Study On The Effect Of Combustion Conditions And Three-way Catalytic Converter On The Physicochemical Characteristics Of Particles From GDI Engine

In recent years, Beijing-Tianjin region and the Yangtze River Delta are oftencovered by haze which makes the public concern more about the control andgovernance of atmospheric aerosols. With the application of GDI engines, its exhaustgas becomes a potential source of fine particulate matter in the atmosphere. Therefore,study on the particulate matter emissions of GDI engine has become a research focus.In this dissertation, the effect of combustion conditions and the three-way catalyticconverter on the number concentration and nanostructure of particulate matter fromGDI engines was investigated. The evolutionary mechanisms and optimizationmeasures of particulate matter from GDI engines were initially identified. Theseinvestigations will provide theoretical basis for reducing particle emissions from GDIengine. The major achievements of this dissertation are listed as follows:1. The exhaust particles from GDI engine show a bi-modal distribution with a mainpeak in the nucleation mode and a second peak in the accumulation mode. When themixture becomes leaner, the number of particles, nucleation mode particles andaccumulation mode particles sharply decreases. Advancing ignition timing raises thenumber of particles, nucleation mode particles and accumulation mode particles.When the injection timing is advanced, the number of accumulation mode particlesdecrease after an increase. When EGR rate increases, the number of particles andnucleation mode particles increases first and then decrease. However, the number ofaccumulation mode particles shows a decreasing trend.2. When GDI engine is operated at idle operating conditions, the number ofnucleation mode particles decreases while the number of accumulation mode particlesincreases after the three-way catalytic converter. When GDI engine is operated at lowspeed and light load, the number of particles, nucleation mode particles andaccumulation mode particles decrease after the three-way catalytic converter. WhenGDI engine is operated under rich mixture, the exhaust temperature is higher whichwill result in increasing the number of nucleation mode particles after the three-waycatalytic converter.3. Combustion conditions affect the nanostructure of the primary particlessignificantly. Employing the lean mixture, delaying ignition timing, advancinginjection timing and decreasing EGR rate will result in a smaller size of exhaustparticles. Employing the lean mixture and increasing EGR rate would increase thefringe separation distances of crystals. Employing the stoichiometric mixture,delaying ignition timing and advancing injection timing will lead to increased tortuosity of crystals. Employing the stoichiometric mixture, delaying ignition timingand advancing injection timing will reduce fringe length of crystals. Employing thestoichiometric mixture, the range of the primary particle sizes is wider after thethree-way catalytic converter. Employing the lean mixture, particle size decreasesafter the three-way catalytic converter. The range of fringe separation distances ofcrystals become narrower. Employing the stoichiometric and lean mixture, thetortuosity of crystals decreases after three-way catalytic converter.4. Employing the stoichiometric mixture, delaying ignition timing, advancinginjection timing and increasing EGR rate will decrease the graphitization degree ofparticles. At higher exhaust gas temperature, the graphitization degree of particlesincreases after the three-way catalytic converter, which means the particles areoxidized more difficultly.