THE INTERACTION BETWEEN A LAMINAR FLAME AND ITS SELF-GENERATED FLOW

The interaction between a premixed laminar flame and its self-generated flow is experimentally studied in a closed duct. The simple geometry of the duct allows fundamental understanding of the mechanisms involved in the flame/flow interaction. This understanding is applicable to more complex combustion situations.;The one-dimensional model accurately predicts the unburned gas motion. The flow in the burned gas is rotational because of vorticity generated from flow deflection through the curved flame front. The density difference between the burned and unburned gas requires a velocity jump at the flame front to maintain continuity of mass flux. The measured velocity jump corresponds to this predicted value.;A large flame cusp, called a "tulip" flame appears during the flame propagation. Flame instability, pressure wave/flame interaction, and large scale circulation in the unburned gas are suggested explanations for the "tulip" flame. Velocity measurements of this work show that no large scale circulation exists in the unburned gas. Instead, the measurements suggest another likely mechanism for the "tulip" formation. The onset of the "tulip" process coincides with the quench of part of the flame at the sidewalls of the combustion vessel. The velocity decrease in the unburned gas and the curved flame shape at the time of quench combine to generate a vortex in the burned gas. The vortex remains in the proximity of the flame and modifies the flame shape and unburned gas field such that the flame cusp or "tulip" is formed.;A laser Doppler anemometer measures two components of the enclosed gas velocity during the flame propagation. The measurements provide a complete vector velocity map of the flame generated flow. High-speed schlieren cinematography is used to observe changes in flame shape and location. Pressure records correlate with the qualitative schlieren movies and help quantify the progress of the combustion process. The experimental results are interpreted using a one-dimensional flame model and a two-dimensional description of flow deflection through an oblique flame sheet.