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Show Firing Rate: Excess Air: Nozzle Pressure: 0.3 62 2.5 0.5 75 5.0 1.0 89 7.5 X 106 Btulh % 15 in. H-,O Gas temperature and composition (C02, CO, THC and NOll) profiles were measured at all five ports (nos. 1, 3, 4, 5 and 10, Fig. 2). Gas velocity and electrical properties profiles were measured at the four ports (nos. 1, 3, 4 and 10) located inside the combustion chamber. 2. Measurements at Base Operating Conditions Figures 3 and 4 show, respectively, radial and axial profiles of electric current measured by the electrostatic probe at the base operating condition. Peak electric current indicates that the highest concentration of electrons and ions in the region appear about 38 mm (1.5 in.) away from the combustor wall and 25 mm (1 in.) downstream of the centerline of the nozzle. Gas temperature profiles shown in Figs. 5 and 6, respectively, for radial and axial surveys, also indicate that the combustion reaction in this region is dramatically intensified due to ignition and flame spread. This conclusion is also verified by axial surveys of CO and 02 shown, respectively, in Figs. 7 and 8. CO emissions drop sharply from over 1000 ppm to about 100 ppm, while 02 decreases from 16% to about 9% because the combustion rate is dramatically increased. Flow velocity profiles presented in Fig. 9 show that the axial component of gas velocity has a negative region indicating that the flow is reversed, i.e., traveling upstream, but the flow travels downstream both near the center and near the wall. As a result, there are two velocity transition zones in going from the combustor centerline to its wall, in which the axial velocity passes through zero and remains small. Near the centerline the flow direction is downstream and switches to the upstream direction with increasing radius. The second transition zone leading to downstream flow appears about 51 mm (2 in.) from the wall and, therefore, is in the region of ignition and flame spread as determined from the previous temperature, electric current, and gas composition measurements. The increased mixing and turbulence in this region due to the velocity gradient shear stress facilitates ignition and flame spread. The point in the second transition zone where the axial velocity is zero would be an ideal location for a stabilizing electrode since the ion concentration is relatively high there. Tangential components of the gas velocity are shown in Fig. 10 and pass through zero near the center! ine as expected. The occurrence of the two velocity transition zones is surprising and was not expected based on model scale and full scale cold flow measurements which indicate only one transition. This is thus an example where combustion plays a major role in determining the overall fluid mechanics. 6 |