HCCI Experiments With Toluene Reference Fuels Modeled By

ARTICLE IN PRESS CNF:7033

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00doCCI experiments with toluene reference fuels modeled bya semidetailed chemical kinetic model

J.C.G. Andrae a,, T. Brinck b, G.T. Kalghatgi c

Department of Chemical Engineering and Technology, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Swedenb Department of Physical Chemistry, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden

c Shell Global Solutions (UK), P.O. Box 1, Chester CH1 3SH, UKReceived 15 February 2008; received in revised form 24 April 2008; accepted 21 May 2008

bstract

A semidetailed mechanism (137 species and 633 reactions) and new experiments in a homogeneous charge com-ession ignition (HCCI) engine on the autoignition of toluene reference fuels are presented. Skeletal mechanismsr isooctane and n-heptane were added to a detailed toluene submechanism. The model shows generally goodreement with ignition delay times measured in a shock tube and a rapid compression machine and is sensitivechanges in temperature, pressure, and mixture strength. The addition of reactions involving the formation andstruction of benzylperoxide radical was crucial to modeling toluene shock tube data. Laminar burning velocitiesr benzene and toluene were well predicted by the model after some revision of the high-temperature chemistry.oreover, laminar burning velocities of a real gasoline at 353 and 500 K could be predicted by the model us-g a toluene reference fuel as a surrogate. The model also captures the experimentally observed differences inmbustion phasing of toluene/n-heptane mixtures, compared to a primary reference fuel of the same researchtane number, in HCCI engines as the intake pressure and temperature are changed. For high intake pressuresd low intake temperatures, a sensitivity analysis at the moment of maximum heat release rate shows that the con-mption of phenoxy radicals is rate-limiting when a toluene/n-heptane fuel is used, which makes this fuel moresistant to autoignition than the primary reference fuel. Typical CPU times encountered in zero-dimensional cal-lations were on the order of seconds and minutes in laminar flame speed calculations. Cross reactions betweennzylperoxy radicals and n-heptane improved the model predictions of shock tube experiments for = 1.0 andmperatures lower than 800 K for an n-heptane/toluene fuel mixture, but cross reactions had no influence onCCI simulations.2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

ywords: Toluene reference fuels; Primary reference fuels; Laminar burning velocity; Autoignition; HCCI

Corresponding author. Fax: +46 8 696 00 07.E-mail address: [email protected] (J.C.G. Andrae).

1. Introduction

Knock, which is a fundamental constraint on theefficiency of spark ignition (SI) engines, is initiatedby autoignition in the end-gas, the unburned mixtureof fuel and air ahead of the advancing flame front.Combustion and Flame lease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10

10-2180/$ see front matter 2008 The Combustion Institute. Pui:10.1016/j.combustflame.2008.05.010) www.elsevier.com/locate/combustflameents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010

blished by Elsevier Inc. All rights reserved.


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homogeneous charge compression ignition (HCCI)gines, fuel and air are premixed as in a SI engine,e mixture is compressed, and heat release occurs bytoignition of the entire charge. Hence it is of greatterest to understand the autoignition phenomenon ininternal combustion (IC) engine.Autoignition depends on the pressure and temper-

ure history of the mixture and on the compositionthe fuel. Fuel autoignition quality, which varies

ry widely across different fuels, is a critical prop-ty of automotive fuels. It is commonly specified

research and motor octane numbers, RON andON, of the fuel. These are determined by compar-g the fuel with primary reference fuels (PRF), mix-res of isooctane and n-heptane, in standard knocksts. However, practical fuels are very different from

F because they are complex mixtures of aromatics,efins, paraffins, and oxygenates. They behave quitefferently than PRF in engines as design and operat-g conditions, which affect the pressure and temper-ure in the engine, change. The same fuel can matchry different PRFs at different conditions. Thus apical European gasoline of 95 RON and 85 MONill match 95 PRF (95% isooctane) in the RON testt match 85 PRF in the MON test, but it might beuch more resistant to autoignition than 95 PRF ifsted in a modern SI engine with lower unburnt mix-re temperatures at a given pressure than for the RONst condition. The implications of such observationse of great practical importance, as discussed in [1].he difference between the RON and MON of a fuelknown as sensitivity, S. For PRF, by definition, S isro, but for non-PRF fuels, S > 0. The autoignitionhavior of practical fuels, with S > 0, needs to bederstood at a fundamental chemical kinetics level.Chemical kinetics models have been developed in

e past to explain the autoignition of PRF, but suchhemes are not useful to describe the autoignitionpractical gasolines. On the other hand, practical

els are too complex for chemical kinetics mod-s to be developed. However, such models can beveloped for simpler fuel mixtures, surrogates forsoline, which are much more like practical gaso-es in that they have S > 0. This approach has alsoen discussed in [2]. The simplest gasoline surrogatea toluene reference fuel (TRF), for which a de-

iled chemical kinetic scheme has been developed re-ntly [3] using data on ignition delay measurementsom shock tubes [46] and from HCCI engines [7,8].etailed chemical kinetics models for other surro-te gasolines [9,10] and ignition delays from shockbes [11] have been reported recently. However, theemical kinetics model developed for the TRF in [3]large (>1000 species) and difficult to use in enginelease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10

odels. In this paper a semidetailed model is devel-ed that might be easier to incorporate into engine

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odels. At the same time, we have tried to improvee chemical mechanism based on new chemical in-ghts.

A semidetailed chemical kinetics model for TRFspresented, consisting of 137 species and 633 re-tions. Skeleton mechanisms for isooctane and n-ptane are added to a detailed mechanism for tolueneidation. Model predictions are compared with ig-tion delay times measured in shock tubes and inrapid compression machine for neat fuels as wellfor fuel mixtures over practical ranges of tempera-

re and pressure. The model has also been validatedainst experiments for laminar burning velocities ofnzene/air, toluene/air, and a real gasoline/air mix-re. New experiments with toluene reference fuelsve been conducted in a HCCI engine under dif-rent operating conditions and model predictions arempared with those and other HCCI experiments tost the capability to correlate ignition delays to em-rical measures of autoignition quality of a fuel un-r different operating conditions.

Construction of kinetic model

The methodology was to have a detailed descrip-n of toluene chemistry as base model with comple-

entary skeletal mechanisms for primary referenceels isooctane and n-heptane. The starting mecha-sm for the toluene chemistry was a kinetic model fornzene from Alzueta et al. [12], developed againstw-reactor conditions at excess air ratios ranging

om close to stoichiometric to very lean, tempera-re range 9001450 K, and residence times on theder of 150 ms. To this validated mechanism fornzene were added reactions for toluene oxidationsed on the work of Sivaramakrishnan et al. [13]d our recent work with a detailed mechanism for

RF [3]. Some additional reactions involving theenyl methyl radical (C6H4CH3) were added, basedthe work by Bounaceur et al. [14]. The toluene sub-

echanism is shown in Appendix A.In [3] it was found necessary to include a global

anching reaction involving benzyl radicals and oxy-n in order to increase reactivity in the toluene mech-ism at high pressure. Here we have tried to improveat description with elementary reactions includingrmation of the benzylperoxy radical [15,16] (thembers in parentheses indicate the reaction numberlisted in Appendix A),

6H5CH2 + O2 C6H5CH2OO, (33)llowed by decomposition of the benzylperoxy radi-ents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010

l to benzaldehyde and the hydroxyl radical,

6H5CH2OO C6H5CHO + OH. (34)


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he rate constants for (33) were taken from the workFenter et al. [17]. For reaction (34) the rate con-

ant was tuned for best fit to shock tube experimentsith toluene/air to have a value between the ones pro-sed by Bounaceur et al. [14] and Lindstedt andaurice [18].The toluene mechanism has been complemented

ith skeleton mechanisms for n-heptane [19] andooctane [20] and these submechanisms are shownAppendixes B and C, respectively.The skeletal n-heptane mechanism describes both

e high- and the low-temperature chemistry and hasen shown to reproduce ignition delay times at vari-s pressures and temperatures reasonably well. Theeletal isooctane mechanism by Tanaka et al. [20],veloped especially for HCCI conditions, has indi-ted good performance over wide ranges of pressure,mperature, and equivalence ratios, especially at highessures and lean equivalence ratios.

Cross reactions were added to the TRF mecha-sm based on our previous work [3,21]. In this worke propose that cross reactions between benzylper-y radicals and the primary reference fuels may alsoof importance. These reactions involve hydrogen

straction from primary and secondary carbons ofheptane. Since reliable experimental data for the ki-tics do not exist, we have analyzed the reactionsing modern quantum chemical methods based onohnSham density functional theory (DFT). Opti-ized geometries of reactants, products, and transi-n states have been obtained at the B3LYP/6-31+G*

vel with the Gaussian 03 suite of programs [22].ccurate energies for the optimized structures haveen determined at the B2PLYP/cc-pVTZ level usinge Orca program package [23]. The B2PLYP//cc-TZ level is expected to produce activation bar-

ers for the studied reactions that are accurate toithin ca. 3 kcal/mol [2325]. The temperature de-ndence of the derived rate constants has been deter-ined from the B3LYP/6-31+G* vibrational frequen-es. Anharmonicity in the vibrations due to hinderedternal rotation was estimated using a locally devel-ed approach [26]. On the basis of the computations,

mperature-dependent rate constants were estimatedr the temperature interval of 3001100 K.

The overall mechanism consists of 137 speciesd 633 reactions. Table 1 shows an overview ofecies included. Only around 15% of the speciesom the mechanism describing the primary referenceels are used, making the mechanism very compact.he full mechanism in CHEMKIN format with asso-ated thermodynamic and transport data is providedsupplementary material to the article.The next section describes the comparison be-lease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10

een experimental values of ignition delay times inock tubes and rapid compression machine as well

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for laminar burning velocities and numerical simu-tions using the chemical kinetic model.

Model validation

1. Comparison with ignition delay times in shockbes

A parameter often used in autoignition studies ise autoignition delay, , which is the time requiredr autoignition to happen once the fuel/air mixture isised to a given pressure and temperature and heldthat condition in a rapid compression machine orshock tube. In this work, model predictions haveen compared with shock tube autoignition delaye data over practical ranges of temperature and

essure.The Chemkin Collection [27] has been employed

handle all kinetic and thermodynamic data, as wellfor simulations. The closed homogeneous constantlume reactor model (AURORA application) hasen used to simulate the conditions behind the re-cted shocks (p5, T5). In shock tube experiments,there is a small change in pressure (generally re-lting from an energy release in the reacting mix-re), the shock tube flow can follow this pressuree. The pressure rise is dependent on how muchergy is released. If very little energy is released,en the constant volume and constant pressure con-raints give approximately the same ignition times.ut for mixtures with higher fuel concentrations, thenstant volume constraint gives shorter and more ac-rate ignition times. What actually happens in theock tube is that as the reacting gas heats up ande pressure rises, about half the maximum pressuree can be achieved/maintained and the other halfthe energy goes into expanding the gas volume.the pressure rise is very rapid, then the constantlume method is a very good approximation, up toe point of ignition. If the pressure rise is slower,e constant volume assumption is still more accu-te [28]. Autoignition delay times, , were definedthe times needed for the mixture to reach a tem-rature of 400 K above the initial temperature. Thisfinition was close to the time for the temperature in-ction point, = t (dT /dt)max, as determined withe AURORA program [27].

1.1. Primary reference fuelsFig. 1 shows the results when modeled results for

imary reference fuels are compared with the oneseasured by Fieweger et al. [29]. The model is sensi-e to changes in both temperature and mixture com-ents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010

sition and captures the negative temperature coeffi-ent (NTC) region. Some tuning and some addition


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C6H3O CH2CHCHO HNO6H3O3 CHOCHCHOH HONO5H7 C.HCHCHO NO25H6 CH2CHC.O N25H5 C2H6 C7H165H5O C2H5 C7H15-15H5OH C2H4 C7H15-25H4O C2H3 C7H15O25H4OH C2H2 C7H14O2H5H4 C2H O2C7H14O2H5H3O C2 HO2C7H13O2H5H3 CH3HCO OC7H13O2HH2CHCHCHCH3 CH3CO OC7H13OH2CHC.HCHCH2 CH2HCO C5H11H2CHCHCHC.H2 C2H2OH IC3H7HCCHCHC.H2 OCHCHO PC4H9H2CHC.HCHCHOH CH2CO C8H18H2CHCHCHCH2OH HCCOH AC8H17HOCH2CH2C.HCHO HCCO AC8H17OOH2CHCHCH2 C2O AC8H16OOHB

reactions were needed on the skeletal mechanismr isooctane by Tanaka et al. [20] to improve thesults (see Appendix C). Tanaka et al. concentrated

lean fuel/air mixtures and did not compare theiroposed model with results involving stoichiometricixtures of isooctane and air.

However, no changes were needed in the skeletalheptane mechanism upon merging with the detailedluene model. When modeled ignition delay timesr stoichiometric n-heptane/air mixtures were com-

This is in strong contrast to the detailed model pre-sented in [3], where the modeled values were a factorof 2 higher than experiments for some temperatures.This indicates that the skeletal n-heptane mechanismused in this work (not a reduced mechanism of thedetailed n-heptane model in [3]) is better tuned topredict ignition delay times in shock tubes. More-over, Herzler et al. [30] measured autoignition delaytimes in a shock tube for lean n-heptane/air mixtures( = 0.10.4) at p = 5.0 MPa and Fig. 2 shows mod-J.C.G. Andrae et al. / Combustion

ble 1st of species included in the mechanism

6H5CH3 CH2CHC.CH26H5CH2 CH2CHCHC.HC6H4CH3 CH2CHCCHOC6H4CH3 HCCHCCH6H4CH3 H2CCCCH6H5CH2OO C4H26H5CH2OOH C4H6H5CH2O CHOCH2CH2CHOlease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10

red with the experimental results by Gauthier et. [6], the average relative error was only around 6%.

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O2CCHOO. AC8H16OOHBOOC2H5CHO OC8H15OOHC2H5CO OC8H15OCH4 JC8H16CH3 IC4H8CH2CH2(S)CHents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010

ed values compared with experiments for = 0.2d 0.3. There is good agreement with the proposed


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g. 1. Comparison between experimental shock tube igni-n delay data for primary reference fuels from Fiewegeral. [29] and numerical simulations using the semidetailedemical kinetic model. Conditions behind reflected shock5, T5) simulated as a closed homogeneous constant vol-e adiabatic reactor.

g. 2. Comparison between experimental shock tube ig-tion delay data from Herzler et al. [30] and numericalmulations using the semidetailed chemical kinetic model.onditions behind reflected shock (p5, T5) simulated as aosed homogeneous constant volume adiabatic reactor.

odel except at temperatures below around 750 K.his is in strong contrast to the detailed model for n-ptane used in [3], where the modeled values haveen found to be systematically a factor of 2 higheran experiments [30].

1.2. TolueneFigs. 3 and 4 show the results when modeled re-

lts for toluene are compared with the ones measuredDavidson et al. [5], and generally the model cap-

res the change in for changes in temperature andixture strength. Reaction (34) was found to be verynsitive to the overall reactivity for neat toluene/airlease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10

ixtures and the rate constant was tuned for best fitmodel to the shock tube data to have a value be-

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g. 3. Comparison between experimental shock tube ig-tion delay data from Davidson et al. [5] and numerical

ulations using the semidetailed chemical kinetic model.nditions behind reflected shock (p5, T5) simulated as ased homogeneous constant volume adiabatic reactor. Ex-

rimental data normalized with exp = f (T )p0.93.

g. 4. Comparison between experimental shock tube ig-tion delay data from Davidson et al. [5] and numerical

ulations using the semidetailed chemical kinetic model.nditions behind reflected shock (p5, T5) simulated as ased homogeneous constant volume adiabatic reactor. Ex-

rimental data normalized with exp = f (T )p0.5.

een the one proposed by Bounaceur et al. [14] andndstedt and Maurice [18].

1.3. Toluene reference fuelsThe next step is to compare the model predictions

ith data for toluene reference fuels. It is not obviousat a model that shows good agreement with data forngle-component fuels gives good agreement for fuelixtures. In [3] we showed that

6H5CH2 + HO2 C6H5CH2O + OH, (27)hereby two unreactive radicals are transformed toore reactive ones, was very sensitive to cross-ents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010

celeration effects for toluene/n-heptane fuel mix-res, not seen for the single fuels, and the rate con-


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as found to be very sensitive under lean condi-ns ( = 0.3), with the estimated rate given by

lzueta et al. [12] overpredicting compared to ex-riments. In order to have better predictions, thete for the forward reaction was lowered from k88 =01013 exp(38 kcal mol1/RT ) cm3 mol1 s1k88 = 8.0 1012 exp(40 kcal mol1/RT ) cm3

ol1 s1. For = 1.0 the model is somewhat tooactive at 5.0 MPa, and also, at temperatures lower

sults for two gasoline surrogate fuels (Surrogates Aand B in Table 2) are compared with the ones mea-sured by Gauthier et al. [6]. Generally good agree-ment is obtained, although it has to be said that noshock tube experiments are available at lower tem-peratures for these two fuels to compare with modelpredictions. However, we have performed new exper-iments in the Shell HCCI engine at Thornton, whichare presented in Section 4.2 of this paper.J.C.G. Andrae et al. / Combustion

ble 2omposition (liquid volume %) of toluene reference fuels invesel n-Heptane Isooctanerr. A 17 63rr. B 17 69LHEP 35LHEP1 36LHEP3 50

g. 5. Comparison between experimental shock tube ig-tion delay data from Herzler et al. [4] and numericalmulations using the semidetailed chemical kinetic model.onditions behind reflected shock (p5, T5) simulated as aosed homogeneous constant volume adiabatic reactor. Ex-rimental data normalized with exp = f (T )p0.883.

ant had to be reduced compared to previous modelsimprove model predictions. For the same reason,has been shown that reaction (27) would be theuse for antagonistic blending octane numbers forixtures with isooctane and toluene [9].

Figs. 5 and 6 show the results when modeled re-lts for a toluene/n-heptane fuel (TOLHEP in Ta-e 2) are compared with the ones measured by Her-er et al. [4]. The semidetailed kinetic model cap-res the change in for changes in temperature andessure satisfactorily. The reaction with phenol andygen to give phenoxy and hydroperoxy radicals,

6H5OH + O2 C6H5O + HO2, (88)lease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10

an around 820 K, the model predictions start to de-ate from experiments (see Fig. 6). The introduction peFlame ()

d and their autoignition properties

luene RON MON Ref.88 85 [6]87 85 [6]83.9 73.2 [7,21]82.3 73.1 [8]64.1 58.1 [8]

g. 6. Comparison between experimental shock tube ig-tion delay data from Herzler et al. [4] and numericalmulations using the semidetailed chemical kinetic model.onditions behind reflected shock (p5, T5) simulated as aosed homogeneous constant volume adiabatic reactor. Ex-rimental data normalized with exp = f (T )p1.06.

cross reactions between benzylperoxy radicals andheptane,

6H5CH2OO + C7H16 C6H5CH2OOH + C7H15-1, (619)

6H5CH2OO + C7H16 C6H5CH2OOH + C7H15-2, (620)proves the predictions at temperatures below

ound 800 K, as illustrated for p = 3.0 MPa in Fig. 6.he estimated activation barrier based on quantumemical methods was 17.6 3 kcal/mol for abstrac-n of secondary hydrogen atoms from n-heptane bynzylperoxy radicals.ents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010

Modeled results having been compared with ex-rimental shock tube ignition delays at practical


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g. 7. Comparison between experimental shock tube ig-tion delay data for Surrogate A from Gauthier et al. [6]d numerical simulations using the semidetailed chem-al kinetic model. Conditions behind reflected shock5, T5) simulated as a closed homogeneous constant vol-e adiabatic reactor. Experimental data normalized with

xp = f (T )p0.83.

g. 8. Comparison between experimental shock tube ig-tion delay data for Surrogate B from Gauthier et al. [6]d numerical simulations using the semidetailed chem-al kinetic model. Conditions behind reflected shock5, T5) simulated as a closed homogeneous constant vol-e adiabatic reactor. Experimental data normalized with

xp = f (T )p0.96.

nges of pressure and temperature for single-compo-nt fuels as well as for fuel mixtures with TRFs,e model can be said to show very good agreementhigh temperatures and in the NTC region, but is

eaker at temperatures below 750 K.

2. Comparison with ignition delay times in a rapidmpression machine

In order to validate the model against rapid com-ession machine (RCM) data, we have simulatedlease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10

e experiments carried out by Tanaka et al. [31] forimary and toluene reference fuels. The results are

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g. 9. Comparison of experimental [31] and modeling re-lts (lines) for PRFs and TSFs in a rapid compression ma-ine (RCM). T = 318 K, p = 0.1 MPa, compression ratio. A heat loss of 15 cal/s was assumed while keeping thelume constant after reaching top dead center in the RCModeling.

own in Fig. 9. Generally the model does a very goodb at predicting the experiments and further validatese semidetailed model to simulate toluene referenceels at HCCI conditions.

3. Laminar burning velocities

The laminar burning velocity is a characteristic re-onse of a given combustible mixture and embodiese fundamental diffusive, reactive, and exothermicixture properties. It is a common target used to par-lly validate kinetic mechanisms. Moreover, flameeed is generally important in engine combustion.Therefore the semidetailed model was also

ecked for validity by comparing model predictionsainst experimental values of laminar burning veloc-es for benzene/air and toluene/air mixtures by Davisal. [32] and a real gasoline/air mixture by Zhao et

. [33]. The calculations were performed with theEMIX program of the Chemkin Collection [27]

d a number of dipole moments and polarizabili-s in the transport data base were updated with data

om the Handbook of Chemistry and Physics [34].first comparison showed that the model predicted

ound 15 cm/s lower burning velocities for ben-ne and toluene than the experiments. That indi-ted that revisions had to be made, and based onflow rate A-factor sensitivity analysis, some ratenstants in the high-temperature chemistry of thenzene submechanism were changed in order to im-ove the predictions. It was also necessary to addreaction for the high-temperature decompositionisobutene (iC4H8), not important in the autoigni-ents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010

n delay time calculations in shock tubes and RCMove. Some additional reactions were also added for


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g. 10. Comparison of experimental [32] and computedminar burning velocities for benzene/air and toluene/airixtures at room temperature and 1 atm. The accuracy ofe experiments was within 12 cm/s.

g. 11. Comparison of experimental laminar burning veloc-es (filled symbols) for a full boiling gasoline fuel/air mix-re [33] and computed values for surrogate gasoline fuels inr. Solid lines and open symbolsSurrogate B in Table 2.ashed lines and open symbolsPRF 87. p = 0.1 MPa.

hylbenzene. Appendix E summarizes the changesade in the mechanism in order to simulate laminarrning velocities. Fig. 10 shows the results for ben-ne/air and toluene/air mixtures. After the revision,e model generally does a good job of predictinge laminar burning velocities of both benzene andluene although the experiments are underpredicted

the model for < 1.1. Zhao et al. [33] measuredminar burning velocities at high temperatures for aal gasoline fuel, CR-87. CR-87 has octane number

and contains more than one hundred components,d the relative concentration of any single compo-nt is less than 2%. In the simulations, two differentrrogates for gasoline to represent the real gasolineere tested, PRF 87 and Surrogate B in Table 2, thats a RON of 87. Fig. 11 shows the result of the cal-lations and the model is able to predict the laminarlease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10

rning velocity as a function of temperature and .he toluene reference fuel gives better prediction for

hiTFlame ()

e peak burning velocity than the PRF 87. Overall,e laminar flame speed simulations have shown thate model is sensitive to molecular structure effectslaminar flame speeds.

Homogeneous charge compression ignitiongine experiments and modeling

In this section the model will be tested againstmogeneous charge compression ignition engine ex-riments, a typical target application, as the autoigni-n process in HCCI engines is driven by chemical

netics.In practice, compared to a primary reference fuel,

sensitive fuel (with aromatics, olefins, oxygenates)comes more resistant to autoignition if the pressureincreased for a given temperature and less resis-

nt to autoignition if the temperature is increased forgiven pressure. For all practical purposes, for bothock and HCCI, the true autoignition quality of an-PRF fuel is given by the octane index [1] OI =

ONKS, where sensitivity S = RONMON. K isnstant depending on operating conditions and issitive or negative depending on whether the tem-rature for a given pressure is higher or lower thane condition where the autoignition quality is de-rmined by RON (K = 0). A single-zone engineodel (no crevices and charge inhomogeneities) hasen used to evaluate how well the validated mech-ism could capture autoignition behavior for condi-ns corresponding to HCCI engine combustion. Theefulness of the single-zone assumption is in provid-g an estimate of ignition delay time as a function ofermodynamic conditions in the combustion cham-r.

1. HCCI engine experiments at KTH

Fig. 12 shows model predictions (single zoneodel) and average pressure and heat release ratesed on 100 engine cycles from the HCCI engineKTH [7] for the TOLHEP fuel in Table 2 validatedainst shock tube ignition delay data as shown ings. 56, and a PRF with RON = MON = 84. Thenditions for the calculations are as OP1 in Table 3ith the heat transfer model the same as in [3]. Ac-rding to the experiment, the two fuels show theme resistance to autoignition under this particularerating condition, where K is +0.07 [7] and theodel is able to predict this as well. Fig. 13 showsodel predictions for OP2 in Table 3 and averageperimental results when the K value is 1.5 at aents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010

gher intake pressure and lower intake temperature.he octane index for the toluene reference fuel is by


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O 120O 40O 250OOg. 12. Experimental and calculated pressure and heat re-ase rate as functions of crank angle in the HCCI engine atTH. OP1 in Table 3. Modeled heat release rates divided byfactor of 10. Initial temperature and pressure at the startcalculations (99 crank angle before top dead center) are7 K and 1.7 bar, respectively.

g. 13. Experimental and calculated pressure and heat re-ase rate as functions of crank angle in the HCCI engineKTH. OP2 in Table 3. Modeled heat release rate divideda factor of 5. Initial temperature and pressure at the startcalculations (99 crank angle before top dead center) are1 K and 3.2 bar, respectively.

finition 101 and would therefore have higher resis-nce to autoignition than PRF 84. Again, the model isle to predict this trend. Thus the model can capturee different autoignition behavior of paraffinic andnparaffinic fuels as the experimental conditions af-

ble 3CCI operating conditions

pin (MPa)P1 0.2857 0.1P2 0.25 0.2P3 0.2857 0.1lease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10

P4 0.25 0.1 250P5 0.25 0.2 80g. 14. Experimental and calculated pressures as a func-n of crank angle in the HCCI engine at Shell. OP3 inble 3. Initial temperature and pressure at the start of cal-lations (99 crank angle before top dead center) are 489 Kd 1.6 bar, respectively.

cting the pressure and temperature development ine engine change.

2. HCCI engine experiments at Shell Technologyentre Thornton

Fig. 14 shows model predictions (single zoneodel) and average pressure based on 100 enginecles from the HCCI engine at Shell Technology

entre Thornton [8] for TOLHEP1 and TOLHEP3 inble 2 and OP3 in Table 3. The model does a goodb of differentiating the two fuels according to theirsistance to autoignition at high intake temperatured low intake pressure (K was +2.2 in this case).For this study, new HCCI experiments have also

en conducted for Surrogate A and B (see Table 2) ine HCCI engine at Thornton, i.e., the same fuels vali-ted against shock tube ignition delay data as shownFigs. 7 and 8 above. The HCCI engine is describedmore detail in [8] and the experimental data from

e engine tests (measured average cylinder pressurea function of crank angle from 100 engine cycles)

r two different operating conditions (OP4 and OP5Table 3) is given as supplementary data to the pa-r. Figs. 15 and 16 show the results for Surrogate B,st where the intake temperature is high and intake

(C) Speed (rpm) Ref.900 [7,21]900 [7,21]

1200 [8]J.C.G. Andrae et al. / Combustion and Flame () 9ents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010

1200 This work1200 This work


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g. 15. Experimental and calculated pressures for Surrogateas a function of crank angle in the HCCI engine at Shell.P4 in Table 3. Initial temperature and pressure at the startcalculations (99 crank angle before top dead center) are9 K and 1.5 bar, respectively.

g. 16. Experimental and calculated pressures for Surrogateas a function of crank angle in the HCCI engine at Shell.P5 in Table 3. Initial temperature and pressure at the startcalculations (99 crank angle before top dead center) are5 K and 3.3 bar, respectively.

essure low (Fig. 15) and second where the intakemperature is low and intake pressure high (Fig. 16),. operating conditions are changing from a highlysitive K value of +2.2 to a strongly negative value1.5. Together with the experimental results are

own model predictions with the semidetailed modelthis work and the detailed model in [3]. Typical

PU times for the semidetailed model were on theder of seconds and for the detailed model (>1000ecies) on, the order of minutes. For both cases thetailed model is much less reactive than the semide-iled model for the same initial conditions. This maylease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10

part be explained by the results presented in Sec-n 3.1.1. CFlame ()

g. 17. Normalized sensitivity coefficients for the 10 mostnsitive reactions at the crank angle for maximum heat re-ase rate (2.3 CA ATDC). TOLHEP fuel and initial con-tions as in Fig. 13.

Discussion

It was seen in Figs. 12 and 13 that the modelas able to predict the shift in resistance to autoigni-n for an n-heptane/toluene fuel compared to a PRF

hen the operating conditions changed in a HCCI en-ne from having high intake temperature and lowtake pressure to low intake temperature and 1 barost intake pressure. In [21] the introduction of crossactions into a detailed model for TRF was foundimprove the results in those particular HCCI sim-

ations. However, the detailed model in [21] hadt been compared with shock tube data under con-tions relevant to HCCI combustion and the ratessigned to those cross reactions were too high [3].

check the importance of cross reactions in therrent semidetailed model, we performed simula-ns with and without the reactions in Appendix D,d no difference could be seen. Therefore we con-ude that there must be some other explanation ine chemistry that would be responsible for the dif-rence in autoignition when changing the operatingnditions. Figs. 17 and 18 show normalized sensi-ity coefficients for the n-heptane/toluene fuel aslculated with Chemkin for the 10 most sensitiveactions at the crank angle for maximum heat re-ase rate. The conditions for the calculations are as ings. 12 and 13. For the case with high intake pressureee Fig. 17), the reaction with the highest positivensitivity (increased rate leads to decreased ignitionlay) is the ring-opening reaction involving the phe-xy radical,ents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010

6H5O C5H5 + CO, (78)


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g. 18. Normalized sensitivity coefficients for the 10 mostnsitive reactions at the crank angle for maximum heat re-ase rate (4.3 CA ATDC). TOLHEP fuel and initial con-tions as in Fig. 12.

ith rate constant k78 = 7.4 1011 exp(43.9 kcalol1/RT ) s1. The reaction to form phenoxy fromenol in

6H5OH + C2H3 C6H5O + C2H4 (90)ith rate constant k90 = 6.0 1012 cm3 mol1 s1,d the one with 2,4-cyclopentadiene-1-one (C5H4O)

5H4O + OH C5H3O + H2O, (171)ith rate constant k171 = 1.1 108T 1.4 exp(1.45al mol1/RT ) cm3 mol1 s1 also shows a highsitive sensitivity.For the case of high intake temperature and low

take pressure, on the other hand, reactions (78),0), and (171) are not among the 10 most sensi-e reactions. Instead it is the decomposition of ben-lperoxide (34) that has the highest positive sensi-ity. Fig. 19 shows temporal profiles of mole frac-ns for phenol (C6H5OH) and 2,4-cyclopentadiene-one (C5H4O) for the two operating conditions. Thetes of disappearance of C6H5OH and C5H4O areower at the moment of autoignition for the case withosted pressure (2 bar) compared to the case withw intake pressure (1 bar), implying that reactions8), (90), and (171) are rate-limiting when increasinge pressure and decreasing the intake temperature.r both operating conditions the reaction

6H5OH + O2 C6H5O + HO2 (88)owed the highest negative sensitivity (increasedte giving longer ignition delay). Reaction (88) alsoowed a strong negative sensitivity for lean condi-ns ( = 0.3) in shock tube simulations for the samelease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10

heptane/toluene fuel mixture as used in the HCCIperiments and modeling.

sharFlame () 11

g. 19. Predicted temporal mole fraction profiles for phe-l (C6H5OH) and 2,4-cyclopentadiene-1-one (C5H4O) for1 and OP2 in Table 3 (see Figs. 10 and 13). Fuel is TOL-P in Table 2.

g. 20. Normalized sensitivity coefficients for the 10 mostnsitive reactions at the crank angle for maximum heat re-se rate (9.0 CA ATDC). PRF 84 fuel and initial condi-ns as in Fig. 13.

In the case with low intake pressure and high in-ke temperature, the consumption of phenoxy radi-ls is not rate-limiting in the same way as for these with high intake pressure and low intake temper-ure.

Figs. 20 and 21 show normalized sensitivity coef-ients for fuel PRF 84 as calculated with Chemkinr the 10 most sensitive reactions at the crank an-e for maximum heat release rate. For both operatingnditions the reaction

C8H16OOHB + O2 AC8H16OOHBOO (605)

ows the highest positive sensitivity and the reaction

C8H17 + O2 JC8H16 + HO2 (609)ents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010

ows the highest negative sensitivity. Although theree some small variations, the trend in sensitivity to


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g. 21. Normalized sensitivity coefficients for the 10 mostnsitive reactions at the crank angle for maximum heat re-ase rate (4.3 CA ATDC). PRF 84 fuel and initial condi-ns as in Fig. 12.

actions is more similar for the PRF with changingerating conditions than for the n-heptane/tolueneel (i.e., the non-PRF). This would indicate thatis the changes in the aromatic chemistry in theheptane/toluene fuel that are responsible for theanges in resistance to autoignition for different op-ating conditions.

The semidetailed model for TRF developed in thisork against ignition delay data in shock tube andpid compression machine at practical conditions foressure and temperature as well as laminar burninglocities has been shown to be predictive in terms oftoignition phasing when tested in single zone calcu-tions (0-D) against experimental data for PRF andRF in two different HCCI engines and under dif-rent operating conditions. This makes us confidentat the model would be very useful in more complexgine simulations. The CPU times encountered arethe order of seconds in zero-dimensional calcula-ns and minutes in laminar flame speed simulations-D).

Conclusions

A semidetailed mechanism (137 species and 633actions) and new experiments in a HCCI engine one autoignition of toluene reference fuels have beenesented.

The model shows generally good agreement whenmpared to ignition delay times measured in shocklease cite this article in press as: J.C.G. Andrae et al., HCCI experimemidetailed chemical kinetic model, Combust. Flame (2008), doi:10Flame ()

bes and rapid compression machines and is sensi-e to changes in temperature, pressure, and mixture

rength.The addition of reactions involving the formation

d destruction of benzylperoxide radicals was cru-al to modeling toluene shock tube data.

Cross reactions between benzylperoxy radicalsd n-heptane improved the model predictions at tem-ratures lower than 800 K for an n-heptane/tolueneel mixture.

Laminar burning velocities for benzene, toluene,d a real gasoline surrogate fuel were well pre-cted by the model after some revision of the high-mperature chemistry, and the model is sensitive toolecular structure effects on laminar flame speeds.

In a HCCI engine, the model can predict the shiftresistance in autoignition for an n-heptane/tolueneel compared to a PRF when the operating condi-ns change from low intake pressure/high intake

mperature to high intake pressure/low intake tem-rature. A sensitivity analysis at the moment of max-um heat release rate shows that the consumptionphenoxy radicals is rate-limiting for high intake

essure case when a toluene/n-heptane fuel is used,hich makes this fuel more resistant to autoignitionan the primary reference fuel.

The new model can also differentiate different n-ptane/toluene fuels at high intake temperature andw intake pressure and shows higher reactivity forfuel mixture of isooctane/toluene/n-heptane whenmpared with a detailed model for TRF (>1000ecies). This would be partly explained by a sloweractivity of the n-heptane submechanism in the de-iled model at lean fuel/air ratios.

cknowledgments

Shell Global Solutions (UK) is acknowledged forancially supporting this work. Bob Head played anportant part in performing the HCCI experimentsShell Technology Centre Thornton.

pplementary material

The online version of this article contains addi-nal supplementary material.Please visit DOI: 10.1016/j.combustflame.2008.

.010.ents with toluene reference fuels modeled by a.1016/j.combustflame.2008.05.010


Please cite this article in press as: J.C.G. Andrae et al., HCCI experiments with toluene reference fuels modeled by asemidetailed chemical kinetic model, Combust. Flame (2008), doi:10.1016/j.combustflame.2008.05.010


J.C.G. Andrae et al. / Combustion and Flame () 13

Appendix A

Table AToluene subset with rate constants

Aa na Ea Ref.1 C6H5CH2 + H C6H5CH3 1.80E+14 0 0 [13]2 C6H5CH3 C6H5 + CH3 1.40E+16 0 99,800 [13]3 C6H5CH3 + O2 C6H5CH2 + HO2 1.81E+12 0 39,717 [13]4 C6H5CH3 + OH C6H5CH2 + H2O 6.70E+09 1 870 [35]5 C6H5CH3 + O C6H5CH2 + OH 6.30E+11 0 0 [36]6 C6H5CH3 + HO2 C6H5CH2 + H2O2 1.30E+11 0 14,070 [35]7 C6H5CH3 + H C6H5CH2 + H2 6.00E+13 0 8,235 [13]8 C6H5CH3 + H C6H6 + CH3 1.20E+13 0 5,148 [13]9 C6H5CH3 + O OC6H4CH3 + H 1.63E+13 0 3,418 [13]

10 CH3 + C6H5CH3 CH4 + C6H5CH2 3.16E+11 0 9,500 [13]11 C6H5 + C6H5CH3 C6H6 + C6H5CH2 7.94E+13 0 11,935 [13]12 C6H5CH3 + H C6H4CH3 + H2 6.00E+08 1 16,800 [14]13 C6H5CH3 + O C6H4CH3 + OH 2.00E+13 0 14,700 [14]14 C6H5CH3 + OH C6H4CH3 + H2O 3.40E+08 1.4 1,450 This work15 C6H5CH3 + HO2 C6H4CH3 + H2O2 4.00E+11 0 28,900 [14]16 C6H5CH3 + CH3 C6H4CH3 + CH4 2.00E+12 0 15,000 [14]17 C6H4CH3 + O2 OC6H4CH3 + O 2.60E+13 0 6,100 [14]18 C6H4CH3 + H C6H5CH3 1.00E+14 0 0 [14]19 C6H4CH3 + H C6H5CH2 + H 1.00E+13 0 0 [37]20 C6H4CH3 + O OC6H4CH3 1.00E+14 0 0 [14]21 C6H4CH3 + OH HOC6H4CH3 1.00E+13 0 0 [14]22 C6H4CH3 + HO2 OC6H4CH3 + OH 5.00E+12 0 0 [14]23 C6H5CH2 C5H5 + C2H2 6.00E+13 0 70,000 [38]24 C6H5CH2 H2CCCH + CH2CHCCH 2.00E+14 0 83,600 [38]25 C6H5CH2 + O C6H5CHO + H 2.50E+14 0 0 [13]26 C6H5CH2 + O C6H5 + CH2O 8.00E+13 0 0 [13]27 C6H5CH2 + HO2 C6H5CH2O + OH 2.00E+12 0 0 [39]28 C6H5CH2O C6H5CHO + H 2.00E+13 0 27,500 [14]29 C6H5CH2O C6H5 + CH2O 2.00E+13 0 27,500 [14]30 C6H5CH2 + C6H5CH2 Bibenzyl 2.51E+11 0.4 0 [40]31 C6H5C2H5 C6H5CH2 + CH3 2.00E+15 0 72,700 [13]32 C6H5CH2 + OH C6H5CH2OH 6.00E+13 0 0 [13]33 C6H5CH2 + O2 C6H5CH2OO 4.60E+11 0 380 [17]

Reverse Arrhenius coefficients: 4.38E+13 0 20,217 [17]34 C6H5CH2OO C6H5CHO + OH 3.00E+09 1.1 29,500 This work35 C6H5CH2 + O2 C6H5CH2O + O 6.32E+12 0 42,920 [41]36 C6H5CHO + O2 C6H5CO + HO2 1.02E+13 0 38,950 [13]37 C6H5CHO + OH C6H5CO + H2O 1.71E+09 1.2 447 [13]38 C6H5CHO + H C6H5CO + H2 5.00E+13 0 4,928 [13]39 C6H5CHO + H C6H6 + HCO 1.20E+13 0 5,148 [13]40 C6H5CHO + O C6H5CO + OH 9.04E+12 0 3,080 [13]41 C6H5CH2 + C6H5CHO C6H5CH3 + C6H5CO 2.77E+03 2.8 5,773 [13]42 CH3 + C6H5CHO CH4 + C6H5CO 2.77E+03 2.8 5,773 [13]43 C6H5 + C6H5CHO C6H6 + C6H5CO 7.01E+11 0 4,400 [13]44 C6H5CO C6H5 + CO 3.98E+14 0 29,400 [13]45 C6H5CH2OH + O2 C6H5CHO + HO2 + H 2.00E+14 0 41,400 [13]46 C6H5CH2OH + OH C6H5CHO + H2O + H 8.43E+12 0 2,583 [13]47 C6H5CH2OH + H C6H5CHO + H2 + H 8.00E+13 0 8,235 [13]48 C6H5CH2OH + H C6H6 + CH2OH 1.20E+13 0 5,148 [13]49 C6H5CH2OH + C6H5CH2 C6H5CHO + C6H5CH3 + H 2.11E+11 0 9,500 [13]50 C6H5CH2OH + C6H5 C6H5CHO + C6H6 + H 1.40E+12 0 4,400 [13]51 C6H5C2H5 + OH C6H5C2H4 + H2O 4.80E+12 0 0 [42]52 C6H5C2H5 + HO2 C6H5C2H4 + H2O2 6.20E+04 2.5 13,522 [43]53 C6H5C2H5 + O C6H5C2H4 + OH 2.23E+13 0 3,795 [43]

(continued on next page)




14 J.C.G. Andrae et al. / Combustion and Flame ()

Table A (continued)Aa na Ea Ref.

54 C6H5C2H5 + H C6H5C2H4 + H2 2.65E+02 3.4 1,003 [43]55 C6H5C2H4 C6H5CHCH2 + H 3.16E+13 0 50,670 [40]56 C6H5CHCH2 C6H6 + C2H2 1.60E+11 0 58,438 [40]57 OC6H4CH3 + H HOC6H4CH3 2.50E+14 0 0 [13]58 OC6H4CH3 C6H6 + H + CO 2.51E+11 0 43,900 [13]59 HOC6H4CH3 + OH OC6H4CH3 + H2O 6.00E+12 0 0 [13]60 HOC6H4CH3 + H OC6H4CH3 + H2 1.15E+14 0 12,400 [13]61 HOC6H4CH3 + H C6H5CH3 + OH 2.21E+13 0 7,910 [13]62 HOC6H4CH3 + H C6H5OH + CH3 1.20E+13 0 5,148 [13]63 HOC6H4CH3 + C6H5CH2 OC6H4CH3 + C6H5CH3 1.05E+11 0 9,500 [13]

a kf = AT n exp(E/RT ),A units: mol, cm, s; E units: cal/mol. Reverse rate constants are calculated through the equilib-rium constant with associated thermodynamic data.

Appendix B

Table Bn-Heptane subset with rate constants

Aa na Ea Ref.573 C7H16 PC4H9 + IC3H7 3.16E+16 0 81,020 [19]574 C7H16 + O2 C7H15-1 + HO2 6.00E+13 0 52,820 [19]575 C7H16 + O2 C7H15-2 + HO2 4.00E+13 0 50,190 [19]576 C7H16 + HO2 C7H15-1 + H2O2 5.00E+13 0 20,430 [19]577 C7H16 + HO2 C7H15-2 + H2O2 3.36E+13 0 17,690 [19]578 C7H16 + OH C7H15-1 + H2O 1.05E+10 1 1,590 [19]579 C7H16 + OH C7H15-2 + H2O 9.40E+07 1.6 35 [19]580 C7H15-1 C7H15-2 2.00E+11 0 18,120 [19]581 C7H15-2 C7H15-1 2.00E+11 0 18,120 [19]582 C7H15-1 + O2 C7H15O2 2.50E+12 0 0 [19]583 C7H15O2 C7H15-1 + O2 2.20E+15 0 27,960 [19]584 C7H15-2 + O2 C7H15O2 2.50E+12 0 0 [19]585 C7H15O2 C7H15-2 + O2 2.20E+15 0 26,960 [19]586 C7H15O2 C7H14O2H 2.00E+11 0 17,010 [19]587 C7H14O2H + O2 O2C7H14O2H 5.60E+12 0 0 [19]588 O2C7H14O2H HO2C7H13O2H 2.00E+11 0 17,010 [19]589 HO2C7H13O2H OC7H13O2H + OH 1.00E+09 0 7,500 [19]590 OC7H13O2H OC7H13O + OH 8.40E+14 0 43,020 [19]591 OC7H13O CH2O + C5H11 + CO 2.00E+13 0 15,000 [19]592 C7H15-1 C5H11 + C2H4 2.50E+13 0 28,920 [19]593 C7H15-2 PC4H9 + CH2CHCH3 1.20E+13 0 28,203 [19]594 C5H11 C2H4 + IC3H7 7.97E+17 1.4 29,876 [19]595 C7H16 + H C7H15-1 + H2 1.88E+05 2.8 6,286 [19]596 C7H16 + H C7H15-2 + H2 2.60E+06 2.4 4,469 [19]597 IC3H7 + O2 CH2CHCH3 + HO2 6.10E+20 2.9 7,910 [13]598 CH2CHCH3 + H (+M) IC3H7 (+M) 5.70E+09 1.2 874 [44]

Low pressure limit: 0.16400E+55 11.1 936.4Troe centering: 0.10000E+01 0.10000E14 260 3000H2O enhanced by 5.000E+00H2 enhanced by 2.000E+00CO2 enhanced by 3.000E+00CO enhanced by 2.000E+00

599 IC3H7 + H C2H5 + CH3 5.00E+13 0 0 [45]600 PC4H9 (+M) C2H5 + C2H4 (+M) 1.06E+13 0 27,828 [13]

Low pressure limit: 0.18970E+56 0.11910E+02 0.32263E5H2O enhanced by 5.000E+00

(continued on next page)





Table B (continued)Aa na Ea Ref.

H2 enhanced by 2.000E+00CO2 enhanced by 3.000E+00CO enhanced by 2.000E+00

601 PC4H9 C2H5 + C2H4 2.50E+13 0 28,800 [13]a kf = AT n exp(E/RT ),A units: mol, cm, s; E units: cal/mol. Reverse rate constants (where applicable) are calculated

through the equilibrium constant with associated thermodynamic data.

Appendix C

Table CIsooctane subset with rate constants

Aa na Ea Ref.602 C8H18 + O2 AC8H17 + HO2 1.00E+16 0 49,000 This work

Reverse Arrhenius coefficients: 1.00E+12 0 0 [20]603 AC8H17 + O2 AC8H17OO 1.00E+12 0 0 [20]

Reverse Arrhenius coefficients: 2.51E+13 0 27,400 [20]604 AC8H17OO AC8H16OOHB 1.14E+11 0 22,400 [20]

Reverse Arrhenius coefficients: 1.00E+11 0 11,000 [20]605 AC8H16OOHB + O2 AC8H16OOHBOO 3.16E+11 0 0 [20]

Reverse Arrhenius coefficients: 2.51E+13 0 27,400 [20]606 AC8H16OOHBOO OC8H15OOH + OH 8.91E+10 0 17,000 [20]607 C8H18 + OH AC8H17 + H2O 3.00E+13 0 3,000 This work608 OC8H15OOH OC8H15O + OH 3.98E+15 0 43,000 [20]609 AC8H17 + O2 JC8H16 + HO2 3.16E+11 0 6,300 This work

Reverse Arrhenius coefficients: 3.16E+11 0 19,500 [20]610 OC8H15O + O2 C2H3 + 2CH2O +H2CCCH2 + CH3 + HO2 2.45E+13 0 32,000 [46]611 AC8H17 IC4H8 + CH2CHCH3 + CH3 1.28E+12 0 49,000 [46]612 JC8H16 IC4H8 + CH2CHC.H2 + CH3 1.92E+12 0 49,000 This work613 IC4H8 + O2 C2H3 + C2H4 + HO2 2.00E+14 0 35,900 [46]614 C8H18 + HO2 AC8H17 + H2O2 3.02E+12 0 14,700 This work

a kf = AT n exp(E/RT ),A units: mol, cm, s; E units: cal/mol. Reverse rate constant in reaction (614) is calculated throughthe equilibrium constant with associated thermodynamic data.

Appendix D

Table DCross reactions and rate constants

Aa na Ea Ref.615 C7H15-1 + C6H5CH3 C6H5CH2 + C7H16 1.00E+11 0 12,000 [3]616 C7H15-2 + C6H5CH3 C6H5CH2 + C7H16 1.00E+11 0 12,000 [3]617 C6H5 + C7H16 C7H15-1 + C6H6 9.00E+11 0 15,000 [3]618 C6H5 + C7H16 C7H15-2 + C6H6 2.00E+11 0 12,500 [3]619 C6H5CH2OO + C7H16 C6H5CH2OOH + C7H15-1 1.40E+06 2.4 16,700 This work620 C6H5CH2OO + C7H16 C6H5CH2OOH + C7H15-2 2.33E+06 2.4 15,000 This work621 C6H5CH2OOH C6H5CH2O + OH 1.50E+16 0 42,000 [14]622 AC8H17 + C6H5CH3 C6H5CH2 + C8H18 1.00E+11 0 12,000 [3]623 C6H5 + C8H18 AC8H17 + C6H6 9.00E+11 0 15,500 [3]624 C6H5CH2OO + C8H18 C6H5CH2OOH + AC8H17 1.40E+06 2.4 16,700 This work625 C8H18 + C7H15-1 C7H16 + AC8H17 9.00E+11 0 13,500 [47]626 C8H18 + C7H15-2 C7H16 + AC8H17 9.00E+11 0 14,500 [47]





16 J.C.G. Andrae et al. / Combustion and Flame ()

Appendix E

Table ERevised rate coefficients for laminar flame speed simulations

Aa na Ea Ref.215 CH2CHCHC.H + O2 C.HCHCHO + CH2O 1.00E+11 0.0 0 This work216 CH2CHCHC.H + O2 CH2CHCCH + HO2 1.00E+08 2.0 10,000 This work298 H2CCCH + H (+M) = H2CCCH2 (+M) 1.66E+15 0.4 0 [13]

Low pressure limit: 0.376E+46 8.52 6,293H2O enhanced by 5.000E+00H2 enhanced by 2.000E+00CO2 enhanced by 3.000E+00CO enhanced by 2.000E+00O2 enhanced by 2.000E+00C2H2 enhanced by 2.000E+00

299 H2CCCH + H (+M) = H3CCCH (+M) 1.66E+15 0.4 0 [13]Low pressure limit: 0.878E+46 8.9 7,974H2O enhanced by 5.000E+00H2 enhanced by 2.000E+00CO2 enhanced by 3.000E+00CO enhanced by 2.000E+00O2 enhanced by 2.000E+00C2H2 enhanced by 2.000E+00

301 H2CCCH + O = CH2O + C2H 2.50E+14 0.0 0 This work627 IC4H8 = CH2CHC.H2 + CH3 1.92E+66 14.2 128,100 [48]

Reverse Arrhenius coefficients: 2.09E+59 13.2 29,530 [48]628 C6H5C2H5 + O2 = C6H5C2H4 + HO2 1.40E+12 0 34,000 [14]629 C6H5C2H4 + O2 = HO2 + C6H5CHCH2 7.00E+11 0 17,000 This work630 C6H5C2H4 + HO2 = OH + C6H5CHO + CH3 2.00E+12 0 0 This work631 C6H5CHCH2 + O = C6H5 + CH2HCO 3.00E+08 1.4 1,000 This work632 C6H5CHCH2 + OH = C6H5CH2 + CH2O 6.00E+12 0 0 This work633 C6H5CHCH2 + OH = C6H5CHO + CH3 1.00E+13 0 0 This work


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HCCI experiments with toluene reference fuels modeled by a semidetailed chemical kinetic modelIntroductionConstruction of kinetic modelModel validationComparison with ignition delay times in shock tubesPrimary reference fuelsTolueneToluene reference fuels

Comparison with ignition delay times in a rapid compression machineLaminar burning velocities

Homogeneous charge compression ignition engine experiments and modelingHCCI engine experiments at KTHHCCI engine experiments at Shell Technology Centre Thornton

DiscussionConclusionsAcknowledgmentsSupplementary materialReferences

Documents

HCCI Experiments With Toluene Reference Fuels Modeled By