Emissions study suggests E10 + renewable hydrocarbons a high bioenergy alternative for conventional cars
Researchers from VTT Technical Research Center of Finland and Neste Oil analyzed the exhaust emissions from three different spark ignition engine technologies—multipoint fuel injection (MPFI); direct-injection spark-ignition (DISI); and flex-fuel (FFV)—using different biofuels—low- and high-concentration ethanol blends; isobutanol; and biohydrocarbons. They report their findings in a paper in the ACS journal Environmental Science & Technology.
Among their conclusions was that the combination of ethanol or isobutanol with renewable hydrocarbon components (i.e., drop-in biohydrocarbons) could offer an option to achieve a high-bioenergy-content gasoline that is compatible with conventional gasoline-fueled cars (i.e., those limited to a 10% ethanol blend) without a significant change in emissions.
The study assessed five biofuels in addition to baseline gasoline: E10 (10% ethanol v/v); E10 + renewable hydrocarbons (R) for a total 26% bio-component by volume; butanol (17% v/v); E30 (31% v/v); and E85 (85% v/v). The bioenergy content of the fuels ranged from 7 to 78%. The E10 + R blend offered a high bioenergy level of 22% compared to the 7% bioenergy content of straight E10.
Neste Oil provided the renewable gasoline component. The batch used was a C5−C9 paraffinic component (oxygen-, aromatic-, and sulfur-free; density, 672 g/L; dry vapor pressure equivalent (DVPE), 45 kPa), which is a side product of producing renewable diesel from vegetable oil and animal fat by using Neste Oil’s NExBTL hydroprocessing technology.
Fuels were match-blended using fossil gasoline refinery components and gasoline biocomponents. The MPFI and DISI cars were model year 2010; the FFV car was model year 2006.
Tests were conducted on a chassis dynamometer in a climatic test cell at −7 °C using a driving cycle according to the Directive 70/220/EEC and its amendments.
Broadly, they found elevated emissions from the spark-ignition cars at the test temperature of −7 °C (19.4 °F). The impact of fuels on exhaust emissions was substantial in many cases, with differences between cars representing different engine technologies. For example, they found that DISI technology showed elevated PM emissions and associated PAH and mutagenicity emissions compared to the indirect-injection engine technology (MPFI and FFV cars).
Some of the more specific findings were:
The use of low-concentration oxygenated fuels reduced CO and HC emissions in most cases for the MPFI and DISI cars, whereas no significant change was observed for the FFV car. Elevated CO and HC emissions were seen with E30 fuel and high acetaldehyde emissions: when changing from E30 to E85 fuel, acetaldehyde emission increased by 7.6 times and ethanol emission by 27 times.
E85 fuel also increased formaldehyde emission. E85 had a strong impact on the correlation between fuel oxygen content and carbonyl emissions.
A combination of biohydrocarbons and ethanol did not produce consistent changes in gaseous emissions when compared with the ethanol-only-containing E10 fuel.
PM mass emissions from the MPFI and FFV cars were low, and changes in PM emissions seemed not to be fuel-related. However, the DISI car showed high PM emissions (10−20 mg/km), and oxygenated fuels seemed to reduce PM emission though a significant change was seen only for E10 fuel.
The amount of PM-associated PAH emissions was high for all three cars. Priority PAH emissions from the DISI car were substantially higher than those from the MPFI and FFV cars on a mass basis (mass per particulate mass) and particularly high in terms of mass emission per kilometer.
The PM emissions and associated PAH emissions of the DISI car could be reduced by oxygenated fuels—ethanol and isobutanol as well as to a combination of ethanol and biohydrocarbons. No clear differences were observed in PAH emissions between fuels with the MPFI and FFV cars in most cases. E85 fuel resulted in higher PAH emissions than other fuels tested with the FFV car. For the MPFI car, isobutanol-containing fuel seemed to slightly elevate PAH emissions.
Fuel compositions may have a minor effect on the mutagenicity of the PM-associated emissions generated. The engine technology appears to have a much more significant effect.
The E10 + R combination did not change emissions significantly when compared to ethanol-only-containing E10 gasoline. Therefore, they suggested a combination of ethanol or isobutanol with biohydrocarbon components offers an option to reach high gasoline bioenergy content (22% bioenergy with the E10 + R blend) for E10-compatible cars.
Spark-ignition gasoline car emissions are concentrated close to living areas and parking places, where cold-start emissions play a significant role. In particular, PAH and mutagenicity emissions from gasoline cars at moderate and cold temperatures warrant further attention. In-depth research on health and environmental perspectives, including the secondary atmospheric reactions, should be considered in parallel with climate change issues when new fuels and technologies are considered.—Aakko-Saksa et al.
Päivi T. Aakko-Saksa, Leena Rantanen-Kolehmainen, and Eija Skyttä (2014) “Ethanol, Isobutanol, and Biohydrocarbons as Gasoline Components in Relation to Gaseous Emissions and Particulate Matter” Environmental Science & Technology doi: 10.1021/es501381h