Temperature Measurement Using Infrared Spectral Band Emissions From H2O

• Main Author: Ellis, Daniel Jared
• Format: Others
• Published: BYU ScholarsArchive 2015
• Subjects: infrared; spectral; temperature; H2O; FTIR; Mechanical Engineering
• Online Access: https://scholarsarchive.byu.edu/etd/5488; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=6487&context=etd

Currently there is no known method for accurately measuring the temperature of the gas phase of combustion products within a solid fuel flame. The industry standard is a suction pyrometer and thermocouple which is intrusive, both spatially and temporally averaging, and difficult to use. In this work a new method utilizing the spectral emission from water vapor is investigated through modeling and experimental measurements. This method was demonstrated along a 0.75m line of sight, averaged over 1 minute in the products of a natural gas flame but has the potential to produce a spatial resolution on the order of 5 cm and a temporal resolution of less than 1 millisecond. The method employs the collection of infrared emission from water vapor over discrete wavelength bands and then uses the ratio of those emissions to infer temperature. A 12.5 mm lens has been positioned within a water cooled probe to focus flame product gas emission into an optical fiber where the light is transmitted to a Fourier Transform Infrared Spectrometer (FTIR). The same optical setup was also used to collect light from a black body cavity at a known temperature in order to calibrate the spectral sensitivity of the optical system and FTIR detector. Experiments were conducted in the product gas of a 150 kWth methane flame comparing the optical emission results to a suction pyrometer with type K thermocouple. The optical measurement produced gas temperatures approximately 1 - 4% higher than the suction pyrometer. Broadband background emission was also seen by the optical measurement and was removed assuming grey body radiation. This background emission can be used to determine particle emission temperature and intensity. Additional work will be needed to demonstrate the method under conditions with significant particle emission. Additional work is also needed to demonstrate the work over a smaller path length and shorter time scale.