Study On Temperature Measurement Based On Laser Frequency Modulation Spectroscopy Of Single Absorption Line Of Water Vapor

Temperature is an important monitoring parameter in the combustion process.Temperature affects the energy conversion efficiency of combustion.However,the existing measurement system of the absorption spectroscopy two-line temperature measurement method is complicated and costly.A more flexible and convenient temperature measurement method is urgently needed.In this thesis,based on frequency modulation spectroscopy（FMS）,a single-line temperature measurement method was studied.Firstly,the construction of the laser FMS experiment system was represented.To improve the sensitivity of spectral detection,an FMS system was built.The responsiveness of the diode laser with high-frequency signals was tested.The modulation coefficient of the laser was measured and set.FMS detection of CO₂ and H₂O was realized.Through Allan’s analysis of variance,the result showed that the lowest detection absorbance of the FMS system under laboratory conditions was1.25×10^-5.Secondly,a single-line temperature measurement method with FMS was proposed.Aiming at the tested environment,the principle of single-line screening was established.According to the measured line parameters and the experimental system parameters,the modulation frequency and the modulation index of the FMS were set.An algorithm was designed to complete the separation of Doppler broadening and Lorentz broadening of an absorption line.And a single-line temperature measurement method of FMS was proposed.Under normal temperature conditions in the laboratory,the measurement uncertainty of this method can reach 2.2%.Thirdly,the research and comparison of FMS and direct absorption spectroscopy（DAS）single-line temperature measurements were carried out.The laser wavelength scanning on-line monitoring unit was designed to correct the wavenumber of the absorption spectroscopy and to solve the influence of the laser scanning nonlinearity and environmental conditions on the accuracy of wavenumber.Under laboratory conditions,the DAS two-line temperature measurement,DAS single-line temperature measurement,and FMS single-line temperature measurement were carried out on the the temperature of gas pool and the combustion flame of Bunsen burner.The uncertainty of temperature measurement results was analyzed and compared.The results showed that both FMS and DAS single-line temperature measurements all can achieve temperature measurement.And the uncertainty of temperature measurement of the combustion field under laboratory conditions was 6.6%and 8.8%,respectively.FMS and DAS single-line temperature measurement methods can achieve temperature measurement and reduce the complexity of the temperature measurement system.And the single-line temperature measurement method of FMS can be used to measure the temperature of weak absorption gas.Therefore,researching single-line temperature measurement methods,while improving the understanding of the combustion process,also provides measurement technical support for the development of new combustion technologies.