The Effect of Fuel Temperature on the Ethanol Direct Injection Spray Characteristics of a Multi-hole Injector

Ethanol direct injection (EDI) is a new technology to use ethanol fuel more efficiently in spark ignition engines. Fuel temperature is one of the key factors which determine the evaporation process of liquid fuel spray, and consequently influence the combustion and emission generation of the engine. To better understand the mixture formation process of the EDI spray and provide experimental data for engine modelling, experiments were conducted in a constant volume chamber in engine-like conditions. The high speed Shadowgraphy imaging technique was used to capture the ethanol spray behaviours. The experiments covered a wide range of fuel temperature, ranged from 275 K (non-evaporating) to 400 K (flash-boiling). Particularly the transition of the ethanol spray from normal-evaporating to flash-boiling was investigated. The temporal Shadowgraphy spray images, spray tip penetration, angle and projected area were applied to evaluate the evaporation of EDI spray under different fuel temperature conditions. The results showed that the non-evaporating spray's characteristics were similar to the normal-evaporating sprays' in terms of spray tip penetration, angle and projected area. When the fuel temperature increased from 350 K to flash-boiling spray, the spray angle and projected area reduced significantly, but the spray tip penetration increased. Increasing the fuel temperature from 275 K to 325 K did not cause significant increase of the evaporating rate, but with further increase of the fuel temperature, the ethanol spray's evaporation became faster. The transition temperature at which the ethanol spray collapsed at atmospheric pressure was between 355 K and 360 K.