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A Shock Tube and Chemical KineticModeling Study of Methy Ethyl KetoneOxidationZ. Serinyel a , G. Black a , H. J. Curran a & J. M. Simmie aa Combustion Chemistry Centre, School of Chemistry, NationalUniversity of Ireland , Galway, Galway, IrelandPublished online: 08 Jun 2010.

To cite this article: Z. Serinyel , G. Black , H. J. Curran & J. M. Simmie (2010) A Shock Tubeand Chemical Kinetic Modeling Study of Methy Ethyl Ketone Oxidation, Combustion Science andTechnology, 182:4-6, 574-587, DOI: 10.1080/00102200903466129

To link to this article: http://dx.doi.org/10.1080/00102200903466129

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A SHOCK TUBE AND CHEMICAL KINETIC MODELINGSTUDY OF METHY ETHYL KETONE OXIDATION

Z. Serinyel, G. Black, H. J. Curran, and J. M. SimmieCombustion Chemistry Centre, School of Chemistry, National University ofIreland, Galway, Galway, Ireland

Shock-tube ignition delay times for methy ethyl ketone (MEK; or 2-butanone) were

measured at a reflected shock pressure of 1 atm (�2%) in the temperature range of

1250–1850K at equivalence ratios of 0.5–2.0 for dilute mixtures in argon with fuel concen-

trations of 1.0%, 1.5%, and 2.0%. Rate constants for unimolecular fuel decomposition

reactions were treated for falloff in pressure and temperature, with 9-parameter fits in

the Troe formulism. A detailed chemical kinetic submechanism was developed and coupled

to an existing C4 mechanism comprising 234 species and 1,369 reversible reactions. Model

simulations show generally good agreement when compared to the available experimental

data. MEK may be used as a fuel tracer, and thus further ignition delay time measurements

were carried out by adding MEK to n-heptane in order to test the effect on ignition delay

timing of blending these fuels together. It was found that autoignition characteristics of

n-heptane remained unaffected by the presence of MEK fuel tracer.

Keywords: Kinetics; Methyl ethyl ketone; Oxidation; Shock tube

INTRODUCTION

Despite recent efforts to reduce pollutant emissions such as NOx, soot,greenhouse gases, and toxic products, road transport and powertrains continue tobe targeted by legislators with demands to meet ever lower emission targets. In orderto achieve this, one strategy is the implementation of new generation biofuels, synthe-sised from biomass to replace or be blended with conventional petroleum-derivedgasoline and fuel oil. A detailed understanding of the combustion characteristics ofbiofuels, their initial identification in terms of suitability, and ultimate performancein engines is therefore of fundamental importance.

Laser imaging diagnostics is being practiced as a tool for monitoring fuel,equivalence ratio, and temperature distribution in combustion systems, and ketonesare often used as fuel tracers due to their ability to fluoresce (Schulz and Sick, 2005).However, their oxidation chemistry and ignition characteristics are not well known.Compared to the relatively high number of experimental studies concerningoxygenated fuels such as alcohols and esters, few studies exist on ketones. Lamoureux

Received 7 March 2009; revised 24 September 2009; accepted 12 October 2009.

Address correspondence to Zeynep Serinyel, Combustion Chemistry Centre, National University

of Ireland, Galway, University Road, Galway, Ireland. E-mail: zeynep.serinyel@nuigalway.ie

Combust. Sci. and Tech., 182: 574–587, 2010

Copyright # Taylor & Francis Group, LLC

ISSN: 0010-2202 print=1563-521X online

DOI: 10.1080/00102200903466129

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et al. (2008) recently performed a laser-induced fluorescence (LIF) study on methaneflames seeded with methy ethyl ketone (MEK) and ethyl acetate and observed adiminution in NOx quantity during oxidation in comparison to the unseeded flame.Gasnot et al. (2002) studied the thermal degradation of MEK in methane–air flames,a study developed further by Decottignies et al. (2002) using a chemical kinetic model.

Moreover, MEK can be used as a fuel tracer. Berckmuller et al. (1994) showedthat acetone, MEK (2-butanone), and 3-pentanone could be used to quantify fuelconcentration in a spark-ignition engine due to the positive dependence of theirrelative fluorescence to temperature. Han and Steeper (2002) used MEK along withacetone, 3-pentanone, and 3-hexanone to develop a technique to quantify equival-ence ratio in internal combustion engines. However, neither of these previouslymentioned studies included the study of the auto-ignition characteristics of MEK.In the present article, experimental ignition delay times for MEK oxidation recordedin a shock tube are described. Thereafter, the development of a detailed chemicalkinetic submechanism is discussed, and comparisons of mechanism simulations withexperimental delay times are presented. Furthermore, comparisons of the model withthe study described by Gasnot et al. (2002) are made.

EXPERIMENTAL

Shock-Tube Ignition Delay Measurements

Ignition delay measurements were carried out in a shock tube consisting of atest section measuring 6.22m in length, with an internal diameter of 10.24 cm anda barrel-shaped driver section measuring 53 cm in length. The two sections wereseparated by a polycarbonate diaphragm, which petalled when forced into contactwith a cross-shaped cutter due to the pressure differential between the high-pressuredriver section and the low-pressure test section. The driver gas used was helium(99.99% pure; BOC).

Four pressure transducers located along the last half metre of the tube wereused to determine the velocity of the incident shock wave. The velocity at the endwallwas determined using linear extrapolation in order to account for attenuation of theshock wave. This value was then used to calculate the temperature and pressure ofthe mixture behind the reflected shock wave using the equilibrium program Gaseq(Morley, 2005). The pressure at the endwall was monitored by means of an in situpressure transducer (Kistler, model 603B). Light emission from CH� at 431 nmwas detected through a fused silica window embedded in the endplate using a photo-detector (Thorlabs Inc. PDA55-EC) and a narrow band-pass filter centred at 430 nmwith a full-width half-maximum of 10 nm.

The ignition delay time was defined as the interval between the rise in pressuredue to the arrival of the shock wave at the endwall and the maximum rate of rise ofthe emission signal. The shock tube was validated before and after performing thiswork by comparison of ignition delays for n-heptane mixtures to those obtained pre-viously Smith et al. (2005) and Horning et al. (2002). The fuel (MEK, 98þ% pure)was supplied by M&B Labs and was degassed through a series of freeze-thaw cyclesuntil no gas was observed to escape on thawing of the solid. Oxygen (99.5% pure)and argon (99.9% pure) were supplied by BOC. Mixtures were prepared by using

METHY ETHYL KETONE OXIDATION 575

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the appropriate partial pressures of fuel, oxygen, and Ar, with the composition ofeach mixture provided in Table 1. Ignition times were recorded in the temperaturerange of 1250–1850K at a reflected shock pressure of 1.02 atm� 2.6%, with equival-ence ratios of 0.5, 1.0, 1.325, 1.5, and 2.0.

CHEMICAL KINETIC MODEL

Mechanism Description

A submechanism has been developed by Serinyel et al. (2008) and integratedwith a previously published C4 mechanism available on the Web page of theCombustion Chemistry Centre at the National University of Ireland, Galway(NUIG, http://c3.nuigalway.ie/naturalgas3.html). Thermodynamic properties ofthe primary fuel radical species resulting from hydrogen abstraction fromMEK havebeen calculated using THERM (Ritter & Bozelli, 1991) and are given in Table 2together with the corresponding bond dissociation energies.

High pressure limits of the unimolecular decomposition reactions are estimatedin the reverse direction, that is recombination of (CH3þC2H5CO), (CH3þCH3COCH2), and (C2H5þCH3CO), and are 3.13� 1014�T�0.5 for Reactions 1and 3, and 1.93� 1014�T�0.32 for Reaction 2 based on Tsang’s recommendations(Tsang, 1989; Tsang and Hampson, 1986).

C2H5COCH3 ðþMÞ $ CH3 þ C2H5CO ðþMÞ ðR1Þ

C2H5COCH3 ðþMÞ $ CH3 þ CH3COCH2 ðþMÞ ðR2Þ

Table 1 Compositions of the MEK=O2=Ar mixtures investigated (Black, 2009)

Mixture MEK % O2 % Ar % /

1 1.00 2.75 96.25 2.00

2 2.00 5.50 92.50 2.00

3 1.50 5.50 93.00 1.50

4 1.25 5.00 93.75 1.325

5 1.00 5.50 93.50 1.00

6 1.00 11.0 88.00 0.50

Table 2 Thermodynamic properties for selected species in MEK oxidation

Species

H0f @ 298K

(kcal=mol)

S0f @ 298K

(cal=mol-K)

CP @ 300K

(cal=mol-K)

BDE (C–H)

(kcal=mol)

C2H5COCH3 �56.88 81.07 24.17 —

CH2CH2COCH3 �7.88 85.86 23.31 101.09

CH3CHCOCH3 �17.08 78.70 22.83 90.50

CH3CH2COCH2 �14.60 80.72 24.38 95.48

Note: BDE=Bond Dissociation Energy.

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C2H5COCH3 ðþMÞ $ C2H5 þ CH3CO ðþMÞ ðR3Þ

These high-pressure rate constants were then treated using Quantum Rice-Ramsperger Kassel (QRRK) theory combined with a master equation analysis asdescribed by Dean (1985) and Dean et al. (1991) in order to account for pressurefall-off effects. This treatment resulted in the generation of rate constant expressionspresented in a nine-parameter Troe form. Hydrogen abstraction reaction rates forthe primary and secondary sites have been estimated based on the recommendationsof Orme et al. (2006) and by analogy with acetone. The corresponding rate constantsare given in Table 3.

Table 3 Reaction rate constants for unimolecular decomposition and hydrogen abstraction reactions for

MEK (cm-mol-s-cal-K units)

No. Reaction A n Ea

1 C2H5COCH3¼CH3þC2H5CO 1atm=in Ar 4.04Eþ 90 �21.90 121908

high P limit 9.13Eþ 18 �0.74 83600

2 C2H5COCH3¼CH3þCH3COCH2 1 atm=in Ar 9.17Eþ 94 �23.24 123810

high P limit 2.96Eþ 22 �1.77 85700

3 C2H5COCH3¼C2H5þCH3CO 1atm=in Ar 3.45Eþ 111 �26.79 109050

high P limit 2.91Eþ 25 �2.30 83500

4 C2H5COCH3þOH¼CH2CH2COCH3þH2O 5.28Eþ 09 0.97 1586

5 C2H5COCH3þOH¼CH3CHCOCH3þH2O 5.52Eþ 02 3.12 �1176

6 C2H5COCH3þOH¼C2H5COCH2þH2O 5.10Eþ 11 0.00 1192

7 C2H5COCH3þHO2¼CH2CH2COCH3þH2O2 2.38Eþ 04 2.55 16490

8 C2H5COCH3þHO2¼CH3CHCOCH3þH2O2 3.44Eþ 12 0.05 17880

9 C2H5COCH3þHO2¼C2H5COCH2þH2O2 2.38Eþ 04 2.55 14690

10 C2H5COCH3þO¼CH2CH2COCH3þOH 9.81Eþ 05 2.43 4750

11 C2H5COCH3þO¼CH3CHCOCH3þOH 1.44Eþ 11 0.23 2970

12 C2H5COCH3þO¼C2H5COCH2þOH 5.00Eþ 12 0.00 5962

13 C2H5COCH3þH¼CH2CH2COCH3þH2 6.66Eþ 05 2.54 6756

14 C2H5COCH3þH¼CH3CHCOCH3þH2 9.57Eþ 05 2.29 2875

15 C2H5COCH3þH¼C2H5COCH2þH2 9.30Eþ 12 0.00 6357

16 C2H5COCH3þO2¼CH2CH2COCH3þHO2 3.00Eþ 13 0.00 52290

17 C2H5COCH3þO2¼CH3CHCOCH3þHO2 2.02Eþ 13 0.00 45850

18 C2H5COCH3þO2¼C2H5COCH2þHO2 2.05Eþ 13 0.00 49150

19 C2H5COCH3þCH3¼CH2CH2COCH3þCH4 4.53E� 01 3.65 7154

20 C2H5COCH3þCH3¼CH3CHCOCH3þCH4 8.52Eþ 00 3.28 5267

21 C2H5COCH3þCH3¼C2H5COCH2þCH4 1.62Eþ 11 0.00 9630

22 C2H5COCH3þCH3O¼CH2CH2COCH3þCH3OH 2.17Eþ 11 0.00 6460

23 C2H5COCH3þCH3O¼CH3CHCOCH3þCH3OH 5.76Eþ 11 0.00 4573

24 C2H5COCH3þCH3O¼C2H5COCH2þCH3OH 2.17Eþ 11 0.00 4660

25 C2H5COCH3þCH3O2¼CH2CH2COCH3þCH3O2H 2.38Eþ 04 2.55 16490

26 C2H5COCH3þCH3O2¼CH3CHCOCH3þCH3O2H 3.44Eþ 12 0.05 17880

27 C2H5COCH3þCH3O2¼C2H5COCH2þCH3O2H 3.01Eþ 12 0.00 17580

28 C2H5COCH3þC2H3¼CH2CH2COCH3þC2H4 5.00Eþ 11 0.00 10400

29 C2H5COCH3þC2H3¼CH3CHCOCH3þC2H4 3.00Eþ 11 0.00 5600

30 C2H5COCH3þC2H3¼C2H5COCH2þC2H4 6.15Eþ 10 0.00 4278

31 C2H5COCH3þC2H5¼CH2CH2COCH3þC2H6 5.00Eþ 10 0.00 13400

32 C2H5COCH3þC2H5¼CH3CHCOCH3þC2H6 3.00Eþ 11 0.00 8600

33 C2H5COCH3þC2H5¼C2H5COCH2þC2H6 5.00Eþ 10 0.00 11600

METHY ETHYL KETONE OXIDATION 577

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Troe centering factors for Reactions 1, 2, and 3 are given below:

FcðR1Þ ¼ 0:911 exp�T

207

� �þ 0:089 exp

�T

9:9� 109

� �

þ exp�1:8� 109

T

� �

FcðR2Þ ¼ 0:14 exp�T

9:9� 109

� �þ 0:86 exp

�T

294

� �

þ exp�1:8� 109

T

� �

FcðR3Þ ¼ 0:911 exp�T

207

� �þ 0:089 exp

�T

1000

� �

þ exp�1:8� 109

T

� �

RESULTS AND DISCUSSION

Measured and calculated ignition delay times for all mixtures are plotted inFigure 1. As a first observation it is shown that rich mixtures ignite slower than leanmixtures, which is consistent with other studies on hydrocarbon fuels at these

Figure 1 Ignition delay times for all methy ethyl ketone (MEK)=O2=Ar mixtures studied (dashed lines

correspond with open symbols, while the solid lines correspond to filled symbols).

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temperatures and pressures (Gaıl et al., 2008; Kim & Shin, 2001; Oehlschlaeger et al.,2004). At a given temperature and for 1% of fuel, the ignition delay time is longer byabout a factor of 5 for the rich mixture (2.75% O2, /¼ 2.0) compared to the lean mix-ture (11.0% O2, /¼ 0.5). Mixtures 3 and 4, with equivalence ratios of /¼ 1.325 and1.5 (with Mixture 3 having 20% more fuel and 10% more O2 than Mixture 4), haveignition delay times that are very close to one another and they fall in the same line.

Figure 2a shows calculated and measured ignition delay times for mixtures 1, 5,and 6, all at a fixed fuel concentration of 1% and Figure 2b shows calculated andmeasured ignition delay times for Mixtures 2, 3, and 5 at a fixed oxygen concen-tration of 5.5%.

Figure 2 Ignition delay times (a) at 1% fuel and (b) at 5.5% O2.

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At 1% of fuel concentration, doubling the concentration of oxygen leads to afivefold decrease in ignition delay time as stated previously, whereas, at a fixedoxygen concentration, increasing the fuel concentration by a factor of two leads toa twofold increase in ignition delay time.

Considering that all measurements fall in the high temperature regime, inwhich the overall reactivity is governed by the chain branching reaction HþO2$OþOH, reactivity is very sensitive to the concentration of molecular oxygen. There-fore the mixture with the highest content of O2 for a fixed fuel concentration (11%O2, Mixture 6) has the highest reactivity and ignites faster than all others, whereasMixture 1, which contains 2.75% oxygen, ignites slowest. On the other hand, for afixed O2 concentration, increased concentration of fuel increases the inhibiting effectof H-abstraction from the fuel by H radical, hence results in longer ignition delaytimes. These trends are captured by the model as well.

Reaction Flux Analysis

A reaction flux analysis was carried out for MEK oxidation at a temperature of1400K, at a pressure of 1 atm for 1% fuel at equivalence ratios of 0.5, 1.0, and 2.0(Figure 3). Fuel decomposition takes place by unimolecular decomposition toacetonyl (CH3COCH2), propionyl (C2H5CO), acetyl (CH3CO), ethyl (C2H5), andmethyl (CH3) radicals, and by hydrogen atom abstraction reactions yieldingCH2CH2COCH3, CH3CHCOCH3 radicals, whereas C2H5COCH2 is produced inrather negligible quantity.

Among the fuel destruction pathways, unimolecular decomposition of MEK toacetyl (CH3CO) and ethyl (C2H5) radicals is the dominant reaction, especially at lean

Figure 3 Fuel destruction path of methy ethyl ketone (MEK) at 1400K, 1 atm (20% of fuel conversion).

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and high temperature conditions, accounting for at least 20% (lean case) of the fuelconversion. Analysis shows that fuel decomposition leads to the formation of ethyl-ene (C2H4), largely via the decomposition of ethyl radical and also by the decompo-sition of propionyl radical and to a lesser extent via the b-scission of the fuel radicalCH2CH2COCH3$C2H4þCH3CO. Therefore, ethylene chemistry is of fundamen-tal importance to the parent fuel and the overall good predictability of the subme-chanism. To this end, the ethylene and vinyl chemistry has been reviewed and themechanism has been revalidated for a range of experimental data including ignitiondelay time, laminar flame speed (Egolfopoulos et al., 1990; Hirasawa et al., 2002;Jomaas et al., 2005; Kumar et al., 2008) and jet-stirred reactor data (Dagaut et al.,1990) for ethylene, and is provided as supplemental material.

Sensitivity Analysis

A brute-force sensitivity analysis was performed at 1% fuel concentrationunder stoichiometric conditions and atmospheric pressure at three different tempera-tures (Figure 4). Each reaction was tested by multiplying (kþ) and dividing (k�) boththe forward and reverse rate constant by a factor of two, without affecting theequilibrium, and recording the resulting ignition delay time (sþ and s�). Thelogarithmic sensitivity coefficient, S, is then defined as:

lnS ¼ lnðsþ=s�Þlnðkþ=k�Þ ¼

lnðsþ=s�Þlnð4Þ ð1Þ

Figure 4 Ignition delay sensitivity analysis for MEK=O2=Ar mixtures at 1% fuel, /¼ 1.

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The reaction which is most sensitive to promoting reactivity under all conditionsstudied is the chain branching reaction HþO2$OþOH. By way of contrast thereactions that are most inhibiting are two involving hydrogen abstraction from thefuel by H atoms. This is because the fuel competes with molecular oxygen for H atomsand thus these reactions compete with the most important chain-branching reactionresulting in the positive sensitivity coefficient. This is also consistent with what is seenin Figures 2a and 2b where increasing oxygen concentration increases reactivitywhereas increasing fuel concentration decreases reactivity.

At 1200K, which is a relatively low temperature, HO2 is an importantradical. At this temperature, the chain termination reaction, CH3þHO2$CH4þO2, and hydrogen abstraction from fuel giving, CH3CHCOCH3þH2 andCH2CH2COCH3þH2, are the most sensitive reactions that inhibit reactivity. Onthe other hand, CH3þHO2$CH3OþOH promotes reactivity by further produc-ing hydrogen radicals from methoxy (CH3O) radical b-scission. Therefore, thereactivity is very sensitive to the branching ratio of the CH3þHO2 reactions.

At 1800K, the concentration of hydroperoxyl radicals is relatively low andthus the importance of HO2 radical chemistry decreases considerably as the tempera-ture increases. The second most sensitive reaction promoting reactivity at 1800K isCH3þOH$CH2(s)þH2O �CH2 goes from singlet to triplet state and produces Hradicals by CH2þO$COþHþH. Moreover, it is interesting to note that theb-scission of the fuel radical CH3CHCOCH3 has a small inhibiting effect becausethe product CH3CHO further gives C2H5 and CO by reacting with H radical.

Comparison of MEK with Acetone

The ignition characteristics of MEK are compared with another smallerketone, acetone, which was previously studied by Black et al. (2008) and Pichonet al. (2009; Figure 5). Acetone ignition delay data was also taken in the NUIGlow-pressure shock tube for dilute mixtures in argon at 1 atm. The comparison iscarried out at a fixed oxygen concentration of 5% and at an equivalence ratio of1.5. For comparison, 1.25% MEK=5% O2 at /¼ 1.325 and 1.5% MEK=5.5% O2

mixture at /¼ 1.5 are plotted for the reasons explained previously.Acetone ignition delay times are significantly slower than MEK: by a factor of

2–3 in the given conditions. This is due to the fact that acetone is largely consumedby unimolecular decomposition to CH3 and CH3CO, which then decomposes intoCH3 and CO in the following manner:

The reaction of methyl recombination results in the formation of a stablemolecule, ethane (C2H6), which slows down overall reactivity hence increases the

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ignition delay times, whereas MEK is more prone to produce a radical pool. InMEK oxidation, as given on Figure 1, fuel decomposition is largely due to unimo-lecular decomposition by Reaction 3 and abstraction of H atom by H, O, and OHradicals giving CH2CH2COCH3 and CH3CHCOCH3. The former radical decom-poses into C2H4 and CH3CO as given in the scheme below. Moreover, sensitivityanalysis in Figure 4 shows that the reaction CH3þCO$CH2(s)þH2O in MEKautoignition is sensitive especially at high temperatures, further producing Hradicals, increasing overall reactivity.

An important criterion in the choice of a fuel tracer is that it has to burn in asimilar fashion to the main fuel. In order to visualize the effect of MEK addition ton-heptane, shock-tube ignition delay measurements were taken for an n-heptane=O2=Ar mixture and compared to another mixture with the same O2 and Ar contentbut by replacing 15% of the fuel with MEK. The result is given on Figure 6. In bothmixtures fuel percentage is 0.4%. Measurements were taken at a temperature rangeof 1340–1850K.

Ignition delay characteristics of n-heptane remained unaffected by addition ofMEK. Similar results were obtained by Pichon et al. (2009) by addition of acetone to

Figure 5 Ignition delay times for acetone (Pichon et al., 2009) and MEK at 1 atm and 5% O2 (Lines

correspond to model results).

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n-heptane, showing that ignition delay times of n-heptane were unaffected as well.Therefore, addition of these two fuel tracers up to a certain percentage (15% asstudied here) to a main fuel under investigation does not alter autoignition charac-teristics of the main fuel.

Application of the Mechanism to the CH4/MEK Study in FlameConditions

The mechanism has been used to simulate a low-pressure premixed laminarstoichiometric CH4=O2=N2 flame seeded with 2% MEK as described by Gasnotet al. (2002). Comparisons of experimentally measured species mole fractions as afunction of height above the burner surface with model simulations are depictedin Figure 7. There was relatively good agreement for the reactants MEK, CH4,and O2 although the model underpredicts the evolution of CO, CO2, and H2O byabout 5–10%. It appears that the model underpredicts the rate of oxidation of COto CO2, with there being an overprediction of the CO mole fraction by the model,whereas CO2 is underpredicted and also both species are predicted to be formedat a slightly higher point above the burner surface compared to the experiment.On the other hand, the peak value of C2H4 is overpredicted by approximately40% while the distance at which the peak occurs agrees well with the experiment.This study highlights the importance of ethylene chemistry for MEK under flameconditions in addition to the shock-tube conditions discussed previously. On theother hand, the peak concentration of ethane is overpredicted by 15% but is inreasonably good agreement with experiment.

Figure 6 Ignition delay times for n-heptane and n-heptane=MEK in O2=Ar at 1 atm. Fuel compositions:

(�) 100% n-heptane: (.) 15% MEK=85% n-heptane (Black et al., 2006).

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CONCLUSIONS

Shock-tube ignition delay times have been measured for MEK for the firsttime, in the temperature range 1250–1850K at 1 atm and at equivalence ratios inthe range of 0.5–2.0. A comprehensive chemical kinetic model including species upto C4 validated against a wide range of experimental data including oxygenatedfuels, such as ethanol, dimethyl ether, and acetone, among others, was used to simu-late the experimental data. Model comparisons are generally in very good agreementwith experimental ignition delay time measurements, but the mechanism does predict

Figure 7 Mole fraction profiles of (a) reactants and major products and (b) major intermediates in

stoichiometric CH4=air flame seeded with MEK (Decottignies et al., 2002). Solid lines correspond to

closed symbols.

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faster ignition for the rich mixture containing 1.25% fuel with the difference incalculated and measured ignition delay time of about 50% near 1700K.

MEK is compared to acetone for which an autoignition study was performedpreviously. It is shown that MEK is more reactive compared to acetone at very simi-lar conditions (given temperature, pressure, and O2 content) due to the formation ofmore reactive ethyl radicals, compared to methyl radicals for acetone, as the radicalpool is established during the induction period.

In order to test whether MEK has an effect on the reactivity of n-heptane, amixture was prepared in which 15% of n-heptane fuel was replaced with MEKand ignition delay times were measured. The measured ignition delay times of thismixture containing 15% MEK=85% n-heptane were identical to those recorded forpure n-heptane. Therefore, ignition characteristics of the main fuel remainedunaffected by this potential fuel tracer.

The mechanism has been applied to the flame study described by Gasnot et al.(2002) and the model is found to be in good agreement with the experimentalmeasurements.

ACKNOWLEDGEMENTS

Financial support from Science Foundation Ireland (SFI) and Irish ResearchCouncil for Science, Engineering and Technology for an Embark Fellowship aregratefully acknowledged.

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