A contribution to the study of low-frequency oscillations in fuel-oil boilers

Abstract

This paper deals with the low-frequency type of oscillations in fuel-oil burners. A simplified theory is presented, which is then used to discuss experimental results concerning the nature of the oscillating system and the conditions of its sustained oscillations. Experiments were performed on a standard domestic boiler fitted with a variable length stack. It is shown that there is no break of continuity between acoustical and nonacoustical types of oscillations. Nevertheless, the experiments indicate that the measured frequencies are of the same order of magnitude as the acoustical frequencies. These frequencies tend to a limit as the length of the stack is increased. In practical systems an important dispersion of the frequency occurs; this, and the fact that the values of frequency are very low, make it difficult to use tuned damping systems. Increasing the pressure head of the fan and improving the stabilization of the flame seem to be the most advantageous means of reducing the oscillation tendency of boilers. Considerable damping is provided by the stack and it is easier to avoid oscillations with greater lengths of stack.