Droplet Measurement of High-Pressure Liquid Ammonia Injection Using PDPA

Liquid ammonia is an ideal zero carbon fuel to reduce carbon emission of internal combustion engines. The high-pressure injection of liquid ammonia is a key technology to fast distribute fuels and prepare better combustion performances. The physical properties of liquid ammonia are different to traditional fossil fuels including diesel and gasoline, which can change the spray and droplet characteristics significantly. However, the spray droplet characteristics of liquid ammonia injection is lack of investigations. In this paper, Phase Doppler Particle Analyzer (PDPA) are used to measure the droplet diameter and velocity of high-pressure liquid ammonia sprays up to 75 MPa and compare to diesel sprays. Effects of flash boiling of liquid ammonia droplet characteristics are also analyzed. Results show that the SMD of liquid ammonia is 50 – 70 % smaller than diesel when injection pressure ranges from 25 – 75 MPa in ambient pressure 1 MPa, due to its lower viscosity and higher evaporation rate. The SMD of liquid ammonia is lower than 12 μm when the injection pressure is higher than 25 MPa. Besides, the droplet velocity of liquid ammonia is higher than diesel due to higher nozzle exit velocity caused by the lower viscosity of liquid ammonia. Furthermore, the flash boiling of liquid ammonia can reduce the SMD of liquid ammonia. Injections in non-flash boiling need to increase the injection pressure by 25 MPa in order to reach the same SMD in flash boiling conditions. Liquid ammonia shows better atomization and evaporation than diesel. The experiment results can provide important droplets data, which is useful for simulations and developments of liquid ammonia engines.