Characteristics of high-pressure ammonia spray combustion under diesel-like conditions

High-pressure direct injection of ammonia is a prospective way for internal combustion engines. In this paper, the characteristics of high-pressure ammonia spray combustion under diesel-like conditions are investigated in a constant-volume combustion chamber and are compared with the diesel spray combustion. The characteristics of ammonia spray and combustion including the spray tip penetration, cone angle, maximum liquid length and liftoff length are obtained under the non-reacting and reacting conditions. The effects of ambient temperature, density, oxygen concentration and initial fuel temperature are evaluated. It is found that the sprays of ammonia and diesel exhibit a similar macroscopic morphology for both the vapor and liquid phases at room temperature, except for a little faster tip penetration of diesel spray. Under the high ambient temperature, the maximum liquid length of ammonia spray is significantly lower than that of diesel. Under the ambient conditions of 900 and 1000 K temperatures and 21 % oxygen concentration, for the first time, the auto-ignition of the high-pressure ammonia spray is successfully observed. The combustion intensity of ammonia spray is drastically lower than those of diesel. Increases in the ambient temperature are more effective in promoting the ammonia spray combustion than increases in the initial fuel temperature. The results obtained under a wide range of operating conditions can serve as valuable references for the practical application of ammonia spray in combustion devices.