Flame characteristics depending on recirculating flows in a non-premixed micro combustor with varying baffles

For an efficient micro combustor, the introduction of a bluff body has been a major design factor due to favorable effects for flame holding. To investigate the relation between flame characteristics and recirculation patterns originated from bluff bodies, three kinds of the plate-type baffle and the multi-hole baffle are introduced for a micro combustor. In this regard, various simulations using the Reynolds Stress Model (RSM) and the Eddy Dissipation Concept (EDC) of GRI-Mech 3.0 are performed for such micro combustors. The pseudo flame extinction is proposed to determine the undesirable combustion condition and the global equivalence ratio which is one of the most important variables is changed to explore the reacting flows near the unstable combustion of the baffled micro combustors. From the results, it is ascertained that wall recirculation, center recirculation, and their mixed flows are variously formed depending on the baffle configuration inside the combustor due to the different baffle blockage. These features are largely connected to the extension of flammable range and the spatial development of flame zone which determines the efficient combustion or flame extinction. Under the same operating condition, combustion characteristics of flame length, maximum temperature, and combustion efficiency are comparatively discussed for plate-type baffles and multi-hole baffle. From the probability distributions of the local equivalence ratio, the plate-type baffle shows a unique role according to its location in the micro combustor like inducing the fuel-lean or fuel-rich mixture. And, it is found that the recirculating flows near the fuel stream produce a more effective combustion than those near the air streams. Also, the key features of flame shape and recirculating flows are examined at near the extinction condition and those are carefully compared for the premixed and non-premixed combustors. Finally, the baffle configuration giving the swirling flow structure is discussed and a flame stability diagram is obtained for the baffled micro combustor. So, the overall change of flame pattern and flammable range of the baffled micro combustor is identified depending on the baffle hole size.