Numerical Study on the Combustion and Emission Characteristics of a Partial Premixed Direct Injection Natural Gas-Diesel Engine

This study investigated the impact of injection strategy on combustion and emission characteristics of a partial premixed direct injection natural gas engine, using the Cummins ISX engine as a numerical model. Specifically, the influence of diesel injection timing and pressure on engine performance was analyzed with a fixed natural gas energy substitution ratio. It is found that advancing the diesel injection timing leads to longer the ignition delay time of diesel since temperature is lower than at top dead center. This resulted in a rapid initial heat release, which further increased the in-cylinder temperature at the beginning of combustion and shortened the combustion duration. Moreover, increasing the pilot diesel injection pressure resulted in longer diesel spray penetration and a higher proportion of natural gas consumption at the beginning of combustion, eventually leading to a faster in-cylinder temperature rise. The findings highlight that optimizing the combustion phasing and combustion temperature by adjusting the diesel injection parameters to avoid too high combustion temperature and negative work at compression end, which can effectively reduce nitrogen oxides emissions while maintaining high indicated mean effective pressure.