Experimental data obtained in this study (Part II) complement the speciation data presented in Part I, but also offer a basis for extensive facility cross-comparisons for both experimental ignition delay time (IDT) and laminar flame speed (LFS) observables.To improve understanding of the ignition characteristics of propene, a series IDT experiments were performed in six different shock tubes and two rapid compression machines (RCMs) under conditions not previously studied. This study is the first of its kind to directly compare ignition in several different shock tubes over a wide range of conditions. For common nominal reaction conditions among these facilities, cross-comparison of shock tube IDTs suggests 20-30% reproducibility (2σ) for the IDT observable. The combination of shock tube and RCM data greatly expands the data available for validation of propene oxidation models to higher pressures (2-40 atm) and lower temperatures (750-1750 K).Propene flames were studied at pressures from 1-20 atm and unburned gas temperatures of 295-398 K for a range of equivalence ratios and dilutions in different facilities. The present propene-air LFS results at 1 atm were also compared to LFS measurements from the literature. With respect to initial reaction conditions, the present experimental LFS cross-comparison is not as comprehensive as the IDT comparison; however, it still suggests reproducibility limits for the LFS observable. For the LFS results, there was agreement between certain data sets and for certain equivalence ratios (mostly in the lean region), but the remaining discrepancies highlight the need to reduce uncertainties in laminar flame speed experiments amongst different groups and different methods. Moreover, this is the first study to investigate the burning rate characteristics of propene at elevated pressures (> 5 atm).IDT and LFS measurements are compared to predictions of the chemical kinetic mechanism presented in Part I and good agreement is observed.

Autoignition experiments for n-butanol have been performed using a heated rapid compression machine at compressed pressures of 15 and 30 bar, in the compressed temperature range of 675-925 K, and for equivalence ratios of 0.5, 1.0, and 2.0. Over the conditions studied, the ignition delay decreases monotonically as temperature increases, and the autoignition response exhibits single-stage characteristics. A non-linear fit to the experimental data is performed and the reactivity, in terms of the inverse of ignition delay, shows nearly second order dependence on the initial oxygen mole fraction and slightly greater than first order dependence on initial fuel mole fraction and compressed pressure. Experimentally measured ignition delays are also compared to simulations using several reaction mechanisms available in the literature. Agreement between simulated and experimental ignition delay is found to be unsatisfactory. Sensitivity analysis is performed on one recent mechanism and indicates that uncertainties in the rate coefficients of parent fuel decomposition reactions play a major role in causing the poor agreement. Path analysis of the fuel decomposition reactions supports this conclusion and also highlights the particular importance of certain pathways. Further experimental investigations of the fuel decomposition, including speciation measurements, are required.

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Autoignition experiments of stoichiometric mixtures of s-, t-, and i-butanol in air have been performed using a heated rapid compression machine (RCM). At compressed pressures of 15 and 30 bar and for compressed temperatures in the range of 715−910 K, no evidence of a negative temperature coefficient region in terms of ignition delay response is found. The present experimental results are also compared with previously reported RCM data of n-butanol in air. The order of reactivity of the butanols is n-butanol>s-butanol≈i-butanol>t-butanol at the lower pressure, but changes to n-butanol>t-butanol>s-butanol>i-butanol at higher pressure. In addition, t-butanol shows pre-ignition heat release behavior, which is especially evident at higher pressures.To help identify the controlling chemistry leading to this pre-ignition heat release, offstoichiometric experiments are further performed at 30 bar compressed pressure, for t-butanol at = 0.5 and = 2.0 in air. For these experiments, higher fuel loading (i.e. = 2.0) causes greater pre-ignition heat release (as indicated by greater pressure rise) than the stoichiometric or = 0.5 cases. Comparison of the experimental ignition delays with the simulated results using two literature kinetic mechanisms shows generally good agreement, and one mechanism is further used to explore and compare the fuel decomposition pathways of the butanol isomers. Using this mechanism, the importance of peroxy chemistry in the autoignition of the butanol isomers is highlighted and discussed.

The autoignition delays of mixtures of methyl-cyclohexane (MCH), oxygen, nitrogen, and argon have been studied in a heated rapid compression machine under the conditions = 50 bar, = 690 − 910K. Three different mixture compositions were studied, with equivalence ratios ranging from = 0.5 − 1.5. The trends of the ignition delay measured at 50 bar were similar to the trends measured in earlier experiments at = 15.1 and 25.5 bar. The experimentally measured ignition delays were compared to a newly updated chemical kinetic model for the combustion of MCH. The model has been updated to include newly calculated reaction rates for much of the low-temperature chemistry. The agreement between the experiments and the model was substantially improved compared to a previous version of the model. Nevertheless, despite the encouraging improvements, work continues on further advances, e.g. in improving predictions of the first stage ignition delays.

In this work, a binary fuel model for dimethyl ether (DME) and propane is developed, with a focus on engine-relevant conditions (10-50 atm and 550-2000 K). New rapid compression machine (RCM) data are obtained for the purpose of further validating the binary fuel model, identifying reactions important to low temperature propane and DME oxidation, and understanding the ignition-promoting effect of DME on propane. It is found that the simulated RCM data for DME/propane mixtures is very sensitive to the rates of C3H8 + OH, which acts as a radical sink relative to DME oxidation, especially at high relative DME concentrations. New rate evaluations are conducted for the reactions of C3H8 + OH = products as well as the self-reaction of methoxymethyl peroxy (in competition with RO2 = QOOH isomerization) of 2CH3OCH2O2 = products. Accurate phenomenological rate constants, (,), are computed by RRKM/ME methods (with energies obtained at the CCSD(T)-F12a/cc-pVTZ-F12 level of theory) for several radical intermediates relevant to DME. The model developed in this work (120 species and 700 reactions) performs well against the experimental targets tested here and is suitable for use over wide range of conditions. In addition, the reaction mechanism generator software, RMG, is used to explore cross-reactions between propane and DME radical intermediates. These cross-reactions did not have a significant effect on simulations of the conditions modeled in this work, suggesting that kinetic models for high-and low-reactivity binary fuel mixtures may be assembled from addition of their corresponding submodels and a small molecule foundation model.

Isopentanol is one of a range of next-generation biofuels that can be produced by advanced biochemical production routes (i.e., genetically engineered metabolic pathways). Isopentanol is a C5 branched alcohol and is also called 3-methyl-1-butanol. In comparison with the most frequently studied ethanol, the molecular structure of isopentanol has a longer carbon chain and includes a methyl branch. The volumetric energy density of isopentanol is over 30% higher than ethanol. Therefore, isopentanol has the capability to be a better alternative than ethanol to gasoline. In this study, a detailed chemical kinetic model for isopentanol has been developed focusing on autoignition characteristics over a wide range of temperatures. The isopentanol model developed in this study includes high- and low-temperature chemistry. In the isopentanol model, high-temperature chemistry is based on a reaction model for butanol isomers whose reaction paths are quite similar to isopentanol. The low-temperature chemistry is based on a reaction model for isooctane which is a branched molecular structure similar to isopentanol. The model includes a new reaction mechanism for a concerted HO2 elimination, a process recently examined by da Silva et al. for ethanol (J. Phys. Chem. A 2009, 113, 8923). In addition, important reaction mechanisms relevant to low-temperature chemistry were considered in this model. The authors conducted experiments with a shock-tube and a rapid compression machine to evaluate and improve accuracies of this model. The experiments were carried out over a wide range of temperatures, pressures, and equivalence ratios (652–1457 K, 0.7–2.3 MPa, and 0.5–2.0, respectively). Excellent agreement between model calculations and experimental data was achieved under most conditions. Therefore, it is believed that the isopentanol model developed in this study is useful for prediction and analysis of combustion performance involving autoignition processes such as a homogeneous charge compression ignition.

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