Structure of a Laminar Premixed Flame with Spatially Non-uniform Stretch Rate

为了进一步了解湍流燃烧，我对具有空间非均匀拉伸效应的层流预混火焰的结构进行了实验研究。通过在稀丙烷/空气混合物的空间周期流场中产生起皱的层流预混火焰，形成了具有拉伸速率变化的火焰表面，并从速度分布和温度分布两个方面讨论了火焰拉伸与火焰温度的关系。分别用PIV和热电偶测量了火焰的速度或温度，在拉伸速率为正/负的火焰段上测得的火焰温度低于或高于绝热火焰温度。这是火焰拉伸和路易斯数大于1的刘易斯数效应的结果。用传统的火焰拉伸理论和基于沿火焰表面均匀拉伸速率的Lewis数效应估算的火焰温度与测量的温度在定量上不一致。因此，我修改了理论，考虑了沿火焰表面和向燃烧气体的热量传递，然后得出了与测量温度定量一致的估计。发现火焰拉伸和刘易斯数效应沿火焰表面发生变化，火焰表面具有空间上的拉伸速率变化，导致沿火焰表面和向燃烧气体方向的温度梯度，进而传递热量，改变火焰温度。因此，这种热传递是估算火焰温度的重要因素。此外，还阐明了沿火焰表面的换热比沿燃烧气体的换热影响更大。

To gain further understanding of turbulent combustion, I investigated experimentally the structures of a laminar premixed flame with spatially non-uniform stretch effect. A flame surface with stretch rate variation was formed by creating a wrinkled laminar premixed flame in a spatially periodic flow field of a lean propane/air mixture, and the relation between flame stretch and flame temperature was discussed from the velocity and temperature distributions. The velocity or temperature was measured using PIV or thermocouple, respectively.The measured flame temperature was lower/higher than the adiabatic flame temperature at flame segments with positive/negative stretch rates. This was a result of flame stretch and Lewis number effect for Lewis number greater than unity. The flame temperature estimated using the conventional theory of flame stretch and Lewis number effect, which is based on a uniform stretch rate along the flame surface, did not agree quantitatively with the measured temperature. Therefore, I revised the theory, taking into account heat transfers along the flame surface and toward the burned gas, and then produced estimates that agreed quantitatively with the measured temperature. I found that flame stretch and Lewis number effect is changed along the flame surface which has spatially stretch rate variation, causing a temperature gradients along the surface and toward the burned gas, which in turn transfer heat and change the flame temperature. Thus, such heat transfers are important factors in estimating flame temperature. In addition, it is clarified that the heat transfer along the flame surface affects more than that toward the burned gas.