Numerical Demonstration of NO Emissions Reduction by Steam Injection in the Aero Engine Combustor IAE V2500

Abstract Reducing nitrogen oxides (NOx) emissions is a key objective in the development of novel aero engines. The climate effect of NOx is not negligible at high altitudes, despite the regulation of NOx within the LTO (Landing and Takeoff) cycle. Various approaches to reducing NOx formation in the combustion chamber are currently under active research. In this study, the Water-Enhanced Turbofan (WET) concept developed by MTU Aero Engines AG is examined in detail, where steam is injected into the combustion chamber. Steam injection offers great potential for mitigating local temperature peaks and thereby reducing NOx formation. To investigate these effects under real aero engine conditions, the IAE V2500 combustor is numerically analyzed using Large Eddy Simulations (LES) and the Flamelet-Generated Manifold (FGM) combustion model. The chemical time scale of nitric oxide (NO) is much longer than that of the major combustion species. Therefore, an additional NO transport equation is solved, with the NO consumption term scaled according to the transported NO mass fraction in the simulation, improving prediction accuracy. Three different levels of steam injection are analyzed, with steam introduced into the diffuser before entering the combustor. The outlet temperature and thermal power are kept constant, leading to an increase in the global equivalence ratio for cases with increased steam injection. The potential for NO reduction is demonstrated under cruise operating conditions. A higher steam content in the oxidizer effectively reduces temperature peaks and gradients, particularly in the rich combustion zone, leading to a notable decrease in NO emissions. The dominant NO formation occurs in the dilution zone for all cases, but absolute NO values are considerably lower compared to the reference dry case. Accordingly, the potential to mitigate the climate impact is demonstrated.