Effects of the swirl number S and the injection velocity ratio α on the structure of a rapidly mixed tubular flame have been experimentally investigated. Extinction limits, distributions of the flame chemi-luminescence, and distributions of local equivalence ratios of the unburned gas have been determined. Results show that, with the burners of different swirl numbers (S = 2.5, 5.0), the total equivalence ratio at the lean and the rich extinction limits are almost the same, however, both the limits shift on the relatively fuel rich side when αst = 4.8, whereas the limits shift in the fuel lean side when αst = 0.5 as compared with αst = 1.0. According to the result of the flame chemi-luminescence measurement, combustion is intensified in relatively fuel rich side when αst = 4.8, whereas combustion is intensified in the fuel lean side when αst = 0.5. Results of the gas analysis have revealed that, these changes in the extinction limits and combustion intensities are attributed to the change in the local equivalence ratio Φlocal. At the center of the burner, a relatively fuel lean mixture is formed when αst = 4.8, whereas a relatively fuel rich mixture is formed when αst = 0.5 as compared with αst = 1.0. These results indicate that, with use of the injection velocity ratio, a flexible, as well as an accurate structure control of rapidly mixed tubular flames is possible.
