| Aerospace power devices,such as aerospace engines,scramjet engines,and gas turbines,are the core components of advanced aircrafts and play a vital role in the national strategic development.The diagnosis of the combustion flow field in these devices is essential for evaluating the combustion efficiency and providing feedback for optimal design.Tunable diode laser absorption spectroscopy(TDLAS)is a nonintrusive technique that has been widely applied for the measurement of combustion flow fields.However,this technique faces several challenges when the engine operates under different conditions,such as large variations of temperature and pressure,rapid changes of flow field,low signal-to-noise ratio,reduced measurement sensitivity,and inaccurate theoretical models.The conventional dual-line measurement method cannot satisfy the demand of high-precision measurement in such environments.Therefore,this thesis aims to achieve high-accuracy measurement in a wide range of temperature and pressure by conducting research on spectral model parameter calibration and parameter inversion methods.The main products of the combustion flow field,H2O and CO2,are selected as the target gases for the temperature measurement method,which covers the whole measurement range from low temperature to high temperature(400～3000 K)and from low pressure to high pressure(0.1～30 atm).A multi-wavelength measurement scheme was adopted to achieve measurement in a wide temperature range.Five H2O absorption lines in the near-infrared band were selected based on the HITEMP2010 database,and a multi-wavelength measurement system was established.The spectral model parameters were calibrated on a hightemperature furnace platform using the Voigt,Rautian,and speed-dependent Voigt line shapes,which reduced the uncertainty of some spectral parameters in the database and filled in the gaps of some missing parameters.The temperature and component concentration in the range of 600～1800 K were measured on the same platform,verifying the high accuracy of the multi-wavelength temperature measurement method in a wide temperature range.The performance of the three-line shapes was compared,and the results showed that the calibrated Rautian line shape had higher measurement accuracy.The temperature measurement under 673～1373 K and 1～6 atm was conducted on a high-temperature and high-pressure furnace,and the comparison of the three-line shapes was repeated.The Rautian line shape also showed higher accuracy in this case.CO2 was chosen as the target molecule,and sixteen absorption lines near 4.2 μm in the mid-infrared band were selected to analyze the measurement capability in 3000 K.The spectral parameters were calibrated using the Voigt,Rautian,and velocitydependent Voigt line shapes.The temperature verification of 800～1800 K was performed in a high-temperature furnace.By using the calibrated line strength values,the temperature measurement accuracy was enhanced to within 1.86%,achieving highprecision measurement.The line mixing effect of the 4.2 μm band was investigated under high temperature and high pressure conditions.Based on the MEG(Modified Exponential Gap)model,the CO2-N2 collision line mixing coefficient was calibrated.The temperature measurement verification of 673～1173 K and 1～30 atm was conducted in a high-temperature high-pressure furnace.The temperature measurement error was within 5%.A light intensity fitting method was developed to address the challenges of severe broadening and unclear non-absorption regions in the wide temperature and pressure flow field,which hindered the extraction of the absorbance signal.This method improved the measurement capability of direct absorption spectroscopy under high pressure and ensured high-precision measurement up to 6 atm.The multi-wavelength Boltzmann plot temperature measurement method was investigated based on the multiwavelength measurement system.The robustness of the multi-wavelength temperature measurement to environmental noise and spectral parameter uncertainties was simulated and analyzed.The results showed that the measurement accuracy of the Boltzmann plot method was enhanced by nearly 30%under different error levels compared with the dual-line method.The multi-wavelength Boltzmann temperature measurement method was integrated with the ART algorithm to achieve high-accuracy reconstruction of the temperature and component field distribution.The measurement of the expansion section of the scramjet engine combustor was conducted on a direct-connect platform.A fiber-coupled transceiver structure was employed to arrange 11×5 optical paths on the wall of the measurement section.The whole dynamic process of engine ignition,hydrogen combustion,hydrogen-guided kerosene combustion,kerosene combustion,and flameout was measured.The experiments under the same conditions were repeated,and the average temperature deviation was within 20 K.The multi-wavelength scheme was successfully applied in the wide temperature measurement of the engine.A 5X4 optical path was set up at the outlet of the aero-engine combustor,combined with an electric displacement platform,to realize the moving scan measurement along the flow direction.The threedimensional temperature distribution results under 6 atm were obtained,and compared with the spatial point measurement results of CARS technology.The relative temperature deviation was within 3.08%.The two technologies were well crossvalidated,verifying the measurement capability of the light intensity fitting algorithm under 6 atm on the engine test bench.The direct absorption spectroscopy-based spectral model and parameter inversion method for high-temperature and high-pressure conditions developed in this thesis have enabled the full-condition measurement of the scramjet engine and have been applied in the test bench experiments,obtaining high-quality measurement results,which provide data support for the optimization design and performance evaluation of the scramjet engine.The method that combines multi-wavelength and light intensity fitting has been successfully applied to the measurement of low and medium pressure aeroengines,and it is planned to further extend the pressure measurement range.In addition,the measurement model based on the line mixing is an important technical means for advancing the combustion measurement of high-pressure and ultra-high-pressure aeroengines in the future. |
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