OH- PLIF studies of acoustically forced swirl flames

Lean premixed combustors are highly susceptible to combustion instabilities, caused by coupling of heat release fluctuations with combustor acoustics. In order to predict the conditions under which these instabilities occur and their limit cycle amplitudes, understanding of the amplitude dependent response of the flame to acoustic excitation is required. This paper describes an experimental investigation of the amplitude dependent processes controlling the nonlinear heat release response of a swirling flame to harmonic excitation. In depth OH-PLIF studies were carried out at representative conditions to visualize the spatial dynamics of the flame and hence identify the key controlling physical processes and qualitatively discuss their key characteristics. These results illustrate that the flame response is not controlled by any single physical process but, rather, by several simultaneously occurring processes which are potentially competing, and whose relative significance depends upon forcing frequency, amplitude of excitation, and flame stabilization dynamics.