Modelling Ammonia-Hydrogen-Air Combustion and Emission Characteristics of a Generic Swirl Burner

Abstract

Abstract Ammonia (NH3) is a promising carbon-free fuel for its potential to reduce greenhouse gas emissions, even if its implementation entails unresolved challenges. Current studies suggest that using typical lean premixed technologies with ammonia may lead to high NOx emissions and poor flame stability. Strategies to contain NOx could require significant combustion architectural changes. One solution is using NH3/H2 blends to improve flame stability, but it may impact emission performance. However, there is still a lack of knowledge and experimental data on the use of ammonia and hydrogen-ammonia blends. The combustion process of both pure NH3 and a NH3/H2 fuel blends is analyzed using CHEMKIN-PRO and CANTERA: detailed reaction mechanisms have been compared in terms of laminar flame speed and ignition-delay-time, aiming at identifying the most suitable for the evaluation of NOx emissions. The generic swirl burner being used in Cardiff University's Gas Turbine Research Centre has been considered as validation test case. Evaluations have been carried out by means of axisymmetric RANS simulations leading to a significant reduction of the computational time. Different pressures and mass flow rates are evaluated to understand the correlation in the NOx emission formation. A direct comparison between experimental and numerical results is carried out. Results show that NOx emissions decrease significantly with increase in pressure, also indicating guidelines for using a simplified RANS analysis, which leads to improved computational efficiency, allowing wide sensitivity and optimization analyses to support the design development of an industrial combustion system.