Optical EngineeringMeasurement of thermal expansion of a piston using holographic and electronic speckle pattern interferometry
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Holographic interferometry and electronic speckle pattern interferometry (ESPI) have both been used to measure the radial expansion of a heated diesel engine piston. A simple "mirror" concept introduced enables simultaneous measurement of in-plane and out-of-plane components of displacements. This concept was verified by using a cantilever and the results agreed to within 5% of the predictions of deflection theory. ESPI and holographic fringes on two views of the piston were recorded on a single frame of a CCD camera. Phase-stepped ESPI fringes were analyzed to obtain two phase maps of different sensitivities on a single video frame. Comparison between holographic and ESPI results were made and possible reasons for the smaller values obtained using ESP1 are proposed. A critical comparison of the two techniques shows that holography has the advantage of enabling study of a 2000 rise in a single stage due to its high quality fringes. ESPI limits the temperature rise to 5°C because of its poorer fringe definition and hence displacement from four stages has to be added vectorially.