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

这项研究的目的是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，并探索环境压力对湍流燃烧速度的影响。用高压喷嘴燃烧器稳定了CH4-空气、C2H4-空气和C3H8-空气混合物的湍流预混火焰。结果表明：1)测量的湍流特性表明，湍流强度随平均速度的增大而增大。然而，在常压下，由于湍流的广泛倾倒，在平均速度较小的区域，增加的幅度很小。在高压下，湍流强度在整个平均速度范围内与平均速度成线性关系。2)高压下，火焰结构变得细小而复杂。S_T/S_L随u‘/S_L增大迅速增大，尤以弱湍流区(u’/S_L&lt；L)为甚，指示…在高压环境下，流体动力不稳定性的影响范围更广。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。在实验条件下获得了OMPA。3)对于C_3H_8-空气火焰，S_T/S_L的增加幅度小于C_2H_4-空气火焰。这是因为C_3H_8-空气混合物的刘易斯数较大，从而抑制了高压下流体动力不稳定性引起的火焰面积的增大。4)大范围的湍流强度数据表明，对于C_2H_4-空气火焰，S_T/S_L与甲烷-空气火焰的u‘/S_L关系基本相同。然而，对于C_3H_8-空气火焰，S_T/S_L比C_2H_4-空气和CH_4-空气火焰的S_T/S_L小。5)考察了S_T/S_L，u‘/S_L和湍流雷诺数R_L之间的现有关联式对高压火焰的适用性，发现我们的实验数据与Abde1-Gayd的关联式的趋势相似，但比它们的关联式大。在强湍流区(u‘/SL&gt；1.0)，S_T/S_L的R_L符合1/4幂规律，与Gouldin提出的湍流燃烧速度的分形火焰面模型一致。6)S_T/S_L*[(P/P_O)(u’/S_&lt；1L&gt；)]^n的指数n接近0.4，能较好地描述u‘/SL与压力的整个实验数据。较少

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