A preliminary investigation of low frequency combustion instability has been conducted in an atmospheric combustion facility.The result indicates that at higher equivalence ratios

typically above 06

the combustion process becomes highly unstable

exhibiting large-amplitude pressure oscillations at some frequencies between 200 Hz and 235 Hz.The frequency and amplitude of instability grow with increasing premixed gas injection velocity.The result also shows that the instability mode changes when the exit area of the combustor decreases to some critical value.