Ammonigy, Heraeus: successful four-stroke engine demonstration
By on July 23, 2025
In the heavy transport space, Ammonigy has already demonstrated successful operations of a retrofitted V8 engine powered by cracked ammonia fuel. The demonstration – completed onboard the modified speedboat GREEN AMY – was intended as a precursor to developing inland barge vessels powered by cracked ammonia fuel, as well as similar low-speed, constant-power transport options like heavy locomotives. In a new project with partners Heraeus Precious Metals and the Technical University of Darmstadt, Ammonigy has now demonstrated operations using cracked ammonia fuel in a four-stroke MAN ES engine.
Performance and efficiency equivalent to gas operations
Click to enlarge. Overall system with energy flow for the four-stroke engine tests, led by Ammonigy and Heraeus. Source: Ammonigy.
The tests were carried out on a 110kW, six-cylinder MAN E0836 engine, with a fuel mixture composed of approximately 80% ammonia and 20% hydrogen. Engine test operations took place under stoichiometric conditions (equal air-fuel ratio) in order to achieve the highest possible engine performance. The partial ammonia cracker (based on Ammonigy’s existing technologies) operates at around 700°C with precious metal-based catalysts, and does not require an external energy source to maintain temperatures during continuous operations. Similar to gas fuel operations, the ammonia-hydrogen fuel mix is added to the intake air of the engine.
The performance and efficiency of the test engine when running on ammonia-hydrogen fuel was comparable to natural gas operations, based on the same compression ratio. Ammonigy indicates that increasing the compression ratio to diesel operation levels would further increase in engine efficiency (approx. 2-3%), as would the engine size (efficiencies above 50%).
Two-stage exhaust aftertreatment produces near-zero tailpipe emissions
Click to enlarge. Emissions vs. time graphs showing the drastic reduction of potentially harmful nitrogen emissions by the exhaust aftertreatment system (EATS) developed by Ammonigy, Heraeus and partners. Source: Ammonigy.
Exhaust gas aftertreatment was carried out by a regulated, two-stage system, consisting of two different, “three-way” catalysts with oxygen storage (a form of aftertreatment already common in stoichiometric engine operations). A small portion of the ammonia fuel feed (1-2%) is diverted and dosed into the first aftertreatment stage (0.995< λ <1) to remove NO and N2O. A small flow of air is dosed into the second aftertreatment stage to remove the surplus of ammonia (0.999< λ <1.001). As shown in the results graph, real-time adjustment of the exhaust aftertreatment system during engine operations drastically reduced potentially harmful nitrogen-based emissions (NO, N2O and ammonia slip) to <5ppm from levels near and above 1000ppm (NO and ammonia slip), and 150ppm (N2O). The results show the critical importance of properly-functioning exhaust gas aftertreatment systems in the operation of ammonia-fueled engines. Larger scale and longer duration tests of the overall system will help validate these promising results.
Similarly promising results have already been seen this year in the four-stroke engine space from technology providers IHI and Wärtsilä, with longer-term testing and testing under real-world operating conditions to follow.