Study On Reconstruction Of Temperature And Concentration In Combustion Based On TDLAS

Tunable diode laser absorption spectroscopy?TDLAS?can detect the gas temperature,concentration,flow rate and pressure.This technique is advantageous because of high sensitivity,fast response,and simple system,and can realize non-contact and undisturbed measurement,which renders TDLAS a great potential for application in the field of combustion diagnosis.Combining TDLAS with CT technology can achieve two-dimensional distribution of the temperature and concentration simultaneously.In this thesis,the study on the detection of temperature and concentration in the combustion process based on the TDLAS technology has been carried out,and gases combustion-related O₂ and H₂O were used as the target for the measurement,respectively.Meanwhile,the research on the ART algorithm and the beam distribution in two-dimensional distribution reconstruction based on the numerical simulation and experiment has been done.The main work and innovation points are as follows:?1?The calibration algorithm of temperature measurement based on wavelength modulation technique has been proposed.A real-time temperature measurement system has been built in the laboratory by using high-temperature tube furnace and two lasers.The harmonic signals of two absorption lines have been demodulated respectively by one lock in amplifier using time-division sawtooth scanning technique.The two experiments of dynamic and steady temperature measurement have been designed,and the response speed,the measurement accuracy and the feasibility of calibration algorithm of the system have been verified respectively.In the range of the 300-900 K,the measurement error of the system is ? 20 K,the relative accuracy is within ± 4%.In addition,the experimental error sources have been analyzed from the perspectives of the experimental system and the factors that affect the second harmonic signal,in detail.?2?In order to improve measurement accuracy of the combustion center area temperature for the nonuniform combustion field,a correction algorithm,which can remove the influence from the low temperature boundary layer,has been proposed.Two H₂O absorption lines located at 1395.51 nm and 1395.69 nm have been selected using Matlab program developed.The experimental results demonstrated that the method is effective,increased the temperature measurement accuracy of the center combustion area from 10%to 3%,and the maximum deviation is less than 30 K.Meanwhile,to verify the stabillity and feasibility of the multi-path on-line measurement system and the correction algorithm,the water vapor temperature and concentration have been measured under the different combustion state by controlling the air flow.?3?The two-dimensional distribution reconstruction algorithm has been improved.The effects and feasibility of the improvement algorithm have been compared using the numerical simulation on the reconstruction and verified in the experiment.The influence of beam distribution on the resolution precision and accuracy of the reconstructed space has been studied through numerical simulation methods.As a result,it suggested that the beams angle should be perpendicular and parallel to the axis of the combustion field symmetry to obtain the efficient use.At the same time,we designed a double-shot device to simplify installation structure,so that larger beam angle and quantities can be obtained under the limited number of installation windows,which made a better applicability for the most combustion fields.An experimental system of the combustion field reconstruction has been constructed,which can reconstruct the two-dimensional distribution of temperature and concentration online simultaneously.The temperature relative error compared with the thermocouple measurement were less than 5.6%,and the H₂O concentration relative error between the inversion and the theoretical calculation results were less than 8.6%.The two-dimensional distributions of temperature and H₂O concentration of different combustion fields consisted by two flat flame burners respectively.The results showed that when the beam directions were perpendicular and parallel to the axis of the combustion field symmetry,the results consistent with the actual combustion field can be acquired.