Dynamics of lean hydrogen/air flame regimes in micro scale combustion

In the present work، the dynamics of lean (ϕ =0. 5) premixed hydrogen/air flames in a micro channel with prescribed wall temperature is studied. The investigation is carried out using the low Mach formulation of Navier-Stokes equations with detailed chemistry and molecular transport for different inflow velocity. Ignition-extinction repetitive، steady symmetry flame and asymmetric flame are observed as the inlet velocity increased. Close to lower flammability limit، ignition-extinction repetitive flame was observed duo to imbalance between chemical time scale and residence time scale. In this regime، the reacting flow is affected by high wall temperature and the extinction occurred by the flow temperature. Upon increasing the inlet velocity، symmetric flame can be observed due to the balance between time scales. It is observed that further increasing the inlet velocity would cause symmetry flame to become unstable because of presence of some perturbations in flow field. Based on the obtained results، it is suggested that the perturbations are created by preferential diffusion of species.