Combustion, thermodynamic and emission performance investigation of a novel ammonia-hydrogen dual-fuel elliptical rotary engine with dual-spark ignition: Effects of equivalence ratio and spark ignition timing

The utilization of zero-carbon ammonia fuel in aviation rotary engine is considered as a potential solution for realizing carbon-neutral in unmanned aerial vehicle sector. However, ammonia combustion faces the challenges of low flame speed and high ignition temperature. To solve the poor combustion issue of ammonia, this paper proposes a novel ammonia-hydrogen dual-fuel elliptical rotary engine with dual-spark igniter. This study investigates and compares the combustion, thermodynamic, and emission performance of elliptical rotary engine equipped with dual/single-spark igniter when fueled by an ammonia-hydrogen dual-fuel energy fraction of 60 %/40 % via the computational fluid dynamics modelling. A hybrid fuel injection strategy of intake-port premixed hydrogen and cylinder direct-injected ammonia is proposed for promoting ammonia combustion. The impacts of igniter position, equivalence ratio and spark ignition timing on comprehensive performance are examined. The results demonstrate that the Upstream-Middle dual-spark igniter configuration in the combustion chamber represents the optimal design. This configuration effectively enhances flame propagation toward the upper section of the combustion chamber and improves the power output by 1.93 %. Combustion efficiency and thermal efficiency of elliptical rotary engine equipped with optimal dual-spark igniter configuration increase firstly and then decrease with increasing equivalence ratio and ignition timing. The highest thermal efficiency of 35.60 % is achieved under the optimal combination of equivalence ratio of 0.8 and ignition timing of 20°CA BTDC. A 2.03 % improvement in thermal efficiency, a remarkable 74.04 % decrease in unburned NH₃ and a NO_x emission of 1.05 g/kW•h are obtained under the optimal dual-spark igniter case comparing with basic single-spark igniter case.