Measurements and Modeling of the Dynamic Response of a Pilot Stabilized Premixed Flame Under Dual-Input Perturbation

Abstract

Pilot flame have been widely used for flame stabilization in low-emission gas turbine combustors. However, effects of pilot flame on dynamic instabilities are not well understood. In this work, the dynamic interactions between main and pilot flames were studied by measurements and modeling in the flame response, with both flames subjected to perturbation, i.e., with a dual-input forcing. The paper analyzed the experimental results of both the total flame response and the interaction process. A burner was designed with central pilot flame to stabilize a premixed axi-symmetric V-shaped methane flame. Servo valve and sirens were used to generate forcing in the pilot and main flames, respectively. A diagnostic system was applied to measure the flame structure and heat release rate. The effects of forcing frequency, forcing amplitude, phase difference between the two forcing signals to the main and pilot flames as well as the Reynolds number were studied. Both the flame transfer function (FTF) and the flame dynamic structure were measured and discussed. It was found that the total flame response was modified by the perturbation in the pilot flame. The mechanism may be lying in the effect of pilot flame on the flow field of the burnt side. To further testify the hypothesis, an analytical model was developed based on the linearized G-equation with low amplitude assumptions. Although the assumptions made in the model to address the effect of pilot flame on the burnt flame flow field were simplified, good agreements were found between the prediction and the experiment results. Based on the analysis conducted in this paper, some further considerations may be needed when developing combustion systems with a central injection, since perturbations in the pilot flame may affect the performance of the main flame. Further experiments and analysis may be needed to dig deeper into the physical basics such as measurements or more realistic modeling of the flow fields and non-linear effects.