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Show just downstream the quarl outlet. In the following this zone will be defined, the "main-flame-zone". Again, significant heat release in the quarl zone itself occurs only close to stoichiometry. Local values of heat release normal to the iso-line of a stoichiometry of 1.0 decrease rapidly to almost zero; either to super- or sub-stoichiometnc conditions. It should be noted that the calculation of local "absolute" heat release, given in Watts, are obviously related to the local grid size. Values of the heat release may change with finer or coarser grid sizes to smaller respectively larger values. However, the qualitative trends of the local heat release pattern will not change when reasonable fine grids are used to predict the flame. Reaction rates and heat release as a function of local temperatures (EBU). For the total range of local stoichiometries considered, Figure 5 plots the turbulent reaction rates over the local temperatures. The most significant result looking at the plot is that the EBU-model in general predicts a decrease of the magnitude of reaction rates with increasing temperatures. To locate super, sub-stoichiometric conditions and the iso-line of 1.0, Figure 6 and 7 show the distribution of local reaction rates at fixed stoichiometries over local temperatures. Figure 6 compiles the results for super-, respectively Figure 7 for sub-stoichiometric conditions. Both figures contain numbered arrows which refer to Figure 8 showing the local marching direction of the reaction rates at different stoichiometries. The upper half of Figure 8 is linked to Figure 6, the super-stoichiometric conditions, respectively the lower part to the sub-stoichiometric areas (Fig. 7). Data or iso-line of stoichiometry 1.0 are plotted in all three figures. The overall trend of decreasing rates with increasing temperatures m a y be confirmed by Figures 6 and 7, with the exception of super-stoichiometric conditions 100-g- 0.0000 0001 0.0001-! close to a value of 20.0 in the far post-flame-zone. In general it can be seen that at constant temperatures reaction rates decrease when leaving the stoichiometric condition at 1.0. In other words, the local m a x i m u m of the CxHy reaction rate at a constant temperature is generally found at a stoichiometry of 1.0 and temperatures above 1000K. 100-a 0.001 -j - 0.0001-!- 0 00001- i i i i | i i i i i i i i i i i i i i i i i ii i i i i i 6 0 0 800 1000 1200 1400 1600 1800 2000 Figure 7: Predicted local reaction rates of CxHy [kg m"3 s'1] over local temperatures [K] at local stoichiometries 1.0, 0.5, 0.2, 0.1, 0.05 and 0.01. Reaction rates at super-stoichiometric conditions. The combination of Figures 6 and 8 allows to locate the predicted reaction rates in the flame for super-stoichiometric conditions. Following the Arabian numbers from 1 to 5, arrow 1 starts at the burner tip, where the natural gas meets the combustion air, and follows the iso-line of stoichiometry 1.0 downstream the flame. Arrow 2 points to the closure of the iso-line of stoichiometry 1.0 on the burner centerline at ca. 2.5 quarl outlet diameter downstream the burner front wall. From this point arrow 3 stays on the centreline until the iso-line of a stoichiometry of 20.0 is reached halfway down the furnace (see also Fig. 3). Form there arrow 4 and 5 are adjacent to the iso-line of stoichiometry of 20.0 pointing back to the burner tip. 2000 Figure 6: Predicted local reaction rates of C xHy [kg m"3 s'1] over local temperatures [K] at local stoichiometries 1.0, 2.0, 5.0, 10.0 and 20.0 Figure 8: Marching direction of reaction rates at defined stoichiometries of Figures 6 and 7 coupled to their location in the flame. 7 |