A high and uniform wall temperature on micro combustors is desirable for micro-thermophotovoltaic system application. In this work, an improved micro-cylindrical combustor with rectangular rib is developed. Numerical investigations on the combustors with and without rectangular rib are conducted under various H-2 mass flow rates and H-2/air equivalence ratios. Moreover, the effects of dimensionless rib positions and heights on the outer wall temperature of micro combustors are also widely investigated. Results suggest that the improved combustor has a higher and more uniform outer wall temperature distribution under the same inlet condition compared with that of the micro combustor without rectangular rib. It is concluded that the inserted rectangular rib makes a recirculation region, enhancing the heat transfer between the combustor inner wall and burned gas. In addition, among all the investigated geometrical models, the geometrical model with the dimensionless rib position of 5/9 and dimensionless rib height of 0.4 has the highest and most uniform outer wall temperature where the H-2 mass flow rate and H-2/air equivalence ratio are fixed at 5.25 x 10(-7) kg/s and 1.0, respectively. More importantly, the optimum dimensionless rib position is related with the inlet velocity of H-2/air mixture and it is increased with the inlet velocity of H-2/air mixture. (C) 2016 Elsevier Ltd. All rights reserved.