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THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 35 E 7th St Yr Y 117 88^GT^^

E The Society shall not be responsible for statements or opinions advanced In papers or disci lion at meetings of the Society or of ias Division s or 1 Sections, or printed in its publications. Discussion is printed only if the paper is published in an ASME Journal. Authorization to photocopy for internal or personal use is granted to libraries and other users registered with the Copyright Clearance Center (CCC) provided $3/rtl r $/p pd t CCC d r nvr MA 193 t fr pl prn r bl rprdtn hld b ddrd t th ASME hnl blhn prtnt

Copyright ® 1998 by ASME All ht rvd Printed in U.SA Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021

EXPERIMENTAL AND NUMERICAL STUDIES OF NOx FORMATION IN TWO-STAGE -AIR FLAMES

S.C. Li and F.A. Williams

Center for Energy and Combustion Research Department of Applied Mechanics and Engineering Sciences University of California, San Diego La Jolla, CA 92093-0411

Presented at the International Gas Turbine & Aeroengine Congress & Exhibition Sthl Sdn — n -n 5 199 Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021

ABSTRACT to the air stream. Results of the numerical inte- grations were in reasonable agreement with these To help understand how staged combustion aids experimental results when suitable selections were in reducing emissions of oxide of from made of certain critical elementary reaction-rate gas turbines, measurements and computations constants. These new NO. measurements and are made of structures of two-stage counterflow computations help to increase understanding of methane-air flames at nomal atmospheric pres- influences of staging and diluent addition, iden- sure and a feed-stream temperature of about 300 tify important reactions for pollutant formation K. The fuel stream is partially premixed, with and suggest means to reduce emissions. equivalence ratios from 1.5 to 3.0. To the air stream is added up to 10% by mass of spray, IOUCIO , or nitrogen. Flame structures, in- cluding formation of species containing two car- Staged combustion is a well-established, practi- bon atoms, are measured by gas chromatography cal method for reducing emissions of oxides of of samples withdrawn by fine quartz probes and nitrogen (NO.) from gas turbine combustors [1- are calculated by numerical integrations of the 4]. Addition of inerts, such as H2O and CO2, conservation equations employing an updated el- for example through burnt-gas recirculation, also ementary chemical-kinetic data base. The same can be beneficial for this purpose. There remains, sampling system is employed with a low-flow-rate however, a lack of detailed understanding of the NOX analyzer to obtain profiles of and reasons that these techniques are so effective. Be- nitrogen dioxide, which are also calculated in the cause of this deficiency, it is difficult to optimize numerical integrations. The two-stage flame ex- combustors for achieving best performance with hibits a green fuel-rich premixed flame and a blue minimum emissions. The present work is designed diffusion flame with the maximum NO. concen- to increase knowledge of the fundamental factors trations found near the blue flame. At an air-side that determine the effects of staging and diluent strain rate of 50 s -1 , for fuel-side equivalence ra- addition, thereby aiding rational approaches to tios of 1.5, 2.0, 2.5 and 3.0, respectively, measured improvements in design of combustors. peak NO. concentrations were about 70, 90, 100 The results reported here represent a continu- and 90 ppm, reduced to 60, 770, 50, and 40 ppm, ation of our earlier efforts [5] to probe two-stage respectively, when 5% water by mass was added combustion. As in that work, methane was se-

lected for the fuel. There are two principal rea- of the sum of C2H2, C2H4 and C2H6, the three sons for studying methane. First, it is the sim- major "C2 species"formed in methane flames, for plest model fuel and thereby serves an air-side strain rate of a = 100 s-1 in the coun- as a starting point for investigating other hydro- terflow flames. The C2 species are important carbons [6, 7]. The chemical kinetics of methane both as soot precursors and as the main source combustion are less uncertain than those of other of the CH2 and CH radicals that are responsible , so that key elementary steps and for the "prompt" mechanism of NO production. rate constants can be determined more accurately, The numerical computations with detailed chem- Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 and the fuel chemistry of higher hydrocarbons istry were found to overpredict the concentrations can be treated in a manner analogous to that of of C2 species by about a factor of two. Although methane, so that the results for methane indicate computational results also were reported for NO what needs to be studied for those other fuels. concentration profiles, it was concluded that be- Second, methane is the principal component of cause of existing uncertainties and the disagree- natural gas, which is becoming of increasing im- ments in profiles of C2 species, the reaction mech- portance as a gas-turbine fuel [8]. Appreciable anism needed revision in the future. No measure- practical interest thus is associated with methane ments of NO concentration profiles were made in combustion. this earlier work. The counterflow configuration investigated here The present paper reports an improved is illustrated schematically in Fig.1. The flames chemical-kinetic elementary data base as well are steady and planar, facilitating probe measure- as experiments for an air-side strain rate of a ments. The premixed flame at the top is observed =50 s -1 . Measurements are made of profiles of to be green, largely as a consequence of C2 band temperature, of concentrations of major stable emissions, while the diffusion flame is blue be- species, of concentrations of the sum of C2H2 and cause of nonequilibrium radiation emitted by ex- C2H4, and of the concentration of C2H6, as well as cited CO2 formed in CO oxidation. The experi- of NO and total NO R , over a range of equivalence mental arrangement has been described in detail ratios of the rich premixed flame, both with and previously [5] and therefore will not be discussed without water addition to the air stream. Com- thoroughly here. Related earlier investigations putational results with the improved chemical- in counterflow configurations also have been re- kinetic data are shown to be in reasonable agree- viewed previously [5]; hence that background in- ment with measurements, including those for C2 formation need not be repeated. It is, however, species and for NO.. Reliable descriptions of the worth stating that NO. measurements also have flame structures and NO production thereby are been reported for laminar coflow flames, both obtained. The results are employed to calculate methane diffusion flames [9] and methane [10] and the influences of the equivalence ratio and inert [11] partially premixed flames; while these addition on the emission index for these two-stage experiments have aspects in common with those flames. addressed here, their nonplanar geometry causes the measurements and the interpretations of ex- EEIME perimental results to be more complicated for the coflow flames. The counterflow burner, which has two coax- The previous work [5] involved measurements of ial ducts placed one above the other, is concentration profiles of main stable species and shown schematically in Fig.1. The single-phase

3 methane-air gas mixture flows through the upper measurement techniques were discussed in previ- duct and the water spray with air through the ous publications [5, 12]. lower duct. The separation distance between the A O analyzer (model 955, Rosemount An- upper and lower duct exits is 18 mm. The up- alytical Inc.) was employed for measuring con- per duct has an exit diameter of 45 mm, and flow centrations of O and total O (the sum of the straighteners produce a uniform gas flow at the concentrations of NO and O The analyzer exit plane. The lower duct is a long contoured can be operated at a low sample flow rate so that tube with the same exit diameter. An atomizer the disturbance to flame structure can be reduced Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 is located at the bottom of the lower duct to pro- to an acceptably small level. The quartz micro- duce water spray. The air enters the duct below sampling probe for the analyzer is a standard thin, the spray nozzle and carries the spray upward to uncooled type as described by Saito et al. [13], and meet the gas flow from the upper duct. Since it is mounted on a two-dimensional positioner to some droplets are lost to the walls or to the bot- fix the probe at the desired location. The inner tom of the lower duct, a drain pipe was installed diameter of the probe tip is smaller than 0.1 mm. to discharge the accumulated liquid. The mass Samples were withdrawn from the flame by the flow rate of water in the counterflow was obtained analyzer continuously at a flow rate of approxi- as a function of the flow rate of the carrier gas by mately 0.4 cm3 /sec. Because the sample flow rate metering the water flowing into the atomizer and was low, the response time of the analyzer was out of the drain. about three minutes at a given probe position. As described previously [5] and as shown in The analyzer was calibrated by measuring sam- Fig.1, this two-phase laminar counterflow configu- ples from bottles of known calibration gas mix- ration exhibits a green premixed flame, a blue dif- tures before the experiment and was checked by fusion flame and a vaporization plane. All three the calibration gas every hour during the mea- are flat and parallel. The separation distances be- surement to ensure that the analyzer performed tween them decrease with increasing equivalence accurately. These procedures resulted in reason- ratio and strain rate. Since the distance between able accuracy, typical uncertainties in mole frac- the two flames is as large as 6 mm, it is easier tions being on the order of 10% or less, although for probes to obtain reliable experimental results small discontinuities in data sometimes appeared with good spatial resolution. when the premixed-flame reaction zone attached The species C CO CO C to the nearby probe. Such discontinuities will be C and C were measured by a Varian 3600 retained in the figures but should be smoothed gas chromatograph. Centerline temperature pro- mentally in interpreting data. Although the re- files in the present two-stage flames were mea- sponse of the NO. analyzer to CO [14] and to sured by a Pt-6%Rh vs. Pt-30%Rh thermocou- C species can produce false high O readings ple with a bead diameter about 130 µm. A pre- (for example, instrument readings for pure sam- viously described [5] PDPA was used to deter- ples of C C and C respectively, indi-

mine the strain rate on the air side by measuring cated 0 ppm, 8 ppm, and 200 ppm O N ), the con- the velocities of the smallest droplets in the air centrations of those species in the present flame stream. By regulating the total flow rates of the are small enough that this effect is not dominant two streams, the strain rate in the present ex- here. The quoted accuracy results to some extent periment was adjusted to be about 50s -1 based from cancellation of errors associated with these on the PDPA measurement. All details for these false high readings and low readings [14] deriving

4 from enhanced collision efficiencies of combustion ties on the order of 10% too high at stoichiomet- products. ric and fuel-lean conditions, if the rate of step 37 is increased (by about a factor of 5) to the es- timates available in the literature. It is for this UMEICA COMUAIOS reason, as well as improved agreement in subse- The computational methods employed here were quent diffusion-flame results, that the revised rate described previously [5, 12]. The numerical in- of step 37 is introduced here. Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 tegrations apply to laminar flames with poten- Principal reaction pathways in the two-stage tial flow in the outer streams. Radiant energy flame with the highest extent of premixing are loss from CO2 and H2O bands is taken into ac- shown in Fig.3. The shape of this diagram is count, with known emissivities [15]. Effects of the same as that for less premixing or for the droplet vaporization are included in energy con- diffusion flame, except that the percentages as- servation. Table 1 summarizes the detailed re- sociated with each path change. The percentages action mechanism and the elementary rate pa- are shown by numbers in parentheses adjacent to rameters employed. The rate-parameter data each arrow, and the attacking species that pro- are taken from the cited references [6, 15-28] on duces the reaction is noted just before the paren- the basis of an evaluation performed in connec- theses. The percentages are obtained by integrat- tion with the present work. The first 31 entries ing consumption rates over the entire field, includ- were developed in studying and carbon- ing both flames. Indications of the fates of some monoxide flames [15]. These investigations pro- of the minor species, such as CH30 and CH2OH vided 34 rates, but three of them are unimpor- isomers, have been omitted from the diagram for tant here and therefore are omitted; inconsequen- simplicity, although these generally proceed along tial steps (for example, reactions involving C2H) mainly to the CO2 and H2O products. The di- from other sources also are omitted here. The agram is designed to track the carbon atom in last 52 steps (starting with step 126) comprise CH4 rather than the hydrogen atoms. The N and the nitrogen chemistry, including thermal (step HCN, derived from CH, are the sources of prompt 126), prompt (step 129) and nitrous-oxide (step N0, through subsequent pathways that are not 172) mechanisms; these rate parameters are taken shown. from a common evaluation [6] following from ear- It is seen from Fig.3 that radicals attack lier work [16, 29). The rate parameters are mostly methane to form methyl (CH3) whose main close to averages of values in the literature, al- combustion path proceeds through though in some cases extreme values are more (CH2O), formyl (CHO) and , as convincing. Some further discussion of specific shown at the left. There is, however, a very im- selections is given below. portant C2 path through ethane (C2H6) to acety- As a test of the mechanism, the laminar burn- lene (C2H2), the main source of the CH species ing velocity SL was computed as a function of giving prompt N0 (the arrow from C2H2 to CH2 equivalence ratio ' for planar, premixed, adia- in Fig.3). There also is a secondary source of CH batic laminar flames. Results for a pressure of species from methyl that does not pass through 1 atm and an initial temperature of 300 K are the C2 path. This general type of fuel chemistry compared with experiments [30, 31] in Fig.2. The is characteristic not only of methane but also of agreement, which is seen to be reasonably good, all hydrocarbons. Although only about 1% of the deteriorates significantly, giving burning veloci- CH is consumed by N2 to form N and HCN, this

5 nevertheless is the main source of NO. in these C2 species, as well as predictions of some flames. Reduction of the CH concentration there- profiles, appear in Figs. 4b and 5b. fore is a method for decreasing emissions. Figures 4a and 5a show very good agreements of Table 1 and Fig.3 indicate that steps 51 and measured and predicted profiles for major species, 53 are the main source of CH, while steps 60, differences typically being less than 10%; the 61 and 62 are the most important consumption largest difference, for H2 in Fig.4a, is attributable steps for this species. A chemical-kinetic steady- mainly to measurement difficulties in the gas- state balance for the CH radical therefore results chromatographic analysis of H2. The two-stage Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 approximately in structure is very evident at the higher degree of premixing in Fig.4a, with the green premixed = {k51[H] + k53[OH]}[CH2] flame on the left, producing CO and 112, which [CH] k60[02] + k61[H20] + k62[CO2]' (1) burn with 02 from the air in the blue diffusion where the k's are specific reaction-rate constants flame about 4 mm away. At the lesser premixing from Table 1, and [ ] denotes the concentration of in Fig.5a the two flames have nearly merged, so the species. It was verified in the present compu- that CO and H2 peak only slightly to the left of tational work that Eq. 1 provides an excellent (er- CO2. If the small amount of CO2 produced in ror less than 5%) approximation for the concen- the premixed flame is neglected, then the overall tration of CH throughout these flames. It is clear stoichiometry of this first stage is from this equation that increasing the concentra- 4)CH 4 + 20 2 -3 tion of CO2 and H2O in the region where CH -PCO + (311-4)112+ (4 — IP)H 2 0, (2) exists reduces [CH] and thus decreases NO. pro- duction rates. This is a chemical-kinetic influence which is seen to consume H 2 if 4 < 4/3 and to that is not simply the reduction of reaction rates consume H 2 O if 4 >4. Practical equivalence ra- through dilution. This chemical-kinetic effect oc- tios of premixing obey 4/3 < 4P < 4, the upper curs in addition to the dilution effect if water or limit of which in rich-quench-lean combustors ac- carbon dioxide is introduced into the flame. In tually is usually reduced to 2 because of excessive lean premixed flames, the prompt path becomes sooting at higher equivalence ratios, especially at negligible in comparison with the thermal path high pressure [3]. because [CH2] is much smaller and [02] is larger, Figures 4b and 5b show that measured peak giving a much smaller value of [CH] in Eq. 1. temperatures are about 100 K below calculated values, mainly because of difficulties in thermo- COMAISOS EWEE EEIMEA A couple temperature measurements and inaccura- COMUAIOA ESUS cies in radiation corrections at these high temper- atures. The C2 species are seen in these figures The computational results are compared with the to be produced rapidly in the premixed flame, the measurements in Figs.4-9. The last four of these colder flame, and to be consumed priori to the dif- figures pertain to NO profiles, to be discussed fusion flame. This effect decreases with increas- later. Figure 4 is for a relatively high degree ing equivalence ratio and, of course, vanishes for of premixing and Fig.5 for a relatively low de- the pure diffusion flame. The removal of the C2 gree. Comparisons for mole fractions Xi of major precursors of prompt NO. from the hot diffusion species are shown in Figs.4a and 5a, while com- flame is, in fact, an advantage of partial premix- parisons for temperature and for mole fractions of ing, as is the associated reduction in their peak

6 concentrations, on the order of a factor of 2 re- additives on its maximum concentration. Table duction in going from 4'=2.5 to 4'=1.5, according 2 summarizes results of those computations. The to Figs.4b and 5b. The agreement between the first column shows the increase in XCH with in- measured and predicted profiles is excellent for creasing 4', discussed above. The first row shows ethane (within 10%), but the prediction overesti- that at low 4' the additives have very little ef- mates the sum of the and ethene mole fect; this is because the agents in the air stream fractions, especially at the lower equivalence ra- are not able to reach the region where CH is pro- tios. This implies that additional study of the ele- duced when the two flames are sufficiently sepa- Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 mentary reactions is needed, beginning with step rated. The entries for N2 show that the addition 80 in Table 1 and ending with step 125, special of nitrogen has very little influence on CH at any emphasis being desirable for step 80 through 94 value of 4', including the pure diffusion flame. It because these are the main contributors to C2H2 may be noted that these species do not appear in and C2H4. Eq. 1 and that their addition will not be expected Figure 4b shows that, at sufficiently high pre- to exert any noticeable effect on prompt NO. be- mixing equivalence ratios, two peaks are predicted cause they do not participate in the associated in the H and OH concentration profiles, a low chemical pathways. On the other hand, the en- peak in the premixed flame and a much higher tries for CO2 and especially for H2O demonstrate one in the diffusion flame, while there is always a that these agents reduce CH concentrations sig- single 0-atom peak in the diffusion flame, farthest nificantly at the higher equivalence ratios and for on the air side; the reasons for the relative posi- the pure diffusion flame. This is consistent with tions of H, OH and 0 peaks are understood on Eq. 1, that is, with the chemical-kinetic removal of the basis of partial equilibrium of steps 1-4 [32]. CH by these species. The CH reduction, and the

In Fig. 5b, at the higher 4', there is only one peak corresponding implied reduction in prompt NO R , for H and OH, the diffusion-flame peak, and it is are seen from the bottom entries in the table to somewhat higher than in Fig.4b. These radical exceed 50% for 10% CO2 addition to the diffusion profiles affect both flame stability and NO. pro- flame and for 10% H2O addition at 4' = 3 and to duction. At the lower 4' the two H and OH peaks be more than a factor of 4 for 10% H2O addition are predicted to result in two CH peaks, as may to the diffusion flame. These observations empha- be expected from Eq. 1 and as is seen in Fig.4b. size, for example, the benefits of water addition at These peaks, however, are much lower than the high equivalence ratios. single peak at the higher 4' in Fig.5b. At the lower Figures 6 through 9 show measured and com- 4', prompt NO. production thus may be expected puted temperature and NO profiles for four dif- to occur in both the premixed flame and the diffu- ferent equivalence ratios both with and without sion flame, but at a much lower rate than that in 5% by mass water added to the air stream. The the diffusion flames at high 4'. The overprediction agreement between prediction and experiment is, of C2 species in Fig.4b, far beyond experimental in general, seen to be good. The computations re- uncertainty, suggests that the true prompt NO X fer to NO rather than total NO. because the NO2 reduction associated with premixing may be even concentrations are predicted to be much smaller greater than predicted. than those of NO in the hot parts of the flame Since the CH radical is the dominant immediate where the NO. concentrations are appreciable. precursor to prompt NO, it is of interest to inves- For the measurements, however, total NO. was tigate computationally the influences of various employed as indicative of NO because of the pos-

7 sibility of conversion of NO to NO2 in the sam- ing at step 129. These differences deserve further pling system. The measurements showed that in investigation with more attention given to the rel- these flames the total NO. was, in fact, nearly evant elementary steps and their rate parameters, entirely O with NO2 making no more than a although even with the current chemical rate pa- 10% contribution. Since the temperature profiles rameters the agreements are not bad, always bet- shown in Figs. 6 through 9 have been discussed ter than a factor of two for NO. above, only the O profiles are discussed here. The previously mentioned data discontinuity as- ISCUSSIO A COCUSIOS Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 sociated with sampling-probe interference is es- A useful way to summarize the implications of the pecially noticeable in Fig.7 for the O measure- present study is to calculate an emission index for ments with 5% water and for the same O in Fig.8 and CO2 in Fig.5a; in these cases the higher NO, defined as values are more correct because the tendency for _1000fMNowNodz I 1g the probe to quench the flame reduces the con- EO f MC, WC, dz kg CH4)' (3) centrations of these products. where M denotes molecular weight, the mo- Both prediction and experiment show that the lar rate of production of O per unit volume and maximum NO occurs in the diffusion flame, irre- wcH, the molar rate of consumption of C per spective of the equivalence ratio. They also show unit volume. The integral over z goes from the that partial premixing decreases the value of this upper to lower duct exit in Fig.l. Results of this maximum and that water addition decreases it integration are plotted in Fig.10 for a = 50 s -i , further, from a value on the order of 100 ppm in with various percentages (by mass) of different the diffusion flame to a value of the order of 50 agents added to the air stream. From this figure it ppm at 4P = 1.5 with 5% water. Moreover, pre- can be seen that water is the most effective agent diction and experiment differ by less than 20% in reducing NO emission. The effect of agent type concerning the fraction of NO X reduction by wa- on emission of O varies as > CO >> ter addition at all equivalence ratios. There is, > Ar. The reasons for this ordering can be under- however, a tendency for the predictions to over- stood by comparing thermal and chemical effects estimate appreciably (by about a factor of 2) the of the different agents. extent of NO reduction achieved by partial pre- The effectiveness of an agent in reducing the mixing. For example, at the lowest premixing flame temperature can be judged on the basis of (4) = 3.0, Fig.9), the computations overpredict the change in the thermal enthalpy per unit mass O , while at the highest premixing (4) = 1.5, of the agent between the air feed-stream tempera- Fig.5) they underpredict it. This discrepancy ex- ture and the flame temperature. This mass-based ceeds experimental error and is not likely due enthalpy change, between 300 K and 2000 K, for to hydrocarbon chemistry because of the good CO and is about 50% that of O and for Ar agreements achieved for C species (the differ- is about 20% that of O These results indicate ence in Fig.4b, for example, would tend to pro- that O has the largest thermal effect, while the duce overprediction rather than underprediction thermal effects of CO and are about equal. of NO. in Fig.6), nor is there likely to be suffi- Figure 10 shows, however, that CO is twice as cient uncertainty in thermal NO. rates. It there- effective as N2 in reducing NO.. This difference fore seems that there must be some inaccuracies can be attributed to the additional chemical effect in the prompt NO chemistry in Table 1, start- of CO2 on reducing prompt NO. through Eq. 1.

8 The chemical effect is shared by H20, which is References more effective than CO2 both chemically (see Ta- [1] Lefebvre, A.H., 1995, "The Role of Fuel ble 2) and thermally, causing H2O to perform bet- ter than CO2 in Fig.10. On the other hand, like Preparation in Low-Emission Combustion," N2, Ar exerts only a thermal effect, which is less Journal of Engineering for Gas Turbines and than that of N2 because of its smaller heat-sink Power, Vol. 117, pp. 617-654. capacity. [2] Howe, G.W., Li, Z., Shih, T.I-P., and Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 Another feature shown in Fig.10 is that the ad- Nguyen, H.L., 1991, "Simulation of Mixing dition of water and carbon dioxide are more effec- in the Quick Quench Region of a Rich Burn- tive in reducing NO when is large. These re- Quick Quench Mix-Lean Burn Combustor," sults are consistent with the data shown in Table AIAA Paper No. 91-0410. 2 and with the present experiments, to the extent that such comparisons can be made. The prompt [3] Griebel, P., Fischer, M., Hassa, C., Magens, contributions become relatively more dominant as E., Nannen, H., Winandy, A., Chrysosto- 4 increases. mou, A., Meier, U. and Stricker, W., 1997, " Experimental Investigation of an Atmo- Well-defined two-stage flames in counterflowing spheric Rectangular Rich Quench Lean Com- streams have been employed here in testing a cur- bustor Sector for Aeroengines," AMSE Paper rent chemical-kinetic data base for H-C-N-O com- No. 97-GT-146. bustion systems. It is predicted that the water va- por added in the air stream helps to increase the [4] Feitelberg, A. and Lacey, M.A., 1997, " The water concentration in the flame zone and thus GE Rich-Quench-Lean Gas Turbine Com- to reduce the concentration of CH radicals. The bustor," AMSE Paper No. 97-GT-127. present work reveals that the prompt mechanism in the two-stage counterflow combustion under [5] Li, S.C., Ilincic, N. and Williams, F.A., the conditions studied here plays a dominant role 1997, " Reduction of NO. Formation by Wa- in NO. formation and that the NO. emission in- ter Sprays in Strained Two-Stage Flames," dex strongly depends on the flame structure, the Journal of Engineering for Gas Turbines and premixing equivalence ratio and the mass frac- Power, Vol. 119, pp. 836-843. tion of water and carbon dioxide added in the air [6] Hewson, J.C., Bollig, M., 1996, "Reduced stream. The NO. emission index can be reduced Mechanisms for NO. Emissions from Hy- substantially by transporting water to the region drocarbon Diffusion Flames," Twenty-Sixth where CH radicals are produced. Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, pp.2171-2179. ACKOWEGME [7] Bollig, M., Pitch, H., Hewson, J.C. and Se- This research was supported by the Department shadri, K., 1996, "Reduced n- Mech- of Energy, Office of Basic Energy Sciences, Divi- anism for Nonpremixed Combustion with sion of Engineering and Geosciences under con- Emphasis on Pollutant Relevant Intermedi- tract DE-F003-87ER13685 and BKM, Inc. and ate Species," Twenty-Sixth Symposium (In- South Coast Air Quality Management District ternational) on Combustion, The Combus- under contract AB2 7 66/97006. tion Institute, Pittsburgh, PA, pp.729-737.

9 [8] Langston, L., 1996, "Market Drivers for Elec- [15] Rightley, M.L. and Williams, F.A., 1997, tric Power Gas Turbines: Reasons for the "Structures of CO Diffusion Flames Near Ex- Revolution," Global Gas Turbine News, Vol. tinction," Combustion Science and Technol- 36, No. 3, pp. 7-10. ogy, Vol. 125, pp. 181-200.

[9] Hewson, J.C. and Williams, F.A.,1994, "CO [16] Hewson, J.C., 1995, "Reduced Mechanisms and NOx Emission from a Laminar Coflow for Hydrocarbon and Nitrogen Chemistry

Diffusion Flame: A Comparison of Ex- in Diffusion Flames," CECR Report 95-01, Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 perimental and Theoretical Results," West- Center for Energy and Combustion Research, ern States Section/The Combustion Insti- Department of Applied Mechanics and Engi- tute, Paper No. 94-046. neering Sciences, University of California San Diego, La Jolla, CA, 92093. [10] Gore, J.P. and Zhan, N.J., 1996, "NOx Emission and Major Species Concentrations [17] Frenklach, M., Wang, H. and Rabinowitz, in Partially Premixed Laminar Methane/Air M.J., 1995, "Optimization and Analysis of Co-flow Jet Flames," Combustion and Large Chemical Kinetic Mechanisms Using Flame, Vol. 105, pp. 414-427. the Solution Mapping Method - Combustion of Methane," Progress in Energy and Com- [11] Kim, T.K., Alder, B.J., Laurendeau, N.M. bustion Science, Vol. 18, pp. 129-160. and Gore, J.P., 1995, "Exhaust and In-Situ Measurements of Nitric Oxide for Laminar [18] Baulch, D.L., Cobos, C.J., Cox, R.A., Esser, Partially Premixed C2H6-Air Flames: Ef- C., Frank, P., Just, Th., Kerr, J.A., Pilling, fect of Premixing Level at Constant Fuel M.J., Troe, J., Walker, R.W. and Warnatz, Flowrate," Combustion Science and Technol- J., 1992, "Evaluated Kinetic Data for Com- ogy, Vols. 110-111, pp. 361-378. bustion Modeling," Journal of Physical and Chemical Reference Data, Vol.21, No.3, pp. [12] Li, S.C. and Williams, F.A., 1996, "Ex- 411-429. perimental and Numerical Studies of Two- Stage Flames," Twenty-Sixth Sym- [19] Hidaka, Y., Nakamura, T., Tanaka, H., posium (International) on Combustion, The Inami, K. and Kawano, H., 1990, "High Combustion Institute, Pittsburgh, PA, pp. Temperature Pyrolysis of Methane in Shock 1017-1024. Waves," International Journal f Chemical Kinetics, Vol. 22, pp. 701-709. [13] Saito, K., Gordon, A.S. and Williams, F.A., 1986, "Effects of on Soot Formation [20] Lim, K.P. and Michael, J.V., 1994, The in Methane Diffusion Flames," Combustion Thermal Reactions of CH3," Twenty-Fifth Science and Technology, Vol. 47, pp. 117-138. Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, [14] Tidona, R.J., Nizaml, A.A. and Cernan- pp. 713-719. sky, N.P., 1988, "Reducing Interference Ef- fects in the Chemiluminescent Measurement [21] Leung, K.M. and Lindstedt, R.P., 1995, "De- of Nitric Oxides from Combustion Systems," tailed Kinetic Modeling of C1-C3 Dif- Journal of the Air Pollution Control Associ- fusion Flames," Combustion and Flame, Vol. ation, Vol. 38, pp. 806-811. 102, pp. 129-160.

10 [22] Frank, P., Bhasharan, K.A. and Just, Th., [29] Hewson, J.C. and Williams, F.A., 1995, 1986, "Acetylene Oxidation: The Reaction "Reduced Mechanisms for Hydrocarbon and C2H2 + 0 at High Temperatures," Twenty- Nitrogen Chemistry in Diffusion Flames," First Symposium (International) on Com- Eighth ONR Propulsion Meeting, G.D. Roy bustion, The Combustion Institute, Pitts- and F.A. Williams eds., pp.52-59. burgh, PA, pp. 885-893. [30] Warnatz, J., 1981, "The Structure of

[23] Markus, M.W., Roth, P. and Just, Th., 1996, Laminar Alkane, , and Acetylene Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 "A Shock, Tube Study of the Reactions of Flames," Eighteenth Symposium (Interna- CH with CO2 and 02," International Journal tional) on Combustion, The Combustion In- of Chemical Kinetics, Vol. 28, pp. 171-179. stitute, Pittsburgh, PA, pp. 369-384.

[24] Li, S.C. and Williams, F.A., "Methanol- [31] Law, C.K., 1993, "A Compilation of Ex- Air Flame Structures Including NO and C2 perimental Data on Laminar Burning Ve- Species," Twenty-Seventh Symposium (In- locities," in Reduced Kinetic Mechanisms ternational) on Combustion, The Combus- for Applications in Combustion Systems N. tion Institute, Pittsburgh, PA,, submitted, Peters and B. Rogg, Eds., Spinger-Verlag, 1997. Berlin, pp. 15-26. [32] Gutheil, E. and Williams, F.A., 1990, "A [25] Baulch, D.L., Cobos, C.J., Cox, R.A., Frank, Numerical and Asymptotic Investigation of P., Hayman, G., Just, Th., Kerr, J.A., Structures of Hydrogen-Air Diffusion Flames Pilling, M.J., Troe, J., Walker, R.W. and at Pressures and Temperatures of High- Warnatz, J., 1994, "Summary Table of Eval- Speed Combustion," Twenty-Third Sympo- uated Kinetic Data for Combustion Model- sium (International) on Combustion, The ing: Supplement I," Combustion and Flame, Combustion Institute, Pittsburgh, PA, pp. Vol. 98, pp. 59-79. 513-521. [26] Liu, A., Mulac, W.A. and Jonah, C.D., 1988, "Kinetic Isotope Effects in the Gas Phase Re- action of Hydroxyl Radicals with in the Temperature Range 342-1173 K and at 1-atm Pressure," Journal of Physical Chem- istry, Vol. 92, pp. 3828-3833.

[27] Westbrook, C.K. and Dryer, F.L., 1984, "Chemical Kinetic Modeling of Hydrocarbon Combustion," Progress in Energy and Com- bustion Science, Vol. 10, pp. 1 -57.

[28] Peters, N., 1993, "Flame Calculations with Reduced Mechanism-an Outline," in Re- duced Kinetic Mechanisms for Applications in Combustion Systems, N. Peters and B. Rogg, Eds., Spinger-Verlag, Berlin, pp. 3-13.

11 Table 1: The elementary reactions and their rate parameters, with the specific reaction-rate constants in the form k = BTme-E/x°T

No. Reactions Ba ma Ea Source

1 + = O + 35E+1 -7 71 [15] 2 H2 + 0 = OH + H 5.06E+04 2.67 26.3 [15] 3 H2 + OH ^ H2O + H 1.17E+09 1.30 15.2 [15] Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 4b H2 O + 0 = 20H 7.60E+00 3.84 53.5 [15] Direct Recombination 5C 2H + M H2 + M 7.20E+17 -1.00 0.0 [15] 6d H + OH + M = H2 O + M 2.20E+22 -2.00 0.0 [15] 7d 20 + M 02 + M 6.17E+15 -0.50 0.0 [15] Formation and Consumption 8d,° H + 02 + M H02 + M 6.76E+19 -1.40 0.0 [15] 9 H02 + H r 20H 1.70E+14 0.00 3.7 [15] 10 H02 + H = H2 + 02 4.28E+13 0.00 5.9 [15] 11 H02 + H T H2O + 0 3.10E+13 0.00 7.2 [15] 1 + = O + E+13 [15] 13 H02 + OH = H2O + 02 2.89E+13 0.00 -2.1 [15] Formation and Consumption 14`'O H2O2 + M T 20H + M 1.20E+17 0.00 190.4 [15] 15 11 + 3E+1 5 [15] 16 H202 + H H02 + H2 4.79E+13 0.00 33.3 [15] 17 H202 + H H2O + OH 1.00E+13 0.00 15.0 [15] 18 H202 + OH = H2O + H02 7.08E+12 0.00 6.0 [15] 19 H202 + 0 = H02 + OH 9.63E-4-06 2.00 16.7 [15] Conversion of Carbon Monoxide to Carbon Dioxide CO + O = CO + E+ 15 -31 [15] 1 CO + = CO + O 3E+13 9 [15] Formyl Reactions 22c,e CHO + M = CO + H + M 2.85E+14 0.00 70.3 [15] 23 CHO + H ^ CO + H2 1.00E+14 0.00 0.0 [15] CO + = CO + O 3E+13 [15] 5 CO + CO + 3E+13 [15] 26 CHO + OH CO + H2O 5.00E-4-13 0.00 0.0 [15] 7 CO + CO + 3E+1 [15] Formaldehyde Reactions 28`,e CH2O + M = CHO + H + M 6.26E+16 0.00 326.0 [15] 29 CH2O + H CHO + H2 1.26E+08 1.62 9.1 [15] 30 CH2O + 0 = CHO + OH 3.50E+13 0.00 14.7 [15] 31 CH2O + OH = CHO + H2O 3.90E+10 0.89 1.7 [15] Methane Consumption 32 CH4 + H H2 + CH3 1.30E+04 3.00 33.6 [16] 33 CH4 + OH H2O + CH3 1.60E+07 1.83 11.6 [16] 34 CH4 + 0 CH3 + OH 1.90E+09 1.44 36.3 [17]

35J CH3 + H CH2 + H2 1.80E+14 0.00 63.2 [17] 36f CH3 + H CH; + H2 1.55E-4.14 0.00 56.4 [17] 37 CH3 + OH = CH; + H2O 1.00E-1-13 0.00 10.5 Present9 38 CH3 + 0 = CH2O + H 8.43E+13 • 0.00 0.0 [17] 1 39 CH3 + CH2 = C2H4 + H 4.20E-1-13 0.00 0.0 [18] 40 CH3 + HO2 - CH30 + OH 2.00E+13 0.00 0.0 [17] 41 CH3 + 02 CH2O + OH 3.30E+11 0.00 37.4 [18] C3 + = C3 + 133E+1 131 [1] 43 2CH3 = C2H4 + H2 1.00E+14 0.00 134.0 [19] 44 2CH3 = C2H5 + H 3.16E+13 0.00 61.5 [20] 45h CH3 + H - CH4 ko 6.26E+23 -1.80 0.0 11E+1 [1] Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 46h 2CH3 = C2H6 ko 1.27E+41 -7.00 11.6 11E+13 [1] Singlet Reactions 47 CH; + OH CH2O + H 3.00E+13 0.00 0.0 [17] 48 CH + 02 = CO + OH + H 3.10E+13 0.00 0.0 [17] 9 C; + CO CO + CO 3E+1 [1] 50 CHZ + M = CH2 + M 6.00E+12 0.00 0.0 [17) Triplet Methylene Reactions 51 CH2 + H CH + H2 6.02E+12 0.00 -7.5 [18] 52 CH 2 + OH CHO + H 2.50E-1-13 0.00 0.0 [17] 53 CH2 + OH = CH + H2O 1.13E+07 2.00 12.6 [17] 5 C + = CO + E+13 [] 55 C + = CO + E+13 [] 5 C + = CO + 3E+13 [1] 57 CH 2 + 02 CO + OH + H 6.58E+13 0.00 6.2 [21] 58 CH2 + CH2 = C2H2 + 2H 1.00E+14 0.00 0.0 [17] Methylidyne Reactions 59 C + CO + E+13 [] C + = CO + 177E+11 7 - [3]j 61 CH + H 2 O = CH2O + H 1.17E+15 -0.75 0.0 [21] C + CO = CO + CO E+1 3 -135 [3]- Hydroxymethyl Reactions 63 CH2OH + H = CH2 O + H2 3.00E+13 0.00 0.0 [24] 64 CH2OH + H = CH3 + OH 1.75E+14 0.00 11.7 [24] 65 CH2OH + OH CH2O + H2O 2.40E+13 0.00 0.0 [24] 66 CH2OH + 02 CH2O + HO2 5.00E+12 0.00 0.0 [24] 67' CH2OH + M CH2O + H + M 5.00E+13 0.00 105.0 [24] Methoxy Reactions 68 CH30+H - CH2O + H2 2.00E+13 0.00 0.0 [24) 69 CH30+H - CH2+H20 1.60E+13 0.00 0.0 [24] 70 CH30+OH = CH2O + H2O 5.00E+12 0.00 0.0 [24] 71 CH30+0 = OH + CH2O 1.00E+13 0.00 0.0 [24] 72 CH30+02 = CH2O + H02 ' 4.28E+13 7.60 -14.8 [24] 73k CH30+M = CH2O + H + M 1.00E-1-13 0.00 56.5 [24] 74d CH30+M CH2OH + M 1.00E+14 0.00 80.0 [24]

75 C2H6 + H = C2H5 + H2 5.40E+02 3.50 21.8 [17] 76 C2H6 + 0 = C2H5 + OH 1.40E+00 4.30 11.6 [17] 77 C2H6 + OH = C2H5 + H2O 2.20E+06 1.90 4.7 [17] 78 C2H6+CH3 T C2H5+CH 4 5.50E-01 4.00 34.7 [17] 79h C2H6 = C2H5 + H ko 4.90E+42 -6.43 448.0 5E+ -13 [17]

13 80 C2H5 + H = C2H4 + H2 3.00E+13 0.00 0.0 [17] 81 C2H5 + 0 C2H4 + OH 3.06E+13 0.00 0.0 [17] 82 C2H5 + 0 CH3 + CH2O 4.24E+13 0.00 0.0 [17] 83 C2H5+02 = C2H4+H02 2.00E+12 0.00 20.9 [17) 84h C2H 5 = C2H4 + H 2.44E+36 -5.36 175.0 k 4.97E+10 0.73 154.0 [17] Ethene Reactions

85 C2H4 + H = C2H3 + H2 5.42E+14 0.00 62.9 [25] Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 86 C2H4 + OH = C2H3 + H2O 2.09E+06 2.01 4.9 [26] 87 C2H4 + 0 T CH3 + CHO 1.60E+08 1.44 2.2 [17] 88' C 2 H4 +M = C2H2+H2 + M 2.60E+17 0.00 332.0 [17] Vinyl Reactions 89 C2H3 + H = C2H2 + H2 3.00E+13 0.00 0.0 [25] 90 C2H3 + 02 = CH2O + CHO 5.42E+12 0.00 0.0 [25] 91 h C 2H3 C2H2 + H 4.16E+41 -7.50 190.0 k 2.00E+14 0.00 166.0 [25] Acetylene Reactions 92 C2H2 + 0 = HC20 + H 4.00E-1-14 0.00 44.6 [22] 93 C2H2 0 = CH2 + CO 1.60E+14 0.00 41.4 [22] 94 C 2H2 + 02 = HC20 + OH 2.00E+08 1.50 126.0 [21] HCCO Radical Reactions 95 HC20 + H T CH + CO 1.50E+14 0.00 0.0 [22] 96 HC20 + OH T CHO + CO + H 2.00E+12 0.00 0.0 [27] 97 HC20 + 0 T 2CO + H 9.64E+13 0.00 0.0 [22] 98 HC20 + 02 2CO + OH 1.00E+13 0.00 0.0 [21] 99 HC20 + 02 = CO2 + CHO 1.00E+13 0.00 0.0 [21] ♦

100 C2 H2 + CH C3H3 + H 8.00E+13 0.00 0.0 [21] 101 C2H2 + CH; C3H4 8.00E+13 0.00 0.0 [21] 102 C2H2 + CH2 = C3H4 1.20E+13 0.00 27.7 [21] 103 C2H2 + CH3 = C3H4 + H 6.74E+19 -2.08 132.0 [21] 104 C3H4 + 0 = CH2O + C2H2 1.00E+12 0.00 0.0 [27] 105 C3H4 + 0 = CHO + C2H3 1.00E+12 0.00 0.0 [27] 106 C3H4 + OH CH2O + C2H3 1.00E+12 0.00 0.0 [27] 107 C3H4 + OH T CHO + C2H4 1.00E+12 0.00 0.0 [27] 108 C3H4 = H + C3H3 5.00E+14 0.00 370.0 [28] Allyl Reactions 109 C3H5 C3H4 + H 3.98E+13 0.00 293.0 [27] 110 C3H5 + H = C3H4 + H2 1.00E+13 0.00 0.0 [27] 111 C3H5 + 02 C3H4 + H02 6.00E+11 0.00 41.9 [27] Formation and Consumption of 112 C2H4 + CH C3H6 6.60E+13 0.00 0 [27] 113 C2H4 + CH2 C3H6 1.80E+10 0.00 0 [27] 114 C3H6 = C3H5 + H 1.00E+13 0.00 326.0 [27] 115 C3H6 = C2 H3 + CH3 3.15E+15 0.00 359.0 [27] 116 C3H6+H C3H5 + H2 5.00E+12 0.00 6.3 [27] 117 C3H6 + 0 = C2H4 + CH2O 5.90E+13 0.00 21.0 [27] 118 C3H6 + 0 = C2H5 + CHO 3.60E+12 0.00 0.0 [27] 119 C3H6 + OH = C2H5 + CH2O 7.90E+12 0.00 0.0 [27]

14 120 C3H6 + OH .- C3H5 + H2O 4.00E+12 0.00 0.0 [27] 121 C3H6+CH3 - C3H5+CH4 8.96E+12 0.00 35.6 [27] 122 C3H6 + C2H5 - C3H5 + C2H6 1.00E+11 0.00 38.5 [27] Formation and Consumption of Normal Propyl 123 C3H7 = C2H4+CH3 9.60E+13 0.00 130.0 [16] 124 C3H7 = C3H6+H 1.25E+14 0.00 155.0 [16] 125 C3H7 + 02 = C3H6 + H02 1.00E+ 12 0.00 20.9 [27] Thermal Mechanism

126 0 + N2 r NO + N 1.47E+13 0.30 315.0 [6] Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 127 N + 02 NO + 0 6.40E+09 1.00 26.3 [6] 128 N + OH = NO + H 3.80E+13 0.00 0.0 [6] Prompt Mechanism 129 N2 + CH = HCN + N 4.40E+12 0.00 92.0 [6] 130 HCN + 0 NCO + H 1.40E+06 2.10 25.6 [6]

131"' NCO + M = N + CO + M 3.10E+16 -0.50 201.0 [6] 132 NCO + H CO + NH 5.00E+13 0.00 0.0 [6] 133 NCO + 0 = NO + CO 4.70E+13 0.00 0.0 [6] 134 NCO + H2 HNCO + H 7.60E+02 3.00 16.7 [6] Reactions 135"° HNCO + M .= NH + CO + M 1.10E+16 0.00 360.0 [6] 136 HNCO + H = NH2 + CO 2.20E+07 1.70 15.9 [6] 137 HNCO + 0 = NCO + OH 2.20E+06 2.11 47.9 [6] 138 HNCO + 0 = NH + CO2 9.60E+07 1.41 35.7 [6] 139 HNCO + OH = NCO + H 2 O 6.40E+05 2.00 10.7 [6] Formation and Consumption of Cyano 140 CN + H2 HCN + H 3.60E+08 1.55 12.6 [6] 141 CN + H2O = HCN + OH 7.80E+12 0.00 31.2 [6] 142 CN + OH NCO + H 4.20E+13 0.00 0.0 [6] 143 CN + 02 - NCO + 0 7.20E+12 0.00 -1.8 [6] Reactions 144 NH + H N + H2 1.00E+13 0.00 0.0 [6] 145 NH + 0 = NO + H 9.20E+13 0.00 0.0 [6] 146 NH + OH HNO + H 4.00E+13 0.00 0.0 [6] 147 NH + OH N + H2O 5.00E+11 0.50 8.4 [6] 148 NH + 02 HNO + 0 4.60E+05 2.00 27.2 [6] 149 NH + NO = N20 + H 3.20E+14 -0.45 0.0 [6] 150 NH + NO = N2 + OH 2.20E+13 -0.23 0.0 [6]

151 NH2 + H .= NH + H2 4.00E+13 0.00 15.3 [6] 152 NH2 + 0 HNO + H 9.90E+14 -0.50 0.0 [6] 153 NH2 + OH NH + H2O 4.00E+06 2.00 4.2 [6] 154 NH 2 + NO = N2 + H2 O 2.00E+20 -2.60 3.9 [6] 155 NH2 + NO N2H + OH 9.30E+11 0.00 0.0 [6]

156" NH3 + M NH2 + H + M 2.20E+16 0.00 391.0 [6] 157 NH3 + H = NH2 + H 2 6.40E+05 2.39 42.6 [6] 158 NH3 + 0 = NH2 + OH 9.40E+06 1.94 27.1 [6] 159 NH3 + OH NH2 + H2 O 2.04E+06 2.04 2.4 [6]

15 NNH Radical Reactions 160 N2H - N2 + H 1.00E+08 0.00 0.0 [6] 161 N2H + H = N 2 + H2 1.00E+14 0.00 0.0 [6] 162 N2H + 0 N20 + H 1.00E+14 0.00 0.0 [6] 163 N2H + OH N2 + H2O 5.00E+13 0.00 0.0 [6] Hydride Reactions 164" HNO + M = H + NO + M 1.50E+16 0.00 204.0 [6] 165 HNO + H NO + H2 4.40E+11 0.72 2.7 [6] 166 HNO+OH = NO+H20 3.60E+13 0.00 0.0 Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 Reburn 167 NO + CH3 HCN + H2O 8.30E+11 0.00 67.3 [6j 168 NO + CH2 .= HNCO + H 2.90E+12 0.00 -2.5 [6] 169 NO + CH HCN + 0 1.10E+14 0.00 0.0 [6] Reactions 170° N2 0 r- N2 + 0 2.00E+14 0.00 237.0 . 8.00E+11 0.00 262.0 [6] 171 N20 + H N2 + OH 2.23E+14 0.00 70.1 [6] 172 N20 + 0 2NO 2.90E+13 0.00 96.9 [6] 173 N20 + OH = N2 + H02 2.00E+12 0.00 41.8 [6] Nitrogen Dioxide Reactions 174` NO2 + M .= NO + 0 + M 1.00E+16 0.00 276.0 [6] 175 NO + H02 .= NO2 + OH 2.10E+12 0.00 -2.0 [6] 176 NO2 + H = NO + OH 3.50E+14 0.00 6.3 [6] 177 NO2 + 0 = NO + 02 1.00E+13 0.00 2.5 [6] a Units: mol/cm3 , s' 1 , K, kJ/mol. b A good Arrhenius fit to the non-Arrhenius formula of [15]. Chaperon efficiencies: N2, 02: 1.0, CO: 1.9, CO2: 3.8, H2: 2.5, H2O: 16.3. d Chaperon efficiencies: Same as ° except H20: 12.0. e Falloff [15] omitted as unimportant at pressures considered here. f The triplet and singlet states of methylene are denoted by CH2 and CH2, respectively. g See text. h Falloff included as given in the cited reference. Chaperon efficiencies: CO: 1.8, CO2: 3.6, H2: 2.4, H20: 15.4, other: 1.0. A fit above 800 K to data available in this reference. k Chaperon efficiencies: All: 1.0. 1 Chaperon efficiencies: N2, 02: 1.2, CO: 2.1, CO2: 4.3, H2: 2.9, H20: 18.5, other: 1.0. m Chaperon efficiencies: N2, 02: 1.5, H20: 18.6, other: 1.0. n Chaperon efficiencies: N2, 02, H2: 2.0, H20: 10.0, other: 1.0. ° Lindemann falloff; Chaperon efficiencies: H20: 5.2, other:1.0.

16

Table 2: Maximum mole fraction of CH for different mass percentage of addition of water, carbon dioxide and nitrogen to the air streams.

l No H2O CO2 N2 Addition 5% 10% 5% 10% 5% 10%

1.5 1.3x10 7 1.3x10 7 1.2x10 7 1.3x10 -7 1.3x10 7 1.3x10 7 1.3x10 7

2.0 3.1x10 7 2.6x10 7 2.1x10 7 3.0x10 7 2.9x10 -7 3.1x10 7 3.1x10 7 Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021

2.5 5.5x10 7 4.3x10 7 3.3x10 7 5.1x10 7 4.7x10 -7 5.5x10 7 5.3x10 7

3.0 7.1x10 7 5.3x10 7 3.7x10 -7 6.4x10 -7 5.6x10 -7 6.9x10 7 6.7x10 7

1.9x10 1.0x10 4.1x10 7 1.4x10 - 9.1x10 -7 1.7x10 1.3x10

Methane/Air (Fuel Rich) Green Premixed Flame (First-Stage Combustion)

Stagnation

.a

z Blue Diffusion Flame Droplet -► (Second-Stage Combustion) Vaporization Plane

Air & Water Spray

Fig. 1: Schematic diagram of a two-stage methane-air flame in a counterflow air stream carrying a water spray.

17 5

5 • •O 35 C

p Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 5 G• u0 O M • r • O 15 O

1 Prediction • • Experiments by Law et al.30 5 o Various Experiments Compiled by Warnatz et al. 9 5 1 15 Equivalence Ratio, 4o Fig2: Comparison of measured laminar burning velocities of methane—air mixture, at 1 atm and an initial temperature of 300 K, with predictions using the detailed chemistry of Table 1.

CH30 C t CO OH(23) H(21) oftti. H2OH oti^^y, ( (S OM C C3 C M( CO C ( CO OH(2) C^O HHH(2) mss) C2H4 (1H(81) O (1 CH3(6) (5n 1 C-; m(Yo) O(3 O C2H4 I 78) (15 I 10(4) CO C3O( C H(60) I M(61) I Co O(3 ( CO (3 CO CO C O(5 (1 z(z ( 3 C3

O(9 1 1 (7 O(1 CO Fig.3: Reaction path for methane in a two-stage methane-air flame with c=1.5 and a = 50 s -1.

1

Fig.4a: Comparison between measurement and prediction for concentration profiles of major species for '=1.5 and o strain rate a = 50 s' 1. N

N Cv Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 x -•O U CC

S O C „ NC t O O O C 0 0 XCOO O O C C O

C O C x1f 2 C — — — — z (mm)

Fig.4b: Comparison between measurement and prediction for profiles of temperature and concentrations of radicals o and C2 species for '1=1.5 and a = 50 s -1. GGGGp

v GGGGCGGGGGG

C O - C C

C U CC

C+C 0 E" XOH O O XC2H6 O XCHX104 XH — — — — z (mm)

19 Fig.5a: Comparison between measurement and prediction for concentration profiles of major species for =2.5 and strain rate a = 50 s'1 . C N

m O N C Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021

t ICl rl I rW C O GO " t C

C O

C - - - z (mm)

Fig.5b: Comparison between measurement and prediction for profiles of temperature and concentrations of radicals o and C2 species for 4)=2.5 and a = 50 s'.

CQ

m r

CO x 1 IM U O tC d Gz

t O O O

- - - z (mm)

Fig.6: Comparison between measurement and prediction for profiles of NO concentration and temperature with 1= 1.5 and a = 50 s -1 . 1 Predicted T --- no water added

1 :000 •--• 57 water added Measured T • no water added

Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 15 ° 5% water added z Predicted NO - ° — no water added O 1 ° — 57 water added 1 ; Measured NO U O no water added z 9 • 5% water added ° O • E 0000• ;F •O O° 0 IISI °

3 1+

— — — — z (mm)

Fig.7: Comparison between measurement and prediction for profiles of NO concentration and temperature with 2100 with 1= 2.00 and strain rates of 50 s -1. _ _ I1r :;.. Predicted T ° • • •'n. , --- no water added 1 °• S •.. 5% water added • Mrd • p1 • no water added x 15 ° 57 water added z U Predicted NO O — no water added Cz 1 Q; — 5% water added 1 Mrd O ; Ono water added O O 9 • ° • 57 water added E O ° W 1 • O « 0 • O • O

3 —8 — — — z (mm)

1

Fig.8: Comparison between measurement and prediction for profiles of NO concentration and temperature with with 4)= 2.50 and strain rates of 50 s' 1. 1 Predicted T ---. no water added • 1 •••.5% water added Mrd • no water added ° 5% water added 15 z Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021 Predicted NO CO- — no water added 1 — 5% water added 1 p Measured NO I ° o no water added 9 ° • 5% water added ° C O • r

300 L.

—8 — — — z (mm)

Fig.9: Comparison between measurement and prediction for profiles of NO concentration and temperature with with 3.00 and strain rates of 50 s-'. 0 1 Predicted T --- no water added 1 -•• 5% water added Measured T • • no water added

15 ■ ° 5% water added z Predicted NO 4- — no water added 1 r —5% water added 1 p G Measured NO f ° no water added 9 • 5% water added / % C

• • • • 300 -

—8 — — — z (mm)

Fig.10: Predicted NO emission index as a function of equivalence ratio with water, carbon dioxide,

nitrogen, or added to the air stream. Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1998/78644/V003T06A001/2411187/v003t06a001-98-gt-073.pdf by guest on 30 September 2021

15 No Additive

° ■ 57O Q -----------

1 / j•• ° 5% H2O // 1 9 ---- I 17 CO -

5 010% H2O

O

11

l.v .v J.0 I}.0 w Equivalence Ratio, 1 Diffusion Flame

3