Study on the Effect of Ammonia Energy Ratio and Injection Timing on Combustion and Emission of Ammonia/Diesel Dual Fuel Engines

Ammonia is an attractive hydrogen carrier and zero-carbon fuel for decarbonization goals. To address the challenges posed by ammonia's low flame velocity and elevated ignition temperature, a dual-fuel approach combining port-injected ammonia with directly injected diesel has proven effective in enhancing combustion performance. This study focuses on optimizing the thermal efficiency and minimizing emissions in ammonia-diesel direct injection (ADDF) engines by examining the influence of ammonia energy ratio (AER) and fuel injection timing on combustion dynamics and emission patterns. Results reveal that the indicated thermal efficiency peaks at 45.06% when AER approaches 20%, with efficiency declining at both lower and higher ratios. The incomplete combustion of ammonia becomes more pronounced at elevated AER levels, reaching 11.06% unburned ammonia at 40% AER, primarily due to ammonia's sluggish combustion rate and its inhibitory effect on dehydrogenation reactions. Regarding nitrogen oxides, nitric oxide (NO) emissions demonstrate a decreasing trend with higher AER values, attributed to the reduction of NO to molecular nitrogen under specific combustion conditions. The greenhouse gas emissions, predominantly comprising carbon dioxide and nitrous oxide, show an upward trend with increasing AER, as nitrous oxide (N₂O) formation is favored in low-temperature ammonia combustion zones. The presence of a well-mixed diesel-air charge during the ignition delay period promotes more complete combustion, thereby reducing residual ammonia emissions. Through meticulous optimization of injection parameters and combustion control strategies, the research achieved a 1.32% enhancement in thermal efficiency, attaining 45.35% at 40% AER, coupled with a significant 29.14% reduction in greenhouse gas emissions.