FEEDBACK-CONTROL OF COMBUSTION OSCILLATIONS

Combustion oscillations are excited by a feedback mechanism which resu lts from the coupling between the flame instability and an acoustic re sonance mode of the combustion chamber. The most important event of th is mechanism is believed to be the upstream feedback from the acoustic resonance to the initial region of the flame, where new disturbances are generated. A control system has been implemented into a commercial household burner to counteract this upstream feedback. This is achiev ed by means of pulsating either the fresh air for combustion or the fu el. The actuators are activated by the signal of a sensor measuring th e pulsation inside either the combustion chamber or the fresh air supp ly pipe. Combustion oscillations of this burner have been eliminated a ltogether, also when two modes were simultaneously excited, without de stabilizing other acoustic modes. This results in 35 dB reduction in t he amplitude of the pressure pulsation. Furthermore, when the combusti on process was stable, i.e. no resonances were excited, the use of act ive control has reduced the broad-band noise by 4 dB. The effect of th e input sensor location on the control system performance has also bee n investigated. (C) 1998 Academic Press.