A study by a team from North Carolina State University, with colleagues from the Urban Air Initiative and 3DATX Corporation, has shown that non-FFVs (flexible-fuel vehicles) can adapt to a mid-level ethanol blend—specifically E27. The study was commissioned by the Urban Air Initiative.

As reported in a paper in the journal Fuel, they quantified differences in fuel use and emission rates of carbon dioxide (CO₂), carbon monoxide (CO), hydrocarbons (HC), nitrogen oxide (NO_x), and particulate matter (PM) for three gasoline-ethanol blends and neat gasoline measured for one FFV (2017 Chevrolet Equinox) and four non-FFVs (2017 Chevrolet Cruze, 2018 Toyota Camry, 2016 Nissan Quest, 2016 Ford Focus) using a portable emission measurement system (PEMS).

To reduce the variability in fuel use and exhaust emission rates related to variations in engine oil, engine oil was changed for each vehicle prior to the measurement using the first fuel. All vehicles were measured with air-conditioning on. For vehicles for which an eco-mode was available, the eco-mode was used. The fuel switching procedure included consuming or defueling the old fuel, refilling one gallon of new fuel, consuming or defueling the one gallon of new fuel, adding new fuel for the measurement, disconnecting/reconnecting the vehicle battery, and driving on a conditioning route. A conditioning route of 29 miles, which takes about 40 min, was driven after switching fuels to ensure vehicle adaptation to the new fuel.

When operating on the mid-level ethanol blend, the measured vehicles, on average, had lower emission rates of carbon monoxide and particles with little to no changes in other measured emissions. The advantage of this study over others is that these measurements were made in the real-world under actual driving conditions, and thus are based on representative data regarding vehicle activity.

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lead researcher Dr. Chis Frey

Each vehicle was measured on neat gasoline (E0); 10% ethanol by volume (E10) “regular” (E10R) and “premium” (E10P); and 27% ethanol by volume (E27).

Four real-world cycles were repeated for each vehicle with each fuel. Second-by-second fuel use and emission rates were binned into Vehicle Specific Power (VSP) modes. The modes were then weighted according to real-world standard driving cycles.

The researchers found that all vehicles, including the non-FFVs, were able to adapt to E27. Among their other findings:

• An octane-induced efficiency gain was observed for higher octane fuels (E10P and E27) versus lower octane fuels (E0 and E10R).

• E27 tends to lower PM emission rates compared to E10R and E10P and CO emission rates compared to the other three fuels.

• HC emission rates for E27 were comparable to those of E10R and E10P.

• No significant difference was found in NOx emission rates for E27 versus the other fuels.

• Intervehicle fuel use and emission rates varied.

The five Tier 2 and Tier 3 vehicles, including four non-FFVs, were able to adapt to each of the four fuels, including the splash-blended E27, by achieving a stable LTFT [long-term fuel trim], achieving empirical AFR [air-to-fuel ratio] near stoichiometric, and adjusting ITA [ignition timing advance]. ITA varied with respect to engine load and fuel octane for each vehicle. More ITA was observed under high engine load for E10P and E27. Fuel injection type, engine CR [compression ratio], and aspiration type contributed to intervehicle variability of ITA. Large ITA was typically associated with octane-induce engine efficiency gain.

Adaptation of each vehicle to each fuel was also indicated by lack of large increases in emission rates under a range of ambient temperature and relative humidity conditions. The ability of all five vehicles, including non-FFVs, to adapt to each fuel blend by controlling AFR, and by adjusting ITA and LTFT, likely mitigated against large differences in emission rates. However, there were some significant differences in emission rates between fuels that are attributable to differences in fuel properties.

On average, E27 tended to reduce CO₂ and CO emission rates compared to E0, E10R, and E10P, and to reduce PM emission rates compared to E10R and E10P. E27 had HC emission rates comparable to E10R and E10P. E27 had lower NOx emission rates than E10P and comparable NOx emission rates with E10R. Octane-induced efficiency gain was indicated by differences in cycle average fuel use and CO₂ emission rates for both E10P and E27 versus E10R in higher power demand cycles, including real-world cycles.

The octane-induced efficiency gain was also indicated by more ITA for E10P and E27 than E10R. Increasing ITA improved engine efficiency, as demonstrated by the Cruze, which had 1%–9% lower cycle fuel use rates for E27 versus E10R among the six higher power demand cycles, even though E10R had 6% higher energy density than E27. These findings indicate the feasibility of counteracting the lower energy density of mid-level gasoline-ethanol blends by octane-induced engine efficiency gain for existing vehicles in real-world driving, including non-FFVs, which was not reported previously.

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Yuan et al.

Resources

• Weichang Yuan, H. Christopher Frey, Tongchuan Wei, Nikhil Rastogi, Steven VanderGriend, David Miller, Lawrence Mattison (2019) “Comparison of real-world vehicle fuel use and tailpipe emissions for gasoline-ethanol fuel blends,” Fuel, Volume 249, Pages 352-364, doi: 10.1016/j.fuel.2019.03.115.