Combustion characteristics and flame bifurcation in repetitive extinction-ignition dynamics for premixed hydrogen-air combustion in a heated micro channel

The characteristics of repetitive extinction-ignition dynamics of flames are investigated numerically for hydrogen-air mixtures in a heated micro channel. A Low Mach number formulation, detailed chemical kinetics and different molecular diffusivities for each species are utilized in all simulations. In this regard, the effects of inlet velocity, equivalence ratio, and channel width on amplitude and frequency of the repetitive extinction-ignition phenomenon is studied. The results show that the frequency of repetitive extinction-ignition dynamics increases with increasing the inlet velocity, while its amplitude has an ascending-descending behavior. With increasing equivalence ratio from 0.5 to 1 and the channel width from 0.4 to 1, the amplitude of repetitive extinction-ignition dynamics increases and the frequency decreases. Regarding flame bifurcation, the details of the flow field show that the creation of recirculation zones at the wall vicinity causes the flame bifurcation. Investigating the role of chemical kinetics, it is found that the mass fractions of O2 and H2O increase inside the zone between the two flame fronts. As a result, the related reactions are activated and produce heavier species such as H2O, HO2 and H2O2. The heavier species absorb more heat, released from the combustion process, causing temperature reduction and lastly flame bifurcation.