Numerical study on influences of intake temperature and swirl ratio on in-cylinder combustion and pollutant formation characteristics of ammonia/diesel dual-fuel engine

In order to improve the combustion efficiency of ammonia fuel, and enhance the operational stability and emission level for ammonia engines, this study constructs an in-cylinder combustion numerical model of ammonia/diesel dual-fuel engine based on CONVERGE software, and investigates the effects of initial intake temperature and swirl intensity on in-cylinder combustion and pollutant formation characteristics of ammonia/diesel dual-fuel engine. The results show that increasing the intake temperature can improve the in-cylinder thermal atmosphere, advance the dual-fuel combustion reaction process, and increase the peak in-cylinder combustion pressure and temperature. The peak in-cylinder pressure increases from 6.05 to 6.44 MPa when the intake temperature is increased from 303 to 343 K. This is effective in improving the emissions of incomplete combustion for the ammonia/diesel dual-fuel engine. The in-cylinder unburned NH₃, CO and HC emissions are reduced by 20.2 %, 77.1 % and 88.21 %, respectively. Increasing the swirl ratio enhances the in-cylinder gas disturbance, reduces the amount of fuel attached to the wall, and improves the quality of in-cylinder fuel-gas mixture. It also accelerates the process of combustible mixture formation, advances the starting point of ammonia fuel consumption, and accelerates the initial reaction rate. When the swirl ratio is increased from 0.5 to 3.0, the in-cylinder unburned NH₃ emission is reduced by 14.85 %. Reasonable adjustment of intake temperature and swirl ratio helps to improve the distribution of direct injection fuel particles inside the cylinder, thereby optimizing the dual-fuel combustion process and enhancing engine performance.