Effects of Mid-Level Ethanol Blends on Conventional Vehicle Emissions

Tests were conducted during 2008 on 16 late-model, conventional vehicles (1999 through 2007) to determine short-term effects of mid-level ethanol blends on performance and emissions. Vehicle odometer readings ranged from 10,000 to 100,000 miles, and all vehicles conformed to federal emissions requirements for their federal certification level. The LA92 drive cycle, also known as the Unified Cycle, was used for testing as it was considered to more accurately represent real-world acceleration rates and speeds than the Federal Test Procedure (FTP) used for emissions certification testing. Test fuels were splash-blends of up to 20 volume percent ethanol with federal certification gasoline. Both regulated and unregulated air-toxic emissions were measured. For the aggregate 16-vehicle fleet, increasing ethanol content resulted in reductions in average composite emissions of both NMHC and CO and increases in average emissions of ethanol and aldehydes. Changes in average composite emissions of NMOG and NOX were not statistically significant. By segregating the vehicle fleet according to power-enrichment fueling strategy, a better understanding of ethanol fuel-effect on emissions was realized. Vehicles found to apply longterm fuel trim (LTFT) to power-enrichment fueling showed no statistically significant fuel effect on NMOG, NMHC, CO or NOX. For vehicles found to not apply LTFT to power-enrichment, statistically significant reductions in NMHC and CO were observed, as was a statistically significant increase in NOX emissions. Effects of ethanol on NMOG and NMHC emissions were found to also be influenced by power-to-weight ratio, while the effects on NOX emissions were found to be influenced by engine displacement.