity of ignition delay to fuel composition [15, 16, 171. A
discussion on other ignition-improving additives appean in the following section on cetane
improvers. 2.3 Cetane Improvement of Natural Gas
It is well known that methane. which is the main constituent of natural gas, is the leÿst reactive hydrocarbon fuel. Previous research has found that methane oxidation, and hence ignition, is not controlled by the difficulty in abstracting H atorns from Chto fom methyl radicals (CH,), but rather by the rate at which CH3 decays to fom a significant radical pool.
Since the direct oxidation of CH3 by Oz, depicted by,
CH3 + O2 + CH30 + 0, (1)
and
CH3+ O3 3 CH20 + OH (3) is relatively slow, and methyl radicals do not undergo thermal decomposition. a large portion of rnethyl radicals recombine to yield ethane, as seen in the following reaction [ 181:
CH3+ CH3+ M + C2H6+ M. (3)
The ethane then oxidizes via a sepante mechanism. producing radicds. For fuel-lean mixtures. recornbination accounts for 30% of the methyl radicals und can approach 80% for fuel-rich mixtures [19]. However, more recent experimental research done by Hunter et al. [18] determined that methyl radical recombination is not as rate-determining as the reaction,
CH3+ HO2 + CH30 + OH. (4)
They found this reaction to be the most sensitive in the decomposition of methane. In contriist to alkyl radicals of higher hydrocmbons. direct oxidation of methyl radicals does not producr HO:. a radical known to promote chain branching 181. The absence of a pool of HO2 would explain the slow rate for reaction (4).
AIthough the rate-determining step for methane oxidation is not univewally cigreed upon throughoui the lirerature. it is known that the presencr of üdditional frer radicds. such as O. H. and OH, increases the oxidation rate significantly by providing additional oxidation paths, but more importandy, because thrir abstraction rates of H atoms are very quick [20]. In fact, the OH radical displays the Fastest abstraction rate [20], which rnay account for it acting as the main oxidizing species for many hydrocarbon compounds 1211. It is therefore desirable to increase the number of free radicals in the chernical reactions leading up to combustion in order to reduce oxidation times, and thus, ignition delay times. This cm be accomplished by utilizing fuel additives. Additives that improve the autoignition characteristics of fiels are referred to as ignition or cetane improven. This may be the best solution to fuels having low cetane numbers since other ignition assist alternatives, such as glow piugs or pilot fuel systems, are relatively more complex and expensive. As well, no modifications to the engine would be required if a cetane improver were employed.
The development of cetane improvers resulted due to the need for improved perforn-îance of aircraft. Coider, less dense, air at higher altitudes necessitated the use of fuel additives to enable airplane engines to operate more smoothly. Since 1960, cetane improven have found increased use in regular diesel hels however, since they allow lower qudity diesel fuels tu be used. For instance. in the period from 1962 to 1980, the neat (no additives) cetiine numbers for diesel fuel had ciecreased from 50 to 45. To date. the use of cetane improvers compensaces for the ever-declining quality of diesel fuels [22]. Suppes et. al. [22] found that the cetane number of a fuel can bc increased by 4 with every 0.18 (W.) addition of a cerane irnprover. However, research h;is found that there is a lirnit to their effectiveness, which is shown below in Figure 2.3 Figure 2.3: Limited Effectiveness of Cetane hprover (Dodecyl nitrate) on the Cetane Number as Concentration is Increased [22]
The above figure displays the decrease in effectiveness of ün ignition improver as its concentration is increüsed. The influence of cetane improvers has also been shown to decreüse as the ambient temperature increases 1231.
There are a variety of cetane improven. however. alkyf nitrates are arnong the most
pppppppppppppppp------effective [22]. Alkyl nitrates quicken ignition by decomposing to produce NOz, and subsequently, OH radicals. The nechanism for ignition promotion of methane by alkyl nitrates is as follows [24,25]: Un fortunütely. rate constants or activation energies for these reüctions are unwailable. Future kinetic modeling would be useful in determining these values.
Substantial research has demonstrated the positive effects of NO2 on igition deluy for methane mixtures. Early tests by Dabon [26] found that when 12% (molar) NO? is added to stoichiometric methane-air mixtures at 1300-1800 K and 14 atm.. the ignition delay decreases by
1/2 to 1/3. Slack and Griiio (271 duplicated the result when they edded 1.5% NO1. =hanoand
Dryer [18], interestingly, compared the promoting effects of NOx and eihane, a major constituent in nanirai gas. They obsewed that additions of NO2, as low as 4.2-421.2 ppm. reduced the induction tempenture by more than 200 K compared to methane with 3% ethane. Thus. it was conciuded that NOx is significantly more effective than hydrocarbon additives. Anlano and
Dryer warn that excessive increases in NO?have been found to inhibit oxidative reactions at low and intermediate temperatures due to the OH radical pool diminishing as a result of the followin; reaction:
NO + OH + HONO. (9)
They continue by theorking that because of the significant effect of NOx in such small increments, its thermai formation in the combustion products and presence in residud gases or recirdulated exhaust should reduce the delay times [18].
It is evident that the addition of a cetane improver can decrease the ignition delay, however the synergy between additives can have a much more substantial effect. Ai-Rubaie et ai. [28] discovered that a 50-50 mixture of di-tertiary butyl peroxide and iso-octyl nitrate (2- ethyl-hexyl nitrate) was 25% more effective. in improving ignition than if the two additives had been added separately. Clothier et al. [23] completed a similar test with a lower compression ratio, and concluded that there wiis no ignition improvement: only a reduction in variability from cycle to cycle. Ir was çoncludrd thiit thrre is no distinçr synergy brtwesn the pçroxidrs and the nitrates. but they dcmonstrared. expcrimentally, an interaction berween NO2 and CH@
(formaldehyde) during the pre-ignition phase. This synergy was hypothcsized eulier by
Zamansky and Borisov [23], who stated thüt maximum ignition improvement results from NO2 king added to the fuel, dong with radicals involved in the brünching process, such formaldehyde. This suggests why iso-octyl nitrate (ION) is such LIeeffecrivc igniiiûii pruiiioirr.
Besides yielding NO2, pyrolysis of ION produces formaldehyde. The formaldehyde reacts with
NO2 to form HN02. and the other product radical, CHO, also reacts with NO2 to yield HN02, as seen in the mechanism [25]:
NO2 + CH@ 3 HNO? + CHO (10)
NO2 + CHO 3 HNOl + CO (1 1)
Referring to reaction (7), HN02 decomposes to yield OH radicals. Therefore. the increased
HNOt, and subsequent OH production, thar results from the presence of both NO2 and CH@. makes iso-octyl nitrate one of the most effective ignition improvers.
The CH20 and NO2 do not have to be supplied by the same ignition improver in order for synergy between them to occur. Two separate additives that cm supply the desired formaldehyde and NO2 are dimethyl ether, and nitrornethane, respective1y. They are discussed in subsections 2.3.1 and 2.3.2.
2.3.1 Dimethyl Ether
A cetane improver that provides the oxidation reaction mechanism with formaldehyde, and displays supenor handling qualities, is dimethyl ether (DME). CH20 is formed in two reüctions (( 13) and (1 6)) of its pyrolysis mechanism [21]: CH30 + M + CH20+ H -i- M (13)
H + CH30CH3+ Hz+ CH20CH3 ( 14)
CH3 + CH30CH3+ Ch+ CH20CH3 (15)
CHIOCH3 + M + CH20+ CH3+ M (16)
CH3 + CH3 + C7& (17)
Currently, DME is used prirnürily as an aerosol propellant for spray cans sincr it does not have negative effects on the ozone layer, as do CFC's. It is virtually non-roxic, and breaks down in the tmposphere [29]. Investigation of DME as a possible fuel began only as recently as the 1980's, by Haldor-Topsoe, a Danish Company. It is increasingly obtüining more attention for its possible use as a primary fuel and a cetme improver for compression ignition engines due to its high cetane number (55-60) [301. Propertiçs of DME compared to diesel-fuel are presented in
Table 2.1.
Properties DME Diesel Boiling Point TOC1 -24.9 180-360 Liquid Density [g/crn3] 0.668 0.84 Viscositv kPl 0.15 4.4-5.4 Ignition Temprature ['Cl 235 250 Cetane Number 55-60 40-55 l~atentHt. of Evap. [kl/kg]l 460 (-20') 1 290 1
Table 2.1: Properties of Dimethyl Ether (Dm)and Diesel-fuel [3 11
DME is promising as a compression-ignition fuel because it has been found to produce less noise
and particulate emissions. Given the absence of particulate matter, the NOx-particulate tradeoff,
typical of compression-ignition engines, does not exist. Therefore, exhaust gas recirculation
(EGR) cm be implementcd to reduce NOx formation. An additional bcnefït ro DME is thnt it
cün be produced quite easily from naturd gÿs or mcthanol [29, 301. N~imcrousensine studies have drrnonstrüted ihr reduction in ignition delays and rrnissions obtainable by iising neüt DME in direct-injection compression-ilnition engines, as opposed to diesel-fuel [3 1. 32. 33. 34. 351.
For instance, incorporating EGR, Christensen et. d. 1341 observed a NOs and pmiçulate ernission decrease of 70% and 90921, respectively, compared to their diesel-fuel tests.
From modeling work by Golovitchev and Chomiak [36],DME appears very prornising
for the reduction of ignition delay tiiiies for mehane-air mixtures. The simulated improvement
in delay times of methane by addition of 5 % and 10 % (by vol.) DME is displayed in Figure
2.4.
Figure 2.4: Ignition Delay Time vs. Temperature for Methane Mixtures Containing DME and H202(P=40 bar, $=1.0 methane-air) [36]
It can be seen from the graph that ût 1000 K, the ignition delay drcreases by approximately 8 ms.
with the addition of 5 % DME to the methane. Also shown in Figure 2.4 is the effectiveness of
hydrogen peroxide (Ht02)as cetane improver and the small delay times achievable through the
injection of pure DME. Anlano and Dryer also obssrved the ignition promoting effects of DME. They detetmined that an addition of 1% (by vol.) DME yielded the same et'frct as adding 3% ethüne.
Therefore the DME appears to be more influenthl than ethane, and is attributrd to the fact that
DME decomposition results in a more direct production of formaldehyde, whereas ethane must decompose via ethyl and vinyl radicals. Despite the effectiveness of 1% DME, Arnano and
Dryer discovered th31 NOA vas more effeciivc with addition of jus; 4.2 ppii?, aiid iherei'ure rhey concluded that NOx was the superior ignition improver [18].
Other research has found that DME alone does not irnprove ignition. Murayarna et. al.
[37] atternpted to dissolve DME in methanol. however the engine did not run at d1. rven with concentrations as high as 258 (by vol.). This result reinforces the thcory that DME. ülone, mrty not produce the maximum improvement in ignition. Rather. the synergy between its decomposition product, formaldehyde. and NOr would result in a much more significant effecr.
2.3.2 Nitromethane
Nitromerhane (CH3N02) was first developed in Germany during World War II for use as a rocket propellant, however it has becorne well known for its use as a fuel in drcig racing. [ts appeal lies in the fact that it is not totally reliant on an oxidizer to combust. Therefore the amount that can be bumed is not dependent on the mount of air that cm be inductrd into the system [38]. Nitromethane is very explosive, and its npid ignition cm be credited to the large quantity of NO2 radicals formed early in its decomposition. Subsequently, the reaction of NO? with H radicals produce large amounts of OH radicds, the main species responsible for consumption of the fuel [39]. Of interest in this reseiuch is the abiliiy of nitrornethane to produce NO?, thcreby aiding in producing OH radicds via reactions (6) and (7). The two major paths for the pyrolysis of gaseous nitrometham are depicted in Figure 2.5.
TO FORM cn ,O I + CH*O
HCO REACTS WlTH NO. CO. CC: NOz TO ÇORM -
Figure 2.5: Major Pathwa.ys in the Decomposition of Gaseo111s Nitromethane [39]
The tlowchan shows that formddehyde is formed in both of the probable mechanisms. It is unknown if this fomaldehyde affects oxidation of methme and improves ignition drlny tinies. üs is the case for iso-octyl nitrate. Unfonunately, there has ken no research to date char has investigated the effects of small concentrations of nitromethane on the autoignition of methane.
This study examines the ignition promotion effects of nitromethane and DME. p~icularly,the interaction between them, when added to methme. 3 Experimental Apparatus
As mentioned, the present research examines the effects of fuel additives on ignition delay of naturd gas during compression-ignition. Testing was completed in both an engine and Ü combustion bomb that allowed optical access to the combustion chamber. This chapter details
the engine and bomb, the fuel injecrion system, intake air heating systems, data acquisition, and
the generd design and operational considentions required for successful operation.
3.1 Optical Engine
Prior to this project, a Ricardo Hydra research engine had been modified to allow optical
access into the combustion charnber. This was accomplished by bolting an alurninum Bowditcli
piston onto the existing Ricardo piston. and adding a cylinder block and hrad tiom a Lister
STW-L marine engine. A spacrr block was also designed to be placed beneath the Lisrer
cylinder block, guiding the Bowditch piston. One side of the spacer block is open, such that
there was an optical path from the combustion chamber, through the quartz window in the top of
the piston, to the rnirror that fits inside the oscillating piston at a 45' angle, and out to the carnera
that is acquiring images. A diagram illustrating opticai access into the combustion chamber is
sliown in Figure 3.1. Figure 3. L : Bowditch Piston [40]
The advantage of this design is that no cylinder head modifications are necessary. The cylinder
head remains as it would be in a normal engine. chus not ciffrcting combustion. Without
windows in the head. more room is allowed for other modifications. such as machining a hole to
pppppppppppp------iEconïi5datei $ow plug. Dimensions of the combustion chamber are as follows:
Bore [mm] 95.25 Stroke ïmml 88.90
Table 3.1 : Optical Engine Specifications
Unfortunately, the opticai accessibility afforded by utilizing the Bowditch piston
compromises the range of.compression ratios that can be used. The long (12.75") aluminum
(606 1-T6) piston expands due to elevated tempemtures achieved throu~hintake air heating and
using compression rütios typicdly encountered in diesel rn_oines. During initial motoring of the rnginr in a compression-ignition configuration. the piston could be hrard contiicting the cylindcr heüd. This observation was corroborated by slight rniirkinss in the shape of the piston crown that were discovered on the cylinder head. To estirnate the maximum ümount of rlongation the piston would cxperience during enginr operation, the engine was run in spark-ignition configuration for short periods of time, after which, surface temperatures were measured dong the height of the Bowditch piston. It was estirnated that under firing conditions, expansion as much as 0.060" was possible, limitinp the cold compression ratio (compression ratio before engine wmsup) to approximately 15.5. Therefore. subsequent trsting was completed using a
15.0 compression ratio. To further reduce the possibility of contact brtween the valves and piston crown, valve reliefs were rnachined into the piston crown. Additionülly, the vülvetiming was examined, revealing that contact between the crown and the exhaust valve was probable. promptin: advancement of the valve-timing by 13 CAD.
Another observation dunng initial engine operation was the tippeiinince of hrated oil droplets flying around the combustion chamber. Oil droplets in the cylinder are undesirable since they serve as ignition points and therefore prevent measurement of the true ignition delay of a fuel and the location of ignition of a fuel jet under compression-ignition conditions. As well, fouling of the window results, preventing images of the combustion to be acquired.
Evidence, in the fom of carbon deposits, suggested that the oii was leaking down the valve stems. A seal (CR secils, mode1 3103) and fixture assembly was designed such thai the seal wouid be press fit into the brass fixnire which was then press fit over the valve guide bosses.
The purchased seal is typically used in applications involving rotaring shafts, not reciprocating
shafts, however. they rninirnized oil sliding down the valves and into the cylinder. Anothrr feature of the rngine that reduces the likelihood of oil entering the cy linder al-e oil-less piston rings used on the Bowdirçh piston. These polyirnide-graphite rinss (C. Lrr Cook) obtain a low coeftlcient of friction and good Wear resistance. However, it has been observed that these rings should be replaced at regular intervals to limit blowby. and consequently. prevent a decrease in compression pressure. To check piston ring Wear, it is advisable to perfom le&- down or compression tests regularly, and to check for visible signs of excessive Wear when the head is removed. Ring Wear cm also be retarded by applying a thin layer of oil to the cylinder wall before installation of the Bowditch piston. Caution should be exercised not to apply too rnuch oil such that fouling of the window occurs or oil droplets form and disperse throujhout the combustion chmber.
Besides fouling, another problem was encountered when using the quartz windows in the optical engine. Often, the windows cracked after short intervals of firing or motoring. Diamond filing a larger chamfer on the undenide of the window to reduce stress concentrations proved successful, dl cracking having ceased.
During engine operation, a McClure DC dynamometer, in combination with a Cussons console (mode1 P8810), controls the engine speed. The console also conuols and displays oil
and coolant temperatures. A very useful feature of this set-up is the motorhbsorb setting, wliich
allows the dynamometer to motor the engine, however when fuel is injected and the engine
begins firing, the dynamometer absorbs the torque produced by the engine and maintains the
user-specified speed. This allows troubleshooting without having to fire the engine, reducing
engine Wear and the amount of fuel used.
Funher discussion of the optical ensine set-up and design consideration can be found in
references [LFO] and 141 1. 3.2 Combustion Bomb
The combustion bomb employed for this research was designrd and assemblecf by a research engineer, Paul Sdanki, in the Engine Research and Development Labontory (ERDL) at the University of Toronto. The bomb is mounted on the side of a Cooperative Fuel Resenrch
(CFR) engine, which is used as a npid-compression-device to achieve pressures, and thus temperanires, sufficient for autoignition of naturai gas. There is a port between the bomb and the combustion chamber of the CFR engine, allowing entrance of the inducted air and expulsion of exhaust gases. This port is tangentid to the round bomb chamber. affording simulation of swirl in an engine. The CFR engine itself is fixed on a test bed dong with a DC dynamonieter. A
Hanke (N3) coolant heater and pump circulates 155 OC coolant through the cooling jacket of the engine to reduce heat losses. Funher prevention of heat Ioss out of the bomb is accomplished using an Omega rope heater with an Omegn temperature controller (CN9000A). Temperatures of the back surface of the bomb are monitored using a type K thennocouple dong with a temperature display. A diagram of the bomb set-up is shown in Figure 3.2. Figure 3.2: Combustion Bomb Mated to CRI Engine [42]
The injector, as seen in the above diagram will be discussed in Section 3.3. The cylindncal bomb chamber is 50.8 mm in diameter and 12.8 mm deep, closely resembling the bowl in the piston used in the Ricardo optical engine. The 25.94 cm3 chamber volume contributes to the overdl clearance volume, dong with clearances and cavities in the CFR cylinder. The compression ratio (r,) was maintained constant throughout testing at 16.6.
A glowplug was also implemented to facilitate ignition and promote smaller delay times.
The ceramic tip of the GM/hzu glowplugs (944392 18) used are 5 mm and have a maximum temperature nting of 1475 K. They were cdibrated using a thennocouple fabricated with 0.00 1"
leads that was placed on the surface. Resistance and temperature of the glowplug was measured
as current supplied to it was varied with a transformer. Therefore, surface temperature as a
function of resistance could be determined. The calibmtions are given in Appendix A. Fisure 3.3 shows a schematic of the bomb chamber including the location of the injector tip and glowplug as seen looking through the quartz window.
Figure 3.3: Bomb Chamber Geometry
The injector is located in the centre of the chamber, the glowplug situated 6.17 mm away, 22.5" clockwise from vertical. The orifice of the injector nozzle is aimed 15" clockwise of the glowplug. Previous research by Vito Abate indicated that this was the optimum injection angle
Supercharging was incorporated into the intake to increase the charge density. thereby
facilitating autoignition. A regulator on the intake piping admits cornpressed air at pressures as
high as 30 psig. in combination with intake air heating, bomb tempentures as high as 1350 K
cari be achieved, lMore details about the combustion bomb can be found in reference [QI. 3.3 Fueling System
3.3. t Fuel blixtures
As discussed previously, the purpose of this research is to examine the effecr of the synergy between dimethyl ether and NOz on the ignition delay times of methane compued to
DME alone and naturd gas. Mixtures had to be supplied at pressures greater than the test injection pressure of 1500 psi. Fuel mixtures were rnixed and supplied by Mnrhrso~z &S
Produc~sCanada in cylinders at 2000 psi. Such elevated pressures limited the amount of
3aaseous DME that could be added. since it is typicdly a liquid at room temperature. Having a vapour pressure of 62.3 psig at 20°C [a],the maximum molar concentrition of DME in a 2000 psi mixture for which condensation would not result is 3.85%. Mcrttzrson 'r modeling program indicated a maximum of 5%. therefore this concentration was chosen.
Supplying NOx to the mixture was a more difficult task. The Iow vapour pressure of the proven cetane improver. iso-octyl nitrate (2-cthylhexyl nitrate) prohibited its use. Mcthyl nitrate
(CH3N02) and rnethyl nitrite (CH3NO) showed promise, having vapour pressures that would allow addition of 1210 ppm and 636.84 ppm, respectively. Amano and Dryer [18] showed that concentrations of NOx even at this magnitude are very influential. Unfortunately, there was concem over the explosivity of methyl nitrate. Methyl nitrate can be very volatile and has n tendency to explode at its boiling point of 64'C [45]. Therefore, due to the questionable
handling characteristics and lirnited availability of the lower alkyl nitrates. thoughts of usine them were discarded. Plans of utilizing a gas mixer and creating the fuel mixtures in situ wem
also entertained, however high cost and long delivery times of the gas mixer made this option
unlirtrüctive. Finülly. nitromethane. which is rrhtively easy to iicquire, wüs rxamined as the
possible source of NOx. Since addition to methane was deemrd safe üt the proposed concentrations. it was desided that it would be cised. Vapour pressure c~ilculationsperfomcd bv the author indictitrd that only approximately 37.33 ppm or 0.00328 could be added at iiiixturr pressures of ZOO0 psi before condensing, however the mode1 used by rktheson Gcis Pruducts
Canada indicated that for the methane mixture, 0.1% rnolar concentration nitromethane could be added. Therefore, 0.1% (molar) nitromethane was the concentration implemented for the fuelç.
To test the heory of additive synergy. a mixture of DME and nitromethane. tojether in a balance of methane, was purchased, dong with a mixture of DME and methane to serve as cornparison. The effects of DME alone could dso be compared to a natural gas baseline. The fuels tested. including molar concentrations of additives are included in Table 3.1.
1 Base Fuel 1 % DMEI % ~itromethanel
1 Methane 1 5.11 1 O. 1 1 --- -. --
Table 3.2: Fuel Mixture Matrix
The natural gas used was obtained from the gas supply line at ERDL. The composition of pipeline natural gas can Vary, however the composition used for testing is given in Table 3.2.
- - Propane 0.09 Normal Butane 0.0 1 i ko-Butane 0.0I Ni trogen 1.84 Carbon Dioxide 0.68
Table 3.3: Composition of Natural Gas Used for Testing [46]
Since the concentration of an additive plays a significant role in the effect it has on a fuel, it is important to know the precise qiiantity thüt is presrnt in the fuel. In the present expcrirnenrs. there was a signiticiint chance of additive phase change in thc fuels that were supplieci. and so composition testing wüs deemed necrssaiy. Oniy anülysis of the nitromrthanelDME mixture
was prrformed. Given the cost of testing, analysis of the methtinr with DME alone wüs no[ considered crucial since DME concentrations in the two methane mixtures were similar. and
amounts of DME condensation could be assumed similar since both mixtures were rit the same
pressure. Testing was cornpleted by the ANALEST [ab in the Department of Chemistry at the
üniversity of Toronto using a gas chromatograph with a tlame ionization detector (FID).
Unfonunately, quantitative analysis was not possible with the testing perfonned at ANALEST.
However, it is possible to conclude that there are trace amounts of gaseous nitromethane in the
mixture tested. As well. there is evidence suggesting that gaseous DME is present in the
mixture, despite not having a chromatognph of a pure DME standard to compare against. An
examination of the chromatograph plots can be found in Appendix B.
3.3.2 Fuel Injector
Since gas is being used as opposed to a Iiquid fuel, a normal automotive injector cannot
be used. Vapour fuels have a density that is roughly an order of magnitude smaller than liquid
fuels. Therefore the amount of energy per unit volume is a lot lower, necessitating injection of a
greater volume of gaseous fuel. hjecting a larger volume of fuel requires a larger injector, and
with a larger injector, more force is necessary to facilitate lifting a larger pintle. The injector
used for the research presented here was developed by Green and Wallace [47]. It contains a
solenoid in the head and is electrically actuated, allowing the start of injection and duration to be
varied while the engine is running. Onginally designrd for use in a Lister head. it is relatively
long to clear the valvetrain, therefore it fits in the present Lisrrr-Rictirdo hybrid. The
combiistion bomb also uses this injector, but a two inch shorter nozzle is substituted to match the bomb mounting configuration. The injector nozzle utilized for the optical engine wris designrd pnor to this study [40], however through rhe course of testing, it wÿs concluded that design and fabrication of a new nozzle was necessüry. This is explüined in the discussion of results in
Chapter 5.
hjector opening and closing times cm be determined by implernenting a fibre optic lift sensor that was developed by Enc Brombacher [40j. The fibre optic probe fits into the hrad of the injector. It emirs a light signal and receives the signal that is reflected back by the pintle mature. The reflected signal is then convertcd to a voltage via a photodiode. The higher the pintle lift, the greater the intensity of the reflected signal, thereby allowing observation of pintle lift by voltage change. Unfortunately, there was a tendency for the tibre to move when the injector was pressurized to the 1500 psi injection pressure. The fibre was pushed back. resulting in measured injector opening times that were later than what they actually were. While
üttrmprin; to remedy this problrm. the fibre optic cable was broken. Whilc awaiting delivery of a new one, it was brlieved that the logic pulse that opens the injector could serve as an adequate indication of the opening time. This is justified by examining a trace of the logic pulse and the fibre optic lift trace, obtained when the lift sensor was operationd. This is displayed below in
Figure 3.2: 1735 1740 1745 1750 1755 1760 1765 1770 1375 CDM
Figure 3.4: injector Logic Pulse and Fibre Optic Lift Trace During S tart of Injection
From the plot, the injector pintle lift, as shown by the fibre optic lift trace, begins at the same time as the injector logic pulse that is supplied by the injector driver. Therefore, the logic pulse cmbe used for detennininp the start of injection. However, it is suggested that thc lift sensor be used whenever possible.
3.3.3 Fuel System Apparatus
The optical engine and the combustion bomb share the same fuel system hardware, which cmbe seen in Figure 3.5. High prcwm hosing
A
Connecird to solrnoid valve * when using methme mx~ures
Ai Hi& pressure rrgulaiior
Fuel mixture cylindrr Injecior
Figure 3.5: Fueling Apparatus
A compressed natural gas fueling system at the ERDL allows refueling of tanks up to 3000 psi.
For the present set-up, these tanks are stationed outside the test ceil with 318" Swtigrlok. high pressure (SAE 100RS,4000 psi) hosing and 114 inch stainless steel tubing supplying the gas to a solenoid valve, and then to a Union Carbide high pressure regulator. From the regulator. the gas flows through a Lucas-Scliaevitz pressure transducer (PS 1006 1-0005) to measure the giis supply pressure, and then through a Nupro check-valve to the injecter. When testîng with the methane mixtures, the Matheson IA-sized cylinders are placed approximately one foot from the solenoid valve. As a safety precaution, a Matheson valve (61A) is employed to permit gas 80w to the solenoid valve.
3.4 Intake Air Heating
As previously stüted, naturd güs requires temperatures of iipproximtitely 12W K [O
achieve autoignition. As stated. for the opticiil engine expenments conductcd in this stiidy. a compression ratio of 15.0 was chosen. Theorericülly, this would provide the necessriry 1 100 K in-cylindrr temperature if the intiikr temperature was 533 K, according to the polytropic equation.
TI = T! (rc)Y*l, (3.1) where r, is the compression ratio, and y= 1.3 is the specific heat ratio. To achieve such high intake ternperatures, heating the intake air was imperative. The intake air temperature must be even greater than the theoreticai value since heat losses during an engine cycle are substantial.
Mass loss throuzh leaicage past the piston rings will also result in a lower pressure and temperature compared to the theoreticai value. A diagram of the optical engine intake heating system is displayed in Figure 3.4. 120 V from walI 4 4
Caloritech cartridge heater (3500 W)
111O O i tcmpc*aturc control Ier
. . - 1.5" piping
1
rope heater (500 W) thermocouple
rempenture display cylinder head
Figure 3.6: htake Heating System for Optical Engine
Heating the intake air is achieved by using a circuit of 1.5" diameter piping that contains two resistance heaten; a Wntiorv Firerod (Ll2A82-1731) cartridge heater with a power riting of 1
kW, and a 3.5 kW Caloriteclz cartndge heater (C1R 4360). A 500 W Omegci ropr heater (FGR-
100) is also wrapped around the piping in which the cartridge heaters are housed and the
incoming air flows. A thermocouple, fabricated by welding the two leads of a Type K
thermocouple wire, is located under one of the windings of the rope heater. The thermocouple is
connected to a LED display to indicate the temperature of the rope so that it cmbe turned off in
the event that it approachrs its maximum opemting temperature of 48Z0C,and ihus. pi-eveniinp it ft-on1 burning out. To measure the temperature of the intake air. ü Type K tlirrmocouplc is located in the intake port of the Lister çylinder head. Wrapprd around the pipins of the systenl are three layers of thermoglass tape-type insulation wrap that is rmd to 540 "C (Inrerrrs Ter1i1r.s.
G52RP372). As well. an air filter is placed at the beginning of the system. The motoring time required to reach the desired intake temperature should be kept to a minimum to reduce piston ring Wear, thererore additional heaters should be added if the time required to reach the desired intake temperature becomes longer than 10- 15 minutes. The intake air temperature is controlled by m Ornego temperature controller (CAL 9900). The 120 V signal sent from the controller provides the current for the switch of a Porter and Briimfirld relay (PRDIIAYO). and thus allows transmission of a 208 V current required to operate the Cchriteclz heater. Using this system. intake temperatures as high as 425OC can be attained while the rngine is motoring at
1200 rpm.
Heatin; of intake air is simpler in the bomb than it is in the optical snginr. One. 1000 W
Chrotnnlox heater (FM-1 IO) is required to heat the air to 350°C. Feedback to an Otnegci temperature controller is provided via a type K thermocouple located in the intake manifold of the CFR engine. Heat losses are reduced by wnpping thermoglass tape insulation around the intake piping.
3.5 Combustion Chamber Pressure Measurernent
Combustion chamber pressure data is vital for determining when autoignition occun in the engine cycle. In kt,the change in pressure is dl that is required, rather than the absolute value.
since drtermining the delay involves examining the pressure trxe for ri steep rise that indicates
ignition and subsequent combustion. Typically. a pressure transducrr is ~isedto masure pressures in the cylinder. Howevcr. rmploying a pressure tnnsducer rrquires mounting it in the cylinder head, taking up space thar may be necessary to accommodate a _elowplug in future testing. Fomnately. since only the change in the cylinder pressure is desired. an unobstructive load cell can be used. In the present study, a Trunsducer Techniques washer-type compression load ce11 (LWO- 14K) was implemented in the optical engine by placing it around one of the four cylinder head studs, and resting it on the cylinder head. It is held in place by the stud nut that is torqued down to 55 ft-lbs. The load ce11 configuration is shown in Figure 3.7.
7/ 16 cylinder head stud
signal ampli fier
washer-type load ce11
Figure 3.7: Washer-type Load Ce11
Voltages are generated by the load ce11 when pressures in the cylinder increase, and a compressive force is exerted on it by the cylinder head. Given that the load cd1 rneasures compressive forces, it is not surpnsing that an increase in pressure results in an increase in
negative voltage. This results in a minor image of whüt a normal pressure transducer would measure, retlected across the x-ais. Another disadvanrage of the loüd ce11 is the relativrly noisy signai it produces compared to a pressure transducrr. However both of these problems are minor and cm be eliminated by filtering the data using analysis software such as MATLAB.
Additiondly, as with al1 load cells and transducers, the emitted signal is very small and requires amplification. For this purpose, Miro Kaiovsky, an electronics engineer in the Depanment of
Mechamcal and hdusuial Engineering at the University of Toronto (UTMIE). assembled a quarter wheatstone bridge amplifier.
This specific compression load ce11 was chosen since it had a maximum capacity of
14000 Ibs., and the resulting force from combustion and torquing of stud nuts was determined to be within its range. Dimensions include an outer diameter of 1 inch. an inner diametrr of 0.454 inches, and a height of 0.350 inches. Its compact size allowed it to fit very well within the limited space available on the top of the cylinder head; only minor machining of the cylinder head cover was necessary.
A more traditional method of pressure measurement was employed in the cornbusrion bomb. A Kisrler pressure tninsducer (1631CSP2M) was mounted in the bomb and a Kistlrr amplifier (5004) augmented the signal.
3.6 Data Acquisition
A signifiant pan of the experimental set-up involves data iicquisition. Controlling the necessary input and output signals is the National Instruments data acquisition (NI-DAQ) board
(AT-MIO-16E-2) that is installed into a pentium pc. It receives and administers signals via a
National Instruments termination board (SC 2070). Communication between these two boards. alon? with the use of LabVIEW data acquisition software, allows precise control over the stan and duration of fuel injection. as well as collecting pressure and temperature data. Schemürics depicting the data acquisition systems for the Ricardo-Lister optical engine and combustion bomb are given in Figures 3.8 and 3.9, respectively. Ti-
Dunnz experiments involving rhe moditled Ricordo engine. timing for data acquisition is afforded by a BEI (H25D-SS-1800-ABZ-7404-LED-EM16) shaft encodrr that is mounird to the crankshaft. On the CFR engine is an AVL encoder (360 C 00). Both encoden emit 1800 iogic pulses, or crank degree rnarken (CDM's), and one TDC signal. per revolution. AI1 data acquisition was triggered to begin at the TDC of the exhaust stroke. referred to as non-firing
TDC. Since the encoders output a trigger pulse at every TDC, an optical pick-up on the Cam boxes had to be implemented to ensure that the LabVIEW program began only at the non-firing
TDC. The signals from the carn box and the shaft encoder were compared using an AND sate. allowing the exhaust suoke TDC to be distinguished. For testing with the Ricardo engine, the non-f~ngtrigger signal required conditioning using a unity gain follower circuit to prevent impedance mismatch. Injection of fuel into the combustion chamber began after the number of crank angle degrees specified in LabVIEW had been counted following the triggering evenr.
The LabVEW program, or virtuai instrument (VI) dso allows input for the injection duration. Opening and closing of the injector is accomplished using a dnver that supplies a high current to the injector upon receiving a signal via the NI-DAQ system. The LabVIEW VI's used to control the injector and collect data were originally programmed by Alvin Cheung [41] and
Paul Saianki, and modified by the author. The VI's used for the optical engine and bomb experirnents are named DAQeng.vi and Bradbomb.vi, respectively. The VI capable of monitoring the glowplug voltage and current is referred to as gptempl.vi. It uses data that is acquired from a second board (AT-MIO-l6DE- IO). 3.6.1 Bomb Combustion Images
Obraining images of the ignition is important for observing the flamr development at the ignition site, and can also be used to verify pressure delay tirnes by optically capturing the star1 of ignition. The images may also expose hot spots in the combustion chambcr that act as undesirable ignition sites. Since combustion duntions occur over such small time periods, quick image acquisition is çmcid. For this work a Princeton instruments intensified charge coupled device (ICCD)was irnplemented. A charge coupled device is a two-dimensional array of photodiodes that converts incorning photons into an elecuic current. The intensity at any point of the consequent image is proportional to the number of photons received at that location in the may. An intensified CCD contains an intensifier prior to the array. allowing amplification of the incoming photon signal under Iow light conditions [JO]. The fast response of such a system is due to the absence of a mechanical shutter. The intensifier essentially acts as the shutter. In fact, the detector can acquire images every 20 ns. However, the image acquisition rate is determined by the time required for data transfer between the detector and the controller. During the present testing, the image acquisition rate was 1725 frarnes/s.
Besides the detector, the ICCD system consists of three other main components: the PG-
200 Pulse Generator, the ST-138 Detector Controller, and the Winview image analysis software.
The PG-200 Pulse Generator produces a high-voltage gate pulse that activates the intensifier. It allows user input to specify ûrray exposure time and intensifier voltage. The ST-138 Detector
Controller has a temperature controller, used to cool the detector to between -20°C and -40°Cin order to minimize noise on the array. More irnportantly, it controls the detector may and performs analog to digital conversion of the data received from it. It then uansfers the data to the cornputer coniaining the Winview software. Winview acts as an interface betwren the user and the detector system and tillows irnmediate image processing and analysis. Operiiring procedures and funher details about the system are provided in reference [4Y]
Given the cornplexity of the data acquisition systems and engine hardware. knowledge of operation and test conditions is vital. Such information is given in the following chapter on test procedures. 4 Test Procedures
4.1 Lister-Ricardo Optical Engine
Since the optical engine had not been operated in compression-ignition configuration pnor to this study. preliminq testing was necessary to detemine the hest procedur; foi operation. It was discovered at this juncture that design modifications to the injector nozzle were necessary, and that testing would have to continue in more closely controlled conditions of the combustion bomb. The operating conditions for the optical engim are provided in Table 4.1.
Stm of Injection (CAD 350, 355,360
Intakc Air Tem~("Cl
Table 4.1 : Operating Conditions for Optical Engine
These conditions were not used for completing a test rnatrix, however they serve as a guideline for stable engine operation.
4.1.1 Operating Procedure
1. The oil and coolant levels were checked. The coolant level should be L/2 inch below the top
of the tank.
2. The load ce11 amplifier was powered and the gain set to 1000.
3. The cooling water valve was opened 1/2 turn.
4. The power for the dynomometer cabinet wÿs tumed on. 5. The oil and wüter pumps were tumed on by pressing the respective buttons on the Cussons
control panel. The oil pressure gauge should read 70 psi.
6. The oil and water heaters were actuated. Before continuing. the oil temperature was allowed
to climb to 45°C.
7. The engine flywheel was cranked 2 revolutions by hand to ensure that the piston could move
sniouilily throuyhout the encire cycie.
8. The speed control was set to 15 revis and the reset burton on the ACU panel engaged.
9. The green stm button was pushed. commencing motoring of the engine.
10. The intake heatets were switched on.
1 1. While the intake air was warming up, the LabVIEW progmms. injcctor start.vi and
DAQeng.vi, were loaded.
12. The valve on the fuel cylinder was opened and the "Fuel" button on the control panel was
pushed to open the solenoid valve. The gas pressure to the injector was adjusted to 1400 psi
using the high pressure regulator.
13. Once the intake air had reached its set temperature, data acquisition could begin. The
prograrn start injector.vi was initiated. After ascenaining stable firing operation by listening,
DAQengvi was commenced, acquiring data for five engine cycles. DAQeng.vi then
terrninated fuel injection, and motoring resumed.
14. When testing was completed, the intake heaten were tumed off, and the intake air
temperature was allowed to decrease to 200°C.
15. The red stop button on the control panel was pushed and motoring ceased. 4.1.2 Analysis of Optical Engine Data
A MATLAB program nlimed engde1ay.m was written to collsct the data. M~dific:ttions should be made to it if further trsting is to be atremp~ed.For instance. engde1ay.m was written to detemine delay times for a skipfire value of zero. Therefore, to acquire motoring pressure data to compare with a firing cycle pressure trace, the VI DAQengvi had to be run twice at each test condition; once io ubtain firing cycies, and again hnediately following to secure motoring cycle dara. It is suggested that future testing employ a higher skipfire value, not only because skipfiring allows residual gases that effect delay times to be exhausted, but iilso because it allows motored and firing cycles to be acquired during the same LabVIEW prognm mn. providing greater accuracy and ease of cornparison between the motored and fired traces. The MATLAB
61e. cngde1ay.m should then be modified iiccordingly.
4.2 Combustion Bomb
Each of the three fuels were tested at different intake pressures: 0, 10, 20, and 30 psig.
Ail fuels were tested on the same day for a given test condition to elirninate day-to-day variability. Variability may result from different barometnc pressures on different days. Table
4.1 lists test conditions employed for the combustion bomb for a given intake pressure. Siart of Injection (CAD 1 rilier non-firing TDC) 1 350 Injection Pressure (psi) 1500 Injection Dumion (CAD) 5 Intake Air Temp ["Cl 325 Coolant Temp [OC] 155 Bomb Rope Heater ["Cl 250,300
Mirror Back Temp [OC] Ifcr xspccti~cintakc pressures of O, IO, 20 psig 1 75,200,225 ------
Table 4.2: Combustion Bomb Test Conditions
Refemng to Table 4.2, the testing completed using a glowplug temperature of 1350 K dso employed a 250°C bomb rope heater temperature. When testin; with a 1375 K plowplug temperature. a rope heater temperature of 300°C was employed. Reasons for thrse diffrrent test parameters will be revealed in the discussion of results in section 5.
There are also varying rnirror back temperatures for each intake pressure. The mirror is the back surface of the bomb combustion charnber. Its rear temperature is measured with a 11 16" type-K Omega thermocouple and is accessed through a 1/16" Swagelok fitting in the back of the bomb. The minor is useful for studies involving laser shadowgraph, however was not ripplied to the present research. Before testing began, it was necessary to motor the engine with the intake heater on for approximately 10 minutes before the intake air reached its 325°C set-point.
Expectedly, the mirror back tempenture increased throughout this duration. Even after the intake heater and bomb rope heaters had reached their set-points, the mirror temperature increased. Since motoring the engine until the temperature of the bornb became steady would be impractical, it was decided that for the various fuels, data acquisition wouid begin when the mirror back had reached a certain temperature. This method is outlined in the operating procedure in section 4.2.1. 4.2.1 O perating Procedure
The coolant heater and pump was tumed on and set to 155°C üpproximüte testing.
At the same time. the oil pump was tumed on and the oil heater set to low. The ail
temperature gauge should read approximately 1 10°F when testing commences.
IL wüs then ensureci tnar the inrake pressure was atmosphenc by closing the valve thrit allows
supercharging via the regulator and opening the bleed valve.
Motoring of the CFR engine was initiated by pressing the black button on the dynomorneter
controller and tuming the speed dia1 slowly until the engine speed display rads
approximately 230 rpm. This speed provides stable operation of the enginr and
dynomometer.
The intake heater and the bomb rope heater were tumed on by engaging the switchrs on the
respective temperature controllen. The intake air temperature controller was programrned to
325°C and the bomb rope controller to 300°C (some testing was completed with a bomb rope
remperature of 250°C).
The valves on the natural gas cylinders were opened.
After ensuring that the injector driver was on, the gas regulator was adjusted until the gas line
pressure was at 1500 psi. This task was facilitated by connecting a cable frorn the Lucas-
Schaevin transducer to a multimeter. The rnultimeter read 3 V for a 1500 psi pressure [43].
Iust pnor to the intake air temperature reaching its set-point, power was supplied to the glow
plug. The dial on the autotransformer supplying the power was increased very slowly since
increasing the current rapidly tisks overheating the glowplug. The temperature was monitored using the LabVlEW progrim gptemp l xi. The _olowplugtemperature was 1375fi
K ( 1350 K for sorne tests).
9. After approximately two minutes. the mirror buck reached a temperature of 175OC. Intiike
air, coolant, mirror back, and bomb rope heater temperatures were recorded. The engine
speed and glowplug power was also obtained. Then, data acquisition was staned using
bradbuntb.vi. nizre was injection only once every 5 engme cycles (skipfire4) to allow
adequate exhausting of residual gases. Five mns of the prognm were completed, eüch
consisting of 4 usable firing cycles.
10. The intake pressure was then increased to 10 psig by üdjusting the intake regiilator.
IL. After an additional two minutes. the mirror attained a temperature of 200°C. Another 20
firing cycles were acquired.
12. Turning the regulator once more. the intake pressure was increüsed to 20 psig.
13. Subsequent to the intake air reaching 2?j°C, data for a final 20 tïring cycles was obtained.
14. The glowplug power was reduced slowly.
15. The intake pressure reduced to 5 psig, and the bomb rope and intake heaters switched off.
16. Motoring the engine continued as the intake heater cooled to approximateiy 200°C.
17. The dial on the dynomometer controller was tumed fully conter-clockwise, stopping the engine.
18. A half hour was allowed to pass to permit the engine to cool down. The mirror back
tempenture read approximately 130°C.
19. The process was then repeated with the rnethanelDME fuel mixture followed by the
methane/DME/nitromethane mixture.
Testing the three bels in the reverse order was also ciimed out and is discussed in section 5. 4.2.2 Analysis of Bomb Data
Data acquired with the LabVIEW program. bridbombS.vi, includçd the pressure in the bomb chamber. the pressure in the CFR cylinder. the absolutr pressure of the intakr air. the pulse
that actuates the injector lift, and the signal from the transducer that monitors the gas line
pressure. The ensemble average of the bomb pressures dunng motoring cycles was then
iomputd using a MATLM progrun nmcd bombdeiayrtl.m and plotted wtth each firing cycle.
This is displayed in Figure 4.1.
i ensemble awrage of 16 p, motoring cycles
difference betwen tlring and awraged motoring cyclcs K.
b \ injector pulse l - 10 std dev line 5 std dev linel \ 1 F------,-'(------,------. 1 O00 1200 1 400 1600 1800 2000 CDM Figure 4.1 Data Plot for Determination of Start of Ignition
Employing a technique similar to one used by Fraser et al. [5], a threshold criterion was
established for determining the start of ignition. The difference between the bomb pressures of
an individual firing cycle and an ensemble average of the motored cycles was detrrmined and
plotted. Values of the difference just before ignition were averclgcd and the standard deviation
calculated. The threshold criterion was this average plus five tiines t hr stünclard dcvi;ition r hat wudetemined. Start of ignition occurs at the intersection bctwern this v;ilur. niid the tcicc representing the difference between the fi ring and motoring pressures. Five standard deviaiions
was necessary to avoid noise in the pressure transducer data. For referencr. the injector pulse is
also included in the plot dong with a 10 standard deviation line incorpomted to detemine the
start of injection. Stm of injection was consistently 1750 CDM's, or 350 CAD. tifter TDC.
Xnalyzed data is inciuded in Appendix C. 5 Discussion of Results
As mentioned, prelhinary testing was can-ied out in the modified Ricardo engine with the bulk of the testing completed ir the combustion bomb. In this section, results from testing in both apparatus wiLl be discussed.
5.1 Testing in the Lister-Ricardo Optical Engine
Consideration of operating conditions was very important when research commenced in the optical engine. given that it had not been run in a compression-ignition contigurition prior to this study. For instance, the greater mass of the Bowditch piston assembly and the higher loads experienced in a diesel engine raised concem over mechanical stresses. Therefore skipfiring was incorporated to reduce the frequency of firing cycles, not only to moderate mechanical loads in the engine. but also to afford thorough expulsion of exhaust gases. However, when skipfire values of three or four were applied (fuel injection every fourth or fifth cycle, respectively), combustion was sporadic, not occumng dunng some cycles in which fuel was injected.
Repeatable combustion was attained injecting fuel every cycle or every second cycle. Not only did utilizing skipfire values of zero or one result in stable firing, but injection timing could be retarded from 35" BTDC to 10" BTDC and the injection duration shortened from 40" to 15'. Ln fact it was necessary to retard the timing due to the occurrence of loud knocking. Pitting of the cylinder head gasket, discovered upon removal of the head, served as verification. The diminished variability in combustion with more frequent fuel injection is thought to be a result of the corresponding increase in residuül gas presence and engine cylinder surface rernperatures.
Stable combustion not occumng with higher skipfire values müy indicate that the ternperiitiire dunng compression is still too low and therefore additional intake heüters or suprrcharging may be necessary. To mesure the temperature in the cylinder. a type-K them~ocouplewas fabricated using 0.0005" thennocouple wire. It was made in a IIS" piece of stainless steel tubing that wu installed in a dummy injector nozzle. The nozzle was then clamped down in the cylinder head and the engine rnotored at 900 rpm with the intake heaters operating. For an intake air icmperaîure si 392"C, the moliiiiuni in-çylinder temperature was 1 153 K. This is slightly greater than the 1 100-1 130 K required for an ignition delay of 2.0 ms as determined by Naber et. al 161. However it is slightly lower than the required 1200-1250 K reponed by Fraser et al. 151.
Therefore, additional insulûtion was wnpped around the intake system.
Despite injecting fuel for each cycle and retarding the timing, a bluish flarne, characteristic of pre-mixed combustion, was still observed. After computing the delay times, it was found that ignition for some cycles occurred even before the stan of injection value specified in the LabVIEW software. This is not possible. of course. so funher investigation was warranted. The engine was run with fuel injection every second cycle and additional data acquired. Cylinder pressure was plotted dong with the injector actuating logic pulse and is presented in Figure 5.1. O i 1 r b I In-cyhnder ~iesnire' Combustion Cycle
005 -
- I O Injection Cycle -0.1 -
-0.15 -
Injector Current -0.2 - I 1
Figure 5.1 : In-cylinder Pressure and Lnjectar Pulse for Skipfire= 1 it cm be seen lrom the trace that combustion was not occurring during the cycle in which fuel was injected. Rather, combustion was seen in the following cycle when no fuel was injected.
This discovery indicates that the combustion is indeed prernixed and corroborates the previous observation of the bluish flame. Figure 5.2 and 5.3 provide more detailed views of the pressure traces for the injection and combustion cycles. respectively. Figure 5.2: Injection Cycle
Figure 5.3: Combustion Cycle
The pressure trace exhibiting combustion shows a sharp increase in slope and a higher peak, characteristic of ignition in a diesel engine, whereas the injection cycle obtains no signs of ignition. Although these plots reveal undesirable combustion, they demonstrate the ability of the washer load ce11 to ascenain when ignition occurs, thereby allowing determination of ignition delay times. This is signifiant for future studies in the optical engine.
Combustion occumng a cycle after injection suggests that there is much unburned fuel in the residuai _oses. It is thought that ;as trüpped in the noule is dmwn out whrn the incylindrr pressure is lower during the exhaust and intake strokes followinj injection. Fijure 5.4 shows a cross-section of the current injector nozzk.
Gas channel, 0.125"
-4.367 " 'I I
Figure 5.4: Original Lnjector Nozzle for Optical Engine
Previous research at the ERDL with an injector nozzle orifice of 0.0135" round thüt ~ising
an injection pressure of 1250 psig. a mass flow rate of 1.443 g/s resulted [40]. Givcn this mass
Bow rate and a typical 15" injection duration, approxirnately 0.1 13 cm3 of natural gas exits the
rxisting nozzle, whereas the volume between the pintle and the orifice (sac volume) is 0.848
cm3. Therefore. only a small proportion of fuel arrives in the cylinder during the compression
suoke. The rernainder is trapped in the nozzle. Additionally, the length of the nozzlr affects the
time required for the gas to reach the orifice once the pintle lifts, thereby influencing the amount
of fuel injected at the desired time in the cycle.
To reduce the sac volume, a new design was developed, consisting of press-fitting a new,
smaller polyirnide seat in the gas channei. nearer to the orifice. A longer pintle also had to De
manufactured such that it could protrude further into the injector nozzle. A compromise was
necessary in this new design, since a longer, more massive pintle may prolong injector opening
and closing times. Unfortunately, it was essential that the nozzle and pintle remain long in order
to clear the valvetrain in the Lisrer cylinder head. The new pintle can be cornpared with the
original in Figure 5.5. Figure 5.5: The Original and New Pintles
Steps were taken in the design to ensure that as little mass as possible was added, while making certain that it could withstand the forces subjected to it by the closing spring. For instance. the hexagonal section used to instali the pintle in the injecter, as well as providing a surface for the closing spring to rest against, was reduced in cross-section and height. The diameter of rhe pinrle was reduced to 118" near the tip so it could fit within the nozzle channel, but it was made certain that it could withstand the forces exened on it by the spring such that buckling would not occur.
Exceptionai diffculties were expenenced press-fitting the seat at the end of the long channel
such that no gas would escape between the seat and the channel wall. Several nozzle
modifications were attempted before a new nozzle was designed and fabricated. A cross-section
is displayed in Figure 5.6. Figure 5.6: New Nozide with Lengthened Pintle
It cm be seen that the nozzle remained ifs original length. however the polyimide sear was inserted into the tip near the orifice. This resulted in a substantially smailer sac volume of 0.003 cm! Abate from the ERDL had found a similar modification to the nozzle used for the combustion bomb resulted in a decrease in ignition delay times. This is na uncxpected since a portion of the measured delay would include the time required for the gas to flow from the seat. through the sac volume, and out the orifice. Therefore the rneasured delay time would not accurately reflect the tue delay since fuel does not enter the combustion charnbrr at rhe same time the pintie lifts. For this reason, the new noule, with the reduced sac volume. holds much promise in affording accunte determination of ignition delay. It was designed in collaboration with Jeff Sansome at the UTMIE machine shop, and is shown in Figure 5.7. Figure 5.7 Current Injector Novie with Tip Removed
An important feature of the new nozzle is that its tip is nmovable, which can be seen in the above figure. Having a threaded end, dong with two fiais that accommodate a 11/31" wrench, it can be removed easily. A 0.020" thick copper gasket is placed in the bottom of the threaded hole in the nozzle where it provides a seal to prevent leakage of gas. Removal of the nozzle tip affords much greater ease when press-fitting the seat to the bottom of the tip. Initial attempts at
inserting the seat in the original nozzle resulted in a poor fit, ûllowing Cas to tlow between the seat and the channel wall and out through the orifice. The removable tip allows precise
placement of the seat before it is pressed in, preventing excessive seat materiai removal. It also
provides for sirnpler extraction of a worn or damaged seat. Previously, the only way to extnct a
seat was to heat the tip using a propane torch. The charred remains of the seat were iheri
dislodged with a reaming tool. With the new design, the seat can be removed easily with a small
tap.
It was decided that testing would resume in the combustion bomb while awaiting
machining of the new injector noule. The current study did not punue Further testing in the
engine since the bomb provided a means for deterrnining ignition delay cimes. Therefore an
optical rngine test matrix wris not developed. It is hoped that future work with the opticul ensine will include chüracterization of injection with the current nozzle md continuation of tssting to determine the delay times of the various hels.
5.2 Combustion Bomb Experiments
Testing in a combustion bomb provides a major advantap to completing experiments in an engine. A bomb combustion chamber can be modified with relative ease since there is no valvetrain to impede access. For example, ports for a glonpiug, pressure transducer, or thennocouple cmbe accornmodated.
5.2.1 Testing without a Glowplug
When rxperirnentation began in the bomb, it was desired that test conditions remüin similar to those in the engine for the sake of cornparison. Accordingiy, the glowplug installed in the bomb was not powered. However. to achieve adequate temperatures for autoignition of natural gas, pior testing at the ERDL discovered diat boosting the intake air pressure was necessary. To reach 1200 K, an intake pressure of 15 psig is required when the intake temperature is 350°C. Figure 5.8 displays the peak bomb temperatures during motoring for intake air temperatures of 300°C and 350°C,and varying intake pressures 1431. Intake Pressure [psig]
Figure 5.8: Peak Bomb Temperature vs. ùitake Pressure
The above graph indicates that temperatures above 1350 K are attainabie. while rmploying no intake boosting results in a temperature of approximately 1000 K.
For each of the three fuels, the latest start of injection (SOI) that provided ignition was detennined for intake pressures of 20, 25, and 29.5 psig through trial-and-error. Even though peak cylinder temperatures were assumed be greater than 1200 K at these pressures, the start of injection required for combustion was extremely early. For combustion to occur using an intake pressure of 20 psig and intake temperature of approximately 340°C, a SOI as early as 90 CAD
BTDC was necessary when injecting natural gas at 1500 psig. A table listing the latest start of injection BTDC for which ignition resulted for each fuel at each intake pressure is presented in
Table 5.1. Intake Pressure [psig] Fue t 20 1 25 1 29.5 I \
*not dctermined rtt specified pressure
Table 5.1: Latest Start of injection BTDC for which Ignition Occurs [CADI, intake temp.=340°C
These findings display the very early injection timing required for combustion to occur. They also demonstrate that DME has a significant effect on the ignition of methane. However, possible ignition-improving e ffects of ni tromethane could not be seen wi th this test. nny small differences in the SOI being undetectable with a triai-and-error method based on visual and auditory observation. Thus, additional testing was carried out to determine delay times for the injection timing sern in Table 5.1. Ignition delays for start of injection values lisied in Table 5.1 and an injection dunrion of 5 CAD are shown below in Figure 5.9.
I 01 15 20 25 30 tntake Pressure [psig]
Figure 5.9: Ignition Delay [ms], injection duration = 5 CAD tt should be noted that these tests were prelirninary and the delay times shown are an average of three firing cycles. As cm be seen in Figure 5.9, tests in die combustion bomb conducted without energizing the glowplug, the use of both DME and the combination of DME and iiiuomethane, produced a very substantial reduction in delay time (approximately a factor of three) compared to natui-ai gas. No significant difference was observed between the two mixtures under these conditions.
Since the two methane mixtures contaiaing additives as well as methane had similar delay times, a larger data set was acquired to obtain more accurate ignition delay values so that statistical differences between the two mixtures could be identified. An intake boost pressure of
20 psig was applied and the temperature controller for the intake heater was set to 350°C.
Twcnty-one cycles were averaged to determine the delay time for the two fuels. The methane mixture containing no nitromethane had an ignition delay of 18.43 ms. whereas the gas with
0.1% nitromethane added yielded a delay of 16.62 rns. This result seerned promising until the recorded temperatures for mirror back, intake, coolant, and bomb heater temperatures were exarnined. niese temperatures are provided in Table 5.2.
Fuel delay [ml int. air [OC] coolant laCl bomb heateri°C] rnirror back [OC3 DMWmethane 18.43 338.4 155.4 347.6 209.6 nitroJDMWmethane 16.62 34 1 .O 155.4 366.3 240.3
Table 5.2: Average Bomb Operating Temperatures
It is noticed that the bomb mpe heater and mirror back are 18.7OC and 30.7"C pater,
respectively. during testing with the nitromethane spiked mixture. The rnirror acts as a surface
of the combustion chamber. Therefore it would be expected that a higher temperature inside the
bomb chamber would correspond with a higher mirror temperature. resulting in a reduced drliiy time. Thus, it cannot be concluded that the mixture containing nitromethrine obtains tt lower delüy time. However, it was surmised that the openting tempentures, rspecially the mirror back temperature, have a significant effect on the delay times and therefore deserve greater attention.
AU test results discussed heretofore are included for reference in Appcndix C.
Even with use of ignition enhancing additives, the ignition delay times achieved under
the ionditions testcd are too iung fur praçtical use in an engine. Opùmizarion oi additive types
and concentrations might change this finding, however.
At this juncture in the testing, it was desired to reduce the ignition delay times to values
that are typically encountered in diesel engines. To lower the delay times to 2 ms. incorporating
a glowplug was essential. Not only would a glowplug decrease the ignition delay. but it enables
the naturai gas to be injected at the same time during the cycle as the other two fuels. nearer to
TDC.
5.2.2 Combustion Images of Glowplug-Assisted Ignition
The primary intent in using a glowplug is to beat a region of the fuel jet that has entrained
air and mixed to near stoichiometric proportions, thereby initiating combustion. Previous
research in the lab by Abate employed a glowplug temperature of 1400 K. It was discovered that
delay times were a minimum when the orifice of the injector nozzle was aimed 15' clockwise
from the glowplug. These parameters were implemented for the current research so that ignition
delay values could be compared. Images acquired using the ICCD camera for these conditions
using nanird gas and atmospheric intake pressure is shown in Figure 5.10. Figure 5.10: ICCD Combustion Images [CADI BTDC, intake pressure=O psig
It should be noted that the first frame in a sequence is overexposed due to an initiation time required for the controller [48]. As well, stixakins appears rhroughout the sequencr. and may be due to suboptimal detector pulse gate widths. The bright spot that üppeius in al1 of the frames is the glowplug. The injector is down and to the left of the glowplug and directs the fuel spray up and to the right, 15" clockwise of the glowplug, as seen in Figure 3.3. In Figure 5.10. it cm be seen that combustion initiates downstream of the glowplug, in the 2 o'clock position. at approxirnately 3.8O BTDC. This translates to a 4.49 ms delay time for an engine speed of 230 rpm. The delay measured with the Kistler pressure transducer was 3.38 ms. The difference in delay tirne between the two methods is not very large considering that the precision afforded by the image frequency implemented is 0.6 ms. Additionaily, determining delay times using the
ICCD camera requires visuai observation, and therefore human error may result.
For a boost pressure of 10 psi, Figure 5.1 1 shows the luminous delay was shorter than the pressure delay, which is opposite to the result obtained for atrnospheric pressure. Figure 5.1 1: ICCD Combustion Images [CADI BTDC,intake pressure= 10 psig
Ignition for 10 psig boost pressure occurs markedly earlier than in the case of atmospheric pressure intake. Some brightness cm be seen 7.8 CAD before TDC, resulting in a luminous drlay time of 1.59 ms. The pressure delay for the same cycle was rnuch higher ai 3.92 ms. The reason for the discrepancy, not explained in this case by the poor time resolution of the images, rnay be a result of combustion becoming visible before a significant increase in pressure is detected by the pressure trakducer. This is what Fraser et. al [5] observed. albeit only for ignition delay times less than 0.2 ms.
The sarne phenornenon-luminous ignition well in advance of the ignition determined from pressure-was observed when using an intake pressure of 20 psig. The image sequence is shown below in Figure 5.1 1.
10.2" 9.4" 8.6" 7.8" 7" 6.2" 5.4" 4.6" 3 .go
Figure 5.12: ICCD Combustion Images [CADI BTDC. intake pressure=20 psig Luminosity is detectable as early as 9.4 CAD before top dead centre. This translates to a 0.43 ms ignition delay. whereas the pressure delay was 1.18 ms. Although there is a difference between the lurninous and pressure delay times, analysis of pressure data provides quick determination of ignition delays, has greater temporal resolution. and is free from the human error that is possible in finding luminous delays. Therefore pressure analysis was the method used to determine ignition delays throughout the testmg.
5.2.3 Testing with a Glowplug Temperature of 1400 K
Experiments in which the glowplug was maintained at 1400 K were completed using four different intake boost pressures: 0, 10, 20, and 30 psig. There were a number of reasons for choosing this range of pressures. Although it is known that higher intake pressures will result in higher compression pressures and ternperatures, and therefore decrease the ignition delay. however a trend that exhibits any sharp decreases in deiay would be notable and useful to know. in fact, prior expenments found that there is a distinct decrease of approximately 8 ms for intake boost pressures above 12.5 psig [43]. A second reason for investigating a range of boost pertains to the actuai delay tirnes rather than a trend. A large intake boost allows insight into the minimum possible delay for the given test apparatus. However, at elevated intake pressures it is difficulr to distinguish significant differences in delays between the various hiels because previous research has shown that as the combustion chamber temperature is increased, the
relative influence of a cetane improver diminishes [23]. Therefore low intake pressures are exploited for the purpose of showing any effect an additive has on ignition delay.
The ignition delays, dong with 958 confidence intervals, for dl three fuels and the
vürious intake boost pressures are displayed below in Figure 5.13. - --- -+-ng
' -C dme - -A - niWdme-
0,; 1 0,; O 5 10 I5 20 3 30 35
Intake Pressure [psigj
Figure 5. L 3: Ignition Delay vs. Intake Pressure, glowplug temp.= 1400 K
The delay times show in Figure 5-13are an average of delay times for 20 firing cycles for each test condition. It is unexpected to sec that the DMUmethane mixture produces a delay tirne of
4.2 ms for atmosphenc intake. whereas natural gas yields a shoner value of 3.6 ms. 011the
whole however, the figure shows lhat, as expected, the ignition delay is reduced as the in-
cylinder temperature is increased (where increasing the intake pressure results in increased in-
cylinder temperature). It be seen that the additives have the greatest effect at lower
temperatures (O psig). This effect is reduced as the temperature is increased and the methane
ignition chemistry becornes fast enough to achieve reasonable ignition delays. For example. at
atmosphenc pressure intak the addition of both DME and nitromethane produces a 308
decrease in ignition delay. At 10 psig intake pressure, the improvement is only 21% while at
higher temperatures, the= is no significant difference between the ignition delay for any of the
fuels- To investigate possible effects of bomb apparatus temperatures on the ignition delay, temperatures of the intake air, coolant, bomb rope heater, and mirror back are presented in
Tables 5.3 through 5.6.
Fuel intake air [OC] codant [OC] 1 bomb heater [OC] mirror back ["Cl ng 350 155 294 207 dme 350 155 26 1 166 nitro/dme 35 1 155 276 184
Table 5.3: Bornb Operating Temperatures, Intake Boost Pressured psi
Fuel intake air [OC] coolant [OC]1 bomb heater [OC] mirror back [OC] ng 350 155 306 224 - dme 1 350 1 155 1 280 I 192
Table 5.4: Bomb Openting Temperatures, Intake Boost Pressure= IO psi
Fuel intake air [OC] coolant [OC] bomb heater [OC]mirror back ["Cl ng 343 L55 32 1 242 drne 347 155 318 240 [nitrofdrne 334 155 308 228
Table 5 -5: Bomb O perating Temperatures, Intake Boost Pressure=20 psi
Fuel intake air [OC] coolant [OC] bomb heater rC] mirror back [OC]
. ng 334 155 339 264 drne 337 155 338 262 ni tro/drne 335 155 330 253
Table 5.6: Bornb Operating Temperatures, htake Boosr Pressure=30 psi Compxing these tables, it can be seen that there was successful control of the intake air and coolant temperatures for the various fuels. Note that as the boost pressure is increased. the intake air temperature decreases modestly. This is a due to the higher mass flow rates that result from higher intake pressures and the inability of the single 1ûûû W intake heater to maintain the set- point temperature of 350°C. If future testing requires a 350°C intake temperature using boost pressures of 20 or 30 psi, an additional intake heater must be incorporated.
The bomb rope heater and mirror temperatures data require closer examination.
Refemng to Table 5.5, the temperatures recorded for atmospheric intake pressure, the bomb rope heater and mirror back temperatures during expenments with the DMUmethane mixture are
33OC and 44OC lower, respectively, than the temperatures when testing with naturd gas. These relatively large differences serve as a possible explanation for the longer 4.2 ms delay time seen
for the DMUmethane, versus the 3.6 ms for natural gas. It cannot be concluded thüt the DME
mixture has a longer ignition delay because for a boost pressure of 20 psi. the deiays of the two
fuels are close and the operating temperatures in Table 5.5 are almost the siirne. As well. for an
intake pressure that is 30 psi above atmospheric. the DMUmethane mixture has a shoner delay
while the temperatures observed during testing of the two fuels were comparable. as sern in
Table 5.6.
A prornising result is chat the delay time for the methane mixture containing nitrometliane
and DME is shorter than that for natural gas. even though the bomb openting temperatures for
tests involving natural gas were greater for dl intake pressures. This suggests that the presence
of nitromethane and DM., and the synergy between them, may lower the delay Urne. This
argument is strengthened by the results for an intake pressure of 10 psig. The naturd gas and
DMUmethane mixtures have comparable delays and testing ternperatures. however the DMUmethane with added nitromethane has an approximately 0.3 ms lower delüy while havins bern tested with reduced bornb ternperatures. US shown in Table 5.4.
It was apparent afier completing this testing that the temperature of the bomb significantly affected the ignition delay. and much more diligent control of heüters and monitoring of temperatures was crucial for fitture testing. Addiuonally, any reductlon in delay timc due to cctanz irnprovzmznt is difficuli tr, deteci at Iiigher intakr pressures due to the smail values of ignition delays. It was therefore decided to eliminate testing with a 30 psig intake pressure and to reduce the glowplug temperamre to magnify differences in delay times.
5.2.1 Testing with a Glowplug Temperature of 1350 K
A new glowplug was installed since the resistance of the previous one chmged. makinz its original calibration unusable. The calibration for two new glowplugs can be found in
Appendix B. Testing was camed out with a glowplug temperature of 1350 K. intake temperature of 32S°C, and a bomb rope heater temperature of 250°C. The resulting delüy times are presented in Figure 5.14. -4- dme
0.0 t 1 1 1 O 10 20 30 Intake Pressure [psig]
Figure 5.14: Ignition Delay vs. Intake Pressure, glowplug temp.= 1350 K
As in earlier testing, each of the values given in the übove figure is an average ddelay tirne for twenty firing cycles.
The results of this testing are very unexpecrrd and difficult to explain. It wrü thought diat the larger times for the mixtures containing ignition improving additives may have resuited from condensation of the additives, thereby diminishing any ignition improvement. Taking the advice of the gas supplier, the gas cylinden were rolled on the ground to promote phase change back to the gaseous form, but diis had no effect.
Throughout the testing, the iniake, coolant, bomb heater, rnirror back, and oil temperatures were maintained constant for the various fuels and carefully recorded. They are presented in the data in Appendix C. Since these temperatures were maintained constant, a
variation in ambient temperature throughout the course of testing would not be the cause of these
unanticipated results. Weather fluctuations obsewed during the day that testing was completed warranted inspection of the barometric pressure. Absolute intake pressures for crich test condition is provided in Table 5.7.
Intake Pressure [psig] 1~uel O 1 10 1 20 [naturai eas 1 100.1 1 175.0 1 249.0 1
Table 5.7: Absolute Intake Pressures [kPa]
The limited variability in absolute intake pressures shown in the chan does not justify the trend seen in the ignition delay data. It was believed that further testing would producr ti noticeiible correspondence of ignition delay with an operating parameter.
5.2.5 Testing with a Glowplug Temperature of 1375 K
A glowplug temperature of 1375 K was chosen for the next set of experiments. It was hoped that a temperature slightiy higher glowplug temperature than the 1350 K used in the preceding testing would reduce the variability in the delay times, especially for a 10 psig intake pressure. Additionally, the fuels were tested in a different order, since testing that occurs later in the day may experience higher engine block and bomb tempentures, given that the coolant and oil heaters have been operational for the whole day, and earlier testing with other fuels.
Heretofore, the sequence of testing was: natural gas, DMUmethane, and then
nitromethane/DMUmethane. However for these expenments, the order of testing was reversed,
with the niuomethanelDMUmethane mixture king tested fisr, followed by DMUmethane. luid
then natural grci. The resulting delay tirnes are plotted in Figure 5.15. -*- dme I
O 5 1 O 15 20 25 Intake Pressure [psig]
Figure 5.15: Ignition Delay vs. Intake Pressure, glowplug temp.= 1375 K
From the figure it is seen that the vend in delay times is what was anticipated by the hypothesis of this study, namely that the mixture containing nitrornethane had the lowest delay timr, followed by the DlWmethane mixture, and naturd gas. It therefore canot be surmised that the order that the fuels were tested in had an effect since the tests completed using a glowplug temperature of 1400 K showed that the nitrornethane typicaily obtained the lowest delay tirne even though it was tested lut.
One cm see however, that the ignition delay is highly sensitive to the glowplug temperature. For a glowplug temperature of 1400 K, ignition delay values were in the range 0.6-
4.5 ms while a decrease to just 1375 K resulted in much longer delay in the range 2- 15 ms. This suggests that a transition between reaction pathways leading to ignition occurs over the temperature range of the experiments. Thus, a small change in temperatures can produce a much larger effect over that could aise from simple Arrhenius kinetics.
In addition, for the two lower glowplug temperatures (1350 and 1375 K). prxtical ignition delays (c 2 ms), cm only be achieved at the highest intake system pressure trsted- Therr was no significant difference in ignition delay values betweeii the methane additive mixtures and natural gas at this highest pressure. At lower pressures the data was contrridiciory. with the niuomethane/DMYmethane mixture showing the lowest ignition drlüys (3s rxpected for 1375 K), while at 1350K. natural gas had the lowest ignition delay.
As with the previous experirnents. there is a large range in delay values measured ÿt a boost pressure of 10 psig. This may be due to the prominence of variability frorn cycle to cycle.
A good indicaior of the spread of delay times for each hiel is demonstrated in Figure 5-16 to 5.18 where ignition delays are plotted versus peak bomb pressure on the cycles that ignite.
! *mi Pd ! ini P=IO I A mt P=70 j
I
Figure 5.16: Ignition Delay vs. Peak Bomb Pressure, Natural Gas Figure 5.17: Ignition Delay vs. Peak Bomb Pressure, DMUmethane
.. + ini P30
, A int P=2û 1
Figure 5.18: Ignition Delay vs. Peak Bomb Pressure, niuo.lDMWmethane
In the above plots, each rnarker represents one firing cycle. Note that this is the peak pressure resulting from combustion as well as compression. The figures display the large range of ignition delays for an intake pressure of 10 psig. More importantly, they indicates the strong dependence of ignirion drlay on the bomb pressure at intake pressures ai-ouiid 10 psi p. The dslay rimes exhibit a large decrease when the bomb pressures are incrensrd ovrr approximareIy 4 MPa.
This verifies Abate's [43] findings that display a sirnilar phenornena ür for boosts of approximately 12.5 psi.
The data obtained in the combustion bomb expenments in this study demonstrate that the ignition process is exceedingly complex depending on mixing between the iniected fuel and the in-cylinder gases. on the transfer of energy from the glowplug to the surrounding gas. and on complex kinetics. The great sensitivity to operating conditions exhibited by the results is indicative of the underlying complexity of the processes involved. Additionai investigation will be required to fully understand the ignition processes. Conclusions and Recommendations
in this snidy, possible synergy between nitromethane and dimethyl ether and its effects on the ignition delay the of methane was investigated. Expenments were completed in both an optical engine and a combustion bomb.
6.1 Optical Engine
Initial engine tests showed the importance of rninirnizing injector sac volume of injectors for gaseous fuels. When there is a significant sac volume, fuel retained in the injector escapes into the cylinder while the pressure is low during the exhaust and intake strokes. The escüped gas foms a combustible mixture with the intake air and is then spontaneously ignited on the subsequent cycle by compression heating. Thus the engine operates as a homogeneous charge compression ignition engine.
To elirninate such engine operation, a new injector noule was design and fabricated. It has not ken tested however. Therefore, before additional data is acquired using the opticai engine, the new injector nozzle should be characterized. The mass 80w rate should be. determined for the intended test injection pressure, as well as injector opening and closing times.
To determine opening and closing times, the fibre optic lift sensor is required, and must first be repaired by installing a new fibre optic coupler. Once operational characteristics of the new nozzle are known, testing in the engine cm resume. Incorporation of a glowplug into the optical engine to fimher promote lower ignition delay tirnes would be beneficial, and hopehilly foreshadow a sirnilar application in a production engine. 6.2 Combustion Bomb
In combustion bomb tests that did not power the glowplug. the use of both DME and the combination of DME and nitromethane. produced a very substantial reduction in delay time
(approximately a factor of three) compared to natural gas. No significant difference was observed between the two additive mixtures under these conditions, however. Even with use of ignition enhancing additives, the ignition delay times achieved under the conditions tested are too long for practical use in an engine, and therefore additive concentration or type may have to be varied.
At the highest glowplug temperature, addition of both DME and nitromethane to the methane provide significant reductions (20-30%) in injection delay times at the lowest intake pressures tested. At the two higher intake pressures. in-cylinder temperatures were sufficiently high to ignite natural gas rapidly. Use of the additives produced no improvement.
For the two lower glowplug temperatures (1350 and 1375 K), practical ignition delays (<
2 ms), can only be achieved at the highest intake system pressure tested. There was no significant difference in ignition delay values between the methane additive mixtures and natural gas at this highest pressure. At lower pressures the data was contradictory, with the nitromethane/DME/methane mixture showing the lowest ignition delays for a glowplug
temperature of 1375 K, while at 1350K, natural gas had the lowest ignition delay.
In this study it was demonstrated that the ignition process is very complex depending on
mixing between the injected fuel and the in-cylinder gases, on the transfer of energy from the
glowplug to the surrounding gas, and on complex kinetics. The substantial sensitivity to
operating conditions exhibited by the results is indicative of the underlying complexity of the processes involved. Additional investigation will be required to fully undrrstand the ignition processes.
For future experimentation, there are a few important issues. Firstly, fibre optic lift sensor use should be resumed to more accurately determine the injector opening and closing times. The method of fixing the cable in the probe should be rnodified such that the cable will not move when subjected to gas injection pressures. As well, the cable and the coupler arc i.cq delicate, so a shielding should be manufactured to protect them. A second consideration that is
very important penains to concentrations of constituents in the fbels. To provide accuracy in
reporting whether or not an additive has a signifcant effect, the concentration of the additive in
the fuel must be known. This necessitates a quantitative gas analysis using güs chromatogrüphy
and mas spectroscopy. This study attempted to determine the concentration of additives,
however only a Iirnited qualitative analysis was achieved. Therefore, it is suggested thiit
emphasis be placed on gas composition analysis in future testing. References
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(481 A. H. M. Cheung. intensified Charge Coupled Device (ICCD) Detector Svstem Suoplementary Operation Manual. Engine Research and Development Laboratory. University of Toronto, 1996. Appendix A: Calibrations
A.1 Glowplug Calibrations
-1 1 Resistance [ohms] 1 1 Surf. Temp. ["cl1Surf. Temp. [I
Calibration for Glowplug A
I 050 , O00 -- 3460~ 385.26 950 y = - FI2 = 0.9942 900 - 850 800 0.3600 0.3800 0.4000 0.4200 0.4400 Resistance [ohm]
Figure A. 1: Glowplug Temp. vs. Resistance. Glowplug A iGP Cal Se~t.2. 2000 i
-., Glowplug B I
1 Resistance [ohms] ( 1 Surf. Temp. ["CI( c rial 1 l~rial2(Trial31average 1 600 873.1 5 1 0.367 0.367 0.367 0.3670 650 923.1 5 0.381 ' 0.382 ' 0.382 0.3817 700 973.1 5 0.396 0.394 0.396 0.3953 750 1023.15 0.407 0.410 0.412 0.4097 800 1073.1 5 0.421 0.423 0.427 0.4237 Table A.2: Calibration Data for Glowplug B
Calibration of Glowplug B
0.3600 0.3800 0.4000 0.4200 0.4400 0.4600 1 Resistance [ohms]
l Figure A.2: Glowplug Temp. vs. Resistance, Glowplug B A.2 Washer Load Ce11 Calibration
This calibration was done in the UTMIE machine shop using the hydmulic press. the load ce11 amplifier, and a multimeter.
Voltage [VI,Gain=SOO,Offset=503 Pressure [psi] Trial 1 Trial 2 Trial 3 Trial 4 Triai 5 Triai 6 Triai 7 Avg. O 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.01 3000 -2.22 -2.89 -1.95 -3.00 -2.45 -1.84 -2.11 -2.21 3000 -3.43 -3.81 -2.88 -3.61 -3.79 -3.16 -3.32 -3.43 4000 -4.53 -4.52 -3.74 -5.20 -4.94 -4.44 -4.98 4-56 5000 -5.94 -5.65 -5.15 -6.53 -6.16 -5.61 -5.93 -5.85 ! by area 1.5"). A=1.767 inA? Convert pressure into force multiplying by of press cylinder (diam= ----- Force [lbfl Volt [VI O 0.0 1
Table A.3: Calibration Data for Washer Load Ce11
Figure A.3: Load Cell Voltige vs Force Appendix B: Gas Analysis
Gas chromatograph testing was completed by the ANALEST Lab in the Department of
Chernistry at the University of Toronto. The plot shown in Figure B. 1 is an analysis of the 0.1% nitromethane/S% dimethyl ethedmethane mixnire. Standards of methane and nitromethane were also mn and appear in Figures B.2 and B.3, respectiveiy. Dimethyl ether was not available to run a baseline with. The large number of peaks in the sarnple, and the magnitude of them suggests that the sample was contaminated. However there is some indication that thrre is nitromethane in the fuel due to the smaller area at t=19 min. methane peak
possible possible DME nitromcc lia tic content (rindhr) content contamination)
Figure B. 1: Chrornatograph for 0.1 %, 5% DME, Methane Mixture possible temperriturc
Figure B -2: Chromatograph of 99.999% Me thane Figure B.3: Chromatograph of Pure Nitromeihüne Appendix C: Combustion Bomb Data
C.l No Glowplug
fuel nat. gas intake temp 335°C inj. press [psïJ 1510
int. press [psi1 20
file ngd5s270 inj. Duration [CAO] 5 SOI [ATDC] 270 cycle start of lift [CDM] start of ignition [CDM] delay fs] 2nd 1366.1 1789.1 0.0597 3rd 1366.1 1775.8 0.0579 4th 1 366.2 1788 0.0596 avg [ms]( 59.067 1
Table C. 1: Ignition Delay, no glowplug, nat. gas. int. P=20
int. press [psi] 25
fiIe ngd5s300 inj. duration 5 SOI [ATDC] 300 cycle statt of lift [CDM] start of ignition [CDM] delay [s] 2nd 151 5.2 1784.2 0.038 3rd 1515.1 1779.0 0.0373 4th 1515.1 ln1.l 0.0362
Table C.2: Ignition Delay, no glowplug, nat. gas. int. P=25 int. press [psi] 29.5 file ngdSs310 inj. duration 5 SOI [ATDC] 310 cycle start of lift [CDM] sbrt of ignition [CDM] delay [s] 2nd injection timing off 3rd 1565.1 1774.4 0.0296 4th 1565.4 1775.7 0.0297 avg [ms]l 29.650 i
Table (2.3: Ignition Delay, no glowplug, nat. gas, int. P=29.5 fuel dme inj. press [psu 1500 int. press [psi] 20 intake temp 341OC file dmedSsoi324 inj. Duration [CADI 5 SOI [ATDC] 324 cycle start of lift [CDM] start of ignition [CDM] delay [s] 2nd 1635.1 1772.0 0.01 97 3 rd 1635.2 1 775.1 0.0201 4th 1635.2 1762.0 0.0182 avg [rnsl~l
Table C.4: Ignition Delay, no glowplug, DMYmeth. int. P=20
int. press [psi] 25 intake temp 338°C file dmedSsoi341 inj. Duration [CADI 5 SOI [ATDC] 341 cycle start of lift [CDM] start of ignition [CDM] delay [s] 2nd 1718.10 1806.70 0.01 28 3rd 1718.10 1795.20 0.01 12 4t h 1 718-50 1798.70 0.01 16
Table CS: Ignition Delay, no glowplug, DMUmeth, int. P=25 fuel inj. press [psq int press [psi] intake temp file nitdSsoi324 inj. Duration [CADI 5 SOI [ATDC] 324 cycle start of lift [CDM] start of ignition [CDM] delay [s] 2nd 1635.1 1788.9 0.0221 3rd 1635.2 1796- 1 0.0231 4th 1635.2 1784.7 0.0215
Table C.6: Ignition Delay. no glowplu;,nitro/DME/meth. int. P=20
int. press [psi] 25 intake temp 338°C file nitd5soi341 inj. Duration [CADI 5 SOI [ATDC] 341 cycle start of lift [CDM] start of ignition [CDM] delay [s] 2nd 1717.1 1798.1 0.01 16 3rd 1717.1 1804.5 0.01 26 4th 1717.1 1801.3 0.0121 avg [rnsl-i
Table C.7: Ignition Delay, no glowplug,nitro/DME/meth,int. P=25 drnelmethane
filename SOI ignition [CDM] delay [s] int, air codant bomb mirror back
avg [rns]( 18.430 1 std. dev. [ms] 1.273 95% conf 0.579
Table C.8: Ignition Delay and Bomb Temperatures no glowplug, dme/methane, int P=20 nitro/drne/meth
filename SOI ignition delay [s] int. air coolant bomb mirror back
avg [msll 16.61 6 ( std. dev. 1 .O79 9SoA conf. 0.491
Table C.9: Ignition Delay and Bomb Ternperatures. no glowplug, nit/dme/rneth. int P=20 C.2 With Glowplug
delays [ms] intPO intPlO intP20 intP30 *g 3.579 1.495 1.062 0.894 Idmelme thane 1 4.197 1 1.502 0.98 1 0.790
Tables C. 10: Sumrnary of Ignition Delay Times, Glowplug T=1400 K
Tables C.L 1: Sunimary of Ignition Delay Times. Glowplug T=1350 K
GP=1375 K delays [ml intPO intP10 intP2O ng f 4.6374 12.6763 1.78795 dmelmethane 13.4866 8.237 1.75 1 ni tro/dme/met hane 13.2735 7.33657 1.63903
Tables C.12: Sumrnary of Ignition Delay Times. GlowpIug T= 1375 K C.t.1 Glowplug Temperature = LJUO K
fuel n9 glowplug YS gp temp [1(1 1400 int air temp rC] 350 SOI [CADI 350 Duration [CADI 5
lntakeP[psigJ O GP Power [WJ 100
filename SOI ignition delay int air coolant bomb rope mirror z reiecb2.575 (COM] [CDM] [ms] [OC] back ["Cl 207 0.627 1.487 0.001 0.490 207 -0.987 1.362 -0.991 0.659 207 -0.849 -0.948 0.658 -0.874 215 0.508 0.068
- - 4.262 - -0.842 215 4.857 -0.881 2.430 -0.798 avg 13.579) std dev t 391 95% 0.885 conf
Table C. 13: Bomb Test Data, nat. gas, GP Temp=1400 K, int P=û psig lntake P (psig] 10 GP Power pî] ?!E
filename SOI ignition delay int air coolant bomb rope mirror z reiect>2.575 [CDM] [CDM] [ms] ["Cl back ["Cl 1761.41 1.654 350 224 0.818 1759.07 1.31 4 -0.933 1759.66 1.400 -0.491 1771.13 8.069 reject 1759.47 1.372 350 224 -0.632 1760.55 1.528 0.171 1761.61 1.683 0.968 1763.15 1.906 2.1 15 1758.8 1.275 350 224 -1.132 1760.9 1.579 0.434 1760.51 1.523 0.146 1759.41 1.364 -0.676 1760.23 1.483 350 224 -0.063 1759.84 1.427 -0.352 1760.08 1.461 -0.1 77 1759.43 1,367 4.660 1760.44 1.513 350 224 0.092 1763.37 1.937 2.276 1759.9 1.435 -0.307 1758.17 1.184 -1.599 avgIïq std dev 0.1 94 95% 0.091 conf
Table C.14: Bomb Test Data, nat. gas, GP Temp=1400 K. int P=10 psig Intake P (psig] 20 GP Power [W1 101.5
filename SOI ignition delay int. air codant bamb rope minor z rejecb2.575 [COMI back ['Cl 242 -1.773 1.162 -0.322 -0.526 242 -0.481 0.72 1 1 .Sm 43.284 242 0.743 -0.254 -0.873 -1.838 250 -1-366 0.709 0.656 1.684 250 -0.030 0.725 -0.305 O. 145 ngpj std dev 0.142 95% conf 0.067
Table C.15: Bomb Test Data. nat. gas, GP Temp=14ûû K. int P=20 psig lntake P [psig] 30 GP Power 105
filename Sot ignition delay tnt. air coolant bomb rope mfrror z rciect>2,~75 [CDM] [CDM] [msj ["Cl back ["Cl 264 0.399 4.427 -0.640 - 1.675 264 -0.082 0.032 1 .l95 -1.468 274 -1.428 0.09 1 t .638 1.181 274 -0.866 9.175 O. 156 -3.576 reject 274 1.239 0.215 1.205 -0.942 avgFI std dev 0.104 95% conf 0.049
Table C. 16: Bomb Test Data, nat. gas, GP Temp= 1400 K. int P=30 psig fuel dme gP temP [K) 1400 int air temp ['Cl 350 SOI [CADI 350 Duratlon [CADI 5
Intake P. gage [psi] O GP Power [W] 100
SOI Ignition delay int air coolant bomb minor z reiecb2.575 [CDM] [CDM] [ms] ["Cl ["CI rope back ["Cl ["Cl 1764.66 2.125 346 155 26 1 166 -0.843 1760.93 1S85 -1 -063 lT'4.18 3.505 -0.282 1763.28 1.924 -0.925 1814.24 9.311 346 155 26 1 166 2.080 1808.14 8.426 1-720 1763.66 1.980 -0.902 1761.87 1.721 - 1 .O07 1764.4 4.986 351 155 268 175 0.321 1765.8 2.290 -0.776 1793.36 6.285 0.849 1783.66 4.879 0.277 1763.63 1.W6 351 155 268 175 4.904 1786.31 5.262 0.433 1763.55 1.964 -0.909 1788.08 5.518 0.537 1797.14 6.773 351 155 273 183 1.048 1762.13 1.743 4.998 1782.18 4.623 0.173 1799.2 7.070 1.168 avgpl std dev 2.458 95% 1.150 conf
Table C. 17: Bomb Test Data, DMUmeth, GP Temp- 1400 K. int P=û psig Intake P, gage [pso tO GP Power r(V] 100
SOI ignition detay int air coolant bomb mirror z reiecb2.575 [CDM] @DM] [ms] ['Cl rope back ['Cl ["Cl 280 192 1.073 0.885 0.405 0.688 280 192 4.722 -1.246 -1.214 -1.071 286 199 0.345 1.703 1.959 -0.616 286 199 -0.164 -0.485 -1.377 -0.269 29 1 207 1 .Of9 0.371 -0.847 1759.65 1.387 -0.497 avg(i std dev 0.232 95% 0.1 O9 conf
Table C. 18: Bomb Test Dm,DMUmeth. GP Temp=1400 K, int P= IO psig htake P @dg] 20 GP Power 103.5
SOI ignition delay int air coolant bomb rnirror z rejecti2.575 (CRMI [COM] [msJ rC] rope back ["Cl ["Cl 318 240 0.300 -0.900 0.324 0.380 318 240 -1.073 -0.756 1.471 1.467 318 240 -0.045 -1.381 -0.846 1324 325 249 -1 .O48 -0.647 -0.476 0.878 325 249 -1.217 0.236 0.177 1.831
std dev 0.124 95% 0.058 conf
Table C.19: Bomb Test Data, DMUmeth, GP Temp=L400 K. int P=20 psig lntake P [psig] 30 GP Power [Wl 107.5
SOI ignition delay Int. air coolant bomb mirror z reiecb2.575 [CDM] [CDM] [ms] ("Cl 1rope back l'Cl ["Cl 338 262 -1.571 -0.240 0.866 -0.850 338 262 0.969 1.094 1.446 -0.257 338 262 -0.094 -0.4 14 0.073 0.148 343 270 0.931 1 .O92 -0.454 0.413 343 270 0.983 -1-798 -0.4 15 -1.922 a,pj std dev 0.100 95% 0.047 conf
Table C.20: Bomb Test Data, DMUmeth. GP Temp= 1 400 K. int P=30 psi? fuel dmefnitm 9P temP [K) t 400 int air ternp ["Cl 350 SOI [CAO] 350 Duration [CADI 5
lntake P [psig] O GP Power pV1 99.5
SOI ignition delay int. air coolant bomb mirror z reiect~2.575 [CDM] [CDM] [msj ['Cl rope back ["Cl ["Cl 276 184 -0.283 -0.568 -0.203 1.733 276 184 2.051 3.607 reject -0.580 -0.454 276 184 -0.419 -0.568 -0.760 -0.380 28 1 194 2,004 -0.593 -0.012 - - - - -0.655 28 1 194 4.568 -0.721 -0.620 1779.11 4.182 1.599 avg~2.4851 std dev 1.061 95% 0.497 conf
Table C.2 1: Bomb Test Data, nitro/DMUmeth, GP Temp= 1400 K, int Pdpsig lntake P [psig] 10 GP Power (W] 100
SOI ignition delay int air coolant bornb mirror [CDMI [COM] [ms] ['Cl ["Cl rope back ["Cl ["CI 1756.57 0.952 347 155 290 206 -1.187 1757.14 1.035 4.747 0.069 1.668 0.01 4 very early start of injection for lhis -6.253 reject cycle 1756.87 0.995 1757.24 1.049
avg std dev 0.188 95% 0.090 conf
Table C.22: Bomb Test Data, nitro/DMUmeth, GP Temp=1400 K. int P=lO psig lntake P, gage [psi] 20 GP Power pi] 102
SOI ignition delay int air coolant bomb mirror 2 reiect>2.575 [CDM] [CDM] [ms] ['CI rope back ["Cl ["CI 1757.19 1.041 334 308 228 0.436 1759.79 3.482 reject 1758.08 1.171 1.483 1758.03 1.164 1 .a0 1757.24 1.050 334 308 228 0.506 1757.11 1.031 0.351 1758.2 1.188 1.620 1755.76 0.835 - 1.233 1758.11 1.176 334 316 236 1 S24 1756.04 0.875 -0.905 1757.14 1 .O35 0.387 1755.76 0.835 -1.230 1757.13 1.O33 339 316 236 0.367 1756.67 0.967 -0.166 1755.74 0.832 -1.254 1756.59 0.956 -0.257 1756.32 0.916 339 316 236 -0.580
--- 1755.94 OJ6V - - --Ir020 - - 1756.16 0.893 -0.759 1756.22 0.901 -0.698 avg 10.987' std dev 0.124 95% 0.058 conf
Table C.73: Bomb Test Data, nitro/DME/meth, GP Temp= 1400 K, int P=20 psig lntake P, gage [psi] 30 GP Power [W] 106
SOI ignition delay fnt air coolant bomb mirror z rejecb2.575 [CDM] [CDM] [ms] ["Cl
1755.92 0.850 335 1756.1 1 0.877 1755.07 0.729 1756.14 0.883 1756.08 0.873 335 1756.07 0.873 1756.44 0.926 1755.72 0.821 1756.23 0.895 332 1755.55 0.797 1756.13 0.881 1754.72 0.678 1756.08 0.874 332 t 755.48 0.787 1754.77 0.685 1756.12 0.879 1756.04 0.868 332 1756.12 0.879 1754.91 0.706 1756.34 0.9 10 avgpl std dev 0.077 95% 0.036 conf
Table C.24: Bomb Test Data. nitrolDMUmeth. GP Ternp=lJ00 K. int P=30 psig C.2.2 Glowplug Temperature=1350 K
fuel ng glowplug 8 9P temP [KI 1350 SOI [CADI 350 duration [CAO] 5
lntake P [psig] O GP Power v] 84.5
filename SOI ignition delay Peak abs int P int air cootant bomb mirror z reiect>2.575 [CDM] [CDM] [ms] bornb P [kPaJ rope back [MPal I0Cl ["Cl sept3nga 1750 1845.97 13.788 2.402 100.09 250 174 1.823 1750 1812.01 8.910 2.944 -2.179 1750 1834.06 12.078 2.632 0.4 19 1750 1819.94 10.049 2.85 - 1.244 b 1750 1824.77 10.743 2.825 100.09 250 179 -0.675 1750 1840.62 13.019 2.516 1.192 1750 1847.06 13.083 2.462 1.244 t750 1837.63 12.591 2.558 0.840 c 1750 1826.1 1 10.935 2.745 100.09 250 182 -0.St8 1750 1833.98 12.066 2.ô47 0.410 1750 1836.26 12.394 2.589 0.679 1750 1834.46 12135 2.582 0.467 d 1750 1825.S 10.T17 2.817 100.08 250 185 -0.648
------1750 - 1823.9 40.527- 2.70s - - -0.852 - 1750 1827.37 11.022 2.n8 -0.446 1750 1836.53 12.326 2.495 (1.624 e 1750 1828.36 11.163 2.665 100.0784 250 190 -0.331 1750 1830.02 11-400 2.798 -0.137 1750 1820.05 9.978 2.732 -1.302 1750 1836.63 12340 2.596 0.635 avgm std dev 1.21 9 95% conf 0.571
Table C.25: Bomb Test Data. nat. gas, GP Temp=1350 K, int P=û psig lntakeP[psigJ IO GP Power [W1 87
filename SOI ignition delay peak abs int P int air coolant bomb rnirror z reject>2.575 [CDM] [CDM] [ms] bomb P C'CI ['Cl rope back [MPal ['Cl ['Cl
324 155
328 1 55
319 155
326 155
320 1 55
avgp385) std dev 1.684 95% conf 0.788
Table C.26: Bomb Test Data, nat. gas, GP Ternp=1350 K,int P= 10 psig filename SOI ignition delay peak abs int P int air coolant bomb mirror z rejecb2.575 [CDMI [CDM] [rnsj bomb P [kPa] ["Cl rope back ["Cl I'CI t 760.98 1-591 250 222 -0.110 1762.28 1.780 0.466 1759.61 1.392 -0.716 1761 .O2 1 .S98 -0.090 1762.29 1.782 250 226 0.471 1776.35 6.676 reject 1760.13 1.468 -0.484 1765.62 2.263 1.937 1759.92 1.438 250 227 -0.576 t771.15 4.377 rejet 1761.64 1.688 O. 184 7763.08 1.895 0.817 1759.28 1 346 250 230 -0.858 17 60.1 1 1.465 -0.494 1761.8 1.710 0.254 1760.21 1.479 -0.450 lï67.Ol 2.465 250 231 2.551 1760.02 1.453 -0.531 1759.1 8 1.331 -0.902 1757.9 1.145 - 1.468 avg 1.627 std dev 0.328 95% conf 0.154
Table C.27: Bomb Test Data. nat. gas, GP Temp=1350 K. int P=20 psig fuel dmeheth glowplug 8 9P temP [KI 1350 SOI (GAD] 350 Duration [CADJ 5
lntakeP[psig] O GP Power w] 85.5
filename SOI ignition delay Peak abs int P int air coolant bomb mirror z reject>2.575 [CDMI [CDM] [msl bomb P [kPa] ['Cl ["Cl rope back WPaI ["Cl I'CI 1836.01 12.357 2.701 99.87 326 155 250 171 0.401 1845.3 13.692 2.356 1.794 1840.18 12.958 2.558 1.028 182 1.49 lO.271 2.8 17 -1.777 1831 11638 2.777 99.87 319 155 250 174 -0.350 1828.1 1 11.223 2.762 -0.783 1837.16 12.522 2.6 0.573 1827.01 11.0ô4 2.901 -0.949 1831 11.638 2.777 99.87 319 155 250 174 -0.350 1828.1 1 11.223 2.762 -0.783 1837.16 12.522 2.6 0.573 1827.01 11.064 2.901 -0.949 1838.07 12.545 2.656 99.87 329 155 250 181 0.597 1827.75 11 .O75 2.793 -0.938 1832-1 3 11.699 2.706 -0.286 1826.88 10.952 2.769 -1 .O66 1844.95 13.525 2.404 99.86 319 155 250 184 1.620 1843.21 13.277 2.519 1.361 1831-63 11.628 2.698 -0.360 1838.38 12589 2.67 0.643 avg[i.9nl std dev 0.958 95% conf 0.448
Table C.28: Bomb Test Data, DMUmeth.. GP Temp=1350 K, int P=O psig lntake P. gage [psi] 1O GP Power WJ 86
filename SOI ignition delay peak abs int P fnt. air coolant bornb rope mirror z rejecb2.575 back ['Cl 1801.33 7.31 2 204 0.246 1846.43 13.736 2.517 1826.05 10.833 1.491 1786.15 5.150 -0.518 1791.35 5.891 208 -0.256 1814.22 9.149 0.896 1792.4 1 6.04 1 -0.203 1790.22 5.729 -0.3 13 1819.78 9.941 210 1.176 1815.31 9.304 0.951 1800.67 7.217 0.213 1779.94 4.265 -0.831 1763.46 1.9 17 212 -1.661 1783.08 4.71 2 -0.673 1784.02 4.846 -0.626 1778.46 4.054 -0.905 1776.92 3.835 214 -0.983 1787.22 5.302 -0.464 1786.18 5.154 -0.517 1805.58 7.91 7 0.460 avg 6.615 std dev 2.829 95%conf 1.324
Table C.29: Bomb Test Data, DMUmeth.. GP Temp=1350 K. int P=10 psig lntake P, gage [psi] 20 GP Power pV) 89
filenarne SOI ignition delay peak int air coolant bomb rntrror z rejecb2.575 [CDM] [CDM) (ms) bomb P [OC] ['CI rope back [MW ["Cl ["Cl 5.964 321 155 250 224 -0.583 5.941 1.457 5.985 1.597 5.975 0.613 5.975 248.73 323 155 250 226 -1,304 5.96 -0.795 5.965 0.793 5.975 -0.541 5.975 248.57 324 155 250 228 -0.214 6.006 0.250 5.97 0.823 6.013 -0.949 6.017 248.60 322 155 250 230 0.041 6.04 -1.001 6-013 -0.636 6.023 -0.864 6.01 9 248.69 323 155 250 232 -0.714 6.026 -0.882 5.955 2.161 6.029 0.749
std dev 0.221 95% conf 0.1 O3
Table C.30: Bomb Test Data. DMUmeth.. GP Temp= 1350 K. int P=20 psig fuel nitrokhneheth glowplug B 9P temP [KI 1350 SOI [CADI 350 Ouration [CADI 5 lntake P [psigj O GP Power w] 80.5
fitename SOI [COM] ignition delay peak abs int P Int air coolant bomb rope mirror z rejecb2.575 [COM] [ms] bomb P ["Cl back [MW ["Cl 325 170 1.348 -0.342 1 -574 -0.795 322 174 -0.539 0.030 O. 140 -0.9 13 328 180 1.149 0.756 -0.651 - 1-478 320 182 1.200 -0.746 1.410 -1.919 325 185 -0.287 0.014 -0.41 1 0.560
std dev0.971 95% conf 0.455
Table C.3 1: Bomb Test Data, nitro/DME/meth., GP Temp=1350 K, int P=O psig fntake P [psig] 10 GP Power [W] 83
filename SOI Ignition defay peak atts int P int air cooiant bomb rope mirror z reject>2.575 [CDM] [CDM] [ms] bomb P [kPa] Iback WPaI ["Cl 1819.44 10.063 201 0.130 1782.09 4-651 -1.838 1788.71 5.610 -1.489 1841-71 13.292 1.304 1805.04 7.977 204 -0.628 1840.70 13.157 1.255 1850.2 14.522 1.75 t 1835.85 tZ.443 0.996 1835.05 12.327 206 0.953 1823.19 10.607 0.328 1816.89 9.694 -0.004 1007.14 8.281 -0.5 17 1821.2 10.318 208 0.223 1816.37 9.61 9 -0.031 1785.17 5.098 -1.675 1831.4 11.798 0.761 1801.55 7.471 208 -0.812 1807.28 8.301 -0.5 10 1814.52 9.351 -0.129 1815.63 9.51 2 -0.070 a~~(9.7051 std dev 2.750 95% conf 1.287
Table C.32: Bomb Test Data, nitrolDMUmeth., GP Temp=1350 K, int P=10 psig lnta ke P (psig] 20 GP Power IW] 86.5
filename SOI isnition delav ~eak abs int P int air coolant bomb mirtor z rejecb2.575 [COMI ~CDM] [msj bomb P (kPa1 rope back [MW ['Cl ['Cl 1760.31 1.481 5.81 6 249.93 250 220 -0.910 1781.12 5.797 -6.236 reject 1761.03 1.585 5.823 -0.538 1766.12 2.316 5.795 2.091 1762.31 1.769 5.823 250.81 250 227 0.1 24 1763.05 1.874 5.846 0.503 1759.73 1.398 5.886 -1.210 misfire -6.236 1761.3 1.624 5,802 250.09 250 230 -0.397 1760.07 1.447 5.791 -1-035 1791.O9 5.635 4.236 relect 1763.03 1.872 5.836 0.494 1760.13 1.456 5.835 249.89 250 231 -1.001 1762.92 1.856 5.n5 0.437 1763.21 1.898 5.78 0.589 1764.53 2.088 5.764 1-270 176122 1.612 5.04 248.49 250 234 -0.439 1762.21 1.755 5.846 0.072 1759.3 1.a36 5.878 -1 -431 1764.75 2.1 19 5.78 1.a81 mgpl std dev 0.278 95% conf O. 141
Table C.33: Bomb Test Data, nitro/DME/meth., GP Temp=1350 K. int P=20 psig C.2.3 Glowplug Temperature = 1375 K
fuel n9 glowplug B gP temP [KI 1375 SOI [CADI 350 Duratfon [CADI 5
lntake P [psfg] O GP Power pV] 82.5
filename SOI ignition delay peak abs int P int air coolant bomb mirror z rejecb2.575 [CW [CDM] [ms] bomb P [kPa] ["Cl ["Cl Irope back W'aI ["Cl ["Cl 155 300 173 2.055 0.01 9 0.570 -0.067 15s 300 176 0.838 0.220 1.291 -0.086 155 300 180 0.548 0.521 0.477 -1-395 155 300 184 -1.027 -0.523 0.981 4.162 155 300 186 9.820 -0.804 -0.277 -2.360
std dev 1.384
Table C.34: Bomb Test Data, nat. gas, GP Temp=l375 K, int P=O psig lntake P [psig] 10 GP Power [W] 85.5
filename SOI tgnition delay peak abs int P int air coolant bomb mirror z rejecb2.575 (CDM] [CDM] [ms] bomb P ['ci rope back ['Cl I'CI 320 300 201 -1.593 1.125 0.816 0.799 324 300 203 0.382 0.437 0.066 -0.208 31 7 300 208 -0.664 -0.7 17 1.623 0.817 317 300 208 -0.664 -0.717 1.623 0.817 325 300 215 -0.433 - 1.849 -0.758 -0.900 avg(18676( std dev 2.268
Table C.35: Bomb Test Data. nat. gas, GP Temp= 1375 K, int P= 10 psig lntake P [psig] 20 GPPower[W1 88
filename SOI Iqnftion delay peak abs int P int air cootant bomb mirror z rejecb2.575 (CDM] [ms] bomb P [kPa] [OC] rope back Pal ['Cl ['Cl 1762.61 1.812 5.949 247.57 317 300 228 0.115 1760.8 1.552 5.91 8 -1.120 1795.81 5.495 22.727 repct 1787.77 5.832 17.255 reject 1762.78 1.852 5.894 247.60 319 300 230 0.301 1763.24 1.919 5.903 0.621 1763.24 1.918 5.876 0.61 8 1761-07 1.605 5.909 -0.867 1765.13 2.174 5.055 247.60 320 300 233 1.831 1763.1 1.a82 5.903 0.448 1762.86 1.848 5.863 0.283 17ô4.17 2.035 5.903 1.174 1763.94 2.003 5.86 247.64 322 300 236 1.021 1764.02 2.014 5.925 1 .O70 1760.47 1.504 5.902 -1 348 1760.3 1.480 5.881 -1.462 1762.07 1.749 5.876 247.74 325 300 239 -0.186 1760.16 1.473 5.891 -1.493 1762.07 1.749 5.906 -0.186 1761.14 1.615 5.855 4.821 avgpl std dev 0.21 1 95% conf 0.099
Table C.36: Bomb Test Data, nat. jas, GP Temp=1375 K. int P=20 psig fuel dme glowplug B gp temp [q 1375 SOI [CAO] 350 Duration [CADI 5
lntake P (psig] O GP Power [WI 82.5
filenarne SOI ignition delay peak abs int P int. air coolant bomb mirror z relect>2.575 [COMI [CDMI [ms] bomb P rope back [MPal ["Cl ["Cl sept4dmea 1750 1835.66 12.307 2.694 300 180 -1.428 1750 1851.94 14.647 2.344 1-405 1750 1846.78 13.905 2.448 0.506 1750 1843.87 13.487 2.499 0.001 b 1750 1852.18 14.681 2.383 300 183 1.446 1750 1851.64 13.603 2.391 1.352 1750 1847.35 13.987 2.57 0.606 1750 1ô40.94 13.066 2.601 -0.509 c 1750 1840.03 12.936 2.563 300 186 -0.667 1750 1835.05 12.220 2.714 - 1.534 1750 1844.35 13.556 2.483 0.084 1750 1850.97 14.507 2.25 1.235 d 1750 1835.1 1 12.229 2.757 300 189 -1.523 1750 1849.1 14.239 2.522 0.91 1 1750 1843.1 1 13.378 2.409 -0.131 1750 1845.55 13.728 2.49 0.293 e very early irijectiondiscard 300 191 -16.329 reject 1750 1841.94 13.210 2.562 -0.335 1750 1839.55 12.866 2.527 -0.752 1750 1838.34 12.693 2.682 -0.961 avg 13.487 std dev 0.826 95% conf 0.387
Table C.37: Bomb Test Data, DWmeth., GP Temp=1375 K, int P=û psig lntake P [psigJ 1O GP Power[WI 87
filename SOI ignitton delay peak abs int P int air coolant bomb mirror z reject>2.575 [CDM) [CDM] [ms] bomb? rope back WPaI ["Cl ["Cl 1817 9.626 300 204 0.518 l8lO.ll 8.637 0.149 1801.1 7.342 -0.334 1848.12 14.098 2.1 86 1768.34 5.509 300 208 -1.018 1774.26 3.485 -1.772 1811.24 8.799 0.21 O 1777.71 3.982 -1.587 l814.Sl 9.269 300 212 0.385 1801.97 7.467 -0.287 1838.96 12.781 1.695 1788.03 5.464 -1 .O34 1818.81 9.886 300 216 0.615 1799.99 7.182 -0.393 1834.23 12.102 1.442 1800.54 7.261 -0.364 1800.6 7.271 300 218 -0.360 1809.65 8.570 0.124 1805.56 7.983 -0.095 1805.81 8-018 -0.082 avgpl std dev 2.681 95% conf 1.255
Table C.38: Bornb Test Data, DMUrnedi., GP Temp= 1375 K, int P= 10 psig lntake P [psig] 20 GP Power [W] 91.5
filename SOI ignition delay peak abs int P int air coolant bomb minor z reiect>2.575 ICDM] [CDM] [ms] bombP [kPal rope back WaI ['Cl ['Cl sept4dmek 1750 1761.3 1.624 5.972 247.25 300 226 4.338 1750 1760.46 1.503 5.941 -0.598 1750 1763.13 t -887 5.93 0.227 1750 1760.22 1.469 5.968 -0.67 1 1 1750 1771.27 3.029 5.936 247.20 300 229 2.681 1750 1760.03 1.429 5.971 -0.757 1750 1763.09 1.864 5.889 O. 178 1750 1759.8 1.395 5.939 -0.829 m 1750 1775.55 5.864 247.09 300 232 3.991 reject 1750 1763.48 1.920 5.882 0.299 1750 1762.3 1 .ïS2 5.897 -0.063 1750 1759.44 1.344 5.932 -0.939 n 1750 1770.86 2.972 5.93 247.07 500 235 2.557 7750 1762.67 1.805 5.882 0.051 1750 t761.W 1.573 5.941 -0.447 1750 1761.5 1.638 5.941 -0.307 O 1750 1763.58 1.934 5.926 247.14 300 238 0.328 1750 1760.95 1.560 5.939 -0.476 1750 1761.04 1.573 5.932 -0.448 1750 1761.05 1.574 5.913 -0.446 avg t.78t std dev 0.466 95% conf 0.218
Table C.39: Bomb Test Data. DMYrneth., GP Temp= 1375 K. int P=20 psig fuel nitro/dme glowplug B 9P temP IV 1375 SOI [CADI 350 Ouration (CADI 5 lntake P [pstg] O GP Power [W] 03.5
filename SOI [CDM] ignition delay peak abs int P int air coolant bomb mfrror z reject>2.575 [CDM] Ems] bomb P fkPa] ["Cl ["Cl rope back WPaI ["Cl ["Cl sept4nita 1750 1839.01 12.789 2.589 100.47 329 155 300 176 -0.508 1750 1850.5 14.439 2.33 1.222 1750 1841.3 13.117 2.51 -0.164 1750 1829.93 11.484 2.788 -1.876 b 1750 1844.49 13.577 2.564 100.48 325 155 300 181 0.318 1750 1852.1 1 14.671 2.358 1.466 1750 1839.79 12.902 2.659 -0.390 1750 1845.82 13.767 2.52 0.51 8 c 1750 1833.71 12.027 2.641 100.48 320 155 300 185 -1.307 1750 1842.82 13.336 2.551 0.066 1750 1838.88 12770 2.542 -0.528 1750 1841.32 13.121 2.639 -0.160 d 1750 1832.72 11.885 2.716 100.48 324 155 300 187 -1.456 1750 1844.91 13.637 2.56 0.381 1750 1844.45 13.570 2.481 0.31 1 1750 1851.47 14.580 2.314 1 A70 e 1750 1849.07 14.234 2.468 100.48 331 155 300 190 1.007 1750 1840.92 13.063 2.533 -0.221 1750 1851.26 14.549 2.404 1.338 1750 1833.18 11.951 2.741 -1 -386
std dev 0.954 95% conf 0.446
Table C.40: Bomb Test Data, nitro/DME/meth., GP Temp=1375 K. int Pdpsig lntakeP[psig] 10 GP Power w] 87
filename SOI ignition delay peak abs int P int air coolant bornb mirror z reiecb2.575 [CQW @DM] [msj bomb P [Wa] rope back WPaI ["Cl ["Cl 1786.28 5.212 4.525 t74.94 300 201 -0.913 1787.37 5.370 4.499 -0.845 1842.02 13.222 3.437 2.528 1784.17 4.910 4.536 -1.O43 1794.19 6.349 4.428 175.11 300 210 4.424 1787.17 5.340 4.528 -0.858 1800.07 7.195 4.328 -0.06 1 1780.49 4.380 4.637 -1.270 1823.99 10,630 3.448 175.15 300 214 1.415 1801.72 7.431 4.323 0.040 1812.71 9.010 3.731 0.719 1786.86 5.296 4.594 -0.877 1817.24 9.661 3.592 175.23 300 216 0.999 181 1.57 8.847 3.773 0.649 1807.58 8.274 4.016 0.403 1820.9 10.187 3.499 1.225 1796.06 6.618 4.423 175.20 300 218 -0.309 1786.09 5.185 4.535 -0.924 1798.89 7.025 4.256 -0.134 1795.88 6.591 4.37 4.320 avg 1 7.337 1 std dev 2.328
Table C.4 1: Bomb Test Data, nitroDMUmeth., GP Temp=l375 K. int P= 10 psig lntake P [pslg] 20 GP Power [Wl 90.5
filename SOI ignition delay peak abs int P int air coolant bomb mirror z rej-2.5f5 EDM] (ms] bombP ["Cl rope back [MPal rc1 ["Cl 1760.45 1.502 6.005 155 300 228 -0.622 1761.2 1.609 6.016 -0.137 1762.01 1.725 6.01 0.39 t 1760.34 1.486 5.973 -0.694 1761.11 1.597 5.922 155 300 230 -0.191 1760.92 1.569 5.951 -0.31 7 1761.13 1.599 5.918 -0.184 1761.15 1.602 5.951 4.169 1761.11 1.597 5.922 155 300 230 -0.191 1760.92 1.569 5.951 -0.3 17 1761.13 1.599 5.918 -0.184 1761.15 1.602 5.951 -0.169 1790.36 5.615 t55 300 235 reject 1764.01 2.013 5.882 1.696 1758.62 1.238 5.877 -1.818 1763.75 1.975 5.871 1.523 1761.11 1.597 5.92 155 300 237 -0.192 1764.56 2.092 5.851 2.053 1758.96 1.287 5.862 -1.597 1763.13 1.886 5.849 1.121 avgll std dev 0.220 95% conf 0.103
Table C.42: Bomb Test Data, nitro/DME/meth., GP Temp=1375 K. int P=20 psig