ENGINE PISTON TEMPERATURE MEASUREMENTS FOR THERMAL LOADING USING A FIBER BRAGG GRATING (FBG) EMBEDDED INTO THE PISTON SURFACE
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Authors
Ward, Dennis M.
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Thesis
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Abstract
Description
Optical fiber sensors have undergone refinements recently that make them attractive
alternatives for traditional measurement devices. Optical fiber sensors are compact in size,
easy to install and relatively inexpensive. These features have made them an ideal
measurement tool for taking piston temperature measurements.
This project investigated embedding an optical fiber sensor into a metal piston,
calibration of the sensor and the feasibility of measuring piston temperature with three
different light sources. The fiber Bragg grating (FBG) sensor was used in this research was
commercially purchased. A detailed procedure was developed that used a low temperature
electroplating process to fully embed the FBG sensor into a small utility engine piston. The
embedded sensor was calibrated by measuring the wavelength shift of the FBG and
comparing it the temperature as measured by a thermocouple.
Of the light sources investigated, two were wavelength scanning lasers while the third
was a broadband source. Attempts to measure piston temperature with the broadband source
were unsuccessful due to the large light loss through the system. The wavelength scanning
lasers used were both successful in measuring piston temperature in a non-contact manner.
Due to cycle-to-cycle variations in the light transmission efficiency the slow scanning laser
could only measured the piston temperature after the engine had been stopped. After running
the engine at 1700 RPM with a load of 710 kPa IMEP the maximum piston temperature
measured was 149 0C. The fast scanning laser technique measured the piston temperature
with the running engine at the same conditions to be 136 0C. Comparing the results from
both temperature measurements yielded only a discrepancy of 13 0C, which is believed to be
good correlation.