Numerical Study of Three Gaseous Fuels on the Reactor Length and Pollutant Formation Under Lean Gas Turbine Conditions

The present paper numerically studies the impact of three gaseous fuels on the reaction characteristics and pollutant formation in a lean combustion system. The models include an equilibrium calculation with Ansys-Chemkin-Pro, as well as a 3D half-width CFD model using Large Eddy Simulation (LES) and Adaptive Mesh Refinement (AMR) models. The outcomes are targeted to benefit the transition to carbon-free operation of aviation turbines. Three fuels, methane (CH₄), hydrogen (H₂), and ammonia (NH₃) as well as blends thereof were compared at constant equivalence ratios to obtain a firing temperature level of T = 1800°C. The kinetic mechanism in use was suggested and validated by Okafor et al., including 42 species to describe CH₄/H₂/NH₃-air combustion and NO_x chemistry. The formation of nitrogen oxide pollutants (NO, NO₂ and N₂O) were analyzed to determine the sensitivity to the three fuels and their blends. Secondly, a fuel injector scaling study was performed, and a significantly larger jet diameter was selected to compensate for the increased stoichiometric mixture fraction and reduced blend density relative to CH₄-fueled architecture. Lastly, the three-dimensional AMR-LES model provided validation of the injector re-sizing, as well as further insight into the expected fuel-air distribution by convective mixing. While the substitution of methane-fueled gas turbines with carbon-free alternatives is generally feasible, blending of H₂ and NH₃ fuels could be a promising strategy to utilize existing turbine combustors, while retaining reaction timescales close to those of CH₄-powered systems.