Optical characterization of combustion processes in a DISI engine equipped with plasma-assisted ignition system

Currently, direct injection (DI) for gasoline engines is a primary trend for improving efficiency allowing reduced fuel consumption and the possibility to 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, as 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 spark ignition (SI) engine equipped with the cylinder head and injection system of a commercial gasoline turbocharged engine. The effects of spark plug geometry and different plasma configurations were investigated. UV-visible digital imaging was applied; the optical data were correlated to in-cylinder pressure traces and exhaust emission measurements.