| OCR Text |
Show From the previous measurements, the two major characteristics believed to affect the performance are the fuel distribution and amount of recirculation. The fuel distribution sets up the burning stoichiometry, while the recirculation zone establishes internal flue gas recirculation and dictates the width of the reaction zone. The recirculation is controlled by the swirl intensity, excess air, and the amount of fuel injection disruption; the fuel distribution, however, has several more controlling effects, including the fuel jet velocity, number of jets, cross-flow velocity, swirl intensity, and injection axial location. These different variables were used as factors in the statistical design and are presented in Table 1. The cross-flow and fuel jet velocities were calculated from baseline values U 0 and Vj, respectively. The cross-flow velocity was decreased by increasing the throat diameter. Since the cross-flow velocity was already incorporated by the throat velocity parameter, the excess air was fixed at 1 0 % for all of the tests. Due to the varying stability for each geometric variation, the swirl amounts are different for each condition, but similar values were used when possible. The premixing distance variable was selected due to previous research which indicated the benefits of a premixing length (Maughan et a/., 1992; Hase and Ohgi, 1989; and Fric, 1992). The responses measured were exhaust emissions, specifically N O x and C O . Table 1: Factors Used in Multivariate Experiments Factor Throat Velocity (U0 = 53 ft/s) Fuel Jet Velocity (Vj = 378 ft/s) ' Number of Fuel Jets Swirl Intensity Premixing Distance Low Level (value) 0.50-Uo (30.2 ft/s) 0.75-Vj (277 ft/s) 4 low z (-3 inches) High Level (value) 1-U0 1.25-Vj (471 ft/s) 8 high 0 The test matrix, which identifies the combination of factors tested for these experiments, is shown in Table 2. The results from these tests are also shown in Table 2 but will be discussed in graphical format in the following section. |
