This comprehensive review examines the application of liquid-ammonia injection and combustion in engine systems, highlighting the potential of liquid ammonia as a carbon-neutral fuel alternative. The study synthesizes recent advancements in liquid-ammonia injection and combustion technologies, addressing critical domains such as fundamental fuel properties, injection and spray dynamics, combustion behavior, and engine performance. Key challenges are identified, including ammonia’s high latent heat of vaporization, slow flame-propagation speed, narrow flammability range, and elevated NO_x emissions, while emphasizing the need for optimized injection strategies and nozzle designs to enhance atomization and mixing. The research findings indicate that liquid-ammonia injection can significantly reduce greenhouse gas emissions, with dual-fuel modes (e.g., ammonia-diesel) proving effective in overcoming ammonia’s low reactivity. Studies show that both low-pressure and high-pressure dual fuel-injection modes can achieve substantial emission reductions, with high-pressure injections offering better thermal efficiency and lower NO_x emissions. Innovative approaches, such as turbulent jet ignition, stratified fuel injection, and hydrogen co-injection, have been explored to improve ignition efficiency and combustion stability. Future research should prioritize the development of integrated solutions that combine advanced combustion technologies, optimized engine designs, and effective emission-control strategies. Collaboration between academia, industry, and policymakers will be crucial in driving the adoption of ammonia as a sustainable fuel alternative.

Highlights the challenge of developing truly calibration-free models, especially for new fuels like ammonia whose properties differ significantly from those of hydrocarbons