Vision-based Measurement for Combustion and Vibration Studies

Vision-based measurement as a useful tool has been applied successfully in many applications. The aim of this thesis is to apply vision-based measurement in both combustion and vibration studies. The purpose is to process and analyse the recorded light information for understanding combustion and vibration conditions. The chemiluminescence emission from a flame contains fundamental information on combustion, and the reflected light from an object’s surface can also provide information on the condition of the measured object. These types of information can be recorded quantitatively into images through a camera. Further processing and analysis of the image data can explore useful information. In this work, a high-speed stereo colour imaging system is employed for both combustion and vibration studies. In each study, a suitable methodology is developed.
In a premixed hydrocarbon flame, the blue-green flame colour is mostly attributed to the presence and mixture of chemiluminescence emissions of CH* and C2*. The modern colour camera with the colour filter array (CFA) scheme inherently encodes with red, green, and blue wide-band wavelength filters. According to the aforementioned principles, a flexible image colour model is proposed to detect flame chemiluminescence emissions of CH* and C2*. A sensor calibration process is employed to refine the CH* and C2* concentration expressions based on different camera sensor spectral sensitivities. The detected CH*/C2* ratio is utilised to analogue the fuel/air ratio for combustion diagnostics. Two cases of flame propagation in tubes and flame ignition to impinging are studied using this proposed image colour-based flame chemiluminescence measurement. Combined with stereo imaging and high-speed imaging, the ability of the proposed method to perform multi-dimensional measurement is demonstrated.
The reflected light from the measured object is the result of the interaction between the incident light and the object’s surface. A camera captures the illumination of the reflected light as intensity in an image. When the positions of the light source and camera are fixed, any image intensity variation from the reflected light could indicate the object’s movement. Hence, the measured images of a vibrating object would show intensity fluctuations. Based on this, an image intensity fluctuation-based vibration measurement is proposed. Two cases, wind turbine blade vibration monitoring and industrial coupling rotation-vibration testing, are studied using the proposed method. The ability of the image intensity fluctuation-based vibration measurement to perform one-dimensional and two-dimensional measurements is demonstrated successfully.