Effects of different injection strategies on n-butanol/diesel engine combustion and emission characteristics

n-Butanol can reduce pollutant emissions while also alleviating dependence on fossil fuels. This study employed numerical simulation methods, keeping the total fuel injection volume constant, to investigate the effects of two-stage injection and three-stage injection (7% pre-injection + 15% main injection + 15% post-injection) strategies on the combustion and emission performance of n-butanol/diesel engines. The model’s accuracy was verified through bench testing. Results indicate that when the pre-injection ratio increases from 3% to 9%, the peak cylinder pressure during the main injection combustion phase gradually rises, increasing by 5.98% compared to single injection. At a pre-injection ratio of 7%, the combustion duration is shortest, the indicated mean effective pressure is highest, NO _x emissions slightly increase, and soot emissions decrease by 39.75% compared to single injection. As the proportion of post-injection ratio increased from 5% to 20%, the secondary combustion heat release rate rose by 16.98%. At 15% post-injection, the longest ignition delay was observed, with the highest indicated mean effective pressure and a 70.19% reduction in soot emissions. The three-stage injection strategy effectively combined the advantages of both pre-injection and post-injection approaches. Compared to other injection strategies, it improved indicated mean effective pressure, achieved NO _x emissions comparable to post-injection, and delivered better soot emission performance than pure pre-injection.