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 ( P max ) and emissions of HC, CO, NO x , and smoke were analyzed. The results indicate that P max 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 P max increase. Moreover, HC and CO increase as the substitution rate of natural gas increases, whereas NO x and smoke emissions exhibit a trade-off trend.