Numerical study on the combustion and emission characteristics of a direct injection natural gas engine ignited by diesel/n-butanol blends

Abstract

Adjusting the composition of pilot fuel has been regarded as an effective method for the improvement of 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 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. In terms of engine performance, thermal efficiency could be improved by up to 2.3% and 6.5% by adding n-butanol into the pilot fuel at low and medium engine loads, whereas lower than 2% reduction in thermal efficiency would be induced by n-butanol addition at high engine load. With regard to emissions, more than 30% reductions in CO and soot emissions could be achieved by adjusting n-butanol blending ratio at low and medium 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 could result in up to 34.7% increases in NOx emissions.