The Propagation of a Fuel-Air Ratio Disturbance in a Simple Premixer and its Influence on Pressure Wave Amplification

The propagation of a fuel concentration disturbance in a premixer is studied analytically with a 3-D spatio-temporal mixing model. A simple analytical method is introduced which permits the frequency response characteristics of multiple points of fuel injection in simple (yet meaningful) premixer passage geometries to be obtained. The results provide physical insight into some of the design parameters that may affect the amplitude of FAR fluctuations coming out of a premixer when it is subjected to finite amplitude pressure waves. The possibility of a given design to lead to amplification of pressure waves (Rayleigh’s criteria) can be influenced by the characteristics of the mixing processes in a premixer channel. Results obtained in this paper may affect the design implementation of some of the proposals made for the control of combustion instability such as introduction of multiple time delays through selective fuel placement in a premixer.Copyright © 2000 by ASME