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The purpose of this work was to gain a fundamental understanding of which fuel property parameters are responsible for particulate emission characteristics, associated with key intermediate behavior in the engine cylinder such as the fuel film and insufficient mixing. Accordingly, engine tests were carried out using various fuels having different volatility and chemical compositions under different coolant temperature conditions. In addition, a fundamental spray and film visualization analysis was also conducted using a constant volume vessel, assuming the engine test conditions. As for the physical effects, the test results showed that a low volatility fuel displayed high particulate number (PN) emissions when the injection timing was advanced. The fundamental test clearly showed that the amount of fuel film on the impingement plate increased under such operating conditions with a low volatility fuel.

For better understanding of in-cylinder soot formation processes and governing factors of the number of emitted soot particles of Gasoline Direct Injection (GDI) engines, Transmission Electron Microscope (TEM) analysis of morphology and nanostructure of the soot particles sampled in the exhaust should provide useful information. However, the number concentration of the soot particles emitted from GDI engines is relatively low, which was impeding reliable morphological analysis of the soot particles based on a sufficient number of sampled particles. Therefore, in the present study, a water-cooled thermophoretic sampler for simple and direct sampling of exhaust soot particles was developed and employed, which enabled to obtain a sufficient number of particle samples from the exhaust with Particulate Number (PN) 105 #/cc level for quantitative morphology analysis.