Combustion and emission characteristics of diesel/n-butanol blends with split-injection and exhaust gas recirculation stratification

Oxygen fuels have broad application prospects and great potential for realizing efficient and clean combustion, and hence this study applies diesel/n-butanol blends to explore the influence of split-injection strategy on combustion and emission characteristics. Simultaneously, changing the way of exhaust gas recirculation (EGR) gas introduction forms uneven in-cylinder components distribution, and utilizing EGR stratification optimizes the combustion process and allows better emission results. The results show that the split-injection strategy can reduce the NO x emissions and keep smoke opacity low compared with the single injection, but the rise in accumulation mode particles is noticeable. NO x emissions show an upward trend as the injection interval expands, while soot emissions are significantly reduced. The increase in pre-injection proportion causes the apparent low-temperature heat release, and the two-stage heat release can be observed during the process of main combustion heat release. More pre-injection mass makes NO x gradually increase, but smoke opacity reaches the lowest point at 15% pre-injection proportion. EGR stratification can optimize the emission results under the split injection strategy, especially the considerable suppression of accumulation mode particulate emissions. Above all, fuel stratification coupled with EGR stratification is beneficial for further realizing the in-cylinder purification of pollutants.