Experimental study on the effects of simulated EGR on ammonia-diesel dual-fuel combustion in a constant volume chamber

Abstract

This study investigates the effects of exhaust gas recirculation (EGR) on ammonia-diesel dual-fuel combustion through optical experiments in a constant volume chamber, varying ambient temperatures (700 K–800 K) and oxygen concentrations (11%–21 %). The results reveal that the combustion process can be divided into three stages based on flame characteristics: diesel premixed combustion, diesel diffusion combustion, and ammonia premixed combustion. As the ambient temperature and oxygen concentration decrease, the luminescence region of the NH₂ group narrows, and its luminescence intensity diminishes, indicating lower NO emissions. Compared to the decrease in oxygen concentration from 16 % to 11 %, the reduction from 21 % to 16 % has a less pronounced impact on ammonia-diesel combustion performance. The peak heat release rate (HRR) shows a non-monotonic trend, initially increasing and then decreasing as the temperature drops. Ammonia-diesel combustion deteriorates at extremely low ambient temperatures and oxygen concentrations, exhibiting a double-peak HRR. These findings suggest that mild EGR can be applied to real ammonia-diesel engines to effectively reduce NO emissions, although it may slightly compromise combustion performance.