Laser tomographic method for flame front movement studies
Laser tomographic method for flame front movement studies
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用于研究火焰锋运动的激光断层扫描方法
DOI：
10.1016/0010-2180(80)90028-0
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发表时间：
1980
影响因子：
4.4
通讯作者：
L. Boyer
中科院分区：
文献类型：
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作者：
L. Boyer
最近的理论发展涉及油籽液滴是否足够小湍流和自湍流火焰 [1,2,3]。 2 然后照亮燃烧区域表明，局部和瞬时的知识——用激光束成形为薄片，火焰前锋的位置或速度约为 50×0.5 ram，粒子散射主要感兴趣的光。事实上，了解未燃烧区域中的火焰以及光束可以是前向运动以及新鲜和可视化的速度。另一方面，除了火焰之外，同时测量的燃烧气体对于了解小于火焰宽度的湍流机制并且不散射预混合火焰的颗粒蒸发厚度至关重要，光：亮与暗之间的边界迄今为止使用的光学技术非常区域是火焰的横截面。它对于定性分析很容易有用；尽管有大量的研究人员拍摄照片、影片或记录下来，但他们对火焰锋面痕迹的录像仍然不够准确。所观察到的火焰是由我们实验室构建的所有火焰上的光路变化的透明燃烧器动态稳定的，因此它位于纹影或阴影图方法中的平面中，或者垂直于沿 z 的平均气流，即光强度在深度轴上的积分（图 1）；此燃烧器与现场其他部分的直接摄影1 [5, 6]。在设备上，即激光风速计，另一方面，静电探头总是与姿态相互作用，稍后将讨论。播种是随流进行的，并且允许人们仅检测用市售设备进行的染色。火焰锋面的交叉[7]。液滴的大小约为直径的1/a。现在我们提出了一种方法，允许人们对狭缝上的发光片（xz'平面）进行观察，从而获得火焰的平面横截面，并平行于z轴，测量光通量，使火焰前锋的形状可视化。此外，通过光电倍增管通过光电流进行检测，一个简单的光学装置给出了瞬时值，该瞬时值与火焰前锋的局部位置成正比，因此，通过对电 2 求导，得到速度。我们可以粗略地计算出汽化时间 r，该信号所获得的信号是达到汽化温度所需的时间和液滴被注入到未燃烧的混合汽化中的时间之和。在我们的实验条件下确实如此。这次穿过火焰锋面时大约10-5秒就蒸发了。该时间远小于液滴在火焰中的停留时间，对于约10cm 1 的火焰速度，即使在Markstein的狭缝燃烧器s-1的特殊情况下，该时间也为10-3秒。此外，我们能够测量速度[4]，火焰宽度约为4毫米，稳定层流火焰服务轮廓的厚度内的ob轮廓，对于稳定的蜂窝火焰的情况，对于[8]并表明油滴在实例中消失，不可避免地是平均轮廓，即火焰厚度。
The recent theoretical developments concerning if the droplets from the oil seeding are small turbulent and self-turbulizing flames [1, 2, 3] enough. 2 Then illuminating the combustion zone show that a knowledge of the local and instantan- with a laser beam shaped into a thin sheet of eous position or velocity of the flame front is of about 50× 0.5 ram, the particles scatter the light primary interest. Indeed, knowledge of the flame- in the unburned region and thus the beam can be front movement and of the velocities of fresh and visualized. On the other hand, beyond the flame burned gases measured at the same time is essential front the particles are evaporated in a thickness in order to understand the mechanism of turbulent smaller than the flame width and do not scatter premixed flames, the light: The frontier between the bright and dark The optical techniques used up to now are very regions is the cross section of the flame. It is easy useful for a qualitative analysis; In spite of a num- to take a photograph or a film or to record on ber of studies, they remain insufficiently accurate videotape this trace of the flame front. The flame because the observed effect results from either a is dynamically stabilized in a transparent burner variation of the optical path over all the flame as built in our laboratory, such that it lies in a plane in the schlieren or the shadowgraph method or perpendicular to the mean gas flow along the z the integration of the light intensity over the depth axis (Fig. 1); This burner and the other parts of of field in direct photography 1 [5, 6]. On the the device, that is, the laser anemometer, for inother hand, electrostatic probes always interact stance, will be discussed later. The seeding is obwith the flow and allow one to detect only the tained with acommercially available apparatus. The crossing of the flame front [7]. size of the droplets is about 1/a in diameter. Now We propose a method that allows one to ob- imaging the luminous sheet (xz'plane) on a slit S tain a plane cross section of the flame and to parallel to the z axis, one measures the light flux visualize the shape of the flame front. Moreover, detected by a photomultiplier by a photocurrent a simple optical device gives the instantaneous that is, consequently, proportional to the position local position of the flame front and, consequently, the velocity by taking the derivative of the electric 2 We can roughly calculate the vaporization time r which signal obtained, is the sum of the time needed to reach the vaporization temperature and of the time for the droplet to be com-An oil-aerosol is injected in the unburned mix- pletely vaporized. In the conditions of our experiments ture. It is evaporated when crossing the flame front this time is about 10-5 s. This time is much smaller than the residence time of the droplet in the flame, which is 10-3 s for a flame velocity of about 10 cm 1 Even in the particular case of the Markstein's slotburner s-1. Furthermore, we were able to measure the velocity [4], the width of the flame is about 4 mm and the ob- profile inside the thickness of a stabilized laminar flame served profile, for the case of a steady cellular flame, for[8] and to show that the oil droplets disappear within instance, is inevitably a mean profile, the flame thickness.