| OCR Text |
Show Vertical centerline profiles for three different stoichiometries are shown in Fig. 8. There is no OH within the unbumt gas, and a sharp peak marks the position of the inner flame tip. The spatial resolution near the tip is limited because of its curved shape. Above the tip the OH first decreases~ while at larger heights it rises again due to OH produced in the diffusion stage. -:; .!. ~ c: Q) (,J c: 0 (,J J: 0 10 8 6 ~ ~ = 1.26 r • 4 -~----f------------ <t> = 1.36 t 2------- o - o 2 . 4 6 height above flame holder [em) 8 Horizontal profiles at a fixed height above the burner (1.4 cm) are compared in Fig. 9. All three profiles cut through the diffusion flame front, the inter-conal region, the premixed flame front, and the unbumt gas. Because the height of the premixed Figure 8. Vertical OH profiles at the centerline of the flames for three different stoichiometries. flame varies with the stoichiometry, the flame front position occurs at larger radii for richer flames. The large radial position and small OH concentration render the inner cone difficult to discern for <l> = 1.56. In contrast to OH in the inner cone, the OH in the diffusion flame is only a weak function of the stoichiometry. Horizontal profiles above the premixed flame demonstrate the presence of the outer cone, but at large heights the profiles are less sharp. Fig. 10 shows an excitation scan taken in the diffusion part of the flame. The resulting temperature is 2090 ± SOK. LIF Measurement of CH Radicals CH was determined with a laser near 431 run. The beam was focused to a diameter of 150 J..l.IIl. The resolution along the beam was on the order of 2 mm. A monochromator was used to distinguish between fluorescence light and scattered light The usual setting of the monochromator totally suppressed scattered laser light and permitted detection only ofLIF. However, nming the monochromator also allowed simultaneous observation of LIF and scattered Rayleigh ligh4 advantageous for observing the relative position of CH and the temperarure gradient. 14 |
