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
Particulate
matter (PM) composition and soot oxidation were investigated
in a single-cylinder spray-guided direct-injection spark ignition
(DISI) research engine using the thermogravimetric analysis (TGA)
technique. Fuels including gasoline, ethanol, 25% volumetric blend
of ethanol in gasoline (E25), and a new biofuel candidate (2,5-dimethylfuran,
DMF) were studied. The engine was operated at 1500 rpm with a rich
fuel/air ratio (λ = 0.9) and late fuel injection strategy, representing
one of the worst scenarios of PM emissions from DISI engines. A TGA
method featuring devolatilization and soot oxidization functions was
developed and a kinetic model was used to analyze the soot oxidation
process. The results show that volatile components are the main contributor
to the PM produced from gasoline, E25, and DMF, and elemental soot
accounts only up to 35% of PM mass at 8.5 bar IMEP. Ethanol combustion
is so clean that only 6.3% of PM mass comes from elemental soot. The
reaction rate of the soot oxidation is highly dependent on fuel and
is sensitive to engine load. Soot from ethanol combustion is the most
easily oxidized, indicated by the lowest temperature and activation
energies (83 kJ/mol) required for oxidization. Soot from gasoline
combustion is the most difficult to be oxidized, requiring the highest
temperature and activation energy. It is found that the activation
energy required for the soot from gasoline combustion increases with
the engine load; however, the increase for soot from DMF combustion
is very small.
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