A large number of experimental and theoretical studies have investigated the flame flicker in diffusion flame. It has been known that the flickering frequency ranges from 10 to 20 Hz for a wide variety of burner sizes, flow rates, and compositions. Employing a linear stability analysis, Buckmaster and Peters showed that a modified Kelvin-Helmholtz type instability exists in diffusion flames, predicting a low frequency oscillation around 17 Hz. As experimental studies, Hamins and Sato measured the flickering frequency and correlated Strouhal number and Richardson number. They showed that the two parameters have power law dependence showing the role of buoyancy-induced velocity field on the flickering frequency.
Although the flame flicker is familiar phenomenon in diffusion flame, it is also reported that there exists flame flicker and the flickering frequency ranges from 10 Hz to 20 Hz in premixed flame. Kostiuk obtained an empirical relationship among Strouhal number, Richardson number and Reynolds number.
In the previous studies, both the diffusion and premixed flames were open to ambient air so that buoyancy driven Kelvin-Helmholtz type instability occurred due to the velocity difference between the ambient air and the hot products which were accelerated by the buoyancy force. But the flickering phenomena exist also in the premixed flame confined by a tube, where the outside disturbance does not exist. The flickering frequency and flickering wavelength were measured. From the results, the generation mechanism of flickering phenomena and correlation between Richardson number and dimensionless wavelength of flickering curvature were studied. It is also interesting that the flickering frequency has wider range from 10 Hz to 40 Hz compared to previous studies.