ИСТИНА

TDL absorption technique and appropriate instrumentation for measurements of temperature and water vapor concentration in a hot zone, characterized by rather strong fluctuations, vibrations and different optical and electrical noises, are developed (see C12). The experimental spectra were registered using a single DFB laser which covered about 1 cm- 1 in one scan. The following absorption lines of H2O were used: 7189.344 cm-1 (E'' = 142 cm-1), 7189.541 cm-1 (E'' = 1255 cm-1), 7189.715 cm-1 (E'' = 2005 cm-1). Relatively high intensities of the selected lines enabled detection of the direct absorption. The technique was applied for detection of temperature and H2O concentration in the post-combustion zone of the supersonic air-fuel flows (see D12). Mach number of the flow in duct was M = 2, static pressure in flow Pst=150-300 Torr, static temperature Tst up to 1500 K. The optical path of the testing DL beam inside the camera was 7 cm. The combustion process in the supersonic flow was ignited and sustained by the pulsed electric discharge. Air was used as the oxidant, hydrogen or ethylene were used as the fuel. The duration of a single run including gas flow injection, plasma ignition, combustion and cooling was about 0.5 s. The duration of plasma-assisted combustion was about 80 ms. The duration of each TDL scan was about 830 s, thus 600 laser frequency scans were registered during the whole process of 0.5 ms. At the first step of data processing 2D image of the transient absorption spectra was constructed (see E10). The hot zone parameters were obtained as the result of fitting of the experimental spectra by the simulated one constructed using the HITRAN and SPECTRA databases. Parameters of the post-combustion zone were measured for different conditions of air and hydrogen or ethylene fuel mixing and different geometry of electric discharge. The high signal-to-noise ratio enabled to obtain the temporal behavior of temperature with the resolution of ~ 1 ms. Precision of the temperature evaluation was estimated to ~ 40 K.