Multi-Objective Optimization and Chemical Reactor Network Modeling to Estimate the Minimum Nitrogen Oxide and Ammonia Slip in an Aviation Combustor

Abstract

Abstract. Ammonia (NH3) has been deemed an attractive option as a carbon-free fuel for power generation in gas turbines, addressing greenhouse gas emissions and contributing to climate change mitigation. Recently, ammonia and its blends with hydrogen have been investigated as a prospective aviation fuel. However, high nitrogen oxide (NOx) emissions and unburnt ammonia slip (NH3) during ammonia combustion make it challenging. This study explores chemical reactor network (CRN) modeling and multi-objective optimization of nitric oxide (NO) emissions and NH3 slip for similar conditions of an aviation gas turbine. The parametric studies considered the equivalence ratio (0.9–1.4), ammonia fuel fraction (0.5–1.0), combustor inlet temperature (644–848 K), and inlet pressure (13–44 bar) for take-off and high-altitude flight conditions. This simulation model was developed using ansys chemkin-pro, which uses a rich-burn stage modeled as a network of ideal reactors. The results of CRN simulations indicate that a lean-to-rich equivalence ratio with 100% NH3/air combustion reduces NO emissions and raises NH3 slip trends in the primary stage. Adding hydrogen to the fuel mixture resulted in a slightly increased NH3 slip and decreased NO emissions at both lower and higher inlet pressures and temperatures. Moreover, the results of optimization studies revealed minimum NOx emissions of 13, 38, and 100 ppm at take-off, cruise, and maximum altitude, with 30 ms, 10 ms, and 5 ms, respectively. NH3 slip was observed at less than 1 ppm in all cases of multi-objective optimizations.