Ammonia/syngas combustion in a premixed micro-gas turbine: LES-FGM investigation on flame dynamics, stability, and emission control

This study investigates the combustion of ammonia/syngas fuel mixtures in a premixed micro gas turbine as part of the transition to renewable fuels. Combustion modeling is performed using large eddy simulation (LES) coupled with the flamelet-generated manifold (FGM) method. The combustion regimes are categorized as compact flame, flashback, distributed flame, and non-combustion. Results show that flashback occurs at lower ammonia mole fractions, while increasing ammonia content eliminates flashback risks but shifts the combustion regime toward a distributed flame. Higher ammonia content results in a more dispersed flame structure, enhancing the heat release rate and combustion efficiency. The increased hydrogen content reduces combustion efficiency because it preferentially reacts with ammonia and carbon monoxide, forming intermediates and radicals, which do not directly contribute to heat release but rather consume energy in secondary reactions. Higher ammonia content reduces NO formation under rich conditions, whereas increased carbon monoxide slows NO reduction by interfering with NO removal processes. A significant challenge remains the high CO emissions under rich conditions, which can be mitigated using a rich-lean strategy with secondary air addition. While this strategy reduces NO significantly, a selective catalytic reduction (SCR) device is still required to filter NO at the outlet.