Research Progress | Marine Engineering Team Publishes Ammonia-Hydrogen Engine Progress in Joule

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Recently, the renowned journal Joule published online the latest research progress from Prof. Li Tie's team in the Department of Naval Architecture and Ocean Engineering, titled "Ammonia-hydrogen engine with single ammonia fuel supply". This work proposes the concept of ammonia-hydrogen engine based on a single ammonia fuel supply, simultaneously addressing the key challenges of ammonia's poor combustion characteristics and the high cost of hydrogen storage and transportation. Dr. Zhou Xinyi is the first author, and Prof. Li Tie is the corresponding author.

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Owing to their high thermal efficiency, unrivaled reliability, and long lifespan, piston internal combustion engines (ICEs) dominate the market as prime movers for international ships and are expected to maintain this dominant role in the foreseeable future. Under the background of the 2050 net-zero target, ammonia has been deemed as one of the most promising alternative fuels in the maritime sector, but its poor combustion characteristics limit its efficient use in engines. Hydrogen-enriched combustion has been demonstrated to be an effective way to significantly reduce unburned ammonia emissions and increase the thermal efficiency of ammonia engines. However, the unacceptable on-board storage capital expenditure for hydrogen has constrained its direct storage on long-voyage international ships. Inspired by the fact that hydrogen can be produced via ammonia reforming or decomposition, this study proposes the concept of "Ammonia-hydrogen engine with single ammonia fuel supply". Two technical pathways (A) External reformer route and (B) In-cylinder reforming route are developed to simultaneously address the key challenges of ammonia's poor combustion characteristics and the high cost of hydrogen storage and transportation. Especially, this study proposes the concept of a pre-chamber-assisted reforming cylinder design to ensure stable ignition, extend the boundary of the ammonia-rich limit, and increase in-cylinder hydrogen production. The study also analyzes the technical feasibility of the two routes, calculates the theoretical thermal efficiency of the ammonia-hydrogen engine under different combustion modes, and summarizes the roadmaps for improving practical thermal efficiency. Finally, the key challenges and future development opportunities of ammonia-hydrogen engines are discussed, with a particular focus on the reforming cylinder design.

Fig. 1. Ammonia-hydrogen engine with single ammonia fuel supply.

(A) External reformer route; (B) In-cylinder reforming route.

Fig. 2. Progress of two routes along with prospects for their integration.

(A-C) NH3 conversion rate for the external reformer;

(D-E) NH3 conversion rate for the in-cylinder reforming route;

(F) A combined approach of in-cylinder reforming and external reformer.

Fig. 3. Thermal efficiency for ammonia-hydrogen engine

(A) Theoretical thermal efficiency under different modes;

(B) Roadmaps for improving the practical thermal efficiency

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About Joule:

Joule, a sister journal to Cell, is widely recognized as a renowned journal in the energy field. Its impact factor has remained between 38.6 and 46.0 over the past three years, placing it among the top two journals in the categories of ENERGY & FUELS and CHEMISTRY, PHYSICAL.

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Paper link:

https://doi.org/10.1016/j.joule.2025.101922