Multi-Objective Optimization and Chemical Reactor Network Modelling to Estimate the Minimum NOx and Ammonia Slip in an Aviation Combustor

Abstract Ammonia has been deemed an attractive option as a carbon-free fuel for power generation gas turbines to address greenhouse gas emissions and to deal with climate change. Recently, ammonia and its blends with hydrogen have been investigated as a prospective aviation fuel. However, high NOx emissions and unburnt ammonia slip during ammonia combustion make it challenging. This study explores chemical reactor networking (CRN) modeling and multi-objective optimization of NO emissions and NH3 slip for similar conditions of an aviation gas turbine. The parametric studies were considered for 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) at take-off, and high-altitude flight conditions. This simulation model was developed using Ansys Chemkin-Pro software, which consists of a rich burn stage as a network of ideal reactors. The results of CRN simulation 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 into the fuel mixture showed a slightly increased NH3 slip and decreased NO emissions at lower and higher inlet pressure and temperature. Moreover, results of optimization studies investigated minimum NOx emissions as low as 13, 38, and 100 ppm at take-off, cruise, and maximum altitude with 30 ms, 10 ms, and 5 ms, respectively, where NH3 slip was observed at less than 1 ppm in all cases of multi-objective optimizations.