Effect of intake composition on combustion and emission characteristics of DI diesel engine at high intake pressure

摘要

The effect of various intake compositions and intake pressure on combustion and emission characteristics has been investigated in a single-cylinder direct-injection diesel engine. The variation of intake composition is simulated using argon, nitrogen and carbon dioxide as intake air diluents, and a screw compressor is used to boost intake pressure up to 200 KPa. All diluents are found to be effective in reducing NO_x emissions when intake pressure is changed from 110 KPa to 200 KPa. Smoke emissions are drastically increased by the addition of argon, moderately increased by the addition of nitrogen. However, the addition of carbon dioxide substantially reduces smoke emissions and NO_x emissions simultaneously. At lower intake pressure, the effects of diluting intake air with argon, nitrogen and carbon dioxide on ignition delay are proportional to their specific heats respectively, whereas the addition of argon has almost no effect on ignition delay when intake pressure is higher than 150 KPa. Further analysis reveals that the oxygen concentration of intake charge plays the most important role in reducing NO_x emissions, and the increased premixed combustion due to longer ignition delay is the main reason of reduction in smoke emissions.