Effects of injection pressure on diesel sprays in constant injection mass condition

As known, the constant injection mass is a criterion for measuring the thermal efficiency of diesel engine. In this study, the effects of injection pressure on diesel free-spray characteristics have been investigated in the condition of constant injection mass. The experiment has been performed in a constant volume combustion chamber. A high pressure common-rail injector with a single-hole nozzle is used. High speed camera and Schlieren visualization set-up are used to capture the behaviors of liquid phase spray and vapor phase spray respectively. For liquid phase spray, the spray penetration length increases as injection time elapsed until the saturated liquid phase spray penetration length is reached. Higher injection pressure causes higher liquid phase spray penetration rate, but the effect of injection pressure on saturated liquid phase spray penetration length is negligible. In addition, the influence of injection pressure on liquid phase spray cone angle can be neglected. For vapor phase spray, the variation of vapor phase spray penetration length can be divided into nonlinear increase period and linear increase period. Higher injection pressure causes higher mean vapor phase spray penetration rate. And higher injection pressure causes higher value of maximum vapor phase spray cone angle. The pure vapor phase spray cone angles at the time of injection stop increase linearly as the injection pressures increase.