Study On Emission Characteristics Of Primary Particles And Formation Potential Of Secondary Particles From Gasoline Engines

Motor vehicle emissions are one of the main pollution sources of atmospheric haze. This paper studies the emission characteristics of primary particles and formation potential of secondary particles from gasoline engines through engine test bench and smog chamber.The experimental results based on engine test bench show that, particle number emission factor of the gasoline direct injection(GDI) engine is two orders of magnitude higher than that of the port fuel injection(PFI) engine, while particle mass emission factor is just one order of magnitude higher than that of the PFI engine. The particulate matter(PM) from the PFI engine mainly consists of organic matter(OM) and a small amount of elemental carbon(EC) and inorganic ions. The PM discharge from the GDI engine mainly consists of EC, OM and a small amount of inorganic ions. As the load of the engine increases, the content of EC increases. The content of OM in PM reduces while EC content increases after three-way catalysts(TWC), and the mass of PM reduces by 28%-35% after TWC. According to elements and morphologies of PM, the PM from GDI engines can be divided into carbonaceous particles and non-carbonaceous particles, and further several small kinds. As the load of the engines increases, the Soot content in the particles gradually increases, and the sum of particles containing organic matter reduce.The emissions of PM reduce with the increase of EGR(Exhaust Gas Recirculation) rate when EGR.≤15%. But too much EGR would make PM emissions increase. It’s best for the emissions of PM to set injection timing as 270°BTDC(Before Top Dead Center), either earlier or later will get the emissions of PM increase. Higher proportion of aromatics, olefins or sulfur in gasoline fuel will lead to higher PM emissions. Higher proportion of aromatics in gasoline fuel will lead to higher polycyclic aromatic hydrocarbons(PAHs) emissions, and the toxicity of PAHs is stronger. Higher proportion of olefins in gasoline fuel has little influence on PAHs emissions, but the toxicity of PAHs is stronger. A small amount of methyl-cyclopentadienyl-manganese-tricarbony(MMT) can reduce the proportion of aromatics and olefins in fuel while the octane number unchanged and thus reduce PM emissions. 10% of ethanol to fuel has little effect on PM emissions. The VOCs emitted from the engines mainly composes of 70 kinds of organic matter, including alkane, olefins, aromatics, oxygenated volatile organic compounds, and alkynes. As the load of the engines increases, the alkane content decrease while the aromatics content gradually rises. Burning of the fuel with higher aromatics content results in higher content of aromatics in VOCs.The experimental results based on smog chamber and engine test bench show that, the mass emission factor of secondary particles from PFI engine is 169 times as much as that of primary particles from PFI engine; and is 17 times as much as that of primary particles from GDI engine. The chemical composition of secondary particles is almost organic matter, and only less than 10% of secondary particles can be explained by current theories.