Impacts of gasoline aromatic and ethanol levels on the emissions from GDI vehicles: Part 1. Influence on regulated and gaseous toxic pollutants

Abstract Gasoline composition is critical to the formation of regulated emissions and gaseous toxic pollutants from spark ignition engines equipped with direct injection fueling. This study investigated the impacts of varying aromatic and ethanol levels on the exhaust emissions of five gasoline direct injection (GDI) vehicles. A total of eight fuels were used, with aromatic levels of 20% and 30% by volume, and ethanol levels ranging from 0% to 20% by volume. The test fleet consisted of 2016 to 2017 model year Tier 3 vehicles operated over the LA92 drive cycle. We showed that total aromatics played an important role for the emissions of non-methane hydrocarbons (NMHC), total hydrocarbons (THC), formaldehyde, and mono-aromatic hydrocarbon species (i.e., benzene, toluene, ethylbenzene, and xylenes), with an increase of gasoline aromatics resulting in higher emissions of these pollutants. Increasing ethanol levels in gasoline led to statistically significant reductions in carbon monoxide (CO) and statistically significant increases in acetaldehyde emissions. Emissions of nitrogen oxides (NOx) were not significantly affected by either aromatics or ethanol levels across the fleet. There was a lack of strong trends between the fuels in the ozone forming potential (OFP). The largest contribution to OFP in the exhaust was from aromatic species, followed by alkenes and alkanes. Overall, aromatics played a more dominant role in emissions formation than ethanol content, indicating multiple formation pathways for these pollutants.