Investigation of Endoscopic Techniques for Flow and Combustion Measurements

This work investigated the application of fiber-based endoscopes (FBEs) in combustion and flow measurements, especially for multidimensional and quantitative measurements. The use of FBEs offers several unique advantages to greatly reduce the implementation difficulty and cost of optical diagnostics. However, the use of FBEs requires registering the locations and orientations of the FBEs carefully for quantitative measurements, and degrades the spatial resolution of the images transmitted. Hence this work conducted a series of controlled tests to quantify the accuracy of the view registration process and the spatial resolution degradation for FBEs. The results show that, under the conditions tested in this work, the view registration process can be accurate within ±0.5 degree and the FBEs can resolve spatial features on the order of 0.25 mm. The combined effects of such view registration uncertainty and spatial resolution degradation are reflected in the re-projection error, which was shown to be within ±0.5 pixels under typical conditions used in this work. Finally, based on these understanding, experiments were conducted to obtain instantaneous measurements of flame structures at kHz temporal resolution using FBEs, demonstrating the capability of resolving flame features on the order of 0.2~0.3 mm in three-dimensional.