Parametric analysis and optimization of the combustion process and pollutant performance for ammonia-diesel dual-fuel engines

As a low-cost, carbon-free, and widely available hydrogen carrier fuel, ammonia has now regained peoples’ attention in the future development of the carbon-neutral engine. To evaluate the feasibility of ammonia as a carbon-reducing fuel for a high-power diesel engine, a computational fluid dynamics simulation model of a Caterpillar 3401 diesel engine has been established and validated. Initially, an analysis was conducted to examine the effects of different ammonia energy fractions on combustion and the generation of emissions. Subsequently, to address issues related to incomplete ammonia combustion and a decline in engine power performance, a novel fuel injection strategy was developed. This strategy optimizes the distribution of diesel within the combustion chamber and the combustion process of ammonia-diesel dual-fuel by coordinating the injection timing of diesel fuel with the injection angle. The results indicate that an ammonia energy fraction of 40% is deemed to be an optimal mixing ratio for ammonia addition. Compared with pure diesel mode, greenhouse gas emissions are reduced by 34.3%, and the indicated mean effective pressure is only reduced by 4% when the ammonia energy fraction is 40%. Collaborative optimization of fuel injection timing and angle can achieve multi-point pilot ignition, shorten the combustion duration, and thus approach the effect of premixed combustion. This leads to a substantial decrease in unburned ammonia emissions, with the optimal unburned ammonia emission injection scheme registering only 0.279 g/kW·h, a mere 1.63% of the emissions under the original injection scheme with a 40% ammonia energy fraction. Additionally, the rapid combustion contributes to an increase in in-cylinder temperature, resulting in a significant reduction in N2O and CO emissions.