| Engine,which is the heart of an aircraft,plays a vital role in the safe flight of the plane.And it is the embodiment of the national scientific and technological level,the level of industrial development and the overall strength of national defense.The combustion products of aero-engine combustion chambers are mainly CO,CO2,NO,H2O,NO2 and residual air,as well as solid particles.CO gas is an important indicative gas reflecting the combustion characteristics.Accurate measurement of the distribution of CO concentrations in combustion chamber is an effective method for the optimization of combustion process and the improvement of combustion efficiency.At the same time,CO gas is also one of the main evaluation factors of air quality index.To realize the real-time monitoring of CO concentration in industrial production is conducive to the establishment of appropriate monitoring methods and emission standards.Tunable diode laser absorption spectroscopy(TDLAS)technology has the advantages of high sensitivity,high precision,fast response speed,non-invasive characteristics and so on.It is suitable for the field of trace gas detection and combustion process diagnosis.Due to the line of sight property of TDLAS,only the average measure along the light direction could be obtained.Combining TDLAS technology with the computer tomography diagnostic technique,the study on the reconstruction of CO concentration distribution in the combustion chamber of aero-engine was developed.The outlines and conclusions are given as follows:1.An absorption line suitable for measuring CO concentration in combustion flame was selected.And the furnace system with a three-stage high-temperature tube was set up.Then,the accuracy of calibration-free wavelength modulation spectroscopy for the measurement of C.O concentration was verified by experiments.According to the principle of line selection,the isolated absorption line 4297.7046cm-1(R(10))was selected in the first overtone of CO gas.The influence of temperature and pressure on the measurement of CO concentration was analyzed quantitatively by simulation.Meanwhile,the influence of O2,H2O and CO2 on the collision broadening of spectral line and the height of wave-peak were analyzed.The CO standard gas of different concentration was measured in the temperature range of 773K-1473K.The experimental results were in good agreement with the set values,and the relative error was less than 2%.2.A method for simultaneous measurement of gas pressure and component concentration was proposed in order to eliminate the uncertain influence between gas pressure and component concentration.The linear relationship between the pressure value and the ratio of the peak value of the second harmonic to the side-lobe was found through theoretical analysis and numerical simulation.Combined with the calibration-free wavelength modulation spectroscopy,the simultaneous measurement of gas pressure and component concentration was realized.A gas measuring system with adjustable pressure is set up.Then,the CO standard gas of different concentration was measured and the experimental results were in good agreement with the set values.3.Based on the superposition about the normalization value of second harmonic signal by the first harmonic at the spectral line center under the condition of weak absorption,the method of reconstructing the concentration distribution of non-uniform flow field was proposed.And the measurement of CO concentration distribution at the outlet of combustion chamber was carried out.The concentration distribution is reconstructed through using the experimental signal of the spectral line and the algebraic iterative reconstruction algorithm.The simulation of CO concentration distribution reconstruction was carried out in the orthogonal and multi-angle light distribution.Then,the feasibility of the reconstruction algorithm was verified by comparing the reconstructed results with the set values.The influence of the error of path matrix and the random noise of measurement on reconstruction results was analyzed systematically.The temperature and concentration at different positions of the combustion chamber outlet were measured by thermocouple and gas analyzer,and the stability of the combustion was verified.According to the situation,the system with the multi-angle light distribution was set up by using two industrial robots,and the measurement of CO concentration distribution was carried out at the aeroengine outlet. |
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