Experimental investigation on liquid length of direct-injection ammonia spray under engine-like conditions

The utilization of ammonia fuel in internal combustion engines holds significant promise in achieving carbon neutrality objectives. High-pressure direct injection technology offers precise control over fuel quantity and mixture formation. However, it is crucial to control the impingement of the liquid phase to minimize emissions, especially in the case of ammonia. In this study, we employ the diffused back illumination imaging technique to investigate the dynamic evolution characteristics of the liquid phase in evaporating ammonia sprays, via a comparison with diesel fuel. Parameters, including injection pressure, fuel temperature, nozzle diameter, ambient pressure, and ambient temperature are examined and assessed under engine-like conditions. Our findings highlight the distinct dynamic evolution behavior of diesel spray, which is characterized by periodic detachments of large droplet clusters and cyclic variations in liquid penetration. This contrasts with the smoother evolution of ammonia spray. Notably, during the quasi-steady state, the liquid penetration in ammonia spray exhibits a significant increasing trend due to the large latent heat of evaporation. Finally, a predictive 1D model is proposed with consideration of multiple influencing factors. The findings offer valuable insights into comprehending and modeling the evaporating ammonia spray, thereby contributing to enhanced efficiency and cleaner combustion processes within ammonia engines.