Diagnostics of flame instability in a premixed surface flame burner using frequency analysis

This study investigates the stability of a surface flame burner using a photodiode and data acquisition system. The light intensity fluctuations were measured by the photodiode and, using fast Fourier transform, they were transferred from the temporal to the frequency space. To illustrate the dynamic behavior of premixed flames, flames are divided into two regions of cellular flames and surface flames. This classification is dependent on the flow rate and the equivalence ratio. In surface flames, as the flow rate increases, the oscillation frequency also increases because the hot burned gas velocity increases. In cellular flames, as the flow rate increases, oscillation frequency decreases. At identical flow rates, the sharp decrease in the oscillation frequency indicates the appearance of cellular flames so we can find the transition from the surface flame to the cellular flame. At a constant flow rate, with an increase in the equivalence ratio, there is no increase in the oscillation frequency, the transition from the cellular flame to the surface flame occurs. The initiation of the transition from the cellular flame to the surface flame occurs at flow rates of 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 m3 / h and at equivalence ratios of 0.6 , 0.62, 0.62, 0.64, 0.66, and 0.67, respectively. The location of the transition corresponds to the start of the liftoff zone based on image processing. This research is innovative because it is possible to evaluate flame stability using a non-intrusive method without disturbing the flame shape and damaging the flame regime.