The flicker of a flame is an important physical parameter associated with the characteristics of a combustion process. This paper presents a novel instrumentation system developed for on-line continuous flicker measurements of combustion flames. The system comprises a high-speed CCD camera, a frame grabber and associated image processing software. The flicker signal was obtained by processing the radiation intensity of individual pixels within the luminous region of a flame image. Power spectral density analysis was performed to obtain the frequency components of the flicker signal. The quantitative flicker of a flame is defined in terms of weighted spectral components in the frequency domain and this definition has been proven to be well suited to quantification of the flickering characteristics of a flame. A tungsten lamp driven by a frequency-varying power supply was employed to calibrate the measurement system. The calibration results show that the system is capable of measung the flicker of an unknown light source with a relative error no greater than 3% . The system developed has been utilized to investigate the relationship between the flicker of a diffusion flame and the burner diameter, and to study the effect of the equivalence ratio on the flicker of a premixed flame under a range of combustion conditions. The experimental results obtained by both motion image analysis and spectral analysis have demonstrated that the flicker of a diffusion flame depends predominantly on the burner diameter. It has also been found that the flicker of a premixed flame varies with the equivalence ratio and a peak flicker exists for a given air flow rate.
System developmentFigure 1: Schematic diagram ofthe flame monitoring and control system. Experimental set-upIn order to examine the suitability of the proposed system for advanced monitoring and control of combustion flames, experimental work has been undertaken on a model combustor. A schematic diagram of the experimental set-up is shown in Figure 1. Butane-gas flames were generated on a burner with an exit diameter of 15 mm. Variations in the air and fuel flow rates were achieved by adjusting the positions of air and fuel valves driven by two stepper motors. A 1/ 2 inch monochromatic CCD camera fitted with a short-wave-pass filter (450±5 om) was used to transmit the image signal of the flameto a frame-grabber at a frame rate of 25 frames/s (50 fields/s). The frame-grabber is capable of performing 8-bit digitisation at 45 MHz and transferring the image signal to the host computer memory at 132 Mbytes/s. A software system was developed to establish the computing imaging from a particular intermediate radical (OH) in the flame zone. And all information derived from each pixel over a specific region of the image was used to construct the neural network. A prototype fuzzy system developed by Tao and Burkhardt 8 was used for the control of gas-fired flames on a miniature combustion model, whereby a flame image was divided into two separate luminous regions. However, the system could only be applied to the control of a single predetermined setpoint.Present work reported in this paper is concerned with the development and experimental evaluation of an intelligent vision system for the monitoring and control of combustion flames by combining image processing and neural network techniques. Both geometrical and luminous parameters of an entire flame are determined over a specific luminous region of the image on a dynamic basis. A neural network is constructed from these param-.
A novel optical instrumentation system has been developed for on-line continuous measurement of two-dimensional temperature distribution of a combustion flame. The system comprises a special optical assembly, a charged coupled device camera, a frame-grabber and associated software. Based on the two-colour principle, the transient two-dimensional temperature of a flame is determined from the ratio of grey levels of corresponding pixels within two images, which are simultaneously captured at two different wavelengths. Accordingly, the instantaneous two-dimensional temperature distribution of the flame is presented by pseudo-colour. Discreet considerations in the design of the instrumentation system are also described, including the choice of wavelengths, correction of location and intensity of pixels, elimination of noise, and calibration of the instrument factor. A series of experiments was conducted for butane-fired open flames on a combustion test rig. The results show that the temperature of a fuel-rich premixed flame is higher than a diffusion flame and decreases linearly with the equivalence ratio. For a diffusion flame, however, the temperature increases with the fuel flow rate.
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