Experimental study of the macroscopic characteristics of methanol low‐pressure injection spray

This study aims to examine the effects of ambient pressure, fuel temperature, and ambient temperature on the macroscopic characteristics of a methanol low-pressure spray. Backlight imaging and high-speed photography are used to record spray morphology. The experimental conditions include the normal, transitional, and strong flash-boiling states. The flash-boiling state significantly increases the spray penetration and angle. The plumes of the strong flash-boiling spray shrink along the injector axis into a long, narrow liquid beam, and the spray morphology is similar to that of a shuttle. The flash-boiling spray yields different performance at various ambient temperatures despite constant fuel superheat, which indicates that the flash-boiling state is affected by both the fuel superheat and ambient temperature. Moreover, the influence mechanism is examined. A high ambient temperature increases the likelihood and severity of bubble burst. By contrast, a low ambient temperature hinders bubble expansion and bursting, reducing the flash-boiling intensity. Furthermore, a dimensionless analysis of the non-flash-boiling spray velocity is performed, and the correlation between the non-flash-boiling spray velocity and air-fuel density ratio, Weber number, and Reynolds number is established. The deviation of the predictive value from the correlation and measured value is within +/- 5%. The results indicate that the Reynolds number has a less significant effect than the air-fuel density ratio and Weber number.