Analysis of the Dynamics of Premixed Methane and Biogas Flames Based on Cross-correlation Maps

In this study, the cross-correlation method (CCM) has been investigated in detail and applied to analyze the dynamic response of premixed methane and biogas flames. CCM mapping was proposed in a recent study as an effective, and notably simple, method to evaluate the actual contribution of different flame zones to its global dynamic response. The physical interpretation of cross-correlation maps has been further investigated and validated by means of spatially resolved measurements of the local flame transfer function along the flame. The results obtained are consistent with vortex shedding being the phenomenon governing the dynamics of the flames studied. Methane and biogas flames exhibited different response to fluctuations. The analysis of cross-correlation maps revealed changes in the location of regions with strongest response to velocity fluctuations. Furthermore, this method was applied to determine the variations in the convective length associated with the phase delay between the oscillations in velocity and in heat release rate. In spite of the broad differences among the flames studied, all of them were consistent with the perturbations traveling along the flame at approximately one half of the flow velocity, in coincidence with the findings of some recent works.