Method for Measuring High Temperature Spectral Line Parameters Based on Calibration-Free Wavelength Modulation Technology

In the diagnosis of combustion flow field by absorption spectra, the accuracy of absorption molecular spectral line parameters directly affects the accuracy of the measurement of flow field parameters. In this paper, the absorption spectral line parameters of water molecules used as the main probe in combustion diagnostic studies arc calibrated accurately. A near-infrared diode laser with a wavelength of 1169 nm is used as the light source, and the highly sensitive calibration-free wavelength modulation technology is used. Combining with the established laboratory high temperature measuring system, we obtain the modulation absorption spectra of the selected spectral lines in the temperature range of 900-1500 K. By using the nonlinear least square L-M fitting method to fit the H2O absorption spectra, the line intensities, self-broadening coefficients, and temperature dependent coefficients of the selected spectral lines at 6807.83 cm(-1) and 6808.01 cm-1 arc accurately obtained. By comparing the HITRAN and HITEMP databases, we obtain that the relative deviations of line strengths arc 3. 91% and 5.10%, the relative deviations of self-broadening coefficients arc 3.01% and -6.49%, the temperature dependence coefficients arc 0.5213 and 0.4567, and the uncertainties of the experimental results of the two line strengths arc 1.05% and 1.96%, respectively. The spectral parameter calibration method based on calibration-free wavelength modulation has the advantages of high detection sensitivity and spectral signal-to-noise ratio in high temperature spectral measurement, which is conductive to improve the accuracy of spectral parameter calibration, and will provide spectral line foundation for accurate inversion of combustion flow field parameters.