OCR Text |
Show 3.3. Gaseous Flat Flame Burner Premixed, quenched flat flames of coal volatiles/air were burned on a 7.5 centimeter diameter water-cooled, sintered copper-shot porous-plug burner. This nonadiabatic device, shown in Figure 3, produces a one-dimensional gaseous flame. Therefore, the height above the burner corresponds to reaction time. By probing at various planes of this geometrically well-defined combustion event, time-resolved physico-chemical data can be obtained. In particular, what was sought was the global apparent activation energy for the combustion of each simulated coal volatile [12b]. This is obtained by associating the burning velocity of the quenched flat flame with the global flame reaction rate and plotting its logarithm versus the reciprocal of the maximum flame temperature [12,14]. Stoichiometric flat flames of coal volatiles were burned at sub-atmospheric pressure in order to expand the reaction zone, thus making in situ probing more facile. Translational flame temperatures were measured using a silicas-coated, fine-wire butt-welded Pt/Pt, 10% Rh thermocouple. Wire temperatures were corrected for radiation loss. The low-pressure flat flame facility yields a combustion zone that is very suitable for optical probing and diagnosis. A schematic of the experimental optical generation/detection system used for hy-droxyl radical concentration [OH] measurements was presented previously [14]. The optical method used as a refined in situ sharp-line ultraviolet absorption/curve-of-growth technique. [OH] was measured by monitoring the intensity of the well-resolved rotational line of the o near ultraviolet bandhead at 3083 A, the Q,4 + Qi^' line pair of the 2 2 0-0 vibrational band of the A E-»-X v electronic transition. 22-11 |