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Structure of a reacting hydrocarbon-air planar mixing layer

机译：反应性烃-空气平面混合层的结构

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The structure of a reacting hydrocarbon-air two-stream planar mixing layer was investigated experimentally with non-premixed reactants under pressurized conditions. Propane and dimethyl ether (DME) diluted with argon or nitrogen was used as the fuel stream while heated air was used as the oxidizer. Experiments were performed at a range of Reynolds numbers in both the pre- and post-mixing transition portions of the mixing layer under conditions where the lean reactant (air) was placed in either the high-speed (AHS) or low-speed stream (FHS). The reacting mixing layer was visualized using a combined OH LIF/soot LII technique, wherein the reaction zone and the region of parent fuel entrainment and decomposition were simultaneously imaged. In both AHS and FHS cases at all Reynolds numbers examined, the mixing layer consisted of two regions: a high temperature reaction zone with a laminar appearance found on the oxidizer side of the mixing layer and an 'internal' mixing layer in which products mixed with pyrolized fuel in a manner reminiscent of a two-stream non-reacting mixing layer. The location and dynamics of the soot formed within the mixing layer were closely related to the mixing behavior of the large-scale structures. The regions of highest soot volume fraction were found in low temperature regions near the location of raw fuel entrainment. There was no significant broadening of the high-temperature reaction zone or increase in flame area under turbulent conditions due to the lack of dilution of the freestream conditions, unlike previous observations in jet flames. Changes in the inlet streams which affected chemistry did not appear to cause significant changes in the overall mixing layer structure shown in the OH/LII images. However, finite-chemistry effects were discernable with temperature measurements and indicated that reduced product formation was observed with reductions in a characteristic Damkohler number, Da. The point of flame lift-off was shown to occur at Da < 1 over a wide range of operating conditions that caused changes in mixing or chemistry.
机译：在加压条件下，用非预混合的反应物对烃-空气两流平面混合反应层的结构进行了实验研究。丙烷和用氩气或氮气稀释的二甲醚（DME）用作燃料流，而加热的空气用作氧化剂。在将贫化反应物（空气）置于高速（AHS）或低速流中的条件下，在混合层的混合前和混合后过渡部分的雷诺数范围内进行实验（ FHS）。使用混合的OH LIF /烟灰LII技术对反应混合层进行可视化，其中同时对反应区和母体燃料夹带和分解区域进行成像。在所有雷诺数下的AHS和FHS情况下，混合层均由两个区域组成：在混合层的氧化剂侧发现具有层流外观的高温反应区和“内部”混合层，其中产物与以类似于两流非反应混合层的方式热解燃料。混合层内形成的烟灰的位置和动力学与大型结构的混合行为密切相关。在靠近原始燃料夹带位置的低温区域中发现了最高烟灰体积分数的区域。不像以前在喷射火焰中观察到的那样，由于缺乏自由流条件的稀释，在湍流条件下高温反应区没有明显的拓宽或火焰面积的增加。影响化学反应的进料流的变化似乎并未引起OH / LII图像中所示的整体混合层结构的显着变化。然而，通过温度测量可以分辨出有限的化学作用，并表明观察到的产物形成减少，而特征性的Damkohler数Da减小。结果表明，在引起混合或化学变化的各种运行条件下，火焰抬升点发生在Da <1处。

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