Experimental and Numerical Study of a Premixed Two Stage Ammonia Combustor at High Pressure

Ammonia combustion at high pressure, in a microturbine combustor configuration, represents a promising avenue for utilization of ammonia as an alternative fuel source. Ammonia is increasingly regarded as a carbon-neutral fuel with potential applications in power generation. Nevertheless, burning ammonia can produce high NOx emissions, which decreases its potential as a clean energy source. Numerical studies show that, by increasing the pressure in the combustor, NOx emission levels can be reduced compared to levels at atmospheric pressure. However, there are few experimental studies that have studied the role of pressure and those that exist show discrepancies regarding the equivalence ratio at which minimum NOx emission levels can be attained. The present study examines the combustion of ammonia in a high-pressure combustion test rig and thus adds to the body of knowledge regarding how pressure and equivalence ratio impact NOx emissions. The combustor configuration utilizes a first stage combustion chamber into which ammonia fuel and air are injected into using a proprietary injection arrangement. This design demonstrates reduced NOx emissions from ammonia combustion, especially at elevated pressures. The research conducted shows that NOx levels below 50 ppm can be achieved under realistic engine conditions. Furthermore, the species concentrations measured at the end of the combustion zone agree with the values predicted by numerical simulations. It is also observed that simulation results are affected by choice of reaction mechanism and the comparison with experimental results affirm further work is needed on the kinetics of ammonia combustion.