Study On 3-D Flame Temperatuere Reconstruction Through Liquid Zoom Lens-Based Optical Sectioning Tomography

Temperature is one of the most significant parameter in the combustion flame. Studying the temperature of every point in the flame contributes to understanding the physical and chemical reactions in the combustion process and revealing the nature and law of the combustion phenomenon. It also has great effects on the efficient use of energy and ultra-low emission of pollutant. In this paper, an optical sectioning tomography based on liquid zoom lens is proposed to study the 3-D flame temperature distribution after evaluating various traditional temperature measurement methods.First, some relative concept on optical imaging system is presented, and on this basis the basic principle is introduced about the optical sectioning tomography. Then a kind of liquid zoom lens is discussed. Due to its high zoom speed, the liquid zoom lens meets the requirement of real-time imaging. In order to apply the optical sectioning tomography to unsteady flame, the liquid zoom lens is introduced in the measurement system of optical sectioning tomography. An improved matrix model is proposed to transform the convolution operation between the objects and images into a system of linear equations. The constrained Van Citter iteration method is used to solve the system of linear equations in order to reconstruct the origin temperature distribution. Simulation experiment of image restoration is carried out in a computer and the results verify the measurement method of optical sectioning tomography.The calibration experiment setup is built aim at the calibration issue concerning the optical sectioning system. Series of images of a calibration board is acquired and evaluated by the entropy function as the sharpness function. So that the relation between the location of the focal plane and the corresponding working voltage of the liquid lens is calibrated. Then with Gaussian de-focal model, the Point Spread Function of the Optical system is calibrated by means of knife-edge method. At last the CCD is calibrated by means of a black body furnace to found out the relationship beween the image gray and the received radiation energy.Finally, the measurement setup is built. The flame is divided into four sections along the direction perpendicular to the main optical axis, with the thickness of 2 mm each. Image the flame under three conditions with optical sectioning method and reconstruct the three-dimensional temperature distribution. The results shows that, along the height direction of the flame, the temperature arises first and then falls due to the degree of the combustion; along the radial direction of the flame, an obvious combustion zone exists. In the combustion zone the reaction is severe so the flame temperature is high. Inside and outside the combustion zone, temperature falls for the lack of air and fuel respectively. In the different conditions, the height of the high-temperature area in the flame arises because of the high velocity of the fuel and air.