Development of High-Accuracy End-Gas Autoignition Prediction Model

– The Nature of Autoignition Prediction Using Livengood-Wu Integral –

Abstract

Simple but high-accuracy knocking prediction modeling is required to develop and validate innovative combustion control technologies for gasoline engines to achieve higher thermal efficiencies. The Livengood-Wu integral has been widely applied as the simplest and most practical model to predict knocking. But, the scientific nature of this empirical model has been unknown. What is X of the Livengood-Wu integral? In the present study, in-cylinder autoignition prediction using the Livengood-Wu integral was investigated using ignition delay times for a premium gasoline surrogate fuel, computed using a detailed reaction mechanism developed by Miyoshi and Sakai. When autoignition occurs at TDC, ignition delay times near TDC are about 10 times as long as time per crank angle degree every engine speed. Therefore, if only the reciprocal of the ignition delay time is integrated over 10 crank angles near TDC, the integrated value can reach 1 for no scientific reason. Apart from this fact, it was concluded that the true X of the Livengood-Wu integral is the ratio of an integration step out of ignition delay time. Assumed that the profiles of heat release rate along the time normalized by ignition delay times are similar, when the integrated value reaches 1, the parts of a profile of heat release rate can be integrated to be the complete profile. According to this finding, for high-accuracy autoignition prediction using the Livengood-Wu integral, it is significant to express the temperature-, pressure-, and equivalence ratio-dependence of ignition delay time as accurately as possible, and predict the profile of heat release rate.