A study of mixture formation processes in direct injection stratified charge gasoline engines by quantitative laser-induced fluorescence imaging and the infrared absorption method

Abstract

Mixture formation processes were investigated of three types of direct injection stratified charge gasoline engine based on wall-guided, air-guided, and spray-guided concepts. Temporal and spatial variations of fuel concentration in the combustion chamber were measured by laser diagnostics such as quantitative laser-induced fluorescence (LIF) imaging and infrared absorption methods on a single-cylinder optical engine. It was found from the experiments that the direct injection gasoline engines based on both the wall-guided and air-guided concepts have long time intervals between the end of injection timing and ignition timing, and this demands early injection and ignition timings in the compression stroke, resulting in lower thermal efficiencies than those of the spray-guided concept. As for the spray-guided concept, fuel is ignited immediately after the end of injection, which enables near TDC (top dead centre) combustion, allowing lower fuel consumption than the other two. However, the condition for stable ignition and combustion achieved with the spray-guided concept is very narrow in terms of injection and ignition timings, so it is essential to widen the condition in order to make the concept a reality.