Quantitative measurement of mixture formation in an impinging spray of ethanol-gasoline blend under cold-start condition via UV–Vis dual-wavelength laser absorption scattering (LAS) technique

Ethanol is considered as the most promising alternative fuel for gasoline, however, the ethanol-gasoline blends used in gasoline engines usually suffer to cold-start difficulties due to the poor mixture formation. While the spray-wall interaction plays a significant role in determining the mixture formation in direct-injection spark-ignition engines (DISI), particularly for the injection occurring near the top dead center (TDC). In this study, the mixture formation of ethanol-gasoline impinging spray (E0, E85 and E100) under cold-start condition for DISI engines were investigated in a constant volume vessel. An ultraviolet (UV) – visible (Vis) dual-wavelength laser absorption scattering (LAS) technique was used to quantitatively measure the liquid and vapor phase distributions respectively. Both the toluene and methyl ethyl ketone (MEK) with the similar physical properties to gasoline and ethanol respectively, as well as with high absorption for ultraviolet were used to determine the vapor and liquid distributions. Two wall temperatures (T_w) of 298 K and 273 K were set to represent typical cold-start conditions. The results show that E100 evaporates faster than E0 before spray impingement. After impingement, E100 exhibits more sensitivity to the wall temperature, and it evaporates faster at near-wall region under T_w = 298 K. For E85 impinging spray, the evaporation of high boiling point component in gasoline is slower under T_w = 298 K than that under T_w = 273 K, probably as a result of the evaporative cooling effect by ethanol component which has higher vaporization of enthalpy. Furthermore, the results indicated that a number of liquid droplets of heavy components in gasoline remain at near-wall region as fuel film. The evaporation characteristics of E85 is significantly enhanced at the initial period of spray impingement under cold-start condition, which is potential to improve the cold-start performance.