Combustion Emissions

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Background: This invention will use water vapor wavelengths to measure the combustion gas temperature in different gases such as coal, and biomass flames. 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 or thermocouple, which are intrusive, spatially and temporally averaging, and difficult to use. A new method utilizing the spectral emission from water vapor is demonstrated through experimental measurements. This method was demonstrated along a 0.75m line of sight, averaged over 1 minute but has the potential to produce a spatial resolution on the order of 5 mm and a temporal resolution of less than 1 ms. 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 180 kWth methane flame comparing the optical emission results to a suction pyrometer with type K thermocouple. The optical measurements showed increasing temperature with increasing equivalence ratio. At low equivalence ration, the optical measurement was within 2% of the suction pyrometer but the uncertainty was found to be at least 3% based on the consistency of the results. When background radiation was present, the optical measurement was 12% higher than the suction pyrometer even when an attempt was made to remove the background component.