Synergic effect of hydrogen and n-butanol on combustion and emission characteristics of a hydrogen direct injection SI engine fueled with n-butanol/gasoline

Abstract

Hydrogen, an ideal carbon-free energy carrier with favorable combustion properties, has drawn worldwide attention as a high-expectation way to enhance fossil fuels’ combustion performance. However, currently, limited investigations are about enhancing n-butanol hybrid gasoline engines through hydrogen addition. Thus, in this paper, the hydrogen direct injection (HDI) was put forward to improve an SI engine fueled with n-butanol/gasoline, and the synergic effect of hydrogen and n-butanol on combustion and emission characteristics was studied. Experimental results indicated the favorable influence of a low n-butanol mixing ratio (νN, νN = 25%) on enhancing combustion can relatively weaken the similar promoting effect of hydrogen. And the sequential increase in hydrogen addition ratio (φH, φH = 15–20%) can compensate for the negative impact of unfavorable atomization and vaporization quality caused by higher n-butanol blending (νN = 75–100%), namely the usage amount of n-butanol in engine can be raised. Further, compared with pure gasoline, the percentage change in BMEP (brake mean effective pressure) at νN = 25% and 100% can be increased from 1.79% to 5.04% and −5.38%–2.01% respectively by φH from 0 to 20%. Besides, the HDI can also shorten the combustion duration, accelerate the heat release process and improve the combustion stability of each νN, while the amplitude of promotion exhibits a relative downtrend with the increase of φH. As for emission characteristics, the HC, CO and particulate emissions decreased monotonously with the increasing φH under all νN, but there was a visible increase in NOX emissions.