An Experimental Study of Coupling between Combustor Pressure, Fuel/Air Mixing, and the Flame
Dal Mo Kang, California Institute of Technology, Graduate Student, 1200 E. California Blvd, m/c 301-46, Pasadena, CA 91125, Albert Ratner, Mechanical Engineering, University of Iowa, Assistant Professor, 3131 Seamans Center, Iowa City, IA 52242, and Fred E. C. Culick, California Institute of Technology, Professor of Mechanical Engineering and Jet Propulsion, 1200 E.California Blvd, m/c 301-46, Pasadena, CA 91125.
Fuel-air mixing behavior under the influence of imposed acoustic oscillations has been studied by investigating the response of the fuel mixture fraction field. The distribution of local fuel mixture fraction inside the mixing zone, which is expected to evolve into the local equivalence ratio in the flame zone, is closely coupled to unstable and oscillatory flame behavior. The Experiment was performed with an aerodynamically-stabilized non-premixed burner. In this study, acoustic oscillations were imposed at 22, 27, 32, 37, and 55Hz. Phase-resolved acetone PLIF was used to image the flow field of both isothermal and reacting flow cases and this data along with the derived quantities of temporal and spatial unmixedness were employed for analysis. The behavior of the unmixedness factor is compared with the previous measurements of oscillations in the flame zone. This comparison shows that local oscillations (of order millimeters or smaller) in fuel/air mixing are closely related to the oscillatory behavior of the flame. For each driving frequency, the mixture fraction oscillates at that frequency but with a slight phase difference between it and the pressure field/flame intensity, indicating that the fuel mixture fraction oscillation are likely the major reason for oscillatory behaviors of this category of flames and combustor geometry.