Investigation of the Effect of Mid- And High-Level Ethanol Blends on the Particulate and the Mobile Source Air Toxic Emissions from a Gasoline Direct Injection Flex Fuel Vehicle

This study examined the influence of low-, mid-, and high-ethanol fueling, as well as the influence of the aromatic hydrocarbons in the fuel blend, on the regulated and greenhouse gas emissions, the mobile source air toxic pollutants, and the particulate emissions from a current model flexible fuel vehicle equipped with a gasoline direct injection engine. This study utilized a total of four fuels, including a baseline U.S. EPA Tier 3 E10 fuel, one E10 fuel with higher aromatics content than the baseline E10, an E30 fuel that was splash-blended with the Tier 3 E10, and an E78 fuel. Testing was conducted over triplicate cold-start and hot-start LA92 cycles. The findings of this study showed that the higher ethanol blends, namely, the E30 and E78, led to statistically significant reductions of 9%-13% for total hydrocarbon (THC), 13%-44% for non-methane hydrocarbon (NMHC), 20%-35% for carbon monoxide (CO), and 17%-36% for nitrogen oxides (NOx) emissions compared to the high-aromatics E10 fuel. The emissions of carbon dioxide (CO2) for the high-aromatics E10 were higher than the Tier 3 E10, E30, and E78 blends. A fuel economy penalty was also observed for lower energy content E30 and E78 blends compared to both E10 fuels. Particulate matter (PM) mass, black carbon, and total and solid particle number emissions showed statistically significant reductions for the E30 and E78 fuels compared to both E10 fuels. Results also showed that the high PM index/high-aromatics E10 produced more particulate emissions than the low PM index E10, as well as higher populations of accumulation (soot) mode particles. Acetaldehyde formation was favored by the higher ethanol content in the fuel, resulting in significant increases compared to both E10 fuels. Benzene, toluene, ethylbenzene, and xylenes (BTEX) emissions enhanced their formation with the high-aromatics E10, whereas the use of E30 and E78 fuels showed important reductions in BTEX emissions.