G0710106 Analysis of compression ignition from explosion limit

Abstract

Homogeneous charge compression ignition HCCI engine, are possible to increase the thermal efficiency with minimum emissions of NOx and PM. However, the problem, of difficult in ignition timing control and, the narrow operating range are yet to be resolved. Intake pressure boosting has been performed to raise the high load limit of HCCI, and it was found that the boosting has an effect to increase ignition stability. In this study, explosion limit in the temperature-pressure diagram is investigated, since the limit curve reflects the ignition reaction mechanism of fuels changing with pressure range. Ignition of n-heptane, iso-octane, and toluene were simulated by using a detailed chemical reaction kinetics model, and explosion limit curves of each fuel were created. A measure of ignition instability is proposed in this study. It is defined as a shift of ignition delay time divided by a shift of initial temperature when the temperature and pressure are shifted according to an adiabatic line. It was found that this instability index is reduced in the region of low-temperature heat release for n-heptane and iso-octane, whereas toluene showed constant instability index throughout the pressure range investigated.