Self-ignition ahead of the flame front in piston spark-ignition engines

The hypothesis that engine knock is a result of competition of two types of chemical reaction - frontal and volumetric - is put forward. A mathematical model for mixture self-ignition ahead of the flame front in an internal-combustion spark-ignition engine is constructed. The operation process was culculated numerically with variation of the ignition angle, the degree of compression, and the rotation frequency of the crankshaft. A critical condition for the occurrence of engine knock is obtained by approximate analytical solution of the problem. Comparison of theoretical results for ten engine parameters and operation, with experimental data of different authors confirms the validity of the proposed hypothesis an the occurrence of engine knock.