ABSTRACT

To solve problems of the low burn-off rate and the flame instability in a conventional rapidly mixed tubular flame (RMTF) burner and problems of the flashback and the narrow extinction limits in a premixed tubular flame burner, a new fuel/air mixing mode with multi-staged inlets was proposed and applied to a tubular flame burner, called the multi-staged tubular flame (MSTF) burner. To understand the mechanism of the fuel/air mixing mode of MSTF burner and their effects on the combustion, a series of experiments and simulations were carried out in comparison with the RMTF burner, operating on RP-3 jet fuel in this work. High-speed photography was applied to examine the flame characteristics of the two burners based on the flame irradiance intensity and flame morphology analysis combined with statistic methods. The results show that the tubular flames can be established stably without flash-back for both two burners in a wide range of equivalence ratios. The lean extinction limits can be extended to a global equivalence ratio as low as Ф_g = 0.26 for MSTF burner, while Ф_g = 0.40 for RMTF burner. Planar laser induced fluorescence (PLIF) measurements and 3D CFD simulations were also conducted to see the difference in fuel/air distributions for the two mixing modes of MSTF and RMTF burners at cold conditions. One of the findings is that the MSTF burner has better flame stability and wider extinction limits than the RMTF burner. The physics is that there stably forms a fuel-rich zone in the upstream of the inlet section which increase the resident time of rich fuel/air mixtures. The reveal of this mechanism for the multi-staged mixing mode is important as it has swept the main hurdles for the burner to find more applications to the industries.

摘要

为解决传统快速混合管式火焰（RMTF）燃烧器燃尽率低、火焰不稳定的问题，以及预混管式火焰燃烧器的回火和熄火极限窄的问题，提出了一种新型的燃料/空气混合模式。提出了多级入口并将其应用于管状火焰燃烧器，称为多级管状火焰（MSTF）燃烧器。为了了解 MSTF 燃烧器的燃料/空气混合模式的机理及其对燃烧的影响，在本工作中，与使用 RP-3 喷气燃料的 RMTF 燃烧器进行了比较，进行了一系列实验和模拟。在火焰辐照强度和火焰形态分析的基础上，结合统计学方法，采用高速摄影对两种燃烧器的火焰特性进行检测。结果表明，在较宽的当量比范围内，两种燃烧器均能稳定地建立管状火焰而不会产生回火。稀薄消光极限可以扩展到全球当量比低至Ф _g  = 0.26 用于 MSTF 燃烧器，而Ф _g  = 0.40 用于 RMTF 燃烧器。还进行了平面激光诱导荧光 (PLIF) 测量和 3D CFD 模拟，以了解 MSTF 和 RMTF 燃烧器的两种混合模式在寒冷条件下的燃料/空气分布差异。其中一项发现是 MSTF 燃烧器比 RMTF 燃烧器具有更好的火焰稳定性和更宽的消光极限。物理原理是在入口段上游稳定地形成富油区，增加了富油/空气混合物的停留时间。揭示这种多级混合模式的机理是很重要的，因为它扫清了燃烧器在行业中寻找更多应用的主要障碍。