Characterization of PF flames under different swirl conditions based on visualization systems

The complex phenomena underlying reacting flows are at present an active research topic for improving efficiency and control of industrial combustion processes. The present study assesses the use of a reliable and low cost visualization system based on CCD (charged couple device) technology for the identification of different flame states as a function of swirl number. The experiments were performed in a 500 kWth pulverized coal (PF) swirl burner. The visualization system was previously used for similar analysis of an atmospheric gas swirl burner of 50 kWth. Both flames were analyzed under low and high swirl conditions in order to identify possible common features concerning swirl flames. The analysis procedure proposed in this work extracts different statistical and spectral parameters from the intensity of radiation stored by each CCD element. The representation of flame features as two-dimensional distributions has led to the identification of typical structures in swirl flows and has allowed us to detect changes in flame structure as swirl number increases. Besides, the quantification of aforementioned parameters has led to relevant findings concerning frequency analysis and flame stability as a function of swirl. Specifically, results show that the characteristic frequency in terms of flame flicker is sensible to changes in swirl conditions.