Multiple combustion regimes and performance of a counter-flow microcombustor with power extraction

Power generation usually requires removal of thermal energy from the system. In this paper, we evaluate the impact of the heat removal on the dynamics of a premixed flame in the case of a simple, but representative, counter-current microburner. In this configuration, two opposed streams of fresh gases with the same equivalence ratio ϕ are introduced, at the same velocity UF, in the burner through narrow, infinitely long channels. The channels are separated by the common wall from which the heat used for power generation is removed. A flame-sheet chemistry model and a realistic, specifically developed, one-step Arrhenius kinetics are used and compared in order to explore the importance of finite-rate chemistry effects. Finite-rate is found to play a significant role especially near the extinction limit (low velocities) and at high temperatures (high velocities) where distributed reaction can lead to autoignition. The changes in the flame stabilization position and operation limits of the burner are analyzed. Significant variations in combustor operation were found when energy is extracted from the system. Power generation efficiency is also studied, to conclude that an optimum level of energy extraction exists for each equivalence ratio and also that an optimum equivalence ratio exists.