Numerical Study On Flame Stability Of H₂/Air Combustion In Micro-combustors Filled With Porous Medium

With the rapid development of MEMS devices,micro-combustion represents a potential means for generating portable power.Through heat recirculation via the solid matrix,filtration combustion could enhance the flame stability of micro-combustion,due to its ability of promoting heat recirculation.Currently,only a few studies dealt with filtration combustion in the millimeter-scale combustors,and insufficient attention has been given to the issue of flame stability.Therefore,based on a planar micro-combustor partially filled with porous medium,a two-dimensional mathematical model was established to carry out numerical simulation using the CFD code Fluent.The present study examines the effects of wall thermal conductivity k_w,porous medium thermal conductivity k_s,and porosity?on the stability limits of H₂/air premixed combustion.Two critical conditions(?₁ for flame breaking through the lower boundary of porous medium and propagating upstream,?₂ for flame leaving the porous medium and stabilized at the exit)are used to define the stability limits.Numerical results show that wall thermal conductivity k_w is an important factor which has significant effects on the stability limits.With the increase of k_w,the stability limits become broader with?₁ getting higher and?₂ first lower then almost unchanged.The porosity?is also an important factor,with the increase of?,the stability limits become narrower,with?₁ getting lower and?₂ almost unchanged.The stability limits appear zero when?is too small because flames can not be stabilized within the porous medium.Under the conditions studied,the effects of porous medium thermal conductivity k_s on the stability limits is insignificant.Effects of porous medium parameters on the difference between the one-temperature and two-temperature models were also investigated.It is shown that the difference between the two models diminishes with the increase of the porosity?and decrease of the thermal conductivity k_s.Therefore,the one-temperature model is more applicable at higher porosity?and lower thermal conductivity k_s.The results of the present study could provide some guidance to the design of porous micro-combustors.