Decomposition of combustion noise scaling rules by direct flame photography

Abstract

In order to estimate the scaling rules for combustion noise, a turbulence autocorrelation function of the reaction rate must be estimated. This depends in part upon the active reaction volume in a turbulent flame. This volume may be measured by direct flame photography centering on the radiation of an active radical in the reaction zone. The paper describes experiments on fuel-lean propane, propylene, and ethylene-air turbulent open premixed flames with burners of 0.4″–0.96″ diameter and velocities to 600 fps. The flame volume is measured from photographs of the flame centered on the CH emission. The volume is correlated to the flow velocity, burner diameter, laminar flame speed and fuel mass fraction in the form of a power law by a regression technique. The scaling rule obtained from experiments is shown to follow the law V∝UD 3F 3 S L . The scaling laws generated are compared with estimates previously drawn from Strahle's theory of combustion noise. Implications concerning the turbulence structure in the reaction zone are drawn from the correlations.