Deflagrative, auto-ignitive, and detonative propagation regimes in engines

Abstract

The paper presents a novel overall quantitative description of the major regimes of engine combustion, covering the influences of both turbulence and auto-ignition parameters on burn rates and flame extinctions. It involves two separate, yet interconnected, correlation diagrams. The first involves the normalized turbulent burning velocity, the Karlovitz stretch factor the strain rate Markstein number, and also includes possible relative auto-ignitive burn rates. The second is a complementary correlating ξ/ɛ diagram, involving the auto-ignitive parameters of ignition delay and excitation times. The ξ parameter is the acoustic speed normalized by the auto-ignition velocity, while ɛ is the acoustic wave residence time in a hot spot, normalized by the excitation, or heat release, time. It also includes an indication of the regime of normal flame propagation. The different auto-ignitive regimes, in which a variety of contrasting fuel/air mixtures might operate, are indicated on the ξ/ɛ diagram, particularly in relation to its peninsula of developing detonation at a hot spot. Operational points, measured on a variety of engines, are also shown on the two diagrams, in terms of the different regimes, including those of mild and “super-knock”, turbulent flame extinctions, and controlled auto-ignition.