Liquid lens-based optical sectioning tomography for three-dimensional flame temperature measurement

Measurement of three-dimensional temperature field of a flame plays a significant role in in-depth insight into combustion process. This paper proposes a novel optical sectioning tomography for the measurement of three-dimensional temperature of flame through a single camera in combination with an ionic electrowetting-based variable focus liquid lens. Firstly, the optical sectioning imaging principle is introduced based on a variable focus liquid lens. Secondly, the calibration works are carried out on a liquid lens-based optical sectioning tomography system for three-dimensional flame temperature measurement to determine the relationship between the working voltages of the liquid lens and its focal planes in combination with entropy function. Further Gaussian model is taken as the defocused model to calibrate the point spread function of the system through edge method, and the CCD sensor is calibrated by a black body furnace to find out the relationship between the image gray and the received radiation energy. The reconstruction algorithms for three-dimensional flame luminosity distribution of the combustion flame are also developed. Finally experimental works are undertaken to evaluate the optical sectioning tomography system. Preliminary experimental results on an ethylene-air co-flow burner verified the feasibility of the optical sectioning tomography for the three-dimensional temperature distribution of a diffusion flame. The developed optical sectioning tomography system is capable of characterizing the structure and combustion characteristics of the diffusion flame.