Effects of pre-injection parameters on spray characteristics of high-pressure common rail diesel engines

A verified hydrodynamic spray model was used to investigate the effects of multiple injection strategies on fuel bundle development and atomization characteristics of diesel fuel under typical conditions of direct-injection, turbocharged, and high-speed automotive diesel engines. Emphasis is placed on the effect of injecting a small amount of pre-injection fuel prior to the main injection on the spray development process. In addition, the effect and degree of influence of pre/main-injection interval time and pre-injection fuel ratio on spray macro- and micro-parameters in the two-injection strategies. The results show that at the end of the injection process, as the pre/main-injection interval time increases, the spray gas phase penetration distance increases, the spray width and the spray volume of the high-temperature region decrease, and the fuel concentration in the vicinity of the nozzle is in a decreasing trend. As the pre-injection ratio increases, the spray gas phase penetration distance decreases, the spray width, the spray volume of the high-temperature region increases, the spray volume between the fuel equivalence ratio of 0.8–1.2 decreases, and the fuel concentration at the front end of the spray tends to increase. The effect of the proportion of pre-injection fuel on spray width, spray volume of the high-temperature region, and spray volume between the fuel equivalence ratio of 0.8–1.2 was 4.88, 4.56, and 11.5 times that of changing the pre/main-injection interval time, respectively. The research provides a basis for optimizing the injection strategy and applying multiple injection technology in high-pressure common rail diesel engines.