INSIGHTS INTO DIESEL SPRAY TRANSIENT PROCESS UNDER ULTRA-HIGH INJECTION PRESSURE AND HIGH AMBIENT DENSITY CONDITIONS

Understanding the diesel spray dynamic development is crucial for modeling the injection process to optimize the design of ammonia-diesel dual-fuel engines. In this study, the effects of injection pressure up to an ultra-high value of 270 MPa, ambient density up to 70 kg/m<sup>3</sup>, and nozzle diameters of 0.12 and 0.181 mm on the spatiotemporal evolution of near-field spray are investigated using long-distance microscopic imaging. The nonevaporating spray images are analyzed using an in-house processing method. The analysis demonstrates that the intensity of the original images qualitatively describes the near-field spray process. In addition, the spray diffusion phenomenon is observed at the initial stage of the injection under all experimental conditions. Results show that the injector with a nozzle diameter of 0.181 mm exhibited a higher relative diffusion ratio and a smaller near-field angle compared with the 0.12 mm nozzle diameter due to poor atomization associated with the larger nozzle diameter. Furthermore, the times corresponding to when the spray reaches its maximum diffusion and stable state are extracted. Notably, an increase in ambient density and injection pressure reduces the maximum diffusion and stable state times of the spray. Finally, empirical correlations for predicting the spray near-field angle, maximum diffusion time, and stable state time are proposed. These correlations provide a foundation for quantitatively characterizing spray dynamics, which can be used to guide the optimization and design of fuel injection system.