Characteristics of non-evaporating, evaporating and burning sprays of hydrous ethanol diesel emulsified fuels

Abstract

Utilization of hydrous ethanol in diesel engines is beneficial not only for reducing the exhaust pollutant emissions but also for improving the lifecycle fuel efficiency including both in engines and refineries. However, so far detailed investigations on spray combustion characteristics of hydrous ethanol diesel emulsified fuels are rarely reported, though this information is crucial in combustion system design for better application of these fuels in diesel engines. In this paper, emulsions of the 20wt% water-containing ethanol and commercial diesel fuel with volume fraction of the hydrous ethanol varied from 10 to 30% were firstly developed. Then, the physicochemical properties including the mixture stability, density, kinematic viscosity, surface tension, distillation temperature, latent heat of evaporation, etc. were investigated. Finally, the characteristics of non-evaporating, evaporating and burning sprays under the various injection and ambient conditions were clarified with the common-rail fuel injection system and the high-temperature, high-pressure, constant-volume combustion vessel. The results reveal that the difference of the spray cone angle and tip penetration length under either the non-evaporating or evaporating conditions for various fuels are relatively small, while the maximum liquid penetration length in the evaporating spray increases drastically with increased addition of the hydrous ethanol in the emulsions. In the case of burning spray, the natural luminosity of the flame decreases remarkably with the hydrous ethanol increasing, indicating the soot reduction in the flame. This effect becomes more pronounced with the ambient oxygen concentration decreasing. The mechanism of the above phenomena is discussed in depth.