Autoignition of methyl butanoate under engine relevant conditions

This study reports the autoignition delay times of methyl butanoate in argon-air (i.e. Ar/O-2 = 3.76 by mole) mixtures under thermodynamic conditions relevant to compression ignition engines, using a rapid compression machine (RCM). The ignition delay times were obtained for the compressed temperature range of 833-1112 K and compressed pressures corresponding to 15, 30, 45, and 75 bar. In addition, the effect of fuel mole fraction on ignition delay times were experimentally studied by covering equivalence ratios corresponding to 0.25, 0.5, and 1.0 under realistic fuel loadings without additional dilution. For the range of conditions investigated, the ignition delay times exhibit an Arrhenius dependence on temperature and an inverse relationship with the compressed pressure. No evidence of two-stage ignition was observed in the current experiments, nor was a negative temperature coefficient trend seen in the ignition delay times. The experimental results were compared to zero-dimensional simulations taking into account the full compression stroke and the heat loss characteristics of the RCM, using chemical kinetic models reported in the literature. The literature models were found to predict significantly higher reactivity when compared to the current experiments. Chemical kinetic analysis was then conducted to identify the reactions responsible for the mismatch between the experiments and the simulated results. Key reactions that could help obtain a better match between the experimental and simulated results were identified using both brute-force and global sensitivity analyses. In view of the large uncertainties associated with the low-temperature chemistry of methyl butanoate, further studies are needed to update the kinetic parameters of the key reactions in order to improve the model comprehensiveness. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.