Effect of Fuel-Air Mixture Heterogeneity on Vibrations in Continuous Combustion Systems

Abstract

High vibration amplitudes can be a sign of impending failure or deterioration of equipment. In this work, a rarely researched phenomena, namely the effect of fuel heterogeneity in continuous combustion systems on the induced vibration and noise, is studied. The vibration pattern is obtained via a real-time spectrum analyzer. The use of spectrum analyzer with proper filtering made it possible to distinguish between the induced aerodynamic and combustion vibration. This could be done by comparing the vibration characteristic of reacting and nonreacting cases. Noise measurements are also obtained using a sensitive sound level meter. The results show a remarkable effect of the fuel heterogeneity ratio on the vibration and noise pattern. For liquified petroleum gas (LPG) and kerosine the vibration amplitudes at all frequencies were found to decrease with the increase of the air mass flow rate and henceforth increase after they attain certain minimum. The minimum amplitudes were in the range of 80 to 100 kg/h depending on the heterogeneity ratio. For intermediate values of LPG percentage an opposite trend was noticed i.e. the vibration level is first increased as the air mass flow rate increases until it attains a maximum then it decreases with any further increase in the air mass flow rate. Concerning the noise, slight effect of heterogeneity was observed in the high frequency noise pattern, however the low frequency noise (combustion roar) was found to be increasing with the increase of heterogeneity ratio.