Development and Evaluation of a Tomographic Technique for Volumetric Imaging of Flames
Abstract: With modern day interest to continue the reduction of harmful emissions and improve the efficiency of combustion devices, the need to further improve upon accuracy and ability to describe combustive processes is of high value. Nowadays, multiple capable point (0D) and two-dimensional measurement (2D) techniques exist for flame investigation, however as combustion nearly always is a three-dimensional (3D) process some limitations do exist within many of these techniques. Therefore, the interest to find alternative ways to gather 3D volumetric information with both high temporal and spatial resolution has grown. This work aims to develop and thereafter evaluate a tomographic technique able to acquire volumetric data from flames and thus put forward a proof of concept that can lay the foundation for future practical applications. Thus, potentially allow for volumetric flame data to be acquired from inside combustion devices with limited optical access. The tomographic technique was built around the Additive Reconstruction Technique (ART) algorithm and was made to reconstruct both 2D and 3D synthetic flame models, the results were then studied and evaluated. Furthermore, the groundwork for an experimental setup using ten cameras was built to allow for future practical appliance of the tomographic technique in flames. This incorporated the evaluation of different cameras to find the most promising, that in turn would serve for the flame imaging. Finally, a calibration process to map each camera into the same coordinate system was performed to allow for future accurate data gathering. The results showed that the method proposed in this work for reconstruction of 2D objects was successful, with complex objects of 200-by-200 pixel resolution being reconstructed using ten projection views. Likewise, the modifications made upon the 2D reconstruction, to allow for reconstruction of 3D objects using 2D projections, proved successful in this work. The results show that the interior intensity structure and outer shape was retained in the reconstruction of a 3D synthetic flame model with only minor aberrations present. In the building of the experimental setup, ten acA1920-40gm-Basler-ace cameras were employed. The model was chosen due to possessing superior signal to noise ratio (SNR) performance than other evaluated models together with a higher resolution that could come of use in future work. The calibration method applied was evaluated to be successful with an individual mean reprojection error of around 0.5 pixels for every camera.
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