Session: 03-04 H2 and NH3 in Aeroengines

Paper Number: 128997

128997 - Multi-Objective Optimization and Chemical Reactor Network Modelling to Estimate the Minimum NOx and Ammonia Slip in an Aviation Combustor 

Abstract

Ammonia has been attracted to serving as a carbon-free fuel and energy carrier in power generation gas turbines to address greenhouse gas emissions and to deal with climate change issues. Recently, ammonia and its blends with hydrogen has been investigated as a prospective aviation fuel.  However, high NOx emissions and unburnt ammonia slip during ammonia combustion make it challenging. Therefore, this study explores the chemical reaction networking (CRN) modeling and simulation of ammonia combustion processes in an aviation gas turbine combustor to predict NOx and NH₃ slip emissions. This simulation model was developed in ChemkinPro software, which consists of a rich-burn stage as a network of combustion reactors, for instance, a perfectly stirred reactor followed by a plug flow reactor. The CRN simulations were performed for similar conditions as aviation combustors. At the same time, parametric studies were considered for the equivalence ratio (0.9 – 1.4), ammonia fuel fraction (0.5 – 1.0), inlet temperature (644 K – 848 K), and inlet pressure (13 bar – 44 bar) at take-off and high-altitude flight conditions. Moreover, multi-objective optimization was performed by developing the rich quench lean (RQL) model in an Ansys using the OptoSlang tool to predict the minimum NOx and NH₃ slip emissions at three flight conditions for 30 ms, 10, and 5 ms residence time. The parameters considered for the optimization setup are selection probabilities, maximum sample count, population size, and the number of generations to 100, 20, and 5, respectively. The fitness evaluation incorporated Pareto dominance, crossover probability, and mutation rate, defined as 0.5 and 0.12. The results of CRN simulation indicate that a lean-to-rich equivalence ratio of 0.9 – 1.4 with 100%/NH₃/air combustion reduces NO emissions and raises NH₃ slip trends in the primary stage. Adding the hydrogen fraction into the fuel mixture of NH₃/air showed a slightly increased NH₃ slip and decreasing NO emissions trends in the primary stage at lower and higher inlet pressure and temperature, respectively. Furthermore, reactor inlet temperature varied from 644 K – 848 K, and inlet pressure changed from 13 bar to 44 bar while keeping the 90%NH₃10%H₂/air mixture showed a trade-off trend in NH₃ slip and NO emissions.  The results from the multi-objective optimization studies showed that the minimum NOx emissions are 13, 19, and 32 ppm at take-off, cruise, and maximum altitude, respectively, while NH₃ slip is observed at less than 1 ppm from all optimizations simulate conditions. The results of NH₃ slip and NO emissions obtained in this work can provide important information on the future direction for the design of CO₂-free, low NOx, and high efficiency ammonia-powered aviation gas turbines. 

Presenting Author: Shahzad Bobi University of Central Florida

Presenting Author Biography: I am a first-year PhD student at the University of Central Florida studying mechanical engineering. My areas of expertise are combustion and alternative fuels. I am currently working on CRN modelling and simulation in order to determine the effect of NH3/H2 combustion on emissions.

Authors:

Shahzad Bobi University of Central Florida
Priyankar Garai University of Central Florida
Ramees Rahman University of Central Florida
David Zamora University of Central Florida
Marzuqa Ahmed University of Central Florida
Subith Vasu University of Central Florida