Papac M J, Dunn-Rankin D
Department of Mechanical and Aerospace Engineering, University of California at Irvine, Irvine, California 92697-3975, USA.
Ann N Y Acad Sci. 2006 Sep;1077:585-601. doi: 10.1196/annals.1362.038.
Electric fields applied to combustion plasmas can be used to manipulate the thermofluid flow field to reduce buoyant forces and, hence, convection in locations near and within the flame. The resulting flow field is similar to that which is obtained in microgravity. Previous work has shown that buoyancy is modified in a non-premixed methane-air capillary flame when it burns in a capillary-to-plane configuration and an electric field is applied, and that regions of neutral or microbuoyancy exist, as indicated by the examined temperature and oxidizer profiles. The aim of this article is to examine in more detail this microbuoyancy condition and the coupling between the ion wind and resulting thermofluid flow field. To this end, the voltage-current characteristics (VCC) of CH4, C2H2, C2H4, C2H6, and C3H8 are measured and compared. Soot generated in the C2H(X) and propane flames lead to a hysteresis in the VCC curve whereby increased sooting leads to lower ion currents at constant flow rates and applied potentials. Buoyancy regimes for these flames in this configuration are determined. Methane can achieve the highest flow rate without sooting at the microbuoyant condition, and does not exhibit hysteresis in the VCC for the flow rates examined here. Furthermore, in this geometry, the microbuoyant condition for methane is found to coincide with ion current saturation when the capillary-to-plane distance is varied. These results allow for several simplifications to be made when modeling the flame at these conditions: the imposition of a spherical flame boundary with known ion current, and negligible recombination in the domain.
施加于燃烧等离子体的电场可用于操控热流体流场，以降低浮力，从而减少火焰附近及火焰内部区域的对流。由此产生的流场类似于在微重力环境中获得的流场。先前的研究表明，当非预混甲烷 - 空气毛细管火焰以毛细管到平面的构型燃烧并施加电场时，浮力会发生改变，并且如所检测的温度和氧化剂分布所示，存在中性或微浮力区域。本文的目的是更详细地研究这种微浮力条件以及离子风与由此产生的热流体流场之间的耦合。为此，测量并比较了CH4、C2H2、C2H4、C2H6和C3H8的电压 - 电流特性（VCC）。在C2H(X)和丙烷火焰中产生的烟灰导致VCC曲线出现滞后现象，即在恒定流速和施加电势下，烟灰增多会导致离子电流降低。确定了这些火焰在此构型下的浮力状态。在微浮力条件下，甲烷能够在不产生烟灰的情况下达到最高流速，并且在所研究的流速范围内VCC中未表现出滞后现象。此外，在此几何构型中，当改变毛细管到平面的距离时，发现甲烷的微浮力条件与离子电流饱和相吻合。这些结果使得在对这些条件下的火焰进行建模时可以进行一些简化：施加具有已知离子电流的球形火焰边界，并且在该区域内可忽略复合作用。
