OCR Text |
Show KIN- and the TK-model may carry the sub-index "ff', which stands for "frozen flow"-field. In this case results of either the KIN- or the TK-model are obtained by applying the temperature, species concentrations, flow and turbulence properties from the predicted results of the EBU-model. Finally, the index L I M is used to identify results obtained by means of limitation laws as shown in eq. (13) andeq. (14). Near burner zone and local stoichiometries (EBU). Local stoichiometrics (eq. (9)) ranging from 0.01 to 20.0, respectively equivalence ratios of 100.0 to 0.05 are compiled to obtain a reasonable range of computational nodes. Figure 3 shows the predicted contours of local-stoichiometries of 0.01, 1.0 and 20.0. The computational domain covered contains 7715 cells out of a total number of 33264 cells used. The chosen domain covers not only the N B Z , but represents as well parts of the post-flame zone. Zoomed into the quarl zone (see circle area in Fig. 3), the contour of the local-stoichiometry 0.01 excludes an area close to the burner tip of lower stoichiometries than 0.01. A s it will be shown later this zone does not contribute significantly to the total heat release generated by hydrocarbon's (CxHy) combustion and is therefore only considered to transport hot combustion products together with the fuel to the ignition zone. Figure 3: Predicted local stoichiometries in the furnace and in the near burner zone (EBU-model). Reaction rates and heat release as a function of position in the flame (EBU). Figure 4 shows in the upper part contours of local reaction rates of hydrocarbons (CxHy) at values of 0.5, 1.0 and 3.0 kg m'3 s"1. The computed rates ranged from 0.0 to 104.0 kg m 3 s ' . The maximum of 104.0 kg m'3 s'1 can be found adjacent to the upper burner tip, where the gas jet meets the swirling combustion air. In addition the iso-line of the local stoichiometry 1.0 is added to Figure 4 both in the upper and lower part. Following mis line downstream from the burner tip reaction rates decrease rapidly to a value of 3.0. Leaving the quarl outlet values of 1.0 and 0.5 are found in the shear layer of the flame. As postulated by the EBU-model local maxima of the reaction EBU. CM, Figure 4: Predicted isolines of local volumetric reaction rates (0.5, 1.0 and 3.0 kg m"3 s1), heat release (625, 1250 and 1875W) and local stoichiometry (1.0) (EBU). rates have to co-exist on the iso-line of the local stoichiometry 1.0. Thus, normal to this iso-line values of reaction rates decrease rapidely. At least for die ignition zone results it should be noted that swul-stabilised flames ignite from within the IRZ. Hence the general agreement that reaction rates follow the iso-lines of the local stoichiometry is doubtful. Local heat releases are plotted in the lower part of Figure 4. The maximum local heat release calculated reaches almost 3kW. A n area of intense high heat release ranging from 1250W to the maximum calculated heat release is located 100 -a 0.00001 0.001 0.0001- i i i .00 r-r 800 2000 Figure 5: Predicted local reaction rates of C xHy [kg m'3 s"1] over local temperatures [K] at local stoichiometries ranging between 0.01 and 20.0 6 |