Experiments and Modeling of the Autoignition of Methylcyclohexane at High Pressure

TL;DR

This study provides new experimental ignition delay data for methylcyclohexane at high pressure and updates a chemical kinetic model to better predict ignition behavior, highlighting the importance of low-temperature chemistry.

Contribution

The paper presents new experimental data and an improved chemical kinetic model for methylcyclohexane autoignition at high pressure, enhancing prediction accuracy over previous models.

Findings

Ignition delay decreases with higher oxygen concentration.

Updated model aligns well with experimental data.

Low-temperature pathways are critical for accurate ignition prediction.

Abstract

New experimental data are collected for methyl-cyclohexane (MCH) autoignition in a heated rapid compression machine (RCM). Three mixtures of MCH/O2/N2/Ar at equivalence ratios of $\phi$=0.5, 1.0, and 1.5 are studied and the ignition delays are measured at compressed pressure of 50 bar and for compressed temperatures in the range of 690-900 K. By keeping the fuel mole fraction in the mixture constant, the order of reactivity, in terms of inverse ignition delay, is measured to be $\phi$=0.5 > $\phi$=1.0 > $\phi$=1.5, demonstrating the dependence of the ignition delay on oxygen concentration. In addition, an existing model for the combustion of MCH is updated with new reaction rates and pathways, including substantial updates to the low-temperature chemistry. The new model shows good agreement with the overall ignition delays measured in this study, as well as the ignition delays measured previously in the literature using RCMs and shock tubes. This model therefore represents a strong improvement compared to the previous version, which uniformly over-predicted the ignition delays. Chemical kinetic analyses of the updated mechanism are also conducted to help understand the fuel decomposition pathways and the reactions controlling the ignition. Combined, these results and analyses suggest that further investigation of several of the low-temperature fuel decomposition pathways is required.