Chapter 7 Autoignition in spark-ignition engines

Abstract

Research on autoignition probably has its most important application in understanding knock in spark-ignition engines. This chapter describes how the autoignition chemistry is applied and shows the progress that has been made in understanding and predicting knock in engines. The goal of knock prevention has resulted in a number of chemical models for autoignition, and, whatever their complexity, they provide a means of extrapolating chemical behavior from idealized laboratory to practical engine conditions. Knock arises, first because the autoignition delay-time has elapsed and second because the volumetric heat release rate at a hot spot is sufficient for generating a pressure pulse that compresses the unburned gas and reduces the effective autoignition delay-time. Comprehensive schemes provide the best description; however, simplified schemes are currently the most appropriate for application in engine models. Reduced schemes have not as yet made much impact in autoignition modeling but are expected to do so in the future. Whether, or not, autoignition occurs, depends upon a race between the reactions in the end gas and its consumption by the propagating flame.