Experimental analysis of liquid ammonia spray with different orifice diameter under marine engine conditions

The application of ammonia in high-power marine engines has been receiving more attention on achieving zero-carbon emission goals. Due to the unique flashing boiling characteristics of ammonia, the influence of orifice diameter on its spray characteristics needs further research. Present study presents a comprehensive experimental analysis of liquid ammonia spray macroscopic characteristics using three injector orifice diameters (0.15 mm, 0.3 mm, and 0.45 mm) under high-pressure conditions (injection pressure up to 100 MPa, ambient pressure up to 6 MPa). The results show that ambient pressure exerts a more pronounced influence on spray characteristics than injection pressure. Notably, flash boiling significantly enhances radial spray expansion, particularly causing substantial axial momentum loss in sprays from larger orifice diameter. In non-flash boiling region, although the spray from small orifice diameter develops rapidly at the initial stage, the spray from large orifice diameter exhibits superior performance in penetration distance, velocity and area during later stages. Based on these experimental results, a developed prediction model on spray tip penetration is proposed and verified to be well applicable to different orifice diameters, which provides a reference for orifice diameter optimization. According to the predicted fuel–air mixing degree of spray analyzed through equivalent ratio calculation, present results indicate 0.3 mm orifice diameter is optimal for flash boiling conditions, whereas a 0.45 mm diameter proves more effective for non-flash boiling and high-pressure marine engine operations. These findings offer significant contributions to the design and optimization of ammonia-fueled marine propulsion systems, advancing the development of sustainable maritime technologies.