| OCR Text |
Show Fig. 6 presents the concentration profile for NO, obtained by exciting the A -X band system of that molecule near 228 nm. The absolute NO concentration was determined by calibration with known amounts of NO. This is possible because NO is a stable molecule. Comparing with Fig. 5, we observe that the CH and NO profiles are closely related. Downstream of the CH maximum the NO increases and attains a constant value after the CH is destroyed. The shoulder at low burner height is caused by backward diffusion of the relatively unreactive NO produced higher in the flame; it is correctly predicted by the flame model Absolute Concentration of CH Because CH is an unstable free radical, it cannot be calibrated like NO. InsteacL we made absolute LIP determinations of CH in the flame by independent measurement of all the quantities in Eqs. (1) and (2). The A and B coefficients were taken from our previous study of these electronic band systems. IL was continuously monitored during the experiment In the low pressure flame, the fluorescence lasts nearly 100 ns, considerably longer than the laser pulse length. This enables direct measurement of Q, and hence <l>n by measuring the fluorescence decay time. Such measurements are shown in Fig. 7. -Q o ~ 11 - NO UF prcffle I - NO simulated pro1i1e 2 3 4 Height above the burner (em) Figure 6. NO number density profile measured by LlF in the lean propane/air flame, the continuous line is the result of the kinetic model. 100 10 0.00 0.05 • A-X (0.0) P t.(6) I a B-X (0.0) ~ (6) 0.10 "Time (J.1s) 't .. = 65 ± 3 ns 0.15 0.20 Figure 7. Semilogarithmic plot of the fluorescence time decays collected after pumping CH A-X and CH B-X in the propane/air rich flame aJong the single exponential fittings. |
