Electronic Design And Experimental Study Of Diffusion Charge Based Motor Vehicle Emission Particles Number Concentration Measurement System

With the rapid development of the national economy and the continuous improvement of people's living standards,China's motor vehicle possession has exceeded 325 million and has continued to rise.The contribution of mobile sources represented by motor vehicles to environmental pollution has become increasingly prominent.The particulate matter emitted by the motor vehicle h as become one of the important source of PM5.5.Due to its small volume and light weight,it is insufficient to reflect the pollution characteristics by just monitoring the mass concentration.Therefore,the limits of number concentration has been given out explicitly in China's latest motor vehicle emission standards.This article is aimed at the research on electronic design and experimental study of diffusion charge based motor vehicle emission particles number concentration measurement system.Firstly,the micro-current measurement module and the aerosol electrometer have been developed and evaluated.Secondly,the diffusion charge based vehicle emission particles number concentration measurement system has been developed by integrating the diffusion charge module,the aerosol electrometer and the total number concentration inversion algorithm together.Finally,the inversion algorithm has been investigated theoretically and experimentally and the comparison test has been carried out in the bench test.The main results are as follows:(1)Based on the principle of micro-current measurement,a fA-level micro-current measurement module with high precision and wide dynamic range and no range switching necessary has been designed by integrating an impedance based ?-? conversion circuit,a level conversion circuit and a high-precision AD conversion circuit together.And then its measurement model and temperature effect model have been established.Through the analysis of the model and the noise influence factors,the guideline of selecting the key components in the circuit and the cleaning and handling processing method and some layout guidelines have been given out.In order to investigate the influence of temperature,electronic components and other factors on the performance of the micro-current measurement module,three micro-current measurement modules with different sensitivity and dynamic range were built and calibrated.Moreover,their linearity and zero drift and noise were evaluated.The results show that their linearity were better than 0.25%,0.85%,and 1.20%,respectively;their peak-to-peak value of zero drift were about 340 fA,45 fA,and 20 fA,respectively;their root mean square values of noise were 3.31 fA,1.01 fA,and 0.31 fA,respectively;their dynamic range were 115.6 dB,105.9 dB,and 96.2 dB,respectively.(2)Based on the principle of static Faraday cup,an aerosol electrometer with high detection efficiency has been developed,its measurement model has been established and analyzed.At last,the flow rate of the module was calibrated,the flow stability,the zero drift,the detection efficiency,and the comparison testing were carried out.The results show that the flow rate error was less than ±0.004 L/min when set to 2 L/min;the peak-to-peak value of the zero drift was 510 fA;the particle detection efficiency was better than 96.6%when measuring particle diameter large than 5 nm;a 99.4%(R2)statistical correlation was achieved when compared with TSI-3068B(more than 1 hour);the measurement range was 40 times that of TSI-3068B at the same root mean square values of noise(<1 fA),(3)A differential measurement scheme has been proposed and the diffusion charge based vehicle emission particles number concentration measurement system has been developed.The inversion algorithm for the measurement system has been established theoretically and verified experimentally,the influence of the trap voltage and the sample flow on particle number concentration inversion has also been investigated experimentally.The comparison test has been carried out preliminarily in the bench test and PEMS test.A 89.3%and 73.7%(R2)statistical correlation were achieved when compared with commercial instruments(MEXA-2000SPCS,HORBIA)in the experiments of heavy diesel vehicles and light gasoline vehicles respectively.In the PEMS experiment of light gasoline vehicles,the statistical correlation were 93.6%and 90.1%when compared with HORBIA's OBS-ONE and AVL's AVL M.O.V.E,respectively.