ИСТИНА

Tunable Diode Laser Absorption Spectrometry (TDLAS) is now the most applicable technique for diagnostics of the combustion. 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 case of relatively low total pressure (< 1 atm) the absorption lines are narrow, so that one can select a spectral range with several resolved or slightly overlapping absorption lines within a tuning range of a single DFB laser (~ 1.5–2 cm-1). For such a case the fitting can be adequately performed. The efficiency and potentials of the developed H2O sensor is tested by detection of the parameters of the hot tail of combustion in the mixing supersonic flows at reduced pressure (250 – 400 Torr). Two algorithms of data processing were compared. The first algorithm is based on the fitting of the transient experimental spectra by the simulated ones, using temperature as a parameter. Another approach is based on the simulation of the set of spectra with the interval ΔT = 50 K and calculation of the correlation function with the experimental spectrum. Temperature is inferred from the maximum of the correlation function. In case of high gas pressure (> 1 atm) the H2O absorption lines are broadened which makes the selection of the resolved lines within the narrow tuning range of a single DFB laser very problematic. The alternative approach for the high pressure sensing of the hot zones is the use of two DFB lasers radiating in different spectral ranges. This approach extends the possibility to select the optimal strong absorption lines from different spectral ranges wider. Different combinations of the excitation wavelengths are theoretically examined with the emphasis on the attainable precision of the temperature evaluation. The new TDLAS system for the measurements of the temperature up to 2500 K and gas pressure up to 3 atm is developed. The peculiarities of the optical scheme, electronic system for TDLs tuning and data recording will be presented. The efficiency of the developed technique was exemplified in the first set of the experiments in Zhukovsky Central Aerohydrodynamic Institute (TsAGI).