Interaction of engine control parameters and exhaust gas aftertreatment system in ammonia-fueled combustion engines for low-emission power generation

Ammonia is a promising carbon-free fuel for maritime and non-road mobile applications, but its unfavorable combustion characteristics and the formation of NH₃, NOₓ, and N₂O require suitable combustion and aftertreatment strategies. This study investigates two ammonia-fueled internal combustion engine concepts on dedicated single-cylinder test benches. A lean-burn NH₃–diesel compression-ignition (CI) engine equipped with selective catalytic reduction and ammonia slip catalysts (SCR+ASC), and a spark-ignited (SI) engine operated with 100% ammonia and a three-way catalyst (TWC).
For the NH₃–diesel CI concept, the effects of air–fuel equivalence ratio, ammonia energy share, and combustion phasing on engine-out emissions were analyzed. An air–fuel equivalence ratio of 1.2 < λ < 1.5 provided favorable engine-out Ammonia-NOₓ ratios (ANR), while ammonia energy shares of up to 95% were achievable at high engine load. The combination of SCR and ASC enabled substantial NOₓ and NH₃ reduction over a wide load range. Additional ammonia dosing was required at selected operating points to achieve high DeNOₓ efficiency, while complete N₂O conversion was observed at sufficiently high exhaust temperatures.
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The SI concept demonstrated stable 100% ammonia operation across the investigated engine map. TWC performance was strongly governed by the air-fuel equivalence ratio with a narrow optimum slightly on the rich side of stoichiometry.
At λ≈0.97, a favorable compromise between NH₃, NOₓ, and N₂O emissions was achieved. Overall, the results demonstrate the technical feasibility of both combustion concepts and highlight the importance of coordinated engine and aftertreatment control for low-emission ammonia operation.