Research On The Method Of Measuring The Temperature Of High Temperature And High Pressure Flow Field By Laser Spectroscopy

After more than 40 years of development,tunable diode laser absorption spectroscopy(abbrevd:TDLAS)technology has become increasingly mature in flow field parameter sensing.This technology enables non-intrusive,in-situ measurement,especially in the harsh combustion flow field diagnosis,with good environmental adaptability.High-temperature and high-pressure flow fields are common in various energy systems(such as coal gasifiers,detonation combustor,homogeneous-charge compression-ignition engines,etc.),and the use of absorption spectroscopy methods will face great challenges in the diagnosis of this type of flow field,such as beamsteering,non-absorbing transmission losses,radiation interference,and spectral overlap and broadening due to pressure rise.Tunable diode laser absorption spectroscopy technology can be divided into direct Absorption(abbrevd:DA)and wavelength modulation spectroscopy(abbrevd:WMS).In this paper,H2O,one of the main combustion products of hydrocarbon fuels,is used as the target molecule.Considering the challenges brought by high temperature and high pressure environment,it is first determined to use the wavelength modulation spectroscopy technology to sense the flow field temperature.According to the line selection rules,three absorption lines of H2O near 7185.6cm-1,6807.834cm-1,and 7444.35/37cm-1 were selected as research objects.An accurate absorption model based on wavelength modulation technology is established.The iterative inversion method of flow field temperature and concentration rotation is realized under fixed pressure,and the highest pressure is 10.58 atm.The temperature measurement error is less than 5.68%.In order to establish a more accurate absorption model,a series of H2O molecular high-temperature spectral parameter calibration experiments were carried out,and the automatic peak-seeking conversion from time domain signal to absolute frequency domain signal was realized when analyzing experimental data,and the free spectral range(FSR)calculation was improved.The method uses the absorption signal to calibrate the free spectral range.Since the refractive index of the etalon medium varies with wavelength,the calibrated free spectral range is more accurate than the theoretical calculation.Combined with the optimized L-M algorithm,the problem of simultaneous fitting of multi-peak absorbance with background is solved.Using the characteristics of laser intensity and frequency modulated at the same time,the wavelength calibration method and laser modulation characteristics in wavelength modulation spectroscopy technology are studied,and the frequency-time description model is improved to obtain more accurate modulation parameters.The 2f/1f signal with background subtraction is obtained by using the absorption model.By directly comparing with the measured 2f/1f,the iterative step and direction of the change are set,simultaneous inversion of temperature and concentration is achieved,and the accuracy of the high temperature and high pressure environment inversion method is verified by simulation.Using WMS-2f/1f peak inversion algorithm,a set of combustion flow field temperature measurement system is integrated.The time resolution of the system is less than 1ms.The laser adopts sawtooth scanning and superimposed sinusoidal modulation to achieve miniaturization.The system measures separately.The tubular high temperature furnace and the single-sector combustion chamber combustion chamber outlet temperature.In the laboratory micro-positive pressure and low-pressure environment,accurate measurement of temperature and concentration in the range of 900?1500K is realized,and the relative errors are less than 3.1%and 2.2%respectively.The on-site bench test measures the outlet temperature of the combustion chamber,and changes the working condition by changing the fuel mass flow field.The measurement was verified at pressure:3.39?10.58atm,temperature:958?1512K,and the error is less than 5.68%,and the high temperature is achieved.Accurate measurement of the high pressure ambient temperature verifies the accuracy of the absorption model,the reliability of the inversion method,and the stability of the measurement system.In this paper,based on WMS-2f/1f high temperature and high pressure flow field temperature measurement method,the inversion of flow field parameters by establishing accurate absorption model solves the problem of difficult diagnosis of high pressure combustion flow field.It provides an accurate absorption model for the diagnosis of combustion flow field by using absorption spectroscopy technology,and provides a spectral diagnosis method for the severe combustion flow field in industrial process control and propulsion system research.