In a micro combustor, various vortices can enhance the wall heat transfer rate and get the best combustion. For an efficient combustion, the swirler of micro fan type is introduced for a micro combustor. In general, the swirling flows can change significantly the wall heat fluxes and this feature is sensitively varied by the fan configuration. So, to examine the geometric effect of fan swirler on the combustion characteristics, reacting flows depending on six blade angles are numerically investigated. The highest efficiency and heat loss related to vortical flows are observed for the specific blade angles. Keywords Micro combustor • Blade angle • Fan swirler • Heat loss • Combustion efficiency • Swirl flow List of symbols A i Surface area of combustion chamber, m 2 D Combustor diameter, m D f Fuel hole diameter, m D o Outer wall diameter, m q i Wall heat flux, W/m 2 m inlet CH 4 CH4 mass flow rate of inlet, kg/s LHV Lower heating value of methane, kJ/kg T Temperature U Streamwise velocity, m/s U c Streamwise velocity at center axis, m/s Z Mixture fraction Z st Stoichiometric mixture fraction ν t Kinematic viscosity ϕ G Global equivalence ratio θ Blade angle, degree