Study of Flame Interference of Counterflow Twin Flames

对于采用逆流喷嘴燃烧器得到的双火焰，研究了丙烷/空气混合物的火焰温度、浓度分布、燃烧速度和火焰距离对喷嘴速度的依赖关系，并考察了相邻两个火焰的存在对火焰干扰的影响。此外，还对双火焰的可燃极限进行了理论分析。得到的结果如下：1.在一定的速度范围内，火焰温度和火焰距离与喷嘴速度的关系存在奇异性，表明火焰干扰对火焰有强化作用。对干扰前和干扰下的两个火焰进行气体分析，稳定组分的浓度分布没有明显差异，说明活性化学组分在干扰火焰中可能起着重要作用。通过考虑活性物质重要性的反应模型的分析，从理论上比较了双子火焰和未受干扰影响的一维流动火焰的可燃极限，发现双子火焰的可燃极限由于干扰的存在而变得更宽。研究了作为活性燃料的氢气对丙烷的加成效应。虽然影响并不是那么简单，但倾斜侧干扰的速度范围扩大了(即干扰效应增强)。用激光测速仪测得的喷嘴速度与燃烧速度之间的关系也存在奇异性。然而，如果燃烧速度与垂直于火焰表面的速度梯度成反比，则关系变得单调，这表明喷嘴速度不能作为火焰拉伸的线性参数。

Concerning the twin flames obtained with a counterflow nozzle burner, the nozzle velocity dependencies of flame temperature, concentration profile, burning velocity, and flame-to-flame distance were investigated for propane/ air mixture, and flame interference effects caused by the existence of two adjacent flames were examined. Furthermore, theoretical analysis was also made on the flammability limits of the twin flames. The obtained results are as follows:1. Some singularities implying the flame strengthening due to flame interference were noticed in the relations of flame temperature and flame distance to the nozzle velocity in a certain velocity range.2. Gas analysis made for the two flames just before and under interference gave no significant differences in the concentration profiles of stable species, which suggests that the active chemical species might play an important role in the flame interference.3. The flammability limits of the twin flames and the one-dimensional-flow flame which is not subjected to interference effects were theoretically compared by the analysis based on a reaction model in which the importance of active species was taken into account, and the limits of the twin flames were found to be more widened owing to the interference.4. The addition effects of hydrogen, well known as an active fuel, to propane was investigated. Though the effect was not so simple, the velocity range of interference was widened (i.e., the interference effect was strengthened ) in the lean side.5. Singularities were noticed also in the relation between the nozzle velocity and the burning velocity obtained by velocity measurements with LDV. However, if the burning velocity is plotted against the velocity gradient normal to the flame surface, the relation becomes monotonous, indicating that the nozzle velocity cannot be regarded as a linear parameter for the flame stretch.