Experimental investigation of fuel adhesion from wall-impinging spray with various injection mass ratios

Abstract

In direct injection spark ignition (DISI) engines, interactions between spray and wall surfaces are a common phenomenon. This interaction results in fuel adhering to the surfaces of the cylinder and piston, which in turn greatly influences both combustion efficiency and emission levels. This work explored the influence of various injection mass ratios (D25-75, D50-50, D75-25) on fuel adhesion properties, employing the refractive index matching (RIM) technique in both non-evaporation and evaporation environments. Findings indicated that the split injection mass ratios notably affected fuel adhesion. Under the non-evaporation condition, the highest adhesion mass ratio was observed for D50-50, which was 14.5 %, whereas D25-75 and D75-25 exhibited adhesion mass ratios of 11.9 % and 12.5 % at 60 ms after the start of injection (ASOI). This increase was attributed to two factors: “fuel adhesion thickness” and “penetration velocity”, both of which contributed to enhance splashing and ultimately resulted in the highest adhesion mass of D50-50. However, under the evaporation condition, the adhesion mass of D50-50 declined quickly in comparison to those of other injection mass ratios. This rapid decrease was caused by the uneven adhesion of D50-50, which tended to collapse and evaporate faster at high ambient temperatures, as the uniformity of D50-50 was poorer than those of other injection mass ratios.