The California Air Resources Board (CARB) has released the results of a multiyear study evaluating exhaust emissions from the use of California Reformulated Gasoline (CaRFG) that contains 15 volume percent ethanol (E15). The study was performed by a team from the University of California at Riverside (UCR) Bourns College of Engineering – Center for Environmental Research and Technology (CE-CERT).

California currently limits the ethanol content of gasoline to 10 percent. The Multimedia Evaluation (MME) of E15 looked at the effects of increased ethanol content on exhaust emissions in 20 vehicles—all model year 2016 or newer.

The study used two fuels—an E10 and E15. The summer-grade E10 fuel was sourced from four different refineries that were selected by CARB. The E10 fuels were blended together in four equal parts to create the final E10 fuel. The E15 fuel was created by splash-blending denatured ASTM D4806 fuel grade ethanol with the final E10 fuel.

The twenty light-duty gasoline vehicles included a mixture of technologies, such as gasoline direct injection (GDI), port fuel injection (PFI) as well as PFI+GDI fuel systems that are representative of the current California gasoline fleet. One hybrid electric vehicle (HEV) equipped with a PFI engine was also used. The vehicle test matrix had provisions for five vehicles on each emissions standards category (i.e., SULEV30, ULEV50, ULEV70, and ULEV125).

Measured emissions included: oxides of nitrogen (NO_x), total hydrocarbons (THC), non-methane hydrocarbon (NMHC), carbon monoxide (CO), carbon dioxide (CO₂), PM mass, particulate number, 1,3-butadiene, benzene, toluene, ethylbenzene, xylene isomers, ethanol, and carbonyl compounds.

The test fleet showed statistically significant effects for some pollutants, but not for others. NO_x emissions, a target pollutant of concern for this program, did not show any statistically significant difference between the fuels for the FTP nor for each individual FTP phase.

Findings included:

• Cold-start and weighted THC emissions showed statistically significant reductions of 6% and 5%, respectively, for E15 compared to E10. For the cold-start NMHC emissions, E15 showed a 7% statistically significant reduction compared to E10, while for the hot-start NMHC emissions, E15 showed a 15% marginally statistically significant reduction compared to E10. The weighted NMHC emissions showed a marginally statistically significant reduction of 9% for E15 compared E10.

• Cold-start and hot-start CO emissions showed statistically significant reductions of 12% and 27%, respectively, for E15 compared to E10. The weighted CO emissions showed a statistically significant reduction of 17% for E15 compared to E10 across the fleet of 20 vehicles.

• Hot-start CO₂ emissions showed a marginally statistically significant reduction of 0.3 % for E15 compared to E10. Carbon-balance weighted fuel economy showed a statistically significant reduction of 1% for E15 compared to E10 across the fleet of 20 vehicles.

• The PM mass showed strong, statistically significant fuel trends over the entire FTP cycle and each individual phase. For the cold-start and hot-running phases, PM mass emissions showed statistically significant reductions of 16% and 54%, respectively, for E15 compared to E10. Hot-start PM mass emissions were 43% lower for E15 compared to E10, at a marginally statistically significant level. The weighted PM mass emissions showed a statistically significant reduction of 18% for E15 compared to E10 across the fleet of 20 vehicles.

• Only the weighted solid particle number (SPN) emissions were included in the statistical analyses. Results showed that E15 was 12% lower than E10, at a statistically significant level.

• For the BTEX and 1,3-butadiene emissions, only ethylbenzene, m/p-xylenes and o-xylene emissions showed statistically significant results between the fuels. For cumulative ethylbenzene emissions, E15 showed a statistically significant reduction of 11% compared to E10. For cumulative m/p-xylenes and o-xylene emissions, E15 showed marginally statistically significant reductions of 10% and 9%, respectively, compared to E10. The cumulative ethanol emissions showed a strong, statistically significant increase of 77% for E15 compared to E10. The cumulative acetaldehyde emissions also showed a strong, statistically significant increase of 31% for E15 compared to E10 across the fleet of 20 vehicles.

• Calculated NMOG and ozone forming potential (OFP) emissions data were not included in the comprehensive statistical analysis, but were examined for fuel effects using a two-sample equal variance t-test. Both NMOG emissions and OFP showed statistically significant fuel effects for some vehicles, but not for others. Overall, NMOG emissions trended lower for E15 compared to E10. Similar to NMOG, OFP showed a decreasing trend for E15 compared to E10, indicating that the introduction of E15 in the California gasoline market will likely not contribute to increases in ozone formation.