Transient 3D Simulations of Hydrogen-Air Premixed Combustion in a Micro-Combustor: Role of Reaction Models and Diameter of Chamber

Micro-combustors are critical for the design of micro-power systems using hydrogen or hydrocarbons as a fuel source. With the modern trend of shifting towards net-zero carbon fuels like hydrogen, the current work provides the basis for future research in this direction by considering the use of various reaction models in simulating the combustion of hydrogen-air mixture in a micro-combustor. As a usual practice, the reaction model adopted for hydrogen-air premixed combustion is the species transport model which uses a source of energy during initialization (patching). Another approach is to use a species transport model with turbulence, which is not consistent with the Reynolds numbers (Re = 21 to 167) observed for the micro combustor (falling in the laminar region). There is also a third method by which the combustion in the microcombustor can be modelled, i.e. the premixed turbulent combustion model. In this work, we will compare the use of these reaction models by simulating premixed hydrogen-air microcombustion in a two-dimensional (2D) axisymmetric framework. Using benchmark results, we will comment on the best reaction model strategy for the problem considered. Furthermore, we perform three-dimensional (3D) unsteady simulations of premixed hydrogen- air combustion in a micro-combustor, showing that the axial distribution of temperature is unaffected by 2D axisymmetric or 3D transient considerations. We also explore the role of the diameter of the chamber in the combustion process by tracking the flame shape and temperature distribution.