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Show APPLICATION TO A CONVENTIONAL DIFFUSION FLAME BURNER A conventional diffusion flame burner is currently being studied in the BERL facility at Sandia. After viewing the burner in operation and studying the measured species and temperature profiles, we decided to model it by applying the single-jet model twice: first for individual jet flames that exist in the quarl, and again for a merged jet exiting the quarl (see Fig. 3). Application of the jet model to the individual flames assumes that they are identical. The jet fluid is fuel, which for this example is a mixture of methane, hydrogen, ethane, and propane. The jet velocity is sonic, and the surrounding of the jet is pure air that enters from below the fuel nozzle. Observation indicates that these jet flames are lifted approximately 10 cm from the fuel nozzle, so the initial condition is established downstream at this location, with a fuel mixture that has been diluted to account for entrainment. The solutions for temperature and mixture fraction are shown in Figs. 4 and 5; the solid curves are the homogeneous reactor, and the dashed curves the flame-sheet reactor. The flamesheet reactor is ignited at the initial condition, while the homogeneous reactor (representing the core of the jet) is cold fuel (partially premixed with air due to the fact that the flame is lifted). As the integration proceeds downstream, the homogeneous temperature increases by entrainment of hot products from the flame-sheet reactor. Integration of the jet model for the individual jets proceeds past the stoichiometric length, to a location past what would be the quarl height. Assuming the individual jets merge at the quarl exit plane, the experimental species measurements indicate that the mixt ure fraction at this point should be approximately 0.07. To apply the jet model a second time for the fuel rich mixture entering the larger chamber, we simply take the solution for the homogeneous mixture at this mixture fraction, and use it as the initial condition for the merged jet. The predicted length at this mixture fraction is roughly 15 cm, compared to the quarl height of 20 cm, but this discrepancy is not large, in light of the approximate nature of this approach. Application of the jet model to the merging flow from the individual jets requires some engineering judgments. Where possible, experimental measurements provide information to reduce the level of uncertainty in choosing conditions for the jet model. The velocity is taken from observation to be roughly 25 m/ s. Conservation the total mass flow rate of fuel and entrained air suggests an equivalent diameter of 15 cm. The surrounding fluid now contains some recirculated flue-gas. The quantity of flue gas is defined by taking the measured O2 mole fraction of about 0.15 at the quarl exit plane and diameter. The surrounding temperature was measured to be approximately 1000 K. With this understanding of the modeling approach, the remaining figures examine the predictions of the air toxic species. The chemical kinetic mechanism for this computation was developed at Lawrence Livermore National Laboratory as part of the cooperative research program. The hydrocarbon mechanism from Pitz and Marinov14 combined with the NO-chemistry from the Miller and Bowman mechanism15 provided the elementary reactions used in the computations. 3 |