Research On Key Technology Of Spectral Processing For Portable Diesel Vehicle Exhaust Emission Monitoring

Due to the increasingly strict regulations on exhaust emission in recent years,the detection technology of exhaust emission receives a lot of attention from researchers.The pollutant emission contribution rate of heavy-duty vehicles,mainly diesel vehicles,is far higher than that of light-duty vehicles.Therefore,accurate detection of CO,CO2 and NOx emissions in diesel vehicle exhaust has strong practical guiding significance for the ecological environment and sustainable development.The thesis takes the optical gas detection technology as the main research content,which studies and analyzes the photoelectric signal detection and spectral data processing methods.Also,the system has been designed,which applied to the diesel vehicle exhaust emission detection.The basic principles of infrared absorption spectroscopy for CO,CO2 detection and ultraviolet absorption spectroscopy for NOx detection are expounded,respectively.Based on the above theoretical basis,the scheme of non-dispersive infrared CO and CO2 detection and UV dual optical path NOx detection are proposed.Select 1-20μm broadband infrared light source and pyroelectric detector with 4.26μm,4.64μm filters as the detection methods of CO and CO2,Broadband pulsed xenon lamp and 390nm LED are selected as light sources,and the spectrometer and photodetector are used to detect NO and NO2 in time-division multiplexing.Finally,the key research issues such as the detector output signal-to-noise ratio,the fixed structure of the light source radiation spectrum,and environmental factors are proposed.The photoelectric signal processing method based on stochastic resonance is studied.For modulated photoelectric signals,the different parameters on the underdamped model in stochastic resonance is discussed,and the detection process of the model is designed.The experimental results showed that the signal-to-noise ratio of the photoelectric modulation signal increases from 2.517dB to 4.263dB,and the signalto-noise ratio gain was 1.673,which proves that the underdamped SR has a good signal enhancement effect,which is more suitable for the signal detection in the strong noise environment.At the same time,Based on the characteristics of stochastic resonance,a monostable system is used to process the low-concentration NO signal.The parameter adjustment monostable algorithm is designed and numerical simulation and actual signal test was carried out.Under the condition of low concentration,the maximum relative deviation was 3.32%,and the detection limit was 1.456ppm,which indicate that the proposed method has better peak detection performance and spectral signal-tonoise ratio.The data processing method of diesel vehicle NOx gas emission absorption spectrum is studied.By means of numerical simulation,the UV NOx absorption spectrum curve under the condition of fine structure in the radiation spectrum of the light source is simulated,and a spectral feature processing method based on Principal Component Analysis(PCA)is proposed to eliminate measurement errors caused by the fine structure of the radiation spectrum.The comparison experiment was carried out using the actual measured NOx spectral data and the traditional polynomial fitting baseline method.The experimental results showed that the correlation of the calibration and fitting curve of the proposed method was 0.99923,and the average measurement error was less than 3%.The design of portable diesel vehicle exhaust gas detection system,which was tested in laboratory conditions,is analyzed.The test results show the average relative error and the relative standard deviation are each less than 2%and 3.2%for the wide range of diesel exhaust gas(NO:2500ppm,NO2:2500ppm,CO:5%,CO2:20%).The size of the whole system is 350x270x150mm and the weight is 14Kg.Also,the designed system was applied to bench monitoring,vehicle monitoring and site monitoring,respectively.Through the comparison test with similar international advanced instrument SEMTECH,the correlation reaches the highest 94%.The three field applications obtain the CO2,CO and NOx emission characteristics of diesel vehicles under different working conditions,different driving environments,and different driving habits.The stability and practicability of the field operation of the portable system can provide effective data support for the rapid supervision of subsequent diesel vehicle exhaust gaseous pollutants.