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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 work reported in this paper contributes to understanding the effects of ethanol/gasoline ratio on mixture formation and cooling effect which are crucial in the development of EDI+GPI engine. The spray simulations were carried out using a commercial CFD code. The model was verified by comparing the numerical and experimental results of spray shapes in a constant volume chamber and cylinder pressure in an EDI+GPI research engine. The verified model was used to investigate the fuel vaporization and mixture formation of the EDI+GPI research engine. The effect of the ethanol/gasoline ratio on charge cooling has been studied. Compared with GPI only, EDI+GPI demonstrated stronger effect on charge cooling by decreased in-cylinder temperature. However, the cooling effect was limited by the low evaporation rate of the ethanol fuel due to its lower saturation vapour pressure than gasoline's in low temperature conditions.