| OCR Text |
Show Centerline predictions of the mole fraction are plotted in Figure 13. Predictions agree qualitatively with the data; i.e., the mole fraction decreases in oxygen and rises in C0? concentration along the combustor. The tip of the vertical dotted lines at an axial position of 0.78 m indicates the predicted local molar fraction of the species. This sharp change in predicted molar concentration indicates a deficiency in the chemistry model. Our current thinking is that the variance, g, of the fuel mixture fraction is underpredicted and consequently, local combustion is overpredicted. In Figure 14, radial molar concentrations are presented. At the exit, all concentration profiles agree fairly well with data collected by T, ,(27) Thurgood The Thurgood evaluation run is the initial application of COMO to a pulverized coal combustion analysis. The good agreement between predictions and data is encouraging since the coal pyrolysis and char oxidation models are quite elementary. SUMMARY The combustion model has been compared with two cases. These initial studies are encouraging because they indicate the basic trends often found experimentally and have provided insight into the complex combustion process. Developmental work, is far from complete; future studies must concentrate on improving the basic physical model. In some areas such as turbulence and chemistry, new approaches and/or concepts may be necessary before better agreement with data is possible. In addition if modeling is to be successful, then additional experimental work must continue. Such work is necessary not only to establish fundamental data required for the models, but also to assist in the validation of the models. In spite of this, computational methods offer promise of assisting the design engineers in the future. -30- |
