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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.

A dual fuel engine fueled with methane from an inlet port and ignited with diesel fuel was prepared. This study focuses on the effects of early injection and exhaust gas recirculation (EGR) on the characteristics of combustion and exhaust emissions. The injection timing was changed between TDC and 50 degrees before the TDC. In the early injection timing, smoke was never seen and hydrocarbons were smaller compared with those at the normal injection timing. However, the combustion becomes too early to obtain an appropriate torque when the equivalence ratio increases. Then, moderate EGR was very effective to force the combustion to retard with lower NOx, higher thermal efficiency and almost the same hydrocarbons and carbon monoxide. The engine operated even under the condition of stoichiometric mixture.