Improving Micro Combustor Stability With External Heating

摘要

Heat loss is the key factor to micro combustor stability. In this experiment, a quartz-glass micro combustor with inner diameter of 2 mm is tested with wind sweeping over its surface. The wind temperature is adjusted from 4 to 728 °C to control the combustor heat loss. According to the experimental results, the combustor stability increases with the wind temperature. Take 0.2 L/min as an example, the equivalence ratio at stability limit is 0.652-3.96 with 4 °C wind, and extends to 0.540-12.0 with 107 °C wind. Computational fluid dynamic simulation reveals that hotter wind intensifies the reaction, thus reaction temperature and OH concentration increase accordingly. Moreover, hotter wind enhances the heat recirculation, which causes shift upstream of flame. Increasing flow rates also inhibits extinction. But the quenching mode transforms from extinction to blowout, while the flow rate exceeds about 0.28 L/min. In the rich cases, hot wind with higher temperature aggravates blowout, which is opposite to the lean cases. According to the experimental phenomenon, the reaction region locates close to the inlet in the rich cases, where the flow velocity increases dramatically. Therefore, the imbalance between flow velocity and burning velocity causes blowout.