Influence of fuel injection timing on combustion and emission in direct injection natural gas engine

Investigation of fuel injection timing on combustion and emission of direct injection natural gas engine is carried out using a rapid compression machine. The results show that early injection (injection timing at 60 ms) brings to slow initial heat release rate and rapid late heat release process. Late injection (injection timing at 75 ms) give rapid initial heat release rate and slow late release rate. The heat release process lasts the shortest duration when the end of fuel injection is set at 80 ms (the same timing of ignition). The shortest combustion duration occurs in the case of injection end at 80 ms. Early injection has long flame developing period whereas late injection has long late burning period. Early injection produces relative low CO while late injection produces relative high CO when equivalence ratio is larger than 0.8. NO_x reaches its peak value in the range of equivalence ratio between 0.6 and 0.8 regardless of fuel injection timings. Late injection gives relatively low NO_x emission. Combustion efficiency maintains high value in the range of equivalence ratio from 0.5 to 0.8, combustion efficiency decreases for both φ>0.5 and φ>0.8.