Turbulent Premixed Combustion in a High-Pressure Environment up to 4.0MPa

本研究旨在对火焰结构进行精确观测，阐明环境压力与湍流尺度和强度的关系，探讨环境压力对湍流燃烧速度的影响。采用高压燃烧器对ch_4 -空气、c_2h_4 -空气和c_3h_8 -空气混合物的湍流预混火焰进行了稳定。得到了以下结果：1)实测湍流特性表明，湍流强度随平均速度的增加而增加。然而，在常压下，由于湍流的大量倾倒，在小平均速度区域的增加很小。在高压下，湍流强度在整个平均速度范围内随平均速度的增加呈线性增加。2)在高压下，火焰结构变得精细和复杂。随着u′/S_L的增大，S_T/S_L迅速增大，特别是在弱湍流区（u′/S_L<l），说明高压环境下流体动力不稳定性的影响越来越广泛。对于ch_4 -空气火焰，S_T/S_L随u'/S_L的增大而增大，在3时达到30。在实验条件下实现了OMPa。3) c_3h_8 -空气火焰的S_T/S_L的增加速率小于c_2h_4 -空气火焰。这是因为在高压下，由于c_3h_8 -空气混合物的Lewis数较大，火焰面积的增加受到了扩散热效应的抑制。4)在较宽湍流强度范围内的数据表明，c_2h_4 -空气火焰的S_T/S_L与ch_4 -空气火焰的S_T/S_L的依赖关系基本相同。但c_3h_8 -空气火焰的S_T/S_L比c_2h_4 -空气和ch_4 -空气火焰的S_T/S_L要小。5)考察了存在的S_T/S_L、u′/S_L和湍流雷诺数R_L之间的相关性对高压火焰的适用性，发现我们的实验数据与Abde1-Gayd的相关性有相似的趋势，但S_T/S_L大于它们的相关性。强湍流区S_T/S_L的R_L呈1/4幂律（u'/SL> 1）。6)在S_T/S_L* [(P/P_O) (u'/S_<1L>)]^n的关系式中，可以很好地表达整个范围内的实验数据，指数n接近0.4。少

This research was aimed to conduct precise observations of the flame structure, to elucidate the relationship between ambient pressure and turbulence scale and intensities, and to explore the effects of ambient pressure on turbulent burning velocities. Turbulent premixed flames for CH_4-air, C_2H_4-air, and C_3H_8-air mixtures were stabilized by a nozzle burner installed in a high-pressure. The following results were obtained.1) Measured turbulence characteristics showed that turbulence intensities increatsed with increasing mean velocities. Nevertheless, at ordinary pressure, the increase was small in the region of small mean velocities because of an extensive dumping of turbulence. At high-pressures, turbulence intensity linearly increased with the mean velocities in the entire range of the mean velocities.2) At high-pressures, flame structure becomes fine and complicated. S_T/S_L increased rapidly with increasing u'/S_L particularly for weak turbulence regions (u'/S_L<l), indicating … More effects the hydrodynamic instability becomes extensive in a high-pressure environment. For CH_4-air flames, S_T/S_L increases with u'/S_L, up to 30 at 3. OMPa for the experimental conditions achieved.3) The rate of the increase in S_T/S_L for C_3H_8-air flames was smaller than that for C_2H_4-air flames. This is because the flame area increase due to the hydrodynamic instability at high pressures was restrained by diffusive-thermal effects because the larger Lewis number of C_3H_8-air mixtures.4) The data for awide range of turbulence intensities showed that the u'/S_L dependence of S_T/S_L for C_2H_4-air flames is almost the same as that for CH_4-air flames. Nevertheless, S_T/S_L for C_3H_8-air flame showed smaller S_T/S_L than in the cases of C_2H_4-air and CH_4-air flames.5) The applicability of existent correlation between S_T/S_L, u'/S_L, aud turbulence Reynolds number, R_L, to high-pressure flames were examined, and it was found that the data of our experiments had a similar tendency to the correlation by Abde1-Gayd but had larger S_T/S_L than their correlation. 1/4 power law of R_L was seen for S_T/S_L in the strong turbulence region (u'/SL>l.0), consistent with the fractal flamelet model of turbulent burning velocity proposed by Gouldin.6) The best general correlation which can express the experimental data for a whole range of u'/SL and pressure was in the for of S_T/S_L* [ (P/P_O) (u'/S_<1L>) ]^n and the exponent n was close to 0.4. Less