Experimental study on the effect of aftertreatment system on the energy flow pattern and emission reduction of a natural gas engine under world harmonized transient cycle

To explore the effect of aftertreatment system (AS) on the energy flow pattern and emission reduction under transient conditions, the energy flow and emissions characteristics of a CNG engine with and without AS are experimentally investigated under world harmonized transient cycle. By comparing and analyzing the energy flow and emissions in both cases, the impact pattern of AS is revealed. Besides, the relationship between the emissions histories and engine behavior is explored thoroughly. The results show that the AS leads to higher coolant loss and lower other energy losses, but overall the thermal efficiency with AS is slightly improved. When considering the emissions, the engine load almost dominates the emissions. The conversion efficiency of CO, NOx and HC with AS is 95%, 93% and 88% respectively. The emissions are reduced significantly and can meet the China 6th stage national emission regulation. However, it is found that the AS sometimes has a negative impact on the CO emissions and HC emissions reduction and these phenomena are analyzed. Therefore, the energy flow analysis from the perspective of engine integrated with AS can clearly elucidate the aftertreatment behavior, which provides insight/direction to improve engine performance.