Fundamental Analysis of Combustion Initiation Characteristics of Low Temperature Plasma Ignition for Internal Combustion Gasoline Engine

In recent years, the study of volumetric ignition using high-speed (nanosecond) pulsed low temperature plasma for gasoline engines was reported by authors [ 1 ]. However, the fundamental analysis of ignition characteristics of the low temperature plasma ignition and the analysis of combustion initiation mechanism of the low temperature plasma ignition was not enough in the previous paper. In this study, a low temperature plasma igniter of a barrier discharge (silent discharge) model was developed for trial purpose. A fundamental analysis of ignition characteristics was carried out when the low temperature plasma ignition was applied as the ignition system for gasoline engine using single-cylinder. The difference between the ignition characteristics of the low temperature plasma and the thermal plasma of a conventional spark plug was investigated by comparing a combustion characteristic of both in various driving conditions. And the mechanism of combustion initiation of the low temperature plasma ignition was analyzed by the chemical kinetic simulation. The result of engine test shows that the ignition performance of low temperature plasma received higher influence of the gas density of the discharge phase than the conventional spark ignition. In the area where the gas density of the discharge phase was relatively high, the ignition delay time of the low temperature plasma ignition was shortened than that of the spark ignition. On the other hand, in the low gas density condition, where relative density of the discharge phase was 2.5 or less, the ignition delay time of the low temperature plasma ignition was increased rapidly with respect to decrease in the gas density. From the results of the ignition characteristic experiment and the chemical kinetic simulation, the hypothesis that the mechanism of combustion initiation characteristics of low temperature plasma ignition was associated with localized autoignition triggered by highly reactive radicals represented by O atoms produced from the discharge phase was derived and strongly suggested.