Interferometric Determination of Heat Release Fluctuations

New concepts of low-emission combustion chambers for gas turbines are operating in the lean regime (equivalence ratio F less than unity) mainly in order to reduce emissions of NOx to meet the stringent pollutant regulations set by the governments. These new technologies are, however, sensitive to combustion instabilities which are indicated by synchronized oscillations of unsteady heat release and pressure fluctuations. The combustion oscillations may reach unacceptable levels leading to flame transition, intensification of heat flux to solid parts, flash-back, and structural damages. For control purposes, perturbations of these quantities have to be assessed in the flame zone, which is in practice difficult to realize and different strategies are therefore investigated. Recent collaboration between TU Graz and ECP has lead to the development of an alternative technique based on laser interferometric vibrometry (LIV). The objective of this project is to obtain time and space resolved data on density and heat release rate fluctuations within the flame region by laser interferometric vibrometry. The technique will be applied to different configurations of increasing complexity starting with premixed laminar generic unconfined pulsated flames and ending up with turbulent confined swirling flames. Effects of the different flow parameters and the underlying physics will be assessed.