Mini-Review of Spray and Combustion Characteristics for Ammonia Engines

Ammonia is a potential zero-carbon fuel, and ammonia engines have also become a research hotspot for zero-carbon power systems for heavy-duty transportation equipment, such as ships, railways, and trucks. Ammonia possesses physical and chemical properties that differ significantly from those of traditional fossil fuels. The process of ammonia injection and mixture formation within the engine cylinder is complex, making it crucial to achieve optimal spray patterns and efficient combustion in ammonia engines. Most current research on ammonia engines has focused on low-pressure injection technologies; whether through intake port injection or in-cylinder injection, the practical application of high-pressure ammonia injection in actual engines still faces many technical challenges. Before the commercialization of ammonia engines, several critical technical issues must be addressed, including fuel flash boiling, mixture formation, spray collapse mechanisms, and efficient combustion. This review offers a comprehensive and systematic review of recent research trends in ammonia spray and combustion performance with the aim of providing directional guidance and a reference point for optimizing spray and combustion processes in ammonia engines.