| OCR Text |
Show 4.2 [02]eq Concentration Scaling 4.2.1 [02]eq in Near-Burner Region The oxygen concentration in the near-burner region changes only with air dilution level and fuel staging ratio, with the resulting scaling in both subregions being identical. The variation with air dilution level can be expressed in terms of air-fuel equivalence ratio "\, defined as ,,\ = (mair/mjuel)actual (mair / mj uel ) stoichiometric (24) with ,,\ = 1.15 at the baseline condition. From the overall methane-air reaction formula the excess O2 level can be expressed in terms of ,,\ as o _ 2("\ - 1) [ 2] - 1 + 9.52,,\ (25) (26) which gives 2.5% (3% dry) excess O2 at baseline. The oxygen concentration then scales with ,,\ as and substituting (26) into (27) gives [1 + 9.52"\],\=1.15 1 + 9.52,,\ (27) (28) Under condi tions of perfect similari ty, [02]'\=1.15 is set to the theoretical 2.5% (3% dry) value in the flue gases. vVhen accounting for departures from perfect similarity, [02L=1.15 is taken fron1 the in-flame measurements at baseline (A = 1.15) conditions. Fuel staging effectively alters the air-fuel ratio in the near-burner region, since less fuel is then injected into the region while the air mass flow-rate remains constant. It can be readily shown that the resulting relation between the effective air-fuel equivalence ratio A' and the fuel staging ratio r is A' A-r 1 - r (29) where r = (mjuel)staged/(mjuet)overall. This effective air-fuel ratio A' is then substituted into (28) to give the O2 concentration levels. 4.2.2 [02]eq in Flan1e-sheet Region The oxygen concentration in the flame-sheet region is set by the equilibrium solution for adiabatic stoichiometric conditions. The STAN J AN chemical equilibrium code [18] gives this value as 0.5% for methane-air reaction. 11 |
