Measurement and modeling of heat transfer characteristics in a rapid compression machine

摘要

The study of autoignition characteristics of fuel-oxidizer mixtures in rapid compression machines (RCMs) requires accurate characterization of the core gas region, where most of the reaction occurs. In most RCMs the core temperature is not uniform, being disturbed by the roll-up of the thermal boundary layer. The present device was designed to avoid that effect by incorporating a crevice on the piston heat that can contain the thermal boundary layer and create well defined core conditions. In order to verify these assumptions, a heat transfer model has been developed that maintains simplicity while including the effects of heat transfer and piston crevice volume. This modal can be easily incorporated into chemical kinetic simulations to include the effect of heat transfer on the core temperatures in the study of autoignition. Comparison of model predictions and measurements of the pressure history in a rapid compression machine are presented. Results show that the simple heat transfer model is able to reproduce the measured pressure profiles prior to autoignition over a wide range of conditions for the specially designed piston, and that heat losses in the normal piston are larger than the stationary gas conduction model indicates.