| Recently, the automobile volume tenure in our country is increasing sharply, the particles and polycyclic aromatic hydrocarbons from the gasoline car pose a serious threat to environment and human health. Due to stringent emission regulation on the size and number of particle matter in engine exhaust, therefore, accurate prediction of the concentrations of PAHs and soot formed in engines is required. Studies have been published that soot formed through physical coagulation of large PAHs. Apparently, a reliable prediction of soot such as soot volume, number density and particle size distribution can't be obtained without an accurate estimate of the amount of PAHs formed in the engines. Therefore a basic understanding of PAHs growth kinetics is of importance theoretical significance.Toluene reference fuel(TRF), the mixture of PRF and toluene, is applied as gasoline surrogate fuel, A detailed reaction mechanism consisting of 287 species and 1569 reactions for gasoline surrogate fuels toluene reference fuels(TRF) with an emphasis on developing an accurate model for the formation of large polycyclic aromatic hydrocarbons(PAHs) is researched and developed in this study. Four kinds of reaction pathways for PAH growth are added to the new mechanism with the largest chemical species for gasoline surrogate fuels of this mechanism being A7. Species like acetylene(C2H2), propargyl(C3H3), vinylacetylene(C4H4) and hydrocarbons with odd number of carbon atoms like cyclopentadienyl(C5H5) and indenyl(C9H7) play an important role in the formation and growth of polycyclic aromatic hydrocarbons(PAHs) molecules according to the analysis of PAH rate of production. This mechanism could predict ignition delay timing, mole fractions of some small important species like PAH precursors C2H2 and C3H4, and mole fractions of PAHs in the flames of PRF and TRF. Comparisons between calculations and experiments indicate the good predictability of this mechanism over wide range of temperature, pressure, and equivalence ratios.The fuel proportion principle is studied in order to give the more realistic reaction progress of real gasoline simulated by the surrogate fuel. It is founded that the aromatic/paraffinic proportions of surrogate fuels should be firstly same with the real fuel to insure the mole fractions of polycyclic aromatic hydrocarbons, then the research octane number(RON) and motor octane number(MON) of the surrogate fuels should be similar with the real fuel through adjusting the proportion of n-heptane and iso-octane. The applicability of the fuel principle has been validated by a series of cylinder pressure and PAH precursors under different conditions.In order to study the process of PAH formation in cylinder,the mechanism should be coupled with three-dimensional software CFD. The mechanism must be simplified to save the computing time. Based on the sensitivities of substance and temperature, a simplified mechanism including 87 species and 480 reactions is developed and validated against a series of experimental data and calculation results simulated with the detailed mechanism. The good consistency have been obtained between the ignition timing and profile of combustion products simulated with the simplified mechanism and the experimental data. |
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