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The combustion and exhaust emissions characteristics of a supercharged dual-fuel natural gas engine with a single cylinder were analyzed. We focused on EGR (Exhaust Gas Recirculation) to achieve higher thermal efficiency and lower exhaust emissions. The combustion of diesel fuel (gas oil) as ignition sources was visualized using a high-speed video camera from the bottom of a quartz piston. The luminous intensity and flame decreased as the EGR rate increased. Furthermore, the ignition delay became longer due to the EGR. Characteristics of the combustion and exhaust emissions were investigated with changing EGR rates under supercharged conditions. The indicated mean effective pressure and thermal efficiency decreased with increasing EGR rate. In addition, NOx emissions decreased due to the EGR. In this study two-stage combustion was observed.

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.

Effects of injection parameters on combustion and emission characteristics of diesel PCCI engine operating on optical and test engine was investigated. PCCI combustion was achieved through slightly narrow included angle injector, low compression ratio coupled with exhaust gas recirculation. Analysis based on diesel spray evolution, combustion process visualization and analysis was carried out. Spray penetration was evaluated and related to the exhaust emissions. Advancing the injection timing and EGR extended the ignition delay, decreased NOx emissions and increased HC, smoke and CO emissions. Higher injection pressure led to low emissions of NOx, smoke, HC and comparable CO. Optimum spray targeting position for minimum emission was identified. Impingement on the piston surface led to deterioration of emissions and increased fuel consumption while spray targeting the upper edge of Derby hat wall showed improvement in emission and engine performance.