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Show IV. l\fAPPING OF COl\fBUSTOR A. APPROACH Determination of the best location for the electrodes is an essential condition for achieving optimum results for flame stability enhancement by a dc electric field. This was achieved by performing an extensive mapping of the flow, combustion and electrical properties in the existing cyclonic combustor. Detailed radial profiles of combustion characteristics in the ignition and flame stabilization region were obtained through measuring ports 1, 3, and 4, shown in Fig. 2, located 51, 178, and 409 mm (2, 7, and 16.1 in.), respectively, from the centerline of the nozzle outlet. Port no. 10 was used to axially survey the gas temperature, composition and electrical properties 2 in. from the main chamber wall, where ignition was expected. The results can be used to explore the progress of the combustion process for typical operating conditions. Port no. 5, located after the exit orifice of the combustor, was used to measure the flue gas parameters. The measurements were carried out with pitot and electrical conductivity probes designe~ and built by AeroChem in conjunction with temperature and species concentration probes supplied by IGT to provide a detailed map of the flame properties. The pitot tube measurements were used to estimate the axial and tangential velocity components. We expected that the tangential component would be quite large, but that the axial component would have to pass through zero at some radial location if there was a recirculating flow pattern. Our hypothesis was that a flame can be supported on a ring-shaped, torus, electrode with a circular flame pattern parallel and close to the electrode surface at locations with zero axial velocity. For stabilization to occur the combustion wave speed must be equal to the component of the flow velocity normal to the flame front at a point greater than the quenching distance from the surface. Increased stabilization due to an electric field requires that the pressure produced by the electric field must be the same order of magnitude as the dynamic pressure component based on the velocity component normal to the electrode. Our reasoning is that only forces and motion normal to the surface are important for stability, i.e., a volume of gas moving tangent to the surface of the electrode ring will be exposed to the same electric body force as one which has no tangential component. The independence of the normal direction balance of forces from the tangential velocity component can be verified from the basic equations of fluid mechanics. The water-cooled pitot tube was inserted through the side ports and acted as a yawmeter6 to determine the direction of the flow. Our primary goal was to determine where the component of the flow velocity parallel to the combustor axis vanishes. 4 |
