Investigation of NOx and Ammonia Slip in an Ammonia- and Hydrogen-Powered Aviation Gas Turbine Using Chemical Reactor Network Modeling

Abstract

Abstract. Ammonia is a promising green fuel with several favorable attributes that could make it a replacement for current nonrenewable aviation fuels. The feasibility of using an NH3–H2 blend as the fuel in terms of the NOx emitted has been explored in this work, consisting of residence times of 10 ms and 5 ms, which represent the residence times in modern aviation gas-turbine combustors. Chemical reactor network (CRN) models have been simulated using ansys chemkin-pro software, implementing air-staging techniques like rich-quench-lean (RQL) to efficiently combust the fuel and bring down the NOx while also minimizing ammonia slip. Various CRN configurations have been investigated for operating conditions reflecting take-off, while varying crucial parameters such as equivalence ratio, NH3–H2 fuel fraction, inlet temperature, and pressure. This exploration aims to understand the trends in NOx emissions and ammonia slip while ensuring that the reactor exit temperature remains within the cycle requirements to prevent any material damage to the components postcombustion. The effect of varying the residence times in the individual CRN components on the NOx and ammonia slip was also investigated and discussed. The minimal NOx possible while varying the parameters was about 20 ppm for the 10-ms overall residence time simulations, and about 30 ppm for the 5-ms overall residence time simulations. The trends obtained from the parametric variations, along with the understanding of the different CRN models explored, can help in optimizing the NOx minimization further and assist in obtaining the optimal conditions for the NH3–H2 blend used, not just for take-off, but additionally for other flight operating conditions as well. This study applies a novel, detailed CRN-based RQL modeling approach for ammonia–hydrogen blends under realistic gas-turbine conditions, identifying air-staging configurations and trends that lower both NOx and NH3 slip. Understanding the parametric trends for minimizing NOx emissions and controlling the NH3 slip from this study can help establish an understanding of using ammonia as aviation combustor fuel, serving as a basis for further computational and experimental research.