Evaluating the potential of mixture formation methods to achieve efficient combustion and near-zero emissions on a hydrogen direct injection engine

Hydrogen energy in transport, particularly in the automotive internal combustion engine sector, is relevant for promoting carbon neutrality and cleaner production. In this study, effect of five mixture formation methods including Homogeneous charge, In -cylinder mildly stratified charge, In -cylinder severely stratified charge, Sparkplug mildly stratified charge, and Spark-plug severely stratified charge were studied on efficiency combustion, emissions, and energy distribution. The results show that equivalent combustion obtained the maximum hydrogen consumption and nitrogen oxide emissions exceeded 2900 ppm for all mixture formation methods. For light and medium lean burn conditions (lambda = 1.6, 2.2, 2.7), Spark-plug severely stratified charge and In -cylinder severely stratified charge methods balanced combustion stability and thermal efficiency, but also maintained nitrogen oxide emissions to at least over 100 ppm. While at ultra-lean burn conditions (lambda = 3.2 and 3.6), all methods limited nitrogen oxide emissions to less than 10 ppm. In addition, at lambda = 3.62, Spark-plug mildly stratified charge method significantly reduced the coefficient of variation on Pmax by about 7 %. Compared to the In -cylinder severely stratified charge method with lambda = 1, Spark-plug mildly stratified charge method with lambda = 3.62 reduced hydrogen consumption by 75.8 g/(kW x h). The energy distribution proved that this reduction was attributed to the reduction of heat loss power from lean burn and a further limitation of exhaust power from Spark-plug mildly stratified charge method, which was considered to be the most promising method to achieve clean, efficient and stable combustion.