Active control of lift-off tendency and blowout limit extension of turbulent jet diffusion flames by peripheral shear flow

An experimental study is performed to investigate effects of an active control technique proposed herein, named peripheral shear flow, on blowout limits and lift-off tendency of turbulent jet diffusion flames. This technique is achieved by ejecting air peripherally from a rectangular tube set at a position off the center of a fuel nozzle where a jet flame is formed. Here the main stream of air does not hit the flame directly but its periphery intervenes with the flame surface to form shear flows. It is found that (1) flame blowout limits and lift-off heights are extended and lowered, (2) the base of a lifted flame is anchored to positions desired by varying axial displacements of the tube, and (3) the above effects are attributed to mixing enhancement as well as the formation of large-scale vortices when this technique is applied.