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Show 3200 C 3000 ;> ...-4 (l) ~ 2800 (l) ~ 2600 ~ +oJ C\1 (~l) 2400 ~ S (l) 2200 E- 2000 0 20 40 60 80 100 Percent 02 Figure 4 Adiabatic flame temperature as a function of oxygen content in the oxygen-nitrogen mixture for stoichiometric methane-oxygen mixtures initially at room temperature and pressure. 0.4 -r-----------------, 0.3 C 0 .~ +oJ c...l C\1 ~ 0.2 to-. (l) ...-4 0 ~ 0.1 CO .. CO2 .. ~ .. ···············7.,~·············· /' -'-'-' /,,' . ___ .--.--.--. H2 ?-- 0.0 -+---~---..-----.-----...-----I o 20 40 60 80 100 Percent 02 Figure 5 Selected species concentrations at equilibrium, plotted as functions of oxygen content in the oxygen-nitrogen mixture. In the plots of species equilibrium concentrations, note that the minor constituents such as CO, H2 and 02 all rise with 02 enrichment. As the percentage of 02 is increased, the equilibria should shift towards C02 and H20 and away from CO and H2, based simply on the Law of Mass Action. However, since the temperature of the products is also increasing, and the position of the equilibrium is even more sensitive to 148 C 0 .~ +oJ c...l C\1 ~ to-. (l) ...-4 0 ~ 0.10 0.08 0.06 0.04 0.02 OH ..... ........ / .... .' ... --.,.:.' /' ...... H / , .:....... ... "-, / ....•. / ( ........... 0.00 -+---......,....=-----.----...----.------4 o 20 40 60 80 100 Percent 02 Figure 6 Selected species concentrations at equilibrium, plotted as functions of oxygen content in the oxygen-nitrogen mixture. temperature than to concentration, the overall result provides more partially oxidized products than completely oxidized species. Note also that the NO level increases rapidly with 02 enrichment, due exclusively to the increased product temperature. In this case, the attainment of these higher equilibrium NO concentrations will also be faster as the 02 enrichment is increased. The sharp drop in NO level at very large 02 enrichment levels is a result of the way the computations were done; at 100% 02 in the oxidizer, there is no molecular nitrogen in the lIairll, so no NO or NOx can be produced . AIR PREHEAT - In many practical systems the oxidizing air stream can be heated prior to mixing with the fuel to provide higher product temperatures. A series of adiabatic flame temperature and equilibrium computations was carried out to examine this issue. The pressure was held fixed at atmospheric, and the air preheat temperature was varied from zero (i.e. room temperature air) to 2000°F. The results of these computations are plotted in Figures 7-9. The final temperature increases steadily with air preheat temperature. This could be expected because for these mixtures the ratio of air to fuel is constant at 5.76/1, so the reactant mixtures are predominantly air. Because of the steady temperature rise, the levels of all of the incompletely oxidized species and radicals also increase with air preheat temperature. Furthermore, the NO level increases steadly with air preheat as well, and again the production rate of NO and its rate of attaining that equilibrium level will also increase with air preheat temperature. |