Effects of Different Kinds of Fuel and Fuel Equivalence Ratio on Flame Structure of Triple Flame.
Effects of Different Kinds of Fuel and Fuel Equivalence Ratio on Flame Structure of Triple Flame.
复制标题
不同种类燃料及燃料当量比对三重火焰火焰结构的影响。
DOI：
10.1299/kikaib.65.775
复制
发表时间：
1999
期刊：
影响因子：
--
通讯作者：
N. Choi
中科院分区：
文献类型：
--
作者：
H. Yamashita;Shinya Tsutsumitani;N. Choi
为了弄清不同燃料种类和燃料当量比对火焰结构的影响，在考虑基本化学反应机理的情况下，对甲烷-空气或氢-空气混合物和气流共流中形成的三重火焰进行了数值模拟。得到以下结论：(1)三元火焰的表观燃烧速度与燃料当量比的关系与相应燃料的一维预混火焰的关系具有相似的趋势。但视在燃烧速度最大时的燃料当量比略大于一维预混火焰。甲烷空气或氢-空气混合物的视燃烧速度比一维预混火焰高2倍和3倍。(2)火焰在混合物与气流交界的下游向前喷出，一部分气流在这一突出的火焰中弯曲分叉，形成三重火焰；该三重火焰由富贫预混火焰分支和扩散火焰分支组成。由一维预混火焰的作用引起的凸部形状的变化，由放热带来的膨胀引起的流体动力不稳定性的作用进一步促进。对于甲烷混合气，两个预混火焰分支的中心几乎存在一个相当强的扩散火焰分支，而对于氢气混合气，一个相当弱的扩散火焰分支接近燃料贫预混火焰分支。(3)在一维预混火焰燃烧速度最大的燃料当量比附近，一维预混火焰的效果变大，富燃料预混火焰向前推进，与流动方向垂直。因此，水动力失稳的影响被削弱。因此，这两种效应都表明，视在燃烧速度最大时的燃料当量比略大于一维预混火焰的燃料当量比。
In order to clarify the effects of different kinds of fuel and fuel equivalence ratio on flame structure, a numerical simulation of triple flame developed in a co-flowing methane-air or hydrogen-air mixture and air stream was made taking into account the elementary chemical reaction mechanism. The following conclusions were reached: (1)The relation between the apparent burning velocity of the triple flame and the fuel equivalence ratio shows a similar tendency to that of the one-dimensional premixed flame of the corresponding fuel. However, the fuel equivalence ratio at which the apparent burning velocity is the largest is a little larger than that of the one-dimensional premixed flame. The apparent burning velocities are two and three times higher than that of the one-dimensional premixed flame for the methane air or hydrogen-air mixture. (2)The flame thrusts out forward in the downstream of the boundary between mixture and air stream, and a part of the flow is bent and forks out in this protruding flame so that a triple flame is originated; this triple flame is composed of fuel rich and lean premixed flame branches and a diffusion flame branch. The change in shape of the convex part, caused by the effect of the one-dimensional premixed flame, is further promoted by the effect of hydrodynamic instability originated in the expansion brought about by heat release. A considerably strong diffusion flame branch exists almost in the center of the two premixed flame branches for the methane air mixture, while a considerably weak diffusion flame branch approaches the fuel lean premixed flame branch for the hydrogen air mixture. (3)Near the fuel equivalence ratio at which the burning velocity of the one-dimensional premixed flame is the largest, the effect of the one-dimensional premixed flame becomes large and the fuel rich premixed flame advances and becomes vertical to the flow direction. As a result, the effect of hydrodynamic instability is weakened. Thus, both of these effects demonstrate that the fuel equivalence ratio at which the apparent burning velocity is the largest is a little larger than that of the one dimensional premixed flame.