The effect of ethanol and iso-butanol blends on polycyclic aromatic hydrocarbon (PAH) emissions from PFI and GDI vehicles

Abstract

This study assessed particulate emissions characteristics from two flexible fuel vehicles (FFVs) equipped with port fuel injection (PFI) and gasoline direct injection (GDI) engines. Emissions testing was conducted over the Federal Test Procedure on E10, E51, and E83, and an iso-butanol blend (iBut55). The results showed significantly higher particulate matter (PM) emissions for the GDI-FFV compared to those of the PFI-FFV. The addition of alcohol blends resulted in PM reductions for the GDI-FFV, while PM emissions gradually increased with higher alcohol blending for the PFI-FFV. Elemental carbon (EC) emissions dominated the PM composition for the GDI-FFV, whereas the organic carbon (OC) fraction was higher for the PFI-FFV. The most prominent polycyclic aromatic hydrocarbons (PAHs) in the vapor-phase were the two- and three-ring aromatic compounds, followed by the middle molecular weight PAHs (four-ring compounds). For the particle-phase PAHs, the middle- and high molecular weight PAHs were the most abundant compounds, especially for the GDI-FFV. Overall, the GDI-FFV exhibited markedly higher PAH emissions compared to the PFI-FFV. Both vapor- and particle-phase PAH emissions showed reductions with higher ethanol and iso-butanol fueling for both vehicles, except for the PFI-FFV, where particle-phase PAHs increased and trended similarly with the PM mass and OC for this vehicle. Alcohol blending reduced the carcinogenic potential of the exhaust emissions for both vehicles. The GDI exhaust showed significantly higher metal emissions than the PFI-FFV. The use of higher alcohol blends led to reductions in metal emissions, including redox-active transition metals and other metals originating from the lubricant oil.