Ultra Lean Combustion Characterization in a Pilot-Scale Gas Turbine Burner Using Image Processing Techniques

The aim of the present investigation is the characterization of the behavior of a lean partially-premixed liquid fuel gas turbine near lean blowout limit. At this combustion regime the onset of instability will occur with negative impacts on combustion efficiency. The identification of the instability occurrence permits an efficient flame control adjusting the combustion parameters (as fuel or air mass flow, temperature, pressure, etc.) to stabilize the flame or designing opportunely flame control system. High-speed images of the flame under stable and near blowout condition were captured in conjunction with simultaneous optical data in order to better understand the phenomenology of the flame blowout process and the onset of instability. In particular the experimental characterization was performed through a High Speed Digital Camera, an Infrared camera and a Photomultiplier Tube (PMT) in association with the use of optical filter (OH*). The data collected with these instrumentations produce useful features for the development of an efficient tool for the flame control in industrial and aeronautical burners. The images acquired by the different cameras were processed considering the luminosity signal of each pixel and evaluating the frequency behavior, the variations of amplitude of the signals and some other descriptive parameters able to define the regime of the flame. Spectral analysis and Wavelet transform of pixel intensities of flame images were used and entropy and energy contents were evaluated. The spatial maps of the different spectral and statistical parameters were shown at different fuel/air equivalence ratio. The OH* emissions data measured by the PMT were processed and compared with the data obtained from the images processing.