Characteristics and mechanism of spray deviation of ethanol and its blended fuel in multi-hole spray

Abstract

Research on renewable fuels is crucial to render engines compliant with energy and environmental efficiency, and alcohol fuels have become hotspots in the field of modern gasoline direct injection engines. This study aims to elucidate the effects of ethanol addition on spray deviation under non-flash and flashing conditions. Macroscopic characteristics and microscopic characteristics can be obtained from Diffused Back Illumination and Phase Doppler Anemometry. The influential factors accounting for the spray deviation were examined, and internal flow simulations were also performed to obtain in-nozzle flow information. The angled momentum induced by the short L/D ratio leaves space for ambient gas ingestion into the counterbore under non-flash conditions. The entrained gas was affected by cavitation intensities, leading to the spray deviation, which was tracked by the Lagrangian particle trajectory method. The spray deviation is also affected by the formation of the low-pressure zone and droplets' migration. The higher surface tension and lower molecular weight of ethanol facilitate the spray expansion, forming the liquid barrier to draw the spray moving toward the injector center. Ethanol's high latent heat of evaporation inhibits the further reduction in droplets' radius, resulting in a persistent decrease in the relative span factor. On the other hand, the high latent heat of evaporation leads to a larger pressure drop induced by the vapor condensation, accounting for the “more powerful” abilities in drawing droplets into the jet center. The trade-off between the droplets' size and migration ability should be achieved to efficiently modulate spray deviation.