A shock tube study of cyclopentane and cyclohexane ignition at elevated pressures

Ignition delay times for cyclopentane/air and cyclohexane/air mixtures were measured in a shock tube at temperatures of 847–1379 K, pressures of 11–61 atm, and equivalence ratios of ? = 1.0, 0.5, and 0.25. Ignition times were determined using electronically excited OH emission monitored through the shock tube endwall and piezoelectric pressure measurements made in the shock tube sidewall. The dependence of ignition time on pressure, temperature, and equivalence ratio is quantified and correlations for ignition time formulated. Measured ignition times are compared to kinetic modeling predictions from four recently published mechanisms. The data presented provide a database for the validation of cycloalkane kinetic mechanisms at the elevated pressures found in practical combustion engines. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 624–634, 2008     

煤油自点火特性的实验研究

在加热激波管中利用反射激波点火,采用壁端压力和CH*发射光作为点火指示信号,测量了气相煤油/空气混合物的点火延时,点火温度为1100-1500K,压力为2.0×105和4.0×105Pa,化学计量比(Φ)为0.2、1.0和2.0.分析了点火温度、压力和化学计量比对点火延时的影响.结果显示,化学计量比为1.0和2.0时活化能几乎是相同的,但与化学计量比为0.2时的活化能差异很大,拟合得到了不同化学计量比条件下点火延时随温度变化的关系式.点火延时与已有的动力学机理进行对比,实验结果与Honnet等人的动力学机理吻合得很好.对不同化学计量比条件下的反应进行了敏感度分析,结果表明在化学计量比为0.2时,对点火延时敏感的关键反应与化学计量比为1.0时的有很大差异.     

正十一烷/空气在宽温度范围下着火延迟的激波管研究

在加热激波管上测量了气相正十一烷/空气混合物的着火延迟时间,着火温度为宽温度范围731-1399 K,着火压力在2.02 × 10⁵和10.10 × 10⁵ Pa附近,化学计量比分别为0.5、1.0和2.0。通过监测管侧壁观测点处的反射激波压力和OH^*发射光测出着火延迟时间。实验结果显示：在910 K以上,着火延迟时间随着火温度的降低而变长,从910到780 K,着火延迟时间随着火温度的降低而变短（显示出了负温度系数效应）,在780 K以下,着火延迟时间随着火温度的降低再次变长。在所研究的压力下,着火压力的增加使着火时间变短。化学计量比对着火延迟的影响在着火压力为2.02 × 10⁵和10.10 × 10⁵ Pa时是不同的,与在高温区相比,着火延迟在低温区对化学计量比非常敏感。在整个温度范围内,当前实验结果和LLNL（LawrenceLivermore National Laboratory）机理的预测值表现出了很好的一致性。现在的正十一烷/空气的着火数据和先前实验测量的正庚烷/空气、正癸烷/空气和正十二烷/空气的着火延迟时间相比较显示了着火延迟时间随着直链烷碳原子数的增加而减小。敏感度分析显示,高、低温条件下影响正十一烷着火延迟过程的反应是显著不同的。在高温条件下起最大促进作用的反应是H + O₂=O+OH,然而在低温条件下,起最大促进作用的反应是过氧十一烷基（C₁₁H₂₃O₂）的异构化反应。本文研究首次提供了正十一烷/空气的激波管着火延迟时间。     

Chemical‐kinetic modeling of ignition delay: Considerations in interpreting shock tube data

High‐pressure shock tube ignition delays have been and continue to be one of the key sources of data that are important to characterizing the combustion properties of real fuels. At pressures and temperatures of importance to practical applications, concerns have recently been raised as to the large differences observed between experimental data and chemical‐kinetic predictions using the common assumption that the shock tube behaves as a constant volume (V) system with constant internal energy (U). Here, a concise review is presented of phenomena that can considerably affect shock tube data at the extended test times (several milliseconds or longer) needed for the measurement of fuel/air ignition at practical conditions (i.e., high pressures and relatively low temperatures). These effects include fluid dynamic nonidealities as well as deflagrative processes typical of mild ignition events. Proposed modeling approaches that attempt to take into account these effects, by employing isentropic assumptions and pressure‐ and temperature‐varying systems, are evaluated and shown to significantly improve modeling results. Finally, it is argued that at the conditions of interest ignition delay data do not represent pure chemical‐kinetic observations but are affected by phenomena that are in some measure facility specific. This hampers direct cross comparison of the experimental ignition data collected in different venues. In such cases, pressure/temperature histories should be provided in order to properly interpret shock tube ignition data. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 143–150, 2010     

A high‐temperature chemical kinetic model for primary reference fuels

A chemical kinetic mechanism has been developed to describe the high‐temperature oxidation and pyrolysis of n‐heptane, iso‐octane, and their mixtures. An approach previously developed by this laboratory was used here to partially reduce the mechanism while maintaining a desired level of detailed reaction information. The relevant mechanism involves 107 species undergoing 723 reactions and has been validated against an extensive set of experimental data gathered from the literature that includes shock tube ignition delay measurements, premixed laminar‐burning velocities, variable pressure flow reactor, and jet‐stirred reactor species profiles. The modeled experiments treat dynamic systems with pressures up to 15 atm, temperatures above 950 K, and equivalence ratios less than approximately 2.5. Given the stringent and comprehensive set of experimental conditions against which the model is tested, remarkably good agreement is obtained between experimental and model results. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 399–414, 2007     

十氢萘/空气混合物高温着火延迟的激波管测量

在激波管上进行了气相十氢萘/空气混合物的着火延迟测量, 着火温度为950-1395 K, 着火压力为1.82×10⁵-16.56×10⁵ Pa, 化学计量比分别为0.5、1.0 和2.0. 在侧窗处利用反射激波压力和CH^*发射光来测出着火延迟时间. 系统研究了着火温度、着火压力和化学计量比对十氢萘着火延迟时间的影响. 实验结果显示着火温度和着火压力的升高均会缩短着火延迟时间. 首次在相对高和低压的条件下观察到了化学计量比对十氢萘着火延迟的影响是完全相反的. 当压力为15.15×10⁵ Pa时, 富油混合物呈现出最短的着火延迟时间, 而贫油混合物的着火延迟时间却是最长的. 相反, 当压力为2.02×10⁵ Pa时, 富油混合物的着火延迟时间最长. 着火延迟数据与已有的动力学机理的预测值进行对比, 结果显示机理在所有的实验条件下均很好地预测了实验着火延时趋势. 为了探明化学计量比对着火延迟时间影响的本质, 对高、低压条件下的着火延时进行了敏感度分析.结果显示, 压力为2.02×10⁵ Pa时, 控制着火延迟的关键反应为H+O₂=OH+O, 而涉及十氢萘及其相应自由基的反应在15.15×10⁵ Pa时对着火延迟起主要作用.     

High‐Temperature Study of 2‐Methyl Furan and 2‐Methyl Tetrahydrofuran Combustion

The ignition behavior of methyl furan (2‐MF) and methyl tetrahydrofuran (2‐MTHF) is investigated using the shock tube technique. Experiments are carried out using homogeneous gaseous mixtures of fuel, oxygen, and argon with equivalence ratios, ?, of 0.5, 1.0, and 2.0 at average pressures of 3 and 12 atm over a temperature range of 1060–1300 K. In addition to ignition delay time measurements, fuel concentration time histories during ignition and pyrolysis of 2‐MTHF are obtained by means of laser absorption spectroscopy using a He–Ne laser at a fixed wavelength of 3.39 µm. With respect to ignition delay times, it is observed that under similar conditions of equivalence ratio and argon/oxygen ratio (D), 2‐MTHF has longer ignition delay times than 2‐MF at 3 atm. In addition, 2‐MTHF has longer ignition delay times than 2‐MF at higher temperatures for the case of 12 atm and under the same conditions of ? and D. The higher reactivity of 2‐MF, as indicated by shorter ignition delay times, is attributed to differences in chemical structure, whereby weaker C–H bond sites are more readily susceptible to radical attack than in 2‐MTHF. It is observed that ignition delay times of 2‐MTHF decrease with increasing equivalence ratio at 12 atm for fixed argon/oxygen ratio. Ignition delay times are compared with model predictions using recent chemical kinetic models of both fuels, showing that both models generally predict shorter ignition delay times than measured. The relatively higher absorption cross section of 2‐MTHF at 3.39 µm allows for its concentration time histories to be determined and compared to model predictions. In line with the observed discrepancy in ignition predictions, predicted 2‐MTHF concentration profiles are such that the fuel is shown to be more rapidly consumed than observed in the experiments. The study advances understanding of the combustion chemistry of these cyclic ethers that are potential alternative fuels.     

Experimental and modeling study of the oxidation of 1‐butyne and 2‐butyne

Ignition delays were measured behind shock waves in the cases of hydrocarbon–oxygen–argon mixtures containing 1‐butyne or 2‐butyne (1 or 2% of hydrocarbons for equivalence ratios from 0.5 to 2). Reflected shock waves permitted to obtain temperatures from 1100 to 1600 K and pressures from 6.3 to 9.1 atm. A detailed mechanism of the reactions of 1‐butyne and 2‐butyne has been explained in the line of the mechanism developed previously for the reaction of C₃–C₄ unsaturated hydrocarbons (propyne, allene, 1,3‐butadiene) [Int J chem Kin 1999, 31, 361]. It is based on the most recent kinetic data values published in the literature and is consistent with thermochemistry. This mechanism has been validated by comparing the results of our simulations to the experimental results obtained for ignition delays in our shock tube and to measurements of species obtained during thermal decomposition [Int J Chem Kin 1995, 27, 321; J Phys Chem 1993, 97, 10977]. The main reaction pathways have been derived from flow‐rate and sensitivity analyses. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 172–183, 2002; DOI 10.1002/kin.10035     

Experimental and kinetic study of shock initiated ignition in homogeneous methane–hydrogen–air mixtures at engine‐relevant conditions

The ignition delay time of two stoichiometric methane/hydrogen/air mixtures has been measured in a shock tube facility at pressures from 16 to 40 atm and temperatures from 1000 to 1300 K. Overall, the observed reduction in ignition delay with some methane replaced by hydrogen is relatively small given the large concentration of hydrogen involved in the current study. With a high hydrogen mole fraction (35% of the total fuel), a reduction of the ignition‐promoting effect was observed with reduced temperature. A detailed chemical kinetic mechanism was used to simulate ignitions of test mixtures behind reflected shocks. An analysis of the mechanism indicates that at higher temperatures, the rapid decomposition of hydrogen molecules leads to a quick formation of H radical pools, which promote the chain branching through H + O₂ ? O + OH. At lower temperatures, the branching efficiency of hydrogen is low; a weak effect of hydrogen on methane ignition could be result from the reaction between H₂ and methylperoxy CH₃O₂, which contributes extra H radicals to the reaction system. The effects of hydrogen also decrease with increasing pressure; this is related to the negative pressure dependence of hydrogen at the second ignition limit. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 221–233, 2006     

Experimental and modeling study of the oxidation of isobutene

This article describes an experimental and modeling study of the oxidation of isobutene. The low-temperature oxidation was studied in a continuous-flow stirred-tank reactor operated at constant temperature (from 833 to 913 K) and pressure (1 atm), with fuel equivalence ratios from 3 to 6 and space times ranging from 1 to 10 s corresponding to isobutene conversion yields from 1 to 50%. The main carbon containing products were analyzed by gas chromatography. The ignition delays of isobutene-oxygen-argon mixtures with fuel equivalence ratios from 1 to 3 were measured behind shock waves. Reflected shock waves permitted to obtain temperatures from 1230 to 1930 K and pressures from 9.5 to 10.5 atm. A mechanism has been proposed to reproduce the profiles obtained for the reactants consumption and the products formation during the slow oxidation and to compute the ignition delays in the shock tube. Simulations were performed using CHEMKIN II. A correct agreement between the simulated values and the experimental data has been obtained in both apparatuses. The main reaction paths have been determined for both series of measurements by a sensitivity and rate of production analysis. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 629–640, 1998     

戊酸甲酯高温点火的激波管研究

戊酸甲酯是生物柴油和长链脂类燃烧过程中的中间产物之一。迄今为止,文献中还没有戊酸甲酯点火延迟的实验结果,因此对其点火特性的研究是必要的。在本文工作中,于反射激波后测量了戊酸甲酯/空气和戊酸甲酯/4%氧气/氩气的点火延迟时间。实验条件为:戊酸甲酯/空气点火温度1050–1350 K,点火压力1.5 × 10⁵和16 × 10⁵ Pa,当量比0.5、1和2;戊酸甲酯/4%氧气/氩气点火温度1210–1410 K,点火压力3.5 × 10⁵和7 × 10⁵ Pa,当量比0.75和1.25。点火延迟时间由在距离激波管端面15毫米处的测量点测到的反射激波到达信号和CH自由基信号所决定。所得实验结果显示：对于戊酸甲酯/空气和戊酸甲酯/4%氧气/氩气,温度或压力的增加都一定会使它们的点火延迟时间变短,但对于戊酸甲酯/空气,当量比对其点火延迟时间的影响在高低压下却是不同的(16 × 10⁵ Pa: τ_ign = 5.43 × 10⁻⁶Ф^−0.411exp(1.73 × 10²/RT),1.5 × 10⁵ Pa: τ_ign = 7.58 × 10⁻⁷Ф^0.193exp(2.11 × 10²/RT)。当压力为3.5 × 10⁵–7 × 10⁵ Pa时,还获得了戊酸甲酯/4%氧气/氩气点火延迟时间随点火条件的变化关系：τ_ign = 2.80 × 10⁻⁵(10⁻⁵P)^{−0.446±0.032}Ф^0.246±0.044exp((1.88 ± 0.03) × 10²/RT)。这些关系式反映了点火延迟时间对温度、压力和当量比的依赖关系,且有助于将实验数据归一到特定条件下进行比较。在本文实验条件下,由于戊酸甲酯/空气的燃料浓度远大于戊酸甲酯/4%氧气/氩气的燃料浓度,所测戊酸甲酯/空气的点火延迟时间远短于戊酸甲酯/4%氧气/氩气的点火延迟时间。通过对戊酸甲酯和其它长链脂类的点火特性比较,发现在相对低温时(空气中1200 K以下,氩气中1280 K以下),戊酸甲酯的点火延迟时间要长于其它长链脂类的点火延迟时间。已有的两个戊酸甲酯化学动力学机理都不能很好地预测本文实验结果,对戊酸甲酯机理的进一步完善是需要的。敏感度分析结果表明,支链反应H + O₂ = O + OH对戊酸甲酯的高温点火起着最强的促进作用。据我们所知,本文首次报道了戊酸甲酯的高温点火延迟实验数据,研究结果对了解戊酸甲酯的点火特性非常重要,并且为完善戊酸甲酯的化学动力学机理提供了实验依据。     

Experimental and modeling study of the oxidation of toluene

This paper describes an experimental and modeling study of the oxidation of toluene. The low‐temperature oxidation was studied in a continuous flow stirred tank reactor with carbon‐containing products analyzed by gas chromatography under the following experimental conditions: temperature from 873 to 923 K, 1 bar, fuel equivalence ratios from 0.45 to 0.91, concentrations of toluene from 1.4 to 1.7%, and residence times ranging from 2 to 13 s corresponding to toluene conversion from 5 to 85%. The ignition delays of toluene–oxygen–argon mixtures with fuel equivalence ratios from 0.5 to 3 were measured behind reflected shock waves for temperatures from 1305 to 1795 K and at a pressure of 8.7 ± 0.7 bar. A detailed kinetic mechanism has been proposed to reproduce our experimental results, as well as some literature data obtained in other shock tubes and in a plug flow reactor. The main reaction paths have been determined by sensitivity and flux analyses. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 25–49, 2005     

Kinetics of ethane oxidation

Ethane oxidation in jet-stirred reactor has recently been investigated at high temperature (800–1200 K) in the pressure range 1–10 atm and molecular species (H₂, CO, CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆) concentration profiles were obtained by probe sampling and GC analysis. Ethane oxidation was modeled using a comprehensive kinetic reaction mechanism including the most recent findings concerning the kinetics of the reactions involved in the oxidation of C₁? C₄ hydrocarbons. The proposed mechanism is able to reproduce experimental data obtained in our high-pressure jet stirred reactor and ignition delay times measured in shock tube in the pressure range 1–13 atm, for temperatures extending from 800 to 2000 K and equivalence ratios of 0.1 to 2. It is also able to reproduce atoms concentrations (H,O) measured in shock tube at ≈2 atm. The same detailed kinetic mechanism can also be used to model the oxidation of methane, ethylene, propyne, and allene in similar conditions.     

Oxidation of methyl and ethyl butanoates

This paper describes an experimental and modeling study of the oxidation of methyl and ethyl butanoates in a shock tube. The ignition delays of these two esters mixed with oxygen and argon for equivalence ratios from 0.25 to 2 and ester concentrations of 0.5% and 1% were measured behind a reflected shock wave for temperatures from 1250 to 2000 K and pressures around 8 atm. To extend the range of studied temperatures in the case of methyl butanoate, two sets of measurements were also made in a jet‐stirred reactor at 800 and 850 K, at atmospheric pressure, at residence times varying between 1.5 and 9 s and for equivalence ratios of 0.5 and 1. Detailed mechanisms for the combustion of methyl and ethyl butanoates have been automatically generated using a version of EXGAS software improved to take into account these oxygenated reactants. These mechanisms have been validated through comparison of simulated and experimental results in both types of reactor. The main reaction pathways have been derived from reaction flux and sensitivity analyses performed at different temperatures. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 226–252, 2010     

Comprehensive H2/O2 kinetic model for high‐pressure combustion

An updated H₂/O₂ kinetic model based on that of Li et al. (Int J Chem Kinet 36, 2004, 566–575) is presented and tested against a wide range of combustion targets. The primary motivations of the model revision are to incorporate recent improvements in rate constant treatment and resolve discrepancies between experimental data and predictions using recently published kinetic models in dilute, high‐pressure flames. Attempts are made to identify major remaining sources of uncertainties, in both the reaction rate parameters and the assumptions of the kinetic model, affecting predictions of relevant combustion behavior. With regard to model parameters, present uncertainties in the temperature and pressure dependence of rate constants for HO₂ formation and consumption reactions are demonstrated to substantially affect predictive capabilities at high‐pressure, low‐temperature conditions. With regard to model assumptions, calculations are performed to investigate several reactions/processes that have not received much attention previously. Results from ab initio calculations and modeling studies imply that inclusion of H + HO₂ = H₂O + O in the kinetic model might be warranted, though further studies are necessary to ascertain its role in combustion modeling. In addition, it appears that characterization of nonlinear bath‐gas mixture rule behavior for H + O₂(+ M) = HO₂(+ M) in multicomponent bath gases might be necessary to predict high‐pressure flame speeds within ～15%. The updated model is tested against all of the previous validation targets considered by Li et al. as well as new targets from a number of recent studies. Special attention is devoted to establishing a context for evaluating model performance against experimental data by careful consideration of uncertainties in measurements, initial conditions, and physical model assumptions. For example, ignition delay times in shock tubes are shown to be sensitive to potential impurity effects, which have been suggested to accelerate early radical pool growth in shock tube speciation studies. In addition, speciation predictions in burner‐stabilized flames are found to be more sensitive to uncertainties in experimental boundary conditions than to uncertainties in kinetics and transport. Predictions using the present model adequately reproduce previous validation targets and show substantially improved agreement against recent high‐pressure flame speed and shock tube speciation measurements. Comparisons of predictions of several other kinetic models with the experimental data for nearly the entire validation set used here are also provided in the Supporting Information. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 44: 444–474, 2012     

煤油裂解产物/空气与煤油/空气在宽温度范围内点火延迟的对比研究

Kerosene is an ideal endothermic hydrocarbon. Its pyrolysis plays a significant role in the thermal protection for high-speed aircraft. Before it reacts, kerosene experiences thermal decomposition in the heat exchanger and produces cracked products. Thus, to use cracked kerosene instead of pure kerosene, knowledge of their ignition properties is needed. In this study, ignition delay times of cracked kerosene/air and kerosene/air were measured in a heated shock tube at temperatures of 657–1333 K, an equivalence ratio of 1.0, and pressures of 1.01 × 10⁵–10.10 × 10⁵ Pa. Ignition delay time was defined as the time interval between the arrival of the reflected shock and the occurrence of the steepest rise of excited-state CH species (CH*) emission at the sidewall measurement location. Pure helium was used as the driver gas for high-temperature measurements in which test times needed to be shorter than 1.5 ms, and tailored mixtures of He/Ar were used when test times could reach up to 15 ms. Arrhenius-type formulas for the relationship between ignition delay time and ignition conditions (temperature and pressure) were obtained by correlating the measured high-temperature data of both fuels. The results reveal that the ignition delay times of both fuels are close, and an increase in the pressure or temperature causes a decrease in the ignition delay time in the high-temperature region (> 1000 K). Both fuels exhibit similar high-temperature ignition delay properties, because they have close pressure exponents (cracked kerosene: τ_ign∝P^-0.85; kerosene:τ_ign∝P^-0.83) and global activation energies (cracked kerosene: E_a = 143.37 kJ·mol^-1; kerosene: E_a = 144.29 kJ·mol^-1). However, in the low-temperature region (< 1000 K), ignition delay characteristics are quite different. For cracked kerosene/air, while the decrease in the temperature still results in an increase in the ignition delay time, the negative temperature coefficient (NTC) of ignition delay does not occur, and the low-temperature ignition data still can be correlated by an Arrhenius-type formula with a much smaller global activation energy compared to that at high temperatures. However, for kerosene/air, this NTC phenomenon was observed, and the Arrhenius-type formula fails to correlate its low-temperature ignition data. At temperatures ranging from 830 to 1000 K, the cracked kerosene ignites faster than the kerosene; at temperatures below 830 K, kerosene ignition delay times become much shorter than those of cracked kerosene. Surrogates for cracked kerosene and kerosene are proposed based on the H/C ratio and average molecular weight in order to simulate ignition delay times for cracked kerosene/air and kerosene/air. The simulation results are in fairly good agreement with current experimental data for the two fuels at high temperatures (> 1000 K). However, in the low-temperature NTC region, the results are in very good agreement with kerosene ignition delay data but disagree with cracked kerosene ignition delay data. The comparison between experimental data and model predictions indicates that refinement of the reaction mechanisms for cracked kerosene and kerosene is needed. These test results are helpful to understand ignition properties of cracked kerosene in developing regenerative cooling technology for high-speed aircraft.     

Methyl formate oxidation: Speciation data,laminar burning velocities,ignition delay times,and a validated chemical kinetic model

The oxidation of methyl formate (CH₃OCHO) has been studied in three experimental environments over a range of applied combustion relevant conditions:

• 1. A variable‐pressure flow reactor has been used to quantify reactant, major intermediate and product species as a function of residence time at 3 atm and 0.5% fuel concentration for oxygen/fuel stoichiometries of 0.5, 1.0, and 1.5 at 900 K, and for pyrolysis at 975 K.
• 2. Shock tube ignition delays have been determined for CH₃OCHO/O₂/Ar mixtures at pressures of ≈ 2.7, 5.4, and 9.2 atm and temperatures of 1275–1935 K for mixture compositions of 0.5% fuel (at equivalence ratios of 1.0, 2.0, and 0.5) and 2.5% fuel (at an equivalence ratio of 1.0).
• 3. Laminar burning velocities of outwardly propagating spherical CH₃OCHO/air flames have been determined for stoichiometries ranging from 0.8–1.6, at atmospheric pressure using a pressure‐release‐type high‐pressure chamber.

A detailed chemical kinetic model has been constructed, validated against, and used to interpret these experimental data. The kinetic model shows that methyl formate oxidation proceeds through concerted elimination reactions, principally forming methanol and carbon monoxide as well as through bimolecular hydrogen abstraction reactions. The relative importance of elimination versus abstraction was found to depend on the particular environment. In general, methyl formate is consumed exclusively through molecular decomposition in shock tube environments, while at flow reactor and freely propagating premixed flame conditions, there is significant competition between hydrogen abstraction and concerted elimination channels. It is suspected that in diffusion flame configurations the elimination channels contribute more significantly than in premixed environments. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 527–549, 2010     

Oxidation of small unsaturated methyl and ethyl esters

The ignition delay times were measured behind reflected shock waves for temperatures from 1280 to 1930 K, pressures from of 7–9.65 atm, fuel concentrations of 0.4, 0.5, and 1%, and equivalence ratios equal to 0.25, 1.0, and 2.0 in the cases of four unsaturated esters: methyl crotonate, methyl acrylate, ethyl crotonate, and ethyl acrylate. Ignition delay times were measured using chemiluminescence emission from OH at 306 nm and piezoelectric pressure measurements made at the shock tube sidewall. No important difference of reactivity was observed between methyl and ethyl unsaturated esters, methyl and ethyl crotonate having the same reactivity as methyl butanoate. The reactivity of acrylates is greater than that of crotonates especially at the lowest investigated temperatures. Detailed mechanisms for the combustion of the four studied unsaturated esters have been automatically generated using the version of EXGAS software recently improved to take into account this class of oxygenated reactants. These mechanisms have been validated through satisfactory comparison of simulated and experimental results. The main reaction pathways have been derived from flow rate and sensitivity analyses. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 204–218, 2011     

Thermal decomposition of monomethylhydrazine: Shock tube experiments and kinetic modeling

The thermal decomposition of gaseous monomethylhydrazine (MMH) was studied by recording MMH absorption at 220 nm of the reacting gas behind a reflected shock wave at temperatures of 900–1370 K, pressures of 140–450 kPa, and in mixtures containing 97.5–99 mol% argon. Based on previous work (Sun and Law; J Phys Chem A 2007, 111(19), 3748–3760), a kinetic mechanism was developed over extended temperature and pressure ranges to model these experimental data. Specifically, the temperature and pressure dependence of the unimolecular rate coefficients on the dissociation of MMH and the associated radicals were calculated by the QRRK/Master equation analysis at temperatures of 300–2000 K and pressures of 1–100 atm based on published thermochemical and kinetic parameters. They were then fitted using the Troe formalism and incorporated in the kinetic model. This unadjusted model was then used to predict the MMH decomposition profiles at different temperatures and pressures for seven groups of MMH/Ar mixtures and the half‐life decomposition times from shock tube experiments. Good agreement was observed below 940 K and above 1150 K for the diluted MMH/Ar mixtures. The model predictions further show that the overall MMH decomposition rate follows first‐order kinetics, and that the N–N bond scission is the most sensitive reaction path for the modeling of the homogeneous decomposition of MMH at elevated pressures. However, the model predictions deviate from the experimental data with the incubation period of ca. 100 μs observed in the 1030–1090 K temperature range, and it also predicts longer ignition delays for highly concentrated MMH/Ar mixtures. The discrepancy between the model predictions and experimental data at these special conditions of MMH decomposition was analyzed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 176–186, 2009     

Shock tube ignition delay time measurements for methyl propanoate and methyl acrylate: Influence of saturation on small methyl ester high-temperature reactivity

We report ignition delay time measurements for methyl propanoate (MP) and methyl acrylate (MA), carried out in a high-pressure shock tube. Experiments were performed behind reflected shock waves across a temperature range of 989-1 367 K, for fuel-air mixtures at equivalence ratios of ϕ = 0.5, 1.0, and 2.0, and nominal pressures of 1 and 4 MPa. Ignition delay times were found to decrease with increasing temperature, equivalence ratio, and pressure, and are well described with correlations involving Arrhenius temperature dependence and power-law dependence on equivalence ratio and pressure. Ignition delay times are compared with model predictions from literature kinetic models, with the models of Zhang et al (Energy & Fuels 2014; 28(11): 7194-7202) and Bennadji et al (International Journal of Chemical Kinetics 2011; 43(4): 204-218.) in good agreement with measured ignition delay times for MP and MA, respectively. Kinetic sensitivity analysis shows that the reactions most important for modeling ignition fall into two categories: initiation reactions (ie, decomposition and H-atom abstraction) and C₀-C₁ chemistry controlling the pool of small radicals. The unsaturated MA was observed to have lower reactivity than MP, due to its greater bond strengths for C─C and C─H bonds, resulting in slower rates for initiation reactions.