An extensive experimental study is carried out to analyze scaling laws for the length of methane oxy-flames stabilized on a coaxial injector. The central methane fuel stream is diluted with N₂, CO₂ or He. The annular air stream is enriched with oxygen and can be impregnated with swirl. Former studies have shown that the stoichiometric mixing length of relatively short flames is controlled by the mixing process taking place in the vicinity of the injector outlet. This property has been used to derive scaling laws at large values of the stoichiometric mixture fraction. It is shown here that the same relation can be extended to methane oxy-flames characterized by small values of the stoichiometric mixture fraction. Flame lengths are determined with OH* chemiluminescence measurements over more than 1000 combinations of momentum ratio, annular swirl level and composition of the inner and outer streams of the coaxial injector. It is found that the lengths of all the flames investigated without swirl collapse on a single line, whose coefficients correspond to within 15% of flame lengths obtained for fuel and oxidizer streams at much larger stoichiometric mixture fractions. This relation is then extended to the case of swirling flames by including the contribution of the tangential velocity in the flow entrainment rate and is found to well reproduce the mixing degree of the two co-axial streams as long as the flow does not exhibit a vortex breakdown bubble. At higher swirl levels, when the flow features a central recirculation region, the flame length is found to also directly depend on the oxygen enrichment in the oxidizer stream.

进行了广泛的实验研究，以分析定标在同轴喷油器上稳定的甲烷氧焰长度的定律。中央甲烷燃料流用N ₂，CO ₂稀释或他。环形空气流中富含氧气，可以用旋流浸渍。以前的研究表明，相对较短的火焰的化学计量混合长度是由在喷油嘴出口附近进行的混合过程控制的。此属性已用于导出化学计量混合物分数较大时的缩放定律。在此表明，相同的关系可以扩展到以化学计量混合物分数较小的特征为特征的甲烷氧化火焰。火焰长度是通过OH *化学发光法测量的，测量的是动量比，环形涡旋水平以及同轴喷油器内流和外流组成的1000多种组合。发现没有旋流的所有被研究火焰的长度在一条直线上坍塌，其系数对应于在大得多的化学计量混合物分数下获得的燃料和氧化剂流的火焰长度的15％以内。然后，通过将切线速度的贡献包括在夹带流率中，将该关系扩展到涡旋火焰的情况，并且发现该关系可以很好地重现两个同轴流的混合程度，只要该流不显示涡流即可。击穿泡沫。在较高的涡流水平下，当流动具有中央再循环区域时，发现火焰长度也直接取决于氧化剂流中的氧气富集。然后，通过将切线速度的贡献包括在夹带流率中，将该关系扩展到涡旋火焰的情况，并且发现该关系可以很好地重现两个同轴流的混合程度，只要该流不显示涡流即可。击穿泡沫。在较高的涡流水平下，当流动具有中央再循环区域时，发现火焰长度也直接取决于氧化剂流中的氧气富集。然后，通过将切线速度的贡献包括在夹带流率中，将该关系扩展到涡旋火焰的情况，并且发现该关系可以很好地重现两个同轴流的混合程度，只要该流不显示涡流即可。击穿泡沫。在较高的涡流水平下，当流动具有中央再循环区域时，发现火焰长度也直接取决于氧化剂流中的氧气富集。