Measurement of the parameters of non-stationary gas flows by diode laser absorption spectroscopy in case of high temperature and high pressure

Abstract

Abstract. Experimental version of diode laser absorption spectrometer (DLAS) for contactless measurements of temperature and water vapor concentration in supersonic gas flows is developed. The spectrometer can be used for the measurements of temperature up to 2500 K and total pressure up to 3 atm. The technique is based on the registration of the transient absorption spectra of a target molecules and fitting of the experimental spectra by the simulated ones constructed using the spectroscopic databases. The temperature is inferred from the ratio of the intensities of the absorption lines with different low energy levels. In gas media with the above parameters the absorption lines are broadened which demands the use of two diode lasers (DL) working in different spectral ranges. The software for selection of the optimal line combinations was developed. The combination of two strong lines in the spectral ranges 1.39 μ and 1.34 μ was selected as the optimal one. The efficiency of the developed technique was exemplified in the first set of the experiments in conditions of real propulsion in Zhukovsky Central Aerohydrodynamic Institute (TsAGI) for the temperatures within (500-2200) К range and total pressure up to 3 atm.Absorption spectroscopy with diode lasers (DLAS) is widely used for diagnostics of gases [1][2][3][4][5][6]. It is particulary the most popular technique for contactless probing of different combustion zones in mixing gas flows because any traditional thermocouples being inserted in a flow strongly modifies the structure of the flow.General approach of DLAS technique is based on the measurement of the integral intensities of two lines of a test molecule with different energies of low levels. Assuming the termodynamic equilibrium the ratio of the line intensities S(T) depends only on gas kinetic temperature. In case of low pressure (<1 atm.) and temperature (<1500 K) the absorption lines are relatively narrow and can be spectrally resolved. One can find a spectral interval in near-ir with different absorption lines of water molecules lieing within a

Data Processing Algorithm for Diagnostics of Combustion Using Diode Laser Absorption Spectrometry

“…A detailed description of the experimental setup and the measurements technique are presented elsewhere. 24 Only brief information is given below.…”

“…Data processing was performed on-line and off-line. 24 The experimental spectra and the results of data processing using the developed algorithm are shown in Fig. 4.…”