A numerical investigation on the effects of gaseous fuel composition in a pilot ignited direct injection natural gas engine

Abstract

Pilot ignited direct injection natural gas engines have the potential to obtain both high efficiency and low emissions, thus, are considered as promising alternations for diesel engines. In order to assess the effects of gaseous fuel composition on this type of engines, a three-dimensional model was constructed based on a new mechanism developed for the high-precision prediction of soot precursors. The numerical results showed that thermal efficiency could be improved by increasing nitrogen proportion at medium and high loads as well as increasing propane proportion at low load. Regarding emissions, it was found that ethane addition will lead to deteriorated NOx and CO emissions at high and medium loads along with increases in soot emissions at all loads. When propane is blended, though notable increased NOx emissions and higher soot emissions could be observed at all loads, improved CO emissions are revealed at high load with small blending ratios and at low load with all blending ratios. In contrast to ethane and propane addition, nitrogen addition is favorable for NOx control at all engine loads and is beneficial for soot control at high and medium loads. CO emissions, however, will suffer from nitrogen addition at high and low loads.