ИСТИНА

Temperature is the critical parameter of any combustion process. In particular, temperature of the combustion zone in mixing flows of oxidant and fuel characterizes the efficiency of a jet and fuel consumption. Absorption spectrometry with tunable diode lasers (TDLAS) is a powerful tool for contactless measurements of gas concentration and temperature in hot zones. The technique is based on the registration of the experimental transient absorption spectra of water molecules and fitting of the experimental spectra by the simulated ones constructed using the spectroscopic data bases. The temperature is inferred from the ratio of the integral intensities of the absorption lines with different low energy levels. Two types of DLAS sensors were designed and tested for different types of combustion at low and high pressure conditions - plasma-assisted combustion in air-fuel mixing supersonic flows (P < 1 atm.) and combustion in a test chamber of high-speed ramjet air-breathing engines (P > 1 atm.). In case of relatively low total pressure 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 – 3 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). 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 Distributed Feedback (DFB) laser very problematic. The alternative approach for the high pressure sensing of the hot zones is the using 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. Different combinations of the excitation wavelengths are theoretically examined with the emphasis on the attainable precision of the temperature evaluation. The new TDLAS sensor for the measurements of the temperature up to 2500 K and gas pressure up to 3 atm is developed. The peculiarities of the TDLAS technique for the case of high pressure (up to 3.5 atm.) and temperature, as well as the algorithms for data processing will be shortly discussed in the talk. The efficiency of the developed technique was exemplified in the first set of the experiments on real test engine.