The mechanism determining the scale of the smallest flame wrinkles of high-pressure, high-temperature turbulent premixed flames was investigated. The fractal inner cutoff of OH planar laser-induced fluorescence images, which is the smallest scale of flame wrinkles, was analyzed for burner-stabilized flames in a high-pressure chamber. Precise measurement of the energy spectrum of turbulence was also performed and the relationship between the intrinsic flame instability and flow turbulence was examined. Experiments were performed for CH4/air mixtures of 300 and 573 K at 0.1, 0.5, and 1.0 MPa. The experimental results clearly showed the Kolmogorov's similarity law for non-dimensional energy spectra of flow turbulence at high pressure and high temperature. A characteristic scale equivalent to the average vortex-tube diameter, lv, which is about 10 times larger than the Kolmogorov scale revealed by recent direct numerical simulation, was used as a scale corresponding to the largest wave number of initial flow disturbances in an unburned mixture. At high pressure, the fractal inner cutoff, εi, and lv decrease with turbulence Reynolds number based on Taylor microscale, Rλ, regardless of mixture temperature. The magnitude of εi is close to lv when lv is larger than the characteristic instability scale corresponding to the maximum growth rate of flame instability, li. When Rλ increases further and lv becomes smaller than li, εi becomes almost constant. At atmospheric pressure, the relationship between lv, li, and εi was not obvious, but the correlation of εi with the integral scale, lg, was rather significant. These characteristics of εi variation for high-pressure, high-temperature turbulent premixed flames can be explained using the scale-relation model based on lg, lv, and li for Rλ variation proposed in this study.
|Number of pages||8|
|Journal||Proceedings of the Combustion Institute|
|Publication status||Published - 2002|
|Event||30th International Symposium on Combustion - Chicago, IL, United States|
Duration: 2004 Jul 25 → 2004 Jul 30