EXPERIMENTAL STUDY ON FLASH BOILING SPRAY OF HIGH-PRESSURE LIQUID AMMONIA JET WITH ROUND AND ELLIPTICAL HOLE NOZZLES

Ammonia is an ideal alternative fuel for mitigating carbon emissions. High-pressure direct injection of liquid ammonia (LNH₃) offers significant advantages in enhancing energy efficiency and minimizing emissions. Due to the high saturation vapor pressure, the injection of LNH₃ is susceptible to flash boiling. In this study, we used high-speed micro-imaging technology with backlight lighting to establish a high-pressure common-rail LNH₃ jet experimental platform and investigate the flash boiling spray characteristics of nozzles with round and elliptical holes. The results demonstrated that under non-flash boiling conditions, the residual LNH₃ in the sac chamber and nozzle can rapidly corrode the acrylic material of the nozzle, leading to deformation and failure of the nozzle structure. Under flash boiling conditions, LNH₃ ejected from the hole will produce spherical macroscopic spray morphology. Then, the spray gradually transitions from an elliptical profile to a conical profile as the back pressure increases. Compared to nozzles with round holes, nozzles with elliptical holes exhibit higher flow velocity, which enhances oil-gas mixing and promotes more pronounced flash boiling phenomena. Flash boiling occurs at an earlier stage with an increase in the spray cone angle, thereby improving the atomization characteristics under both flash and non-flash boiling conditions. The tail jet of nozzles with elliptical holes terminates earlier while exhibiting a higher decrease rate in the average gray value, which improves the atomization quality in the tail spray stage and meets the requirements of timing, quantification, and precise control of the fuel injection system.