The Study On The Formation Mechanism Of Aromatic Hydrocarbons In Gasoline Engine

A better understanding of the formation of aromatic hydrocarbons in gasoline engines is of practical interest due to the apparent environmental health effects of more and more aromatic hydrocarbons emission from more and more gasoline engines.For the PAHs are trace components in automotive emission gas, the PAHs Sampling Device was designed with gas-washing bottles, by theoretical analysis. and The sampling efficiency calculated is more than 98%.By using the sampling devices, the aromatic hydrocarbons emission from gasoline engine and constant volume bomb was sampled and analyzed. The result showed: the Sampling Method is efficiency and reliable. The concentration of single-ring aromatic hydrocarbons is more than PAHs in gasoline engine emission, while the benzene is the major constituent in single-rings. Before passing by TWC,the concentration of benzene is about 50ppm in varied loads, at 2600 rpm. While after passing by TWC, the concentration alters obviously, and increases much more especially in 46kW power-output, which suggests that TWC induces the benzene formation. However, the toluene and dimethylbenzene reduced after passing by TWC. As for PAHs, the Naphthalene is the major constituent, and its concentration increases with load. But in constant volume bomb tests, the toluene and dimethylbenzene emission from laminar premixed flames are less than the analysis limits, so the benzene is the only aromatic hydrocarbon found in the emission gas.Based on The constant volume bomb flame images and detailed chemical kinetic simulation, we get the following conclusions: the perfect combustion of hydrocarbon fuels, like gasoline, is a three-stage process. They are cool flame stage, blue flame stage and hot flame stage. And the flame domain in constant volume bomb or in gasoline engines can be divided into perfect combustion (hot flame) region and imperfect combustion (cool flame, blue flame) region. In imperfect combustion region, the combustion stops in stage 1 or 2. The aromatic hydrocarbons form in cool flame stage and blue flame stage, and are oxidized completely in hot flame stage. So aromatic hydrocarbons do not exist in perfect combustion region, but survive in imperfect combustion region. And their major constituent is benzene. Therefore, in emission gas, benzene only exists in the imperfect combustion region and its emission mass depends on it's concentration in imperfect combustion region and the volume of imperfect combustion region.