Abstract：Carbon monoxide (CO) is one of the important products of insufficient combustion of hydrocarbon fuels and is often used as a marker of reaction combustion efficiency. The accurate measurement of CO concentration in the combustion field is of great significance to the engine to improve combustion efficiency and reduce pollutant emissions. Off-axis Integrating Cavity Output Spectroscopy (OA-ICOS) is a technology to analyze and measure a material by using the specific absorption of the substance to the laser spectrum. It has the advantages of non-contact, stability and high sensitivity. Aiming at the characteristics of low CO concentration and strong background signal interference in the combustion field, an OA-ICOS system was built with a distributed feedback (DFB) laser to measure the CO concentration in high-temperature combustion field by direct absorption spectroscopy (DAS) method. The first broadband R(10) absorption line, which is more prominent at room temperature and not interfered with by other combustion products at high temperature, was selected near the center wavelength of the DFB laser by absorbance simulation. The effective optical length of the OA-ICOS system was calibrated by comparing the absorbance with the fixed optical path cell. The best wavelength scanning frequency was obtained by comparing the signal-to-noise ratio of the absorption line at different scanning frequencies and the standard deviation of the linear fitting residuals; The system error was analyzed by measuring the absorption signal of CO mixed gas of different concentrations. The production of CO on the CH4/Air premixed flat flame furnace under different combustion conditions was evaluated. The influence of the temperature distribution uncertainty on the CO measurement results was described by the temperature distribution in the measurement area of the combustion field. A minimum concentration detection limit of 5.83×10-6 was achieved under the time resolution of 10 ms, the system measurement error was less than 4.5%, and the uncertainty of CO concentration measurement caused by the temperature uncertainty of the combustion field was 5.6% when the equivalence ratio is 1.0. The variation ranges of average temperature and CO concentration are 1 275~1 368 K and 0.041%~1.57% when the equivalence ratio changes from 0.8 to 1.2. The experimental results show that the OA-ICOS has the advantages of a high signal-to-noise ratio and high detection sensitivity to measure the gas parameters in the combustion field and can develop an accurate measurement of the concentration of trace gas components.
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