Flame saturation current as a measure of the flame thermo-acoustic behavior

This paper explores the idea to use the chemi-ionization process present in combustion to detect the thermo-acoustic instabilities and to determine the response of flames to acoustic velocity fluctuations. Burner stabilized flat methane-air flames of various mixture parameters are investigated. The flame acoustic interaction is characterized by flame transfer functions. The thermo-acoustic behavior of the flame is measured using the saturation current as indicator for the flame response. The results are compared with transfer functions, where the flame response is characterized by the emitted OH ^* chemiluminescence intensity. The thermo-acoustic response measured by these two methods show excellent agreement in the TF phase shift. Good correspondence in gain is observed for lean flames, for stoichiometric and rich flames a difference in gain is measured. The obtained results indicate that the chemiionization process can be a promising alternative indicator for thermo-acoustic instabilities.