Maps of flame dynamics for premixed lean hydrogen-air combustion in a heated microchannel

In the present work, flame dynamics are extracted for combustion of premixed lean hydrogen-air in a heated microchannel using numerical simulation. In this simulation, Navier-Stokes equations along with energy and species conservation equations are considered by formulation of low Mach number and with consideration of detail chemical kinetics. Regarding different conditions, three dynamics are observed in the microchannel which are periodic repetitive ignition-extinction, steady symmetric flame, and steady asymmetric flame. The effects of different parameters such as inlet velocity, equivalence ratio, and channel width are investigated on the flame dynamics. The periodic repetitive ignition-extinction dynamics is observed at low velocities close to the lower flammability limit. Upon increasing the inlet velocity and creating a balance between the reaction time and fluid residence time in the channel, a steady symmetric flame is shown in the channel. In this situation, the maximum temperature and mass fraction of species are located on the symmetry line of the channel. Then by increasing the inlet velocity in a specific channel, the flame moves toward downstream at the symmetry line of the channel and it will be stretch near the walls. Hence, the surface of the flame front is susceptible to instability and becomes unstable due to the flow perturbations. The maps of flame dynamics in the small scales are presented for the hydrogen-air mixture based on three parameters, inlet velocity, and equivalence ratio and channel width in the microchannel. The obtained results show that by increasing the equivalence ratio, channel width, and inlet velocity, the steady symmetric dynamics is eliminated, replaced by a steady asymmetric dynamics.