Self-excited noise generation from laminar methane/air premixed flames in thin annular jets

Abstract

Self-excited noise generation from laminar flames in thin annular jets of methane/air premixture have been investigated experimentally. Various flames were observed in this flow configuration, including conical shape flames, ring shape flames, steady crown shape flames, and oscillating crown shape flames. Self-excited noise with the total sound pressure level of about 70 dB was generated from the oscillating crown shape flames for the equivalence ratios larger than 0.95. Sound pressure and CH* chemiluminescence were measured by using a microphone and a photomultiplier tube. The frequency of generated noise was measured as functions of equivalence ratio and premixture velocity. A frequency doubling phenomenon has also been observed. The measured CH* chemiluminescence data were analysed from which the corresponding sound pressure has been calculated. By comparing the data with those of measured ones, the noise source can be attributed to the flame front fluctuation near the edge of the oscillating crown-shape flames. The flame stability regime was influenced sensitively to the supplying air through the inner tube.</p