Development Of Exhaust Mass Concentration Sensor Of Diesel Engine Based On Light Scattering

As characteristics of mixture formation and combustion in diesel engine,the PM (Particulate Matter) emission of diesel engine is much more than gasolineengine. The high-PM-emission hinders seriously diesel engine‘s wide application.Since emission control technology of diesel engine has made significant progress,diesel engines get more extensive application in passenger cars. Mean times,traditional measuremental techniques (Method for Smoke Exhausted and Method forFilterpaper Weight) expose their limitations when measuring high performance dieselengine. Light scattering is a photoelectrical modern analysis and testing technology,which has advantages of instant inspection, non-destructive inspection and widemeasuring range in small particles measurement. The theoretic foundation of dieselengine exhaust particles inspection by light scattering is studied. A sensor is designedto inspect exhaust particles based light scattering. It mainly finished the followingseveral problems:(1) Theoretical analysis and simulation. Soot particulates from dieselengine are general clusters, aggregated by several nearly spherical highcondensed primary particles, not ideal homogeneous spherical particles. Tojudge whether particle-scattering theory can be used to diesel engine exhaustparticle measurement, a mathematics model of aggregates quality and lightscattering flux is created and simulated. The simulation result shows thatthe light scattering flux has linear relationship with aggregates quality incertain range. As a result, it is a reliable method to measure the massconcentration by inspecting light scattering flux.(2) The design of hardware structure and circuit. the main structuralparameters of sensor-the power and wavelength of light source, the size of photosensitive area, solid angle of light collecting and sample rate are calculated; three key optical components-Photodetector, Light source and light trap are introducedand analyzed. On this basis, the structure of sensor is designed and the sensor is fitout. In addition, several thoughts for very slight signals in variety noises aboutpreamplifier circuit design are introduced.(3) Main functions and realization of upper computer software.①communication with data acquisition card on PCI Interface,real-time receivingand displaying digital waveforms from data acquisition card;②dataprocessing,real-time displaying voltage waveform from sensor,converts it intoparticle mass concentration by filtering and operations;③data access, includingsaving and browsing historical data, seismic alarm and so on.(4) Experimental research. Experiments are designed to analyze zero drift,measurable range and the minimal resolution of sensor. Some modifications andoptimizations of sensor are made based on the experiment results and analysis.According to Method of Measuring Concentration of Dust In the Air on thePrinciple of Scattered light LD98-1996‘‘, voltage-mass concentration conversioncoefficients K is calculated with12groups experimental data and the development ofmeasuring system is completed. To analyze actual measuring effect, sampled dieselengine exhaust is tested by the measuring system this paper designed.Theexperiment results show that the sensor response quickly with exhaust particleconcentration, but the measurement result dispersed a lot both in low concentrationand high concentration.The main reasons caused deviation is listed in this paper.