DIRECT AND INDIRECT MEASUREMENTS OF MARKSTEIN NUMBERS OF PREMIXED FLAMES

This work reports experimental measurements of the Markstein number (sensitivity to strain and curvature) of premixed diluted flames of hydrogen, methane, ethylene, and propane. Measurements are made on weakly stretched freely propagating quasi-planar flames. Three different methods of deducing the Markstein number are presented and compared-a direct method in which the stretch and the change in burning velocity are measured locally, a global method based on the amplitude of the response of the flame to a periodic shear flow, and a third method that relates the Markstein number to the burning velocity at which an unperturbed flame spontaneously develops cellular structures. The direct method is found to give the least precise results.