The influence of a flameholder on a plane flame, including its static stability
The influence of a flameholder on a plane flame, including its static stability
复制标题
火焰稳定器对平面火焰的影响，包括其静态稳定性
DOI：
10.1098/rspa.1980.0118
复制
发表时间：
1980
期刊：
影响因子：
--
通讯作者：
A. McIntosh
中科院分区：
文献类型：
--
作者：
J. F. Clarke;A. McIntosh
本文用大活化能渐近法分析了共面多孔塞式燃烧器附近的平面预混火焰。结果表明，对于给定的混合物当量比，通过保持器的反应物质量流量与燃气温度之间存在唯一的关系。火焰保持器的一个简单的线性热通量温度模型引入了一个比例常数，称为保持器的电导。传导性对火焰行为的细节有很大的影响;特别是从火焰预热区到火焰保持器的热通量受传导性的控制，保持器表面和火焰片之间的距离也受传导性的控制。它还表明，尽管上述事实，热通量，必须提供在保持器或从一些外部机构，如冷却剂，实际上是独立的电导。对火焰-火焰稳定器系统进行了详细和全面的分析，确定了电导的临界值（取决于混合气当量比）。此外，一个无量纲数，称为a，等于比热乘以反应物的质量通量除以电导，对火焰和火焰稳定器之间存在的平衡类型有重要的影响。如果a < 1，所有平衡解通过保持器的质量通量都小于给定当量比下的绝热质量通量;它们要求冷却剂从系统中带走热量。当a > 1时，平衡质量通量必须超过绝热值，并且“冷却剂”必须向系统提供热量。对于几个固定的单位面积单位时间冷却剂热损失值，进口流速与当量比的关系图表明，对于给定的当量比，要么有两个平衡进口速度，要么根本没有平衡进口速度。这一结果与博塔和斯伯丁（*954）的实验观察结果雅阁。火焰稳定器表面存在一个可分辨的空间原点，这意味着火焰的静态稳定性可以被定义为一个单一的平面薄片。域的静态稳定性和不稳定性的确定，并帮助解释观察火焰行为的共面保持器。静态稳定性或不稳定性补充了扩散不稳定性;然而，静态稳定性边界不受刘易斯数的影响，扩散机制也是如此。尽管在给定当量比下质量流量超过绝热值的气流中的火焰大多数是静态不稳定的，因此在实践中是找不到的，但分析预测，在某些情况下，如果流速超过可计算的最小值，在大于绝热的流速下，平面火焰可以稳定在保持器上。
The plane pre-mixed flame adjacent to a coplanar porous-plug type of burner is analysed with the aid of large-activation energy asymptotics. It is shown th at there is a unique relation between the mass flux of reactants through the holder and the burnt-gas temperature for a given value of the mixture equivalence ratio. A simple linear heat-flux-temperature model of the flameholder introduces a constant of proportionality called the conductance of the holder. The conductance has a strong influence on the details of flame behaviour; in particular the heat flux from the preheat regions of the flame into the flameholder is governed by the conductance, as is the stand-off distance between the face of the holder and the flame-sheet. It is also shown that, despite the foregoing facts, the heat flux that must be provided at the holder to or from some outside agency, such as a coolant, is actually independent of the conductance. A detailed and general analysis of the flame-flameholder system identifies a critical value for the conductance (that depends upon the mixture equivalence ratio). In addition a dimensionless number, called a, that is equal to the specific heat multiplied by the mass flux of the reactants divided by the conductance, has an important bearing on the type of equilibrium that exists between the flame and the flameholder. If a < 1 all equilibrium solutions have a mass flux through the holder that is less than the adiabatic mass flux at the given equivalence ratio; they require that heat shall be abstracted from the system by the coolant. When a > 1 the equilibrium mass flux must exceed the adiabatic value, and the ‘coolant’ must supply heat to the system. A plot of inlet flow speed against equivalence ratio for several fixed values of the heat-loss to the coolant per unit area per unit time shows that there are either two equilibrium inlet speeds for a given equivalence ratio or none at all. This result is in in accord with the experimental observations of Botha & Spalding (*954)- The existence of a distinguishable spatial origin (the flameholder surface) means that the static stability of the flame, considered as a single plane sheet, can be defined. Domains of static stability and instability are identified, and help to explain observations of flame behaviour on a coplanar holder. Static stability or instability complements diffusional instabilities; however, static stability boundaries are not affected by the Lewis number, as are those of the diffusional mechanism. Despite the fact that most of the flames in streams the mass flux of which exceeds the adiabatic value at a given equivalence ratio are statically unstable, and are therefore not to be found in practice, the analysis predicts th at plane flames can be stabilized on a holder in some circumstances at flow rates greater than the adiabatic if the flow speed exceeds a calculable minimum.