Research On Influence Factors Of Particulate Matter Emission Detection From Gasoline Engine

At present,gasoline vehicles take a large proportion in motor vehicles,therefore the influences of the exhaust particles from them on the human beings and the environment have been paid more and more attention.In this dissertation,the chemical composition,formation mechanism,physicochemical characteristics,and influence factors of the exhaust particles from gasoline vehicles were analyzed firstly.Through the comparison of the commonly used particles monitoring technologies and sampling method of exhaust particles from gasoline vehicles,the particles concentration detector based on laser testing technique was selected to mainly detect the primary exhaust particles concentration in automobile exhaust gas.Then,an exhaust particle detection system was designed,and used to detect the exhaust particles of test car.Based on the analysis of the variation characteristics and influence factors of exhaust particles,and the comparison of the differences in the distribution of particles in different working conditions,suggestions on improving the detection method were proposed,and the detection scheme was continuously improved.The work will provide a convenient reference for the research on the detection of exhaust particles in gasoline vehicles.The results show that the mass and concentration of particles with different particle size could reach an equilibrium state within 20 min after the engine startup;and the particles increased to peak value then decreased rapidly after flameout10 min.Therefore,an equilibrium value should be chosen when doing a real-time detection on exhaust particles from vehicles,while an accumulation peak should be chosen for sampling detection.Fine particles is the major(more than 65%)exhaust particles at engine idle condition.And the exhaust condition and other exhaust components are more relative with fine particles,however do not associated with the coarse particles or have a weak correlation in them.Therefore,the fine particles should be chosen as the main index and the coarse particles as the auxiliary index for the detection of exhaust particles.Because the exhaust particles concentration severely affects by humidity in high idle speed,the effect of humidity on particles concentration can be reduced through improving the condenser and increasing the volume of test box to reduce humidity for the exhaust particles detection at high idle speed of the vehicles.Comparing with the detection experiments,it is shown that the changes of particles concentration are basically the same under different working conditions when the engine reaches an equilibrium after startup.However the equilibrium values differ greatly and the equilibration time is also different.Therefore not only the testing time should be adjusted according to the actual conditions,but also the detection results of exhaust particles concentration in different diameter range should be corrected in the detection of exhaust particles.And when the engine is out of order,the variations of the particles concentrations under different working conditions are quite different,therefore it is not recommended to detect the particle emission after the engine flameout.