Research On Key Technology And Application Of Portable FTIR Spectrometer

In recent years,with the continuous improvement of vehicle exhaust emission standards,FTIR technology,with the advantages of multi-channel,high resolution and high throughput,can achieve real-time measurement of multi-component VOCs in exhaust gas,to meet the high standard of non-methane hydrocarbon(NMHC)and non-methane organic gas(NMOG)measurement requirements.Aiming at the three problems of portability,high resolution and rapidity required by exhaust gas measurement,the key technologies of portable FTIR spectrometer are studied to solve the problems of optical path alignment and driving uniformity of moving mirror,so as to meet the requirements of exhaust gas measurement.At the same time,the system can be integrated into SOF-FTIR for VOCs emission flux monitoring,which can meet more advanced applications.Based on the Michelson interferometer model,the main factors affecting the performance of FTIR spectrometer are analyzed,such as resolution,signal-to-noise ratio and equal optical path difference sampling.Through theoretical analysis,the relationship between the moving distance of the moving mirror and spectral resolution,the moving speed and the modulation frequency,the stability of the speed and the sampling accuracy of the same optical path difference are clarified,and the main factors affecting the SNR of the FTIR spectrum are identified.The simulation model of blackbody radiation interferogram and spectrum is established,and the effects of phase error and moving mirror driving error on FTIR interferogram and spectrum are compared and analyzed.The phase error can be corrected by Mertz algorithm,but the moving mirror driving error requires a high-precision control method to solve.In order to meet the requirements of vibration resistance and optical path collimation performance of portable FTIR interferometer,a new structure of pendulum-sweep interferometer based on cube corner reflector is proposed.The geometrical optics method is adopted to establish the optical path difference equation,the ray trajectory is analyzed through numerical simulation.The analysis results show that the proposed interferometer can meet autocollimation optical path and portability,but exists nonlinear optical path difference change.Based on the nonlinear characteristics of optical path difference,the control law of angular velocity of moving mirror under equal optical path sampling is analyzed,and the equal optical path sampling method is compared and analyzed,and the control scheme of moving mirror based on auxiliary He-Ne laser is determined.The mathematical model of the control system based on the ADRC algorithm is established for the anti-disturbance requirement of the Angle mirror swing sweep.According to the requirement of fast starting of moving mirror set by fixed value,the ADRC structure is optimized,and the ADRC control simulation is verified by MATLAB\Simulink,and the optimal parameters of the controller are obtained.The optical path differential speed control system of voice coil motor based on DSP is developed.The experiment shows that the system has higher optical path differential speed control precision and fast dynamic response.(stability interval of optical path difference peak-to-peak change speed instability±0.5%,±2%error with transition time 62ms,±0.5%error with transition time 162ms,He-Ne laser modulation frequency 50kHz,resolution lcm-1).The whole FTIR system is designed based on the swing-sweep interferometer and the self-reactance mirror drive and control system,combined with the peripheral optical path,data acquisition card and PC.The mixed standard gas of CO and propylene is analyzed quantitatively by multi-component spectral analysis method based on least square method,and the relative errors of measurement are 0.86%and 0.58%,respectively.By carrying the portable FTIR on the mobile tracked vehicle platform to test its anti-vibration performance,resolution and SNR.Finally,in view of the complex process of vehicle exhaust analysis and detection and the difficulty in achieving real-time online measurement of multi-component(VOCs),the application research of vehicle exhaust detection is carried out.The emission characteristics of CO,CH4,NO,CO2 and more than 10 typical VOCs are monitored in real time by carrying out NEDC and WLTC condition experiment based on AVL platform and Vehicle-carrying experiment including cold start and urban road test.Compared with traditional exhaust detection technology,the instantaneous emissions data from multiple components of a vehicle exhaust,which help optimize engine preheating strategies,can be obtained quickly and in real time based on a portable FTIR measurement system.Under the requirements of the new regulations,higher standards of NMHC and NMOG measurements can also be achieved,while providing reliable data support for the analysis and simulation of vehicle emissions characteristics on the actual road.