Three years ago, Volkswagen announced that it was testing two different types of renewable diesel fuel in a pair of its TDI diesel-engined cars sold in the U.S.
Now, the company says it has finished its testing, and the results are in.
The renewable fuel gave the same performance as conventional crude oil-based diesel, and cut wells-to-wheels carbon dioxide emissions by about 50 percent, VW said.
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The two cars used in the test, both 2012 models, were a Volkswagen Passat TDI mid-size sedan and a Volkswagen Jetta TDI compact sedan.
The diesel Passat used an aftertreatment system with urea injection, while the Jetta did without urea, meeting emissions goals with a selective catalytic reduction (SCR) system.
(All Volkswagen TDI diesels for the 2015 model year now use urea injection, which is standard on the new-generation EA288 2.0-liter four-cylinder diesel engine in North America. The test cars used an earlier generation of VW diesel engines.)
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VW notes that the diesel fuels it tested were "pre-commercial renewable diesel formulas," developed together with renewable-fuels specialty companies Solazyme and Amyris.
The Soladiesel RD is derived from algae, while Amyris produces its renewable diesel from plant sugars. Common additives were blended into each fuel to meet U.S. fuel specifications.
The pair of cars together logged more than 134,000 miles in total, operating not on test tracks but on real-world roads and highways.
VW said that "driving dynamics were not negatively impacted" while the on-road fuel economy was the same or better than the same cars running on fossil fuel-derived diesel.
During the entire test, no engine errors were triggered, nor were failures or "extreme wear" attributable to the use of the renewable fuels.
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Less soot was produced while using the experimental fuels, VW said.
The reduction of more that 50 percent in wells-to-wheels carbon emissions per mile comes from Amyris and Solazyme, not from Volkswagen itself.
The results highlight "how far advanced fuel technology has come in recent years, proving that sustainable fuels are not only produced in more environmentally friendly ways, but can offer similar performance and lower emissions from a well-to-wheel perspective,” said Ewald Goessmann, executive director of VW's Silicon Valley-based Electronics Research Laboratory.
The results, VW said, "highlight the tremendous market potential that renewable fuel solutions offer, combining comparable performance and fuel economy, helping reduce emissions, while utilizing more sustainable methods to produce the products."
Volkswagen said it will "continue to analyze engine components and other data accumulated during the evaluation" that could help the company "enhance" its future vehicles and components to use renewable fuels.