Emission, efficiency, and influence in a diesel n-butanol dual-injection engine

•Dual-injection combustion for diesel n-butanol dual-fuel is investigated.•Higher EGR rate results in lower NOx and ITE, but higher smoke, HC and CO.•Larger butanol fraction results in lower smoke and ITE, but higher NOx, HC and CO.•Advanced injection can decrease smoke, HC and CO, and increase ITE.•Coupling of butanol fraction, EGR and injection timing makes for a better performance. In this work, a dual-injection combustion mode for diesel n-butanol dual-fuel, combined direct injection (DI) of diesel with port fuel injection (PFI) of n-butanol, was introduced. Effects of n-butanol fraction, EGR rate and injection timing on this mode were studied on a modified single-cylinder diesel engine at the speed of 1400r/min and the IMEP of 1.0MPa. The results indicate that with increased EGR rate, NOx emissions reduce, but smoke emissions increase. As n-butanol fraction is increased, smoke emissions decrease with a small increase in NOx. However, higher HC and CO emissions, higher indicated specific fuel consumption (ISFC) and lower indicated thermal efficiency (ITE) have to be paid with increased n-butanol fraction, especially at high EGR condition. Advancing diesel injection timing suitably has the capacity of mitigating those costs and further decreasing smoke emissions with a small penalty in NOx emissions. Coupling of large butanol fraction, high EGR rate, and advanced injection suitably contributes to a better balance between emissions and efficiency in the diesel n-butanol dual-injection engine.