Experimental and numerical study on flow, combustion and emission characteristics of CI engine fueled with n-butanol/diesel blends under post-injection strategy

Since the technology of n-butanol/diesel blending fuel coupled with post-injection (PI) strategy increases the complexity of engine combustion process, the disputes that the interpretation of the formation mechanism of pollutants are still existed. Moreover, studies on the effects of this coupling-strategy on fine-particles (DP < 25 nm) have not been carried out. Therefore, this paper first adopts an experimental approach to study the macroscopic effects of the coupling-strategy on commercial engines, especially the change of fine-particles is analyzed. Then, the influence mechanism of coupling-strategy on atomization, combustion and pollutant generation is clarified by revealing the difference between intermediate products and combustion variables by using simulation method. The results show that the mixture has the higher evaporation rate and smaller SMD, and the PI strategy significantly increases the velocity and turbulent kinetic energy of gas in terms of atomization and flow. In terms of combustion, the brake thermal efficiency of D100 reaches 36.9% when the PI rate is 25%. About conventional emissions, the coupling-strategy reduces CO emissions by enhancing the CO + OH = CO2 + H reaction process. In addition, both blending fuel and PI strategy reduce soot precursors A1 and A4. Especially, the PI strategy increases the oxidation of soot by enhancing air entrainment. In terms of particulate emissions, the coupling-strategy reduces aggregation mode particles and total particulate mass concentration, but result in a higher proportion of fine-particles.