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

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.