An experimental study on the flame structure control in a rapidly mixed type tubular flame burner

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 α st = 4.8, whereas the limits shift in the fuel lean side when α st = 0.5 as compared with α st = 1.0. According to the result of the flame chemi-luminescence measurement, combustion is intensified in relatively fuel rich side when α st = 4.8, whereas combustion is intensified in the fuel lean side when α st = 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 Φ local. At the center of the burner, a relatively fuel lean mixture is formed when α st = 4.8, whereas a relatively fuel rich mixture is formed when α st = 0.5 as compared with α st = 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. © 2012 The Japan Society of Mechanical Engineers.