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10In recent years, particulate emissions from the gasoline direct injection (GDI) engine, especially the 11 ultrafine particulates, have become a subject of concern. In this study, the impact of fuel (gasoline versus 12 ethanol) and injection system on particle emissions was investigated in a single cylinder spray-guided GDI 13 research engine, under the operating conditions of stoichiometric air/fuel ratio, 1500 rpm engine speed and 14 3.5-8.5 bar IMEP. Two fuels (gasoline and ethanol), four injection pressures (50, 100, 150 and 172 bar) and 15 three injectors (one clean and two fouled injectors) were studied. The results show that, in a spray guided GDI 16 engine, ethanol combustion yields much lower particle mass (PM) but higher particle number (PN) emissions, 17 compared to gasoline. Depending on the fuel used, the PM and PN emissions respond differently to injection 18 pressure and injector condition. For gasoline, the injection system has a significant impact on the PM and PN 19 emissions. High injection pressure and clean injector condition are both essential for low particle emissions. 20Compared to gasoline, the particle emissions from ethanol combustion is less sensitive to the injection system, 21 due to its higher volatility and diffusive combustion which produces less soot. Furthermore, a PM and PN 22 trade-off was observed when using gasoline and ethanol, and when using high injection pressures. 23 24 25

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