Methods For Stabilizing Premixing Flame In Micro Scale

The portable electronical device in the modern times requires the compatible power source with longer operation period. The micro power system has higher power density, thus prolongs the operation period effectively. Therefore, minimizing the large power plant system into portable power source, through MEMS technology, is feasible. However, the micro combustor, which is the core of micro power system, has scale of micro or micron meter. It is difficult to overcome quenching or blowout and stabilize flame in such small scale.The methods for stabilizing flame in macro scale is mainly enhancing the reaction intensity, through increasing the temperature of fuel mixture, or improving the circumfluence section. The similar principle is applied in the micro scale combustor. The micro flame stability is improved, through increasing the reaction temperature or decreasing the critical quenching temperature with methods of heating, catalyst, heat recirculation, etc. Experiment is conducted in the quartz-glass combustor with straight-tube shape, having inner diameter of 2 mm. The combustor is operated with H2/air premixture.The effects of different stabilizing methods are tested under various operation conditions. The stability limits, surface temperature distribution, and heat loss of the micro combustor during operation are measured under different flow rates and equivalence ratio of fuel gases. Numerical simulation is also applied to analyze the details of internal combustion processes.Inhibiting quenching requires sufficient heat for ignition energy. According to the experimental results,both heating the combustor and preheating premixture stabilize the flame. Take preheating as an example:at the total flow rate of 0.12 L/min, the equivalence ratio extends from 0.339-3.639 to 0.317-4.304 after the premixture temperature increases from environment temperature to 250℃. Catalyst stabilizes the combustion through decreases the quenching temperature. According to the experimental results of catalytic combustor, at 0.12 L/min, the equivalence ratio in the rich case increases from 11.90 to 18.03 after applying catalyst.In the catalytic combustor, the reaction intensity is weakened, because the heterogeneous reaction inhibits the homogeneous one. As a result, the combustor wall has relatively even and low temperature distribution. For the purpose of investigating the interaction of two reaction modes, performances of catalytic combustors with different wall materials are compared. Moreover, numerical simulation is applied to analyze the details of combustion processes. According to the simulation results, wall material affects the reaction mode. The combustor wall with lower thermal conductive coefficient converts the reaction mode to homogeneous reaction, thus enhances the reaction intensity. For example, at the total flow rate of 0.12 L/min, the order of magnitude of OH concentration is -3 in the quartz-glass combustor, indicating homogeneous reaction domains. But in the copper combustor, the order of magnitude decreases to -10, thus heterogeneous reaction domains. Accordingly, the reaction temperature decreases from 1474 K to 1000 K. Although the catalytic combustor inhibits quenching effectively, the weak reaction intensity may induces blowout.