UC Riverside researchers find mixed emissions impact from use of higher ethanol and butanol fuels in FFVs

24 November 2014

A study by University of California, Riverside researchers found that the use of higher ethanol blends and a 55% butanol blend in port-fueled and direct injection flexible fuel vehicles (FFVs) could lead to emission changes of GHGs, CO, aldehydes, BTEX (monoaromatic hydrocarbons of benzene, ethylbenzene, toluene, m/p-xylene, and o-xylene), and particulates.

In a paper in the ACS journal Environmental Science Technology, they reported that the higher alcohol fuels would decrease PM mass and number emissions, although current technology direct injection fueling produces higher particle number and soot mass emissions than the PFI fueling as a result of liquid fuel wetting effects and insufficient air fuel mixing. Particulate emissions were clearly influenced by certain fuel parameters including oxygen content, hydrogen content, and aromatics content.

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The results also suggested that BTEX emissions would decrease with higher ethanol blends and the isobutanol blend—an important finding since benzene is a known carcinogen to humans and these other compounds play an active role in the atmospheric chemistry and contribute to the photochemical smog present in many metropolitan areas.

Emissions of nonmethane hydrocarbons (NMHC) and carbon monoxide (CO) showed some statistically significant reductions with higher alcohol fuels, while total hydrocarbons
(THC) and nitrogen oxides (NO_x) did not show strong fuel
effects.

However, they also found that the use of higher ethanol blends in FFVs would significantly increase acetaldehyde emissions—classified by the National Institute of Occupational Safety and Health (NIOSH) and by the International Agency for Research on Cancer (IARC) as a potential human carcinogen. The isobutanol blend resulted in higher butyraldehyde emissions; butyraldehyde possesses similar reactivity and mutagenicity to acetaldehyde.

For the study, which was supported by the California Energy Commission, South Coast Air Quality Management District (SCAQMD) and the University of California Transportation Center (UCTC), the researchers used an E10 blend as the baseline for comparison with E51 and E83 blends. They also tested a Bu55 blend (55% isobutanol)—the highest volume of isobutanol that could be blended while still meeting the California summer gasoline specifications.

Testing was conducted on two late-model FFV pickup trucks with similar horsepower ratings and certification levels: a 2013 model year (MY) Ford F150 (PFI-FFV) with a 3.7 L V6 engine and PFI fueling having a rated horsepower of 302 hp at 6500 rpm and a 2014 MY Chevrolet Silverado (GDI-FFV) with a 5.3 L V8 engine and wall-guided direct injection fueling having a rated horsepower of 355 hp at 5600 rpm.

Both vehicles had three-way catalysts (TWCs) and were certified under California ULEV II/Tier 2 Bin 4 emission standards. The vehicles had accumulated mileages of 13700 for the Ford F150 and 2649 for the Chevrolet Silverado at the beginning of the testing. Each vehicle was tested on each fuel over three FTPs and three UC tests.

In terms of GHGs, the impact of the higher alcohol fuels was mixed, with the higher alcohol fuels showing some increases in CH₄ emissions, but the E83 fuel also showing some reductions in CO₂ emissions over the UC cycle.

Overall, the differences in tailpipe GHGs between fuels are probably relatively minor compared to other factors that might influence a full life cycle analysis assessment of GHGs for different fuels. The PM emission levels for these vehicles on the low level ethanol blend (i.e., E10) are above or right at the future California LEV III and Tier 3 standards for PM mass emissions to be implemented by 2017 (3 mg/mile) and are clearly above the ultralow PM standard of 1 mg/mile, which is expected in 2025 in California, indicating that meeting future regulations will require additional PM reductions from the levels observed for this current technology GDI-FFV. For GDI-FFVs, this would likely be achieved by a combination of engine calibration and different fuel injection design, such as a spray-guided architecture. Higher levels of fuel oxygenates could also potentially provide PM reduction benefits for future GDI and PFI vehicles.

Resources

• Georgios Karavalakis, Daniel Short, Robert L. Russell, Heejung Jung, Kent C. Johnson, Akua Asa-Awuku, and Thomas D. Durbin (2014) “Assessing the Impacts of Ethanol and Isobutanol on Gaseous and Particulate Emissions from Flexible Fuel Vehicles”
  Environmental Science Technology doi: 10.1021/es5034316