While ammonia has received increasing attention as a potential zero-carbon fuel, it is known to pose significant technical challenges that have stalled its commercialisation to date. These include poor combustion characteristics, NOx emissions, and ammonia slip – a term used to describe unreacted ammonia (NH₃) that escapes exhaust gas treatment systems without being fully used to convert harmful nitrogen oxides into harmless nitrogen and water.
In addition, the fuel is as yet unproven for long-term durability at engine scale. Through 5 years of collaborative research, MAHLE Powertrain and the University of Nottingham have made substantial progress in addressing and overcoming these issues, moving the technology beyond proof-of-concept and closer towards practical deployment than ever before.
The collaboration has successfully demonstrated stable combustion using pure ammonia in spark-ignited engines, while combining hydrogen co-fuelling, ammonia cracking (a chemical process that breaks down ammonia into its basic parts: nitrogen and hydrogen), and advanced after-treatment to reduce NOx and ammonia slip to extremely low levels. The programme is now progressing beyond laboratory-scale testing, with work underway on larger-capacity engines for real-world applications across marine, rail, stationary power generation, and other heavy-duty sectors.
The recently opened Hybrid Propulsion Systems Laboratory significantly expands the University of Nottingham’s capability, in partnership with MAHLE Powertrain, to support industry-led propulsion research. Bringing together advanced engine testing, hydrogen technologies, electrification, and hybrid powertrain integration under one roof, it is a major national facility designed to help bridge the gap between academic research and commercial product development.
This is not just a traditional university research project; the partnership has evolved into a fully integrated engineering programme, combining academic expertise with MAHLE Powertrain's experience of developing commercially viable propulsion systems. The research programme is concrete proof of how collaborative research and development can accelerate technology readiness and reduce development risk for future OEM adoption.
Key points:
MAHLE Powertrain and the University of Nottingham have demonstrated how ammonia combustion is progressing from laboratory research towards commercially relevant heavy-duty applications.
Addressing the major technical barriers – Research has focused on overcoming slow combustion speed, NOx emissions, and ammonia slip through a combination of combustion system development, hydrogen co-fuelling, ammonia cracking, and advanced after-treatment technologies.
Scaling up the technology – Development is progressing from single-cylinder research engines to larger-capacity platforms capable of demonstrating real-world performance and durability.
Applications where electrification remains challenging – The programme targets sectors including marine, stationary power generation, freight rail, and off-highway machinery, where energy density and operational requirements make combustion engines likely to remain part of the future energy mix.
A new national research capability – The University's Hybrid Propulsion Systems facility provides world-class testing infrastructure, enabling industry and academia to develop complete hybrid propulsion systems within a single collaborative environment.
Collaboration as a catalyst for innovation – The long-term partnership illustrates how collaborative R&D can accelerate technology readiness while reducing commercial risk.
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