旋回噴流燃焼器を用いた強乱流予混合火炎の研究 : 第1報, レーザトモグラフィー法による火炎構造の可視化

概要

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By using a cyclone-jet combustor, we have investigated premixed flames in a highly turbulent flow over a wide range of turbulent properties, with u'/S_L exceeding 10 in a stationary jet flame. With Mie scattering, we obtained tomographic images to visualize the flame structure. We have investigated the velocity field in cold flow with a hot wire anemometer. Results show that, as the turbulence is relatively low, the scale of the turbulence is large and one flame sheet wrinkles, which shows that a typical wrinkled laminar flame is formed. As the exit velocity is further increased, the flame wrinkling is increased, but the size of its wrinkles becomes small with many cusps of the flame front. In some cases, the burned gas may exist in the unburned gas, and vice versa. When the velocity exceeds 30 m/s, one continuous flame sheet cannot be sustained, and the destruction of laminar flame structure occurs, in which small reacting eddies in an intermediate stage of combustion may be embedded. These results are supported by the fact in previous experiments that the probability of intermediate temperature between those of unburned and burned gases becomes high and the PDF of temperature is no longer bimodal. Thus, it appears that, a flame structure changes to be that with distributed reaction zone as the intensity of turbulence is increased.
1999-09-25