Research And Application Of Data Processing Algorithm For On-line Portable Detection Of The Vehicle NO_x Emission Based On Pulsed Xenon Lamp

With the development of the national economy,the number of motor vehicles in China is growing rapidly and the annual rate increases more than 10%one year.The environmental pollution caused by the vehicle exhaust emissions is becoming more and more serious.NO and NO2 are collectively referred to NOx and they are important components of the vehicle exhaust.Monitoring of the NOx concentration from the vehicle exhaust is very important for assessing the vehicle exhaust emission level and protecting the urban atmosphere.The spectral analysis method has become the mainstream development direction and research focus on the concentration detection technology for the motor vehicle components because it's not easily interfered by the superposition absorption of other components.The research content of this paper is the portable vehicle exhaust NOx online detection data processing algorithms based on the pulse xenon lamp and their application,its research purpose is to establish the theory and technology foundation for the portable vehicle exhaust NOx online detection instrument with independent intellectual property rights.First it's introduced the basic theory of pulsed xenon lamp and material absorption spectra in the paper.An experimental platform has been set up to collect NOx absorption spectrum data using a Hamamatsu L9456-1 pulsed xenon lamp as the light source.The practical problems that occurred during the experiments such as the light source fluctuations,spectral acquisition time and its average time have been all studied with the platform,then the corresponding solutions have been proposed and operating parameters of the experimental platform have been determined.The experiment results show that with the built platform the NO detection limit is 2.45ppm,the range can reach 2500ppm and the NO2 detection limit is 2.6ppm,the range can reach 500ppm.Then,the effect of spectral noise on the accuracy of NOx concentration inversion is discussed.Based on the insufficiency analysis of the general noise reduction methods for the vehicle exhaust NOx absorption spectrum,an adaptive normalized and index-optimized EEMD spectral preprocessing algorithm has been researched with the experimental platform.The experimental results show that the effect of noise reduction with NIO-EEMD is better than that of EMD low-pass filtering and db3 Wavelet decomposition algorithm under the same circumstances.The SNR index has increased from the initial value of 17.8985 to 28.1347.Then,to solve the problem of superposition absorption interference which can't be avoided in measuring the NOx concentration of the vehicle exhaust,the weighted partial least squares(WPLS)regression has been introduced.Based on the spectral characteristics of exhaust multi-components NO and NO2(including interference components SO2 and NH3),a regression model for multi-components' concentrations has been established.After that,the WPLS-VIP-ACO wavelength selection algorithm for NOx concentrations prediction model has been researched to screen the spectral datas.The experimental results show that the approximation degree between the NOx inversion value and the actual concentration of the samples has been increased from 0.99 to 0.999 after the wavelength selection,even reaching the maximum of 0.9999.Then based on the requirements for the portable,in-situ,on-line and rapid detection of the vehicle exhaust NOx concentrations,the design indicators have been studied out.Through the theoretical analysis and experimental verification,a vehicle exhaust NOx concentration detection system based on the pulsed xenon lamp has been designed.Combined with the already researched adaptive NIO-EEMD preprocessing algorithm for NOx absorption spectrum,WPLS-NOx concentration inversion algorithm and W-V-A wavelength selection algorithm,the detection system software has also been designed.Finally,the practical application of the NOx concentration data processing algorithm researched above has been carried out with the prototype of the developed detection system,including the calibration of the instrument,comparison experiments between the NOx detection system and the US Sensors.co and field testing experiments on NOx emissions from the motor vehicles.The experimental results show that the developed prototype has a detection accuracy of ±2%for NO&NO2,its range is 0?2500ppm for NO and 0~500ppm for NO2.