With gasoline prices volatile and the Obama administration committed to easing the United States' addiction to oil, Americans seem to be taking more interest in alternative fuels, including those derived from farm crops and other renewable organic sources. Among the most widely available are biodiesel and vegetable oil, both of which can be used to power a diesel engine.
Developed from vegetable or animal fats, biodiesel is functionally identical to petroleum diesel. Adherents claim it pollutes much less than regular diesel.
Biodiesel is most commonly sold in blends with normal diesel; B5, which is 5 percent biodiesel and 95-percent petroleum diesel, and B20, or 20 percent bio diesel. B20 sells for about 20 cents a gallon more than petroleum diesel according to the U.S. Department of Energy. Pure biodiesel (B100) sells for aboiut 85 cents more per gallon than regular diesel.
A relative of biodiesel is plain, edible cooking oil. But because it's not financially practical to fuel a car with cooking oil from grocery store shelves— a gallon costs about $8—some people are modifying diesel engines to run on the used deep-fryer oil that restaurants often throw away. Discarded oil is sometimes available free, though more restaurants are now charging for it.
To see how biodiesel—B5 and B100—and fryer grease compare with conventional petroleum diesel fuel, we converted a diesel-powered 2002 Volkswagen Jetta TDI so that it could operate on all three. We found that they all allowed the car to perform well but differed in price and convenience.
We experienced the best overall results using B5, the 5 percent biodiesel blend. It provided the best balance of performance, emissions, fuel economy, and convenience. B5 will run in any diesel engine without requiring vehicle modifications, and it is pumped into the tank just like any standard fuel. But because it is 95 percent petroleum diesel, it does little to wean drivers from fossil fuels.
Our Jetta ran well on the used cooking oil, but the inconvenience of finding fuel sources and preparing the oil for use in the engine limits its appeal and offsets its low price.
Automakers are now beginning to warranty new diesel cars on biodiesel blends of up to 20 percent. At concentrations higher than that, or on cooking oil, engineers say they find too many impurities and inconsistencies in the fuel to be comfortable providing warranty coverage.