E-fuels are made by combining green hydrogen with CO2 to produce liquid fuel that can be similar to gasoline or diesel used in conventional engines (as well as kerosene used in aviation). Proponents claim that if renewable electricity is used and CO2 is captured from the air, then the e-gasoline and e-diesel are climate-neutral fuels that will also reduce pollution.
The European NGO Transport & Environment commissioned IFP Energies Nouvelles to run a series of lab-based tests simulating real-world driving (WLTC and RDE) to measure the emissions of different electrofuel blends in an A-class (A180) Mercedes.
Due to the lack of commercially available e-fuels, IFPEN had to blend three e-fuel blends itself representative of potential future fuel that are compatible with gasoline cars. The three blends were:
100% paraffinic e-fuel. A blend with 100% hydrocarbon chains and no ring-shaped hydrocarbon with delocalized electrons such as benzene (i.e. aromatics). Future e-fuels are likely to be mostly paraffinic blends as these aree the chemicals produced during the Ficher-Tropsch process, T&E said.
90% paraffinic, 10% aromatic. Aromatics may be added to e-fuels to improve combustion properties.
90% paraffinic, 10% second-generation ethanol. Fuel manufacturers may consider future use of e-fuel and second-generation ethanol blends to reduce the fuel cost and increase total volume of renewable fuel available in the market, T&E suggested. A 10% blend was chosen due to existing fleet and EN228 standard compatibility. Adding ethanol to the paraffinic e-fuel blend did not work due to miscibility issues. The ethanol and e-fuel would separate out similarly to oil and water. This could not be solved with addition of up to 20% aromatics into the blend. Finally, 1% fusel oil had to be added to the blend for the ethanol not to separate out.
The emissions were compared to the standard E10 EU gasoline.
The pollutant emissions testing found:
No difference in NOx emissions were observed for any of the e-fuels tested either on the lab or on road tests compared to today’s gasoline fuel. This means that e-fuels emit the same amount of NOx pollution as fossil fuels today, so the use of e-gasoline in cars will have little impact on NOx emissions which are at the heart of NO2 pollution across Europe’s cities.
A substantial decrease in particle emissions was observed on all tests. The number of particle emissions (PN) larger than 10 nm decreased by 97% on the lab test, and by 81-86% on the RDE test cycle. This was a significant improvement compared to the fossil fuel tested and is many times below the legal limit. However, said T&E, particle pollution was far from eliminated. Even with the use of 100% e-gasoline blends, at least 2.2 billion particles were still released for every kilometer driven. There was no difference observed in particle mass (PM) emissions.
Carbon monoxide emissions were much higher with the e-gasoline blends tested. Emissions were up to almost 3 times higher on the lab WLTC test and 1.2-1.5 times higher on the RDE test compared to fossil fuel. The largest increase in emissions occurred when the engine was first switched on, which happens often in towns and cities.
Hydrocarbon emissions decreased by 23-40% on the WLTC test but no difference was observed on the RDE test due to low emissions for all fuels. Emissions of dangerous but not yet regulated aldehydes—acetaldehyde and formaldehyde—decreased with the use of e-fuels when the engine was first switched on, but no significant difference was seen on the test overall.
Ammonia emissions of two e-gasoline blends roughly doubled on the RDE test, with emissions particularly increasing after the engine is first switched on (cold start) which frequently occurs in towns and cities. These results indicate that some e-gasoline blends may cause an increase in ammonia emissions which is a precursor to PM2.5 pollution.
E-fuels have lost the race to clean up cars, but in truth it was never even close. Battery electric cars offer drivers the cleanest, most efficient and affordable way to decarbonize, while synthetic fuels are best suited to planes where electrification is not an option. The credibility of Europe’s clean car policy is on the line and any diversion into e-fuels is a new lease of life for old polluting engines.—Julia Poliscanova, senior director for vehicles and e-mobility at T&E