On the Simulation of Rapid Compression Machine Autoignition Experiments

Abstract

Rapid compression machines are often used to measure the ignition delay time (IDT) of fuel-oxidizer mixtures at relatively low temperatures. To evaluate the performance of a chemical kinetic mechanism in predicting the IDT, the analysis traditionally begins by calculating the volume after the compression stage, assuming a 0-dimensional configuration based on the so-called adiabatic-core hypothesis. According to this theory, there exists an isentropically compressed core region in the gas mixture derived from the measured pressure trace in an inert mixture whose composition remains constant after the compression stage and it is unaffected by heat losses. This approach, neglects the effect of heat release on the specific volume during the first stages of ignition and may differ from that of the inert mixture as result of heat release in the adiabatic core due to chemical reactions. This approach typically predicts IDTs that are shorter than the experimental measurements. In this work, we propose an alternative method for analysis using the experimental nonreactive pressure trace, \({{p}_{{{\text{in}}}}}(t)\). This approach disregards the effect of heat release on pressure during the initial stages of ignition, which increases the specific volume and results in a slight overprediction of ignition delay times. By combining both approaches, we establish upper and lower boundaries for IDTs, providing a framework that facilitates the optimization of chemical mechanisms.