In-Situ Fuel Concentration Measurement Near Spark Plug by 3.392 μm Infrared Absorption Method-Application to a Port Injected Lean-Burn Engine

In this study, a spark plug sensor for in-situ fuel concentration measurement was applied to a port injected lean-burn engine. Laser infrared absorption method was employed and a 3.392 μm He-Ne laser that coincides with the absorption line of hydrocarbons was used as a light source. In this engine, the secondary valve lift height of intake system was controlled to obtain appropriate swirl and tumble flow in order to achieve lean-burn with the characteristics of intake flow. For such in-cylinder stratified mixture distribution, the fuel concentration near the spark plug is very important factor that affects the combustion characteristics. Therefore, the mixture formation process near the spark plug was investigated with changing fuel injection timing. Under the intake stroke, the timing that fuel passed through near the spark plug depended largely on the fuel injection timing. Under the compression stroke, mixture formation process near the spark plug indicated different characteristics with injection timings. As the injection timing was retarded, rich mixture remained near the top of the combustion chamber. Furthermore, the relation between the fuel concentration near the spark plug and the combustion characteristics was discussed. The initial combustion became faster and the coefficient of variation in IMEP became lower as the rich mixture existed near the spark plug.