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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.

An Experimental Investigation on Flame Stability and Lean Extinction Limit in Tubular Flame Burners Operating on Jet Fuel