OCR Text |
Show Figure (5) displays the predicted velocity field for two tangential planes in the combustor, one of which is an injection plane. The diffusion of the inlet jet and subsequent formation of the central vertical jet and the recirculating vortex flow can be seen clearly. Good agreement has been obtained between measured and computed velocity vectors for non-reacting flow in a toroidal vortex combustor(12), Figure (6). Regarding the evolution of the temperature and species fields, Figures (7) to (9) depict typical patterns for the relevant variable along the injector plane. The temperature field, Figure (7), displays local peaks near the dome of the combustor as well as in regions along the centre-line close to the exit. Such predictions appear qualitatively plausible, as at these locations combustion is sustained by the transfer of heat from the recirculating combustion products to the incoming fuel-air mixture which ignites producing a new charge of products. Furthermore, substantial asymmetry (not shown) of the temperature field exists, with considerable axial and radial gradients located near the location of the primary vortex indicating the presence of intense reaction there. The evolution of the volatile contours (of approximate elemental ratio C6H12 and C6H6) shown in Figure (8), appears compatible with the computed coal particle trajectories and the temperature field, as well as the O2 field. As this combustor concept employs staged operation burning rich in the primary stage to limit NO formation and to convert solid fuel to gaseous products CO and x H2, O2 utilization is virtually complete, Figure 9. However, up to 2 \ by weight unburned volatile concentrations were predicted at the exit. Such levels could be potentially explained by incomplete turbulent mixing of the volatiles or alternatively, shortcomings in the model regarding the lack of the kinetic route for gasification of the gaseous fuel to CO and H2 could be blamed. Typical CO contours throughout the combustor, as influenced by the finite rate kinetic scheme adopted in the study, is also shown in Figure (9). 11 |