Dynamic Mixing Model of a Premixed Combustor and Validation with Flame Response Measurements

Abstract

Convective time delays remain critical for the stability of modern premixed industrial combustors. Because burner design often starts with non-reacting investigations, a method to determine the effective time delay of a swirl-inducing burner from non-reacting measurements and simple flame visualization is proposed. High Speed Laser Induced Fluorescence is used to identify the parameters of a one dimensional convection-diffusion model characterizing the mixing process within the burner. A step function is applied on the fuel injection mass flow, and the mixing response is recorded in a cross plane at the burner outlet. The model is able to predict the complex flow field response and allows for extracting the response of the recirculation zone. Recirculation of fuel in cold flow condition disappears in reacting flow and has to be specifically considered. The flame position is used to correct the time delays estimated in cold flow. Flame transfer function measurements are performed to measure the effective time delays of different fuel injection configurations. A calibration procedure, which estimates the temperature profile upstream of the flame, is necessary to obtain a good agreement between the time delays of the new methods and those obtained with flame transfer function measurements. The results show that the method is able to capture quantitatively the convective time delays associated with the different injection configurations and allow to obtain additional information on the dynamical mixing process of complex swirl-inducing burners from non reacting investigations.