Study On The Characteristics Of Exhaust Paticulate Matter Emission From Gasoline Engine

The size of gasoline engine exhaust particulate is smaller than diesel.Most of theparticulate are nanoscale particles that they are very bad for human health andenvironment.And the number of gasoline engine is higher than diesel.With GDI enginesgradually access to market, their particulate emissions have become the research focusof internal combustion engine scholars. Therefore, it’s necessary to study on thecharacteristics of particulate emission from gasoline engine. In this paper, thecharacteristics of particulate emission form a PFI gasoline engine and a GDI enginewere investigated with the fast particle spectrometer DMS500.For PFI gasoline engine, effect of speed and load on particle emission was studyed,and the mechanism of particles removed by the catalytic converter was explored.Particles produced in the low to medium load, almost all were nanoscale nucleationmode particles.With the load increased, the particle number concentration increasedmonotonically and the peak particle size increased.Geometric mean diameter andmedian diameter of particles were gradually increased with the load increased. Lots ofaccumulation mode particles produced in the high load conditions. With speed increased,the particle number concentration increased monotonically. From the penetration ratioof particle number concentration through the catalytic converter, it was got thatthree-way catalytic converter can reduce particle emissions. The particle numberconcentration and HC conversion efficiency has a similar trend, it was got indirectlythat some nucleation mode particles were formed by HC condensed.Particulate removalmechanism is that gaseous phase hydrocarbon was oxidized in the catalytic converter.For GDI engine, it was investigated that effect of air-fuel ratio, ignition timing,injection timing and EGR on the characteristics of particulate emissions. When theair-fuel ratio was less than14.7, the particle number concentration showed a trimodaldistribution, most of particulate were accumulation mode particles. When the air-fuelratio greater than14.7, the particle number concentration distribution was a single peak,they were nucleation mode particles mainly. With the air-fuel ratio from small to big,the particle number concentration peak and peak particle size reduced gradually. Withthe ignition timing advanced, accumulation mode particle number concentrationdecreased firstly and then increased gradually.With the ignition angle was advanced to20degree from5degree before TDC, the particle total number and total mass were declined.But the particle total number concentration and total mass concentraion wererised from20degree to50degree in advance.With the injection timing from70degreebefore TDC to170degree, the particle total number and mass were droped sharply. Inthe EGR rate changed test conditions, the particle size distribution showed bimodal withnucleation mode and accumulation mode. With the increase of EGR rate, the nucleationmode particle number concentration was increased sharply,but the accumulation modeparticle number concentration was declined gradually. With the EGR rate increased, theparticle total number concentration increased, whereas the particle total massconcentration is decreased.