EFFECTS OF THE AIR - FUEL EJECTION VELOCITY RATIO ON THE COMBUSTION CHARACTERISTICS AND THE UNBURNED GAS COMPOSITIONS OF THE PROPANE -AIR RAPIDLY MIXED TUBULAR FLAME COMBUSTION

摘要

In this paper, effects of the difference between the air injection velocity and the fuel injection velocity on the rapidly mixed tubular flame have been investigated. A parameter of α_(st), which is the ratio of the air injection velocity to the fuel injection velocity at stoichiometric condition has been introduced, and five tubular flame burners with different α_(st) 0.6,1.2,2.4, 6.0 and 11.9 were examined. Stability limits of the propane-air flame and the local fuel concentrations of unburned mixture have been determined. Results show that, with α_(st) = 0.6 and α_(st) =1.2, in burner a stable tubular flame can be established in the range of Φ = 0.45 to 2.1 and Φ= 0.48 to 2.15. When α_(st) is increased to 2.4, in which the air injection velocity is almost two times higher than that of the fuel at stoichiometric condition, the stable combustion range shifts to the relatively fuel rich side of Φ = 0.55 to 2.35. With further increase in the α_(st) to 6.0 and 11.9, stable combustion range shifts to richer side of Φ= 0.6 to 2.45, and 0 = 0.7 to 2.9, respectively. Results of gas analysis have revealed that, for α_(st) =0.6 and α_(st) =1.2, although the total equivalence ratio of supplied air and fuel were stoichiometric, a fuel rich mixture gas of Φ= 1.13 and Φ = 1.17 was formed locally at the center of the burner. Increasing in the α_(st), leads to a decrease in the local equivalence ratio, such as Φ= 0.95, 0.42, and 0.19 for α_(st) = 2.4, 6.0 and 11.9, respectively. These results indicate that the mixing process of air and fuel in the rapidly mixed tubular flame is greatly affected by the injection velocity ratio, suggesting the possibility of the flame front structure control by the injection velocity ratio.