Ammonia and Hydrogen as Carbon-Free Fuels for Internal Combustion Engines: A Comprehensive Review on Combustion, Emissions, and Performance

The transition to carbon-free energy sources is critical for combating climate change. This review explores the potential of hydrogen (H₂) and ammonia (NH₃) as promising zero-carbon fuels for internal combustion engines (ICEs). It examines their production methods, highlighting the shift from carbon-intensive "grey" processes to renewable-based "green" production. The study contrasts the fundamental properties of H₂ and NH₃: hydrogen offers high reactivity and wide flammability but poses storage challenges, while ammonia features higher energy density and easier handling but suffers from low flame speed and high ignition resistance. The core analysis focuses on combustion characteristics, engine performance, and emissions. Hydrogen enables efficient lean-burn combustion in spark-ignition engines but risks NOx emissions and abnormal combustion. Its use in compression-ignition engines requires dual-fuel operation. For ammonia, strategies like hydrogen enrichment, dual-fuel operation, and advanced injection are essential to enhance combustion efficiency and stability. Although both fuels eliminate CO₂ emissions, controlling nitrogen oxides (NOx) and nitrous oxide (N₂O) remains a challenge. The review concludes that hydrogen and ammonia represent viable pathways for decarbonizing ICEs, with their synergistic use—using ammonia as a hydrogen carrier and enriching it with hydrogen—offering a particularly promising solution for a sustainable future.

کلیدواژه ها:

Carbon-free fuels ، Hydrogen ، Ammonia ، Emissions ، Performance ، Dual-fuel combustion