Effects of the substitution rate of natural gas on the combustion and emission characteristics in a dual-fuel engine under full load

Abstract

Diesel-piloted natural gas has been considered one of the most promising methods of using natural gas in a compression–ignition engine with few modifications, as this approach benefits from a high thermal efficiency resulting from a high compression ratio. This study experimentally investigated the impact of the natural gas substitution rate on the characteristics of combustion and emissions. Tests were performed under full-load operating conditions at a fixed speed of 1200 r/min with optimized injection timing, and the substitution rate of natural gas was varied with the fixed total fuel energy for different analyses. The in-cylinder pressure, pressure rise rate, heat release rate, cyclic variation of the maximum cylinder pressure (Pmax) and emissions of HC, CO, NOx, and smoke were analyzed. The results indicate that Pmax and the maximum pressure rise rate initially increase and then decrease as the substitution rate of natural gas increases, whereas the heat release rate and standard deviation of Pmax increase. Moreover, HC and CO increase as the substitution rate of natural gas increases, whereas NOx and smoke emissions exhibit a trade-off trend.