Experimental study on the flash boiling spray characteristics and jet fluctuation of high-pressure direct injection liquid ammonia

Abstract

The high-temperature environment of actual engines significantly influences the characteristics of high-pressure liquid ammonia flash boiling spray and leads to jet instability. Therefore, this study investigated the influence mechanisms of different ambient temperatures on the high-pressure liquid ammonia flash boiling spray characteristics in a constant volume chamber. Simultaneously, it conducted the first exploration of the fluctuation characteristics of liquid ammonia jets, laying a foundation for achieving the stable and efficient combustion. The results indicate that the spray exhibits a three-stage axial development process at different ambient temperatures and ambient pressures, and the non-dimensional empirical formulas for describing the different stages of ammonia were proposed. In high-temperature conditions, the spray area is subject to the synergistic effects of flash boiling and evaporation. During the early stages, the spray development is dominated by flash boiling, leading to a rapid increase in the change rate of the spray area. However, during the later stages, the spray development is dominated by high-temperature evaporation, resulting in a rapid decrease in the change rate of spray area. Therefore, with increasing ambient temperature, the spray area experiences a significant reduction during the later stages. Through an analysis of spray centroid fluctuations at different ambient temperatures, it is evident that with rising ambient temperature, thermal disturbances intensify, leading to an increase in the oscillations deviation of the near-nozzle local region, and the maximum growth rate reaches 59.16%. Regarding different flash boiling stages, the spray centroid fluctuation is more stable during the transition flash boiling stage, with oscillation deviations below 0.02 at all ambient temperatures.