The importance of unsteady phenomena of ammonia/methane combustion in an experimental swirl burner: Comparison of steady-state and transient simulation results

Abstract

Ammonia is a potential advanced green fuel. Combustion simulations play a crucial role in facilitating the usage of ammonia in existing combustion systems as a drop-in fuel. Choosing between the unsteady and steady simulation methods should be done carefully depending on the investigated phenomena. In this study, steady-state and transient Computational Fluid Dynamics simulations were performed using detailed chemistry of the Okafor mechanism for a wide range of ammonia/methane blend combustion under lean conditions. The results revealed that the steady-state simulations could provide close values to the unsteady mean results at the outlet in magnitude, while outlet temperature and intermediate species concentration slightly differ with ammonia concentration-dependent extents. The unsteady simulations provided valuable insights into the temporal evolution of the combustion and flow field characteristics, and the Root Mean Square and mean properties were evaluated comprehensively, indicating that the oscillations highly depend on the fuel composition. The model was validated using measurement data from the literature, including Particle Image Velocimetry, OH* chemiluminescence, and pollutant emission. The velocity and OH* distribution matched acceptably, while the CO, NO, and NO2 emissions were underpredicted, which implies necessary reaction model improvements.