Two Types of Autoignition and Their Engine Applications

The generally accepted explanation of autoignition in engines is that the reactivity is driven by temperature, where autoignition occurs after the mixture has reached some critical temperature (approx. 1000 K) by a combination of self-heating due to preignition reactions and compression heating due to piston motion and flame propagation. During the course of our investigations into autoignition processes and homogeneous charge compression ignition we have observed some ignitions that begin at much lower temperature (< 550 K). In this paper we describe these observations, our attempts to investigate their origins, and an alternative explanation that proposes that traditional models may be missing the chemistry that explains this behavior. Finally, applications of lower temperature chemical reactions are discussed.