Experimental Study on Macroscopic Characteristics of Ammonia Spray under Flash Boiling and Non-Flash Boiling Conditions with Large-Diameter single-hole Nozzles

Ammonia is regarded as a potential alternative fuel, and its spray characteristics are crucial for efficient combustion in engines. For large-bore engines suitable for heavy-duty vehicles or ships, the adoption of large-diameter nozzles is expected to ensure an appropriate fuel flow rate while improving fuel-air mixing efficiency, thereby enhancing in-cylinder combustion performance. This paper conducted an experimental study on the characteristics of liquid ammonia sprays under wide thermodynamic conditions, a wide range of injection pressures, and a wide range of nozzle diameters. The study found that at room temperature, as the ambient pressure increases from 0.1 MPa to 4 MPa, the development of spray penetration slows down. However, at 0.05 MPa, the radial expansion of the near-field spray is greater, and the penetration is slightly behind that at 0.1 MPa. The liquid penetration increases with the increase in ambient temperature. This was because the increase in temperature reduced the ambient gas density, thereby decreasing the aerodynamic resistance. Under the high-temperature and high-pressure ambient conditions of 4 MPa and 800 K, the liquid penetration is greatly limited when a 0.2 mm nozzle is used due to insufficient spray momentum and high spray vaporization rate, with the maximum penetration only about 40 mm. In contrast, the penetration of the 0.7 mm nozzle could develop to more than 85 mm. Under the ambient conditions of 4 MPa and 800 K, a "stagnation" of penetration was observed for the 0.7 mm nozzle with injection pressure of 60 MPa, where the penetration does not increase continuously. This was the result of the synergy between spray velocity gradient, aerodynamic shear force, and high-temperature evaporation. This paper conducts the first experimental study on liquid ammonia sprays using large-diameter nozzles up to 0.7 mm, providing an experimental basis for the injection optimization of large-bore liquid ammonia direct-injection engines.