Abstract
Elliptical diesel nozzles affect the fuel–air mixing process, and thus combustion and exhaust emissions. Experiments were conducted to study biodiesel spray liquid-phase behaviors for elliptical and circular nozzles through the Mie-scattering method under evaporative conditions. Based on the measurements, the results show that the elliptical nozzle spray liquid-phase penetration is smaller than the circular one under steady-state conditions. The deformation and the axis-switching behaviors of the elliptical jet are helpful in accelerating the breakup of the liquid core. Moreover, the injection pressure has little impact on the penetration of the liquid-phase spray for either geometrical orifice. Additionally, increasing the ambient temperature can reduce the penetration of liquid-phase spray, because an increase in temperature increases the rate of evaporation. The differences in steady liquid-phase penetration between circular and elliptical sprays decrease as the ambient temperature increases. Additionally, increasing the backpressure can decrease the liquid-phase penetration. The differences in steady liquid-phase penetration between circular and elliptical nozzles are reduced with the increase in backpressure, probably due to the axis-switching and deformation behaviors of the elliptical jet being restrained under high-backpressure conditions. Finally, the application of an elliptical orifice is beneficial for decreasing the spray liquid-phase penetration, and thus avoiding the fuel impingement in small engine combustion chambers. The lower liquid-phase penetration for elliptical spray indicated higher fuel and air mixture quality, which is helpful for reducing the diesel engine exhaust soot emissions.
Highlights
Fuel spray evaporation and liquid fuel penetration, before ignition and combustion, are relevant issues concerning diesel spray behavior subsequent to air–fuel mixing, and is related to combustion processes and exhaust emissions [1]
The differences in steady liquid-phase penetration between circular and elliptical nozzles are reduced with the increase in backpressure, probably due to the axis-switching and deformation behaviors of the elliptical jet being restrained under high-backpressure conditions
Molina et al [24] carried out a computational study in order to investigate the influence of the use of elliptical orifices on the inner nozzle flow and cavitation development, and the results showed that elliptical geometries with a vertically oriented major axis were less prone to cavitation and had a lower discharge coefficient, whereas elliptical geometries with a horizontally oriented major axis were more prone to cavitation and showed a higher discharge coefficient
Summary
Fuel spray evaporation and liquid fuel penetration, before ignition and combustion, are relevant issues concerning diesel spray behavior subsequent to air–fuel mixing, and is related to combustion processes and exhaust emissions [1]. In the traditional research related to fuel injection and atomization, spray and atomization quality is improved by increasing the injection pressure and reducing the diameter of the nozzle hole [2,3]. When blindly increasing the injection pressure, the penetration of the long spray tip is prone to adverse effects such as wall impingement and lubricating oil dilution [4,5]. People have tried to use orifices with new structures, having different cross-section shapes, in order to improve the fuel atomization quality. Yu et al [8,9,10] compared the spray characteristics of a diesel injector with circular and elliptical cross-section shapes under room temperature, the results showed that using an elliptical nozzle reduced
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