Abstract
The response characteristics of a lean methane-air premixed flame to equivalence ratio oscillation was investigated experimentally. In order to clarify unsteady flame response from the actual measured values of the burning velocity, we developed a new burner that allowed measurement of the flow field by using particle image velocimetry (PIV). Chemiluminescent emission intensity of CH radical, which is correlated with the combustion intensity of the lean flame, was also measured by using high speed camera with a band pass filter. The equivalence ratio was varied sinusoidally only in the direction of the main flow at burner exit by two speakers. For an oscillation with mean equivalence ratio of 0.85, amplitude of 0.05 and the oscillation frequency ranging from 5 to 10 Hz, following results were obtained: The variation widths of burning velocity and CH radical emission intensity in fluctuating flame are increased as oscillation frequency increases. These variation widths are larger than those of a steady flame in the equivalence ratio range corresponding to the fluctuation. This means that when the flame moves against (along) the fuel flow, the mass flux at the flame front increases (decreases) as compared with that of the steady flame.
