Wrinkled Laminar Flames

Akira Yoshida
Tokyo Denki University

Burner setup. A propane air turbulent premixed flame is stabilized on a 30 mm Bunsen-type burner by an annular pilot. The equivalence ratio is 0.68. The flame height is about 85 mm. The mean velocity of the unburned mixture is 2.36 m/sec. Turbulence is given to the mixture by a perforated plate. The turbulence rms fluctuations at the burner exit is 0.15 m/sec. The Taylor and the Kolmogorov microscales are 1.81 and 0.22 mm, respectively, and the Reynolds number based on the Taylor microscale is 17.4.

Figure 1

Photographic setup. This schlieren photograph was taken by a Canon-F1 camera with a 300 mm telephoto lens of f=5.6. Two 200 mm schlieren mirrors with the focal length of 2000 mm were used for the Z-light path arrangement. The vertical knife edge is mounted at the focal point of one mirror. The light source was a xenon stroboscope with a condenser lens and a pinhole. The maximum light power is 8 J (170 1x-sec). The flash duration time is typically 15 ?sec. The flash timing was synchronized with the camera shutter. The film used was the Neopan SS (ASA 100) and was developed by Fujidol.

Interpretation. With a moderate or weak turbulence of the unburned mixture, the instantaneous turbulent premixed flame zone consists of a continuous wrinkled laminar flame front. The wrinkle size seems to be irrelevant to the turbulence scale. Along the unburned mixture flow, the amplitude of wrinkles...