Flow fields and turbulent characteristics in non-evaporating diesel sprays

Due to global warming, air pollution problems, and increases in the oil price, increased thermal efficiency meeting stringent future standards are now requirements for commercially available diesel engines. The characteristics of intermittent sprays are known to be factors that affect the air fuel mixing, combustion, engine performance, and emissions of diesel engines, making a thorough understanding of fuel spray processes urgently necessary. A particle image velocimetry technique together with high-speed video camera and continuous wave green laser light were applied to non-evaporating diesel sprays injected from single-hole nozzles in a quiescent constant volume vessel. The velocity fields and the turbulent properties were studied to elucidate the turbulent mixing processes, with emphasis on the impacts of injection pressure and ambient density, which are the principal combustion control parameters in modern diesel engines. The experimental and analytical results showed that the distribution of the normalized turbulence intensity of diesel sprays is unchanging regardless of the fuel injection conditions and is identical with the turbulence of gas jets. The turbulence intensity depends on the motion of large eddies and the size of these large eddies determines the spray shape.