Numerical Study on the Combustion And Emission Characteristics of a Direct Injection Natural Gas Engine Ignited by Diesel/N-Butanol Blends

Adjusting the composition of pilot fuel has been regarded as an effective method for the improvement the performance and emissions of pilot ignited direct injection natural gas engines. In this paper, the effects of employing diesel/n-butanol blends as the pilot fuel in a direct injection natural gas engine were assessed by numerical simulations. The simulation results indicated that adding n-butanol into the pilot fuel will result in notable extensions in ignition delay and obvious reductions in combustion duration at low and medium engine loads; at high engine loads, the effects of n-butanol blending on combustion parameters are relatively small due to the higher temperature during the pilot ignition period. In terms of engine performance, adding n-butanol into the pilot fuel is beneficial for the improvement thermal efficiency at low and medium engine loads, whereas slightly lower thermal efficiency would be induced by n-butanol addition at high engine load. With regard to emissions, considerable reduced CO and soot emissions could be achieved by adjusting n-butanol blending ratio at all engine loads; at low and high engine loads, blending n-butanol into the pilot fuel is favorable for the control of NOx emissions while at medium engine load, n-butanol blending will inevitably result in increases in NOx emissions.