Stoichiometry adiabatic equilibrium temperature

Figure 3.4 Computed wall temperature profiles for the catalytic channel geometry in Fig. 3.3 and two H2/air stoichiometries =0.3 and 6.9) having the same adiabatic equilibrium temperature Tad. In the fuel-lean =0.3, results are shown for Case 1 which is adiabatic and transport-limited, Case 2 with only catalytic reactions (C), and Case 3 with both catalytic and gas-phase reactions (C-G). In the fuel-rich

Figure 1.14 is a similar plot of the adiabatic equilibrium flame temperature for CH4 flames as a function of the stoichiometry, for four different oxidizer compositions ranging from air to pure 02. The peak flame temperatures occur at stoichiometric conditions. The lower the 02 concentration in the oxidizer, the more the flame temperature is reduced by operating at nonstoichiometric conditions (either fuel rich or fuel lean). This is due to the higher concentration of N2, which absorbs heat and lowers the overall temperature. Actual flame temperatures will be less than those given in Figures 1.13 and 1.14 because of heat losses from the flame, which is not an adiabatic process. 

Figure 2.3 shows a plot of the adiabatic equilibrium flame temperature for an air/CH4 flame and an 02/CH4 flame, as functions of the flame stoichiometry. There are several things to notice. The flame temperature for the air/CH4 flame is very dependent on the stoichiometry. For the 02/CH4 flame, the temperature is very dependent on the stoichiometry only under fuel-rich conditions. The temperature is not very dependent on the stoichiometry when the 02/CH4 flame is fuel lean. 

NO doped Methane Flames. Most of the NO passes through the flame unreacted, and the NO primarily acts as an inert diluent. Diluting the flames with 1.5% NO causes the adiabatic flame temperatures to drop by about 100 K and the calculated flame speeds to decrease by about 10%. The NO fraction decreases by less than 10% through the flame front for these flames which were doped far above the equilibrium NO concentrations (420-3700 ppm depending on stoichiometry). In the experiments there was no post flame decay in the NO concencentrations ( 5%), while the calculations do show some decay (<2%/mm) which depends upon stoichiometry. The calculated post flame conversion rate of NO to Nj decreases as the super-equilibrium radicals (e.g. 0 and OH) decay. 

When the kinetics are unknown, still-useful information can be obtained by finding equilibrium compositions at fixed temperature or adiabatically, or at some specified approach to the adiabatic temperature, say within 25°C (45°F) of it. Such calculations require only an input of the components of the feed and produc ts and their thermodynamic properties, not their stoichiometric relations, and are based on Gibbs energy minimization. Computer programs appear, for instance, in Smith and Missen Chemical Reaction Equilibrium Analysis Theory and Algorithms, Wiley, 1982), but the problem often is laborious enough to warrant use of one of the several available commercial services and their data banks. Several simpler cases with specified stoichiometries are solved by Walas Phase Equilibiia in Chemical Engineering, Butterworths, 1985). 

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