Two-dimensional distribution measurement of direct-connect scramjet combustion flow field based on TDLAS multi-absorption lines

Aiming at the demand of two-dimensional distribution high-resolution measurement of temperature and water vapor concentration in non-uniform scramjet combustion chamber expansion section, advanced tunable diode laser absorption spectroscopy (TDLAS) reconstruction method has been developed. By increasing the number of water vapor absorption lines obtained by scanning the laser wavelength, the number of equations for solving the reconstruction problem correspondingly increased, combining the absorbance equations of all absorption spectra under all laser paths, constructing the optimization objective function with temperature and concentration as unknowns, and using the global optimization simulated annealing algorithm to reconstruct the temperature and water vapor concentration distribution. In the direct-connect scramjet combustion test, the orthogonal optical path layout is adopted, and the square optical mechanical structure with 16 measuring optical paths of 5 horizontal and 11 vertical channels is designed. TDLAS measurement system is assembled, and the time division multiplexed direct absorption detection method is adopted for 5 DFB lasers, with the measurement frequency of 4 kHz. Five water vapor absorption spectral lines (7467.77、7444.36、7185.60、7179.75 and 6807.83 cm) can be obtained at each measured optical path, the system has carried out thermometric validation by using high-temperature furnace on the laboratory, and the temperature measurement deviation is within 2.7%. In the test, the absorption spectrum data synchronously collected under 16 optical paths are processed offline, and the distribution data of temperature field and water vapor partial pressure under various states of ignition, combustion and flameout are obtained. The test results show that TDLAS multi-absorption measurement technology can realize accurate and stable reconstruction, and meet the engineering application requirements of complex combustion flow field diagnosis and bad working conditions.