| OCR Text |
Show pressure, a methane/air flame front will be only a mm or less thic~ but at 40 Torr it increases to approximately a cm. This permits high spatial resolution analysis using the laser beam. For a meaningful test of the flame chemistry, this is crucial: because of the highly nonlinear dependence of reaction rate coefficients on temperature, the temperature must be known to an accuracy of about lOOK or better at each point in the flame. We describe here results from an extensive series of LIF studies in a propane/ air flame at 40 Torr. As noted above, much of the pertinent chemistry in the flame front is the same as in a methane/air flame. This has been confirmed by preliminary measurements in a methane/air flame at 25 Torr. The flames are burnt on a 6 em diameter, porous disk McKenna burner, which creates a nearly onedimensional flame near the centerline. Rapid flow lifts the flame one to two em off the bmner surface. The burner is housed in an evacuable chamber. Mass flow controllers regulate the flow of gases, and a pressure controller operating a choke valve maintains constant pressure. Concentration and Temperature Profiles A profile of temperature throughout the flame is needed as input to the flame chemistry model. This is done using OH 9 ( '°9 1, 8 12 7 i i 4 4' J06.7 I 14 J06.a I I J3' 306.9 I • I R, lS 2 r T-1612K T .1'53 K 307.0 307.1 LfSS WAVELENG7"r4 (nm) Figure 3. OH excitation scans at three positions above the burner surface in a 30 Torr methane/air flame. Top: 3.22 cm height, T = 1672 K; middle, 0.89 cm, 1153 K; bottom, 0.25 cm, 405 K. The ground state rotational quantum number N" is labeled. |
