Autoignition of methyl palmitate in low to intermediate temperature: Experiments in rapid compression machine and kinetic modeling

Autoignition characteristics of methyl palmitate (C17H34O2), a waxy solid at room temperature, were in-vestigated in a newly developed heated rapid compression machine. Ignition delay times (IDT) of methyl palmitate were firstly measured at the low-to-intermediate temperatures of 780-980 K and equivalence ratios of 0.3-1.0 under three pressures of 10, 15, and 20 bar. A negative effect of the increase in com-pressed pressure, equivalence ratio, and oxygen mole fraction on IDTs at different compressed tempera-tures was qualitatively and quantitatively revealed. Besides, the dependence of IDTs on compressed pres-sure and equivalence ratio decreases with increasing temperature. A recently optimized mechanism was used to predict the experimental results. The simulations show an obvious negative temperature coeffi-cient (NTC) behavior at the compressed temperatures of 780-830 K which was not observed in the ex-periment. Meanwhile, the mechanism pronouncedly underestimated the reactivity of methyl palmitate at higher temperatures in this study. Sensitivity analyses at different temperatures and pressures for equiva-lence ratios of 0.5 were conducted to determine the crucial reactions that caused the difference between the simulation and experiments. On this basis, further optimization was carried out and the simulation results of the latest mechanism show a good agreement with the experimental data. It is verified against shock tube experimental data that the optimization adjustment in this paper has a small positive impact on the prediction ability of the originally documented mechanism under temperatures above 10 0 0 K. In the end, validation for the optimized mechanism against experimental data in a jet-stirred reactor (JSR) was performed. Overall, the experimental results fill in gaps in IDT data on methyl palmitate at low-to -intermediate temperatures and provide a reference IDT database for the development and validation of methyl palmitate mechanisms.(c) 2023 The Combustion Institute. Published by Elsevier Inc. All rights reserved.