Experimental investigation of combustion processes in an optical DISI engine equipped with plasma-assisted ignition system

Currently, direct injection for gasoline engines is a primary trend for improving the efficiency allowing to reduce fuel consumption and meet stringent emission standards. A large temporal and spatial variation of mixture composition near the spark location during low speed and high load operation are driving the demands for significantly improved ignition systems. Recently, plasma-assisted ignition systems received increasing interest, they are used for combustion initiation and control and show the potential for flame stabilization. The aim of this paper is to improve the understanding of the processes related to the use of a plasma-assisted ignition system and its influence on combustion development.
Experiments were performed in an optical SI engine equipped with the cylinder head and injection system of a commercial SI turbocharged engine. The effect of the spark plug geometry and of the plasma configurations were investigated. UV-visible digital imaging was applied. The optical data were correlated to in-cylinder pressure-based data and exhaust emission measurements.
Significantly higher stability, quantified through the coefficients of variation of IMEP and of flame radius, was obtained using the alternative ignition system. An improvement in engine performance and pollutant emissions was achieved.