engines with the aim of meeting both performance expecta-
tions and pioneering emission targets.
The first combustion concept represents a retrofittable
approach: premixed ammonia combustion with diesel pilot
ignition. The second concept pursues a pure zero-carbon fuel
strategy by using a mixture of ammonia and hydrogen, ignited
via a hydrogen-scavenged pre-chamber with a spark plug. The
third concept demonstrates a diesel-ignited, high-pressure
direct-injected ammonia concept.
Experimental Validation and Simulation
Measurements conducted on the AVL high-speed single-cyl-
inder test engine SCE175, with a newly designed clean-sheet
power cylinder unit, enabled a fair comparison of engine
performance and emissions across the different fuel setups
and combustion concepts. These results revealed both the
potential and the challenges of ammonia combustion.
All experiments were supported by 1D thermodynamic and 3D
CFD simulations to provide a clear understanding of the phys-
ical and chemical processes. In turn, the experimental results
were used to validate the numerical models.
Comparative Results and Key Findings
All three combustion concepts showed that they contribute to
reducing GHG emissions compared to pure diesel operation.
The diesel-ignited ammonia concept, which requires only
minor modifications to a base engine, demonstrated a reason-
able reduction of CO2-equivalent emissions. However, potential
remains for further optimization by maximizing the ammonia
energy ratio and minimizing the excess air ratio. Reducing
unburned ammonia and nitrous oxide emissions will be key
success factors.
The spark-ignited ammonia concept demonstrated excellent
potential for CO2-equivalent reduction with low unburned
ammonia and nitrous oxide emissions. However, excessively
high NO2 emissions were observed, indicating the need for
further optimization of operational parameters – particularly
the energy ratio of the additional hydrogen.
The diesel-ignited, high-pressure direct-injection dual-fuel con-
cept, with substitution rates of up to 96 %, not only reduced
CO2 emissions but also achieved significantly lower ammonia
emissions than the port injection concept. Engine-out NO2 and
N2O emissions remained within acceptable limits.
Methodology as a Success Factor
Beyond proving that each concept can significantly reduce
GHG emissions, the project also underlined the robustness of
AVL’s long-established development methodology. The combi-
nation of experimental work, advanced measurement technol-
ogies such as optical combustion analysis, and predictive sim-
ulation proved equally effective for ammonia-powered engines
as it was for the development of conventional fuel-powered
engines. The ability to accurately model and simulate complex
physical and chemical processes is of particular importance
in the field of large engines, where prototype production is
associated with immense cost and time – or may not even be
feasible.
“Our expertise in engineering, testing,
and simulation makes maritime CO₂
targets an achievable reality.”
Andrej Poredos,
Team Leader Powertrain Systems Simulation
Shinsuke Murakami,
Expert Gas & Dual-Fuel Large Engines
2025