Advanced Ammonia Combustion Process Development for Maritime Applications

The urgent need to reduce CO2 emissions in all areas demands the swift development and implementation of appropriate solutions for the worldwide shipping branch both for sea-going and inland waterway vessels. Green ammonia, produced from renewable energies, represents one of the few carbon-free fuels with realistic large-scale implementation potential. Despite its promising characteristics, the inherently low reactivity of ammonia poses challenges for engine ignition stability and complete combustion, which has so far prevented its use as a stand-alone fuel in internal combustion engines. As a result, dual-fuel strategies with hydrogen or diesel are typically required, increasing system complexity and fuel infrastructure demands on board.
As part of this work, two different ammonia-based combustion concepts were developed, implemented, and systematically investigated with the overarching goal of maximizing the energetic ammonia share while minimizing the required pilot energy. The first concept is based on a spark-ignited NH₃–H₂ combustion process with variable hydrogen fractions ranging from small ignition-support quantities up to pure ammonia operation. ... mehrThe second concept relies on a dual-fuel diesel pilot combustion process in which highly premixed ammonia–air mixtures are ignited by a small quantity of Diesel-pilot-fuel.
To investigate these concepts, a Liebherr D966 single-cylinder engine was installed on the test bench of the Institute of Internal Combustion Engines (IFKM). The setup included comprehensive thermodynamic, optical, and emissions analytics, enabling detailed assessment of mixture formation, ignition behaviour, and pollutant formation. A major outcome of the study is the demonstration that, with an optimized ignition system and tailored mixture formation concepts, stable 100% ammonia combustion can be achieved across the entire load range of the engine. This represents a substantial step forward, as it allows a significant downsizing of the onboard infrastructure.
The work is closely linked to ongoing activities within the German Campfire alliance, where a complete ammonia-fueled cracker-engine-unit is being developed as a propulsion solution for inland waterway vessels. The findings of the present single-cylinder study form the technological foundation for transferring the combustion concept to the multi-cylinder engine, which will subsequently be tested under maritime boundary conditions together with the cracker and an adapted exhaust aftertreatment system.
Overall, the results highlight the feasibility and potential of ammonia as a fuel for future maritime engine propulsion systems. Both the spark-ignited NH₃–H₂ concept and the diesel-pilot dual-fuel approach offer viable pathways for new engine developments as well as retrofit solutions for existing diesel engines, supporting the transition towards sustainable, carbon-free shipping.