Laminar premixed V-shaped flame response to velocity and equivalence ratio perturbations: Investigation on kinematic response of flame

Abstract

The response of a rod-stabilized, V-shaped, premixed flame to upstream velocity and equivalence ratio perturbations was characterized as a function of excitation frequency. The response of the flame to equivalence ratio perturbations was calculated, assuming that the heat release response is controlled by contributions from three disturbances. These disturbances include flame speed, heat of reaction and flame area. Using an analytical model, based on linearization of the front tracking equation for inclined flames, the kinematics of a V-flame anchored on a central obstacle was investigated and its response was compared with that of a conical flame. The results suggest that the phase response of the V-flame increases quasi-linearly with excitation frequency, indicating that the fluctuations require a certain time to reach the flame surface. Longer V-flames exhibit more sensitivity to the convected flow disturbances. The stronger contribution of the flame-area perturbations in the case of a V-flame, which is due to the intensified effect of displacement at the tip of the flame, leads to higher values of the overall response of the flame, compared with that of the conical flame. The flame response to equivalence ratio perturbations indicates that V-flames behave as an amplifier at a certain range of frequencies, and they are more susceptible to flow oscillations than conical flames.