Behavior of a Triple Flame Changing in Concentration Gradients

研究了不同燃料浓度梯度下二维甲烷-空气三重火焰的特性。本文首次定义了无量纲浓度梯度（Cm/xm），在稳态条件下，用干涉滤光片测量OH自由基的发光强度。结果表明，在较平缓的浓度梯度下（Cm/xm<2.5），OH自由基发光强度与火焰热值无相关性。该区域（Cm/xm<2.5）被定义为主要由预混火焰组成的三重火焰区域（区域I）。利用PIV和激光层析成像技术对三重火焰前缘的流场和热结构进行了测量。根据这些结果，我们将区域（Cm/xm>50.0 <$50.9）定义为主要由非预混火焰组成的三重火焰区域（区域II）。将区域I和区域II之间的区域（2.5<Cm/xm<50.0 <$50.9）定义为非线性。 关于我们 三重火焰区（III区）。由具有浓度梯度的预混混合物构成的三重火焰的燃烧速度大于在均匀混合物中形成的预混火焰的最大燃烧速度。预混火焰翼和非预混火焰之间存在火焰相互作用。由于这种相互作用，火焰强度随浓度梯度的增大而增大，利用浓度梯度由陡变缓或由缓变陡的瞬时变化研究了三重火焰的过渡响应。在由陡变缓的条件下，到达火焰浓度变化的时间与预混火焰翼打开的时间之间存在滞后。这种现象是由于火焰相互作用，特别是非预混火焰与富油预混火焰的融合效应造成的。定态条件的结果表明，并合效应作用于Ⅲ区。当燃烧室内浓度梯度发生非定常变化时，必须考虑从Ⅱ区到Ⅲ区过渡的时滞。少

Characteristics of a 2D methane-air triple flame are made clear in various fuel concentration gradients. In this research non-dimensional concentration gradients (Cm/xm) are defined originally.At the stationary condition, OH radical luminous intensity is measured by using an interfering filter. The results show that the OH radical luminous intensity does not correlate with flame heat values at gentle concentration gradients (Cm/xm<2.5). This region (Cm/xm<2.5) is defined as a triple flame region mainly composed of premixed flame (region I).Next, flame positions and distributions of luminous intensity are measured from visible flame images. The flow field and thermal structure at the leading edge of the triple flame are also measured by PIV and laser tomography. From these results, we define the region (Cm/xm>50.0 〜 50.9) as a triple flame region mainly composed of non-premixed flame (region II). And the region between region I and region II (2.5<Cm/xm<50.0 〜 50.9) is defined as the nor … More mal triple flame region (region III). A burning velocity of the triple flame composed of premixed mixture with a concentration gradient is larger than the maximum burning velocity of a premixed flame formed in the uniform mixture. There is a flame interaction between the premixed flame wing and the non-premixed flame. Because of this interaction effect, Hie flame intensity goes up with the increase of the concentration gradient.The transitional response of triple flame is studied using the instantaneous change of concentration gradient from steep to gentle or vise versa. Under the condition from steep to gentle, there is a lag between the time of reaching the concentration change to the flame and the time of opening the premixed flame wing. This phenomenon is due to the flame interaction, especially the merging effect between the non-premixed flame and the rich premixed flame. The results of the stationary condition indicate that merging effect acts at region III. When the concentration gradient change in unsteady state at the combustor, we have to consider the time lag of transition from region II to region III. Less