NO/NO2 Concentration of direct injection stratified combustion under constant volume condition fuelled by compressed natural gas and gasoline

Abstract The concentrations of NO, NO2 and NOx for direct injection (DI) combustion were analysed on the basis of experimental data by using a rapid compression machine fuelled with compressed natural gas (CNG) and gasoline. The analysis showed that the maximum values of NO and NO2 for stratified combustion would shift to a smaller overall equivalence ratio than that of homogeneous mixture combustion, and this phenomenon was more obvious for gasoline stratified combustion. The NOx concentration drops to a very low level at the stoichiometric equivalence ratio but still remains relatively high at an equivalence ratio of 0.6 in the case of stratified combustion. The ratio of NO2/NOx increased with decreasing equivalence ratio. A high ratio of NO2/NOx was observed in the constant-volume combustion experimental study which differs from that of an engine. This was caused by the long residence time of NO at high temperature after combustion, leading to the conversion of more NO into NO2.