Analysis of the temporal flame kernel development in an optically accessible IC engine using high-speed OH-PLIF

The investigation of the combustion process of a direct injection spark-ignition internal combustion (IC) engine is crucial in modern engine development. The present study is aimed at inspecting the temporal development of the spark induced flame kernel within single combustion cycles using high-speed planar laser-induced fluorescence (PLIF). The analysis is based upon the excitation of OH radicals, which are an indicator of the transient flame front. To achieve an adequate temporal resolution of the early combustion phase, the image sampling rate was set to 6 kHz, recording one image per crank-angle (CA) degree at 1000 rpm. A further feature of the technique is a large field of view spanning ∼54×53 mm. The performance of the transient combustion process is characterized by temporally tracking subsequential engine cycles individually. Flame front dynamics with different dilution levels of the intake air, simulating exhaust gas recirculation (EGR) are investigated. Resolving flame front dynamics especially with varying EGR is an important step towards an improved understanding of cyclic variations and pollutant formation.