CH_4/空气和C_3H_8/空气预混湍流火焰结构及湍流火焰速度测量

Measurement of Flame Front Structure and Burning Velocity of Premixed Turbulent Flames of CH_4/Air and C_3H_8/Air

利用OH-PLIF技术探测了CH4/空气和C3H8/空气混合气在不同湍流强度下的预混湍流瞬时火焰前锋面结构,通过湍流产生板产生了弱湍流区内的不同湍流强度,通过控制当量比调节火焰密度比和路易斯数,计算了实验中的层流火焰特征参数,分析了湍流强度和火焰特征参数对预混湍流火焰结构、湍流火焰速度的影响.结果表明:火焰前锋面结构的褶皱程度随湍流强度的增大而明显增强.在相同湍流强度下,CH4/空气火焰比C3H8/空气火焰更加褶皱.通过提取火焰OH-PLIF图像锋面,分别用角度法和面积法计算了湍流火焰速度,获得了弱湍流条件下湍流火焰速度与湍流强度的一般关系式.在相同密度比下,即相同流体动力学不稳定性下,热扩散不稳定性更大的CH4/空气比C3H8/空气的湍流火焰速度更大,而在路易斯数接近且热扩散不稳定性处于次要地位时,密度比大的CH4/空气流体动力学不稳定性更大,其对湍流火焰速度的影响也更大.

Measurement of the instantaneous flame front structure of premixed turbulent flames of CH4/air and C3H8/air mixtures was conducted using OH-PLIF technique.A variety of stable turbulenceintensity was generated by perforated plates and laminar flame parameters were calculated.The effects of turbulence intensity and flame charac-teristics on turbulent flame structure and turbulent burning velocity were analyzed.Results showed that with the in-crease of turbulence intensity,the wrinkled intensity of flame front structure increased.For the same turbulence in-tensity,CH4/air mixtures have more wrinkled flame front than C3H8/air mixtures.The flame front structure was ob-tained from the OH-PLIF images and the turbulent burning velocity was calculated by angle method and area method.The correlation was proposed to fit the turbulent burning velocity and turbulence intensity under weak turbu-lence.Meanwhile,at the same density ratio,i.e., with the same hydrodynamic instability,CH4/air with greater thermo-diffusive instability shows higher turbulent burning velocity than C3H8/air.Moreover,with similarLewis number and less significant role of thermo-diffusive instability,CH4/air with larger density ratio has greater hydrody-namic instability,which has a significant influence on turbulent burning velocity.