Diesel engines may not be glamorous, but they’re a great example of tradeoffs that affect environmental health. They burn less fuel than standard gasoline engines, but also can produce more dangerous pollution. Can biodiesel fuel—a diesel fuel made from vegetable oil or animal fat—decrease some of the risks of diesel engines and increase the benefits? Some environmentalists are betting on it.

Like gasoline engines, diesel engines burn liquid fuel. The burning fuel produces hot, high-pressure gases, which pump the pistons that move a car or truck. In a gasoline engine, the fuel is ignited with a spark plug; in a diesel engine, the heat of the engine itself ignites the fuel. This small difference makes diesel engines more efficient and reliable than gasoline engines, and they produce very little carbon monoxide. However, they can produce clouds of black smoke (or more specifically, diesel particulate matter) when the carbon compounds in the fuel are not fully burned. Diesel engines produce more smoke when starting; the engine block is too cold to fully burn the fuel, so it coughs out smoke until it’s warmed through. This smoke can contribute to health problems such as asthma, lung cancer, and cardiovascular issues.

Biodiesel may provide a partial solution. Manufacturers usually make biodiesel from soybean oil, but they can use other plant oils or animal fats, from french fry grease to chicken fat. To create biodiesel, the oil or fat is modified by a chemical process that breaks down its molecules. Most commonly, a chemical reaction replaces the glycerin portion of an oil molecule with an alcohol molecule. After the glycerin is drained off, the result is biodiesel. Pure biodiesel does not contain any petroleum; some of the “Buff Buses” in the video run on a pure, “B100” formulation. However, biodiesel is often blended with petroleum diesel. The most common blend, “B20,” contains 20 percent biodiesel and 80 percent petroleum diesel. A vehicle running on this produces 12 percent less carbon monoxide than regular diesel fuel, and 12 percent less particulate matter.

Any diesel engine can run on biodiesel without modifications. However, biodiesel will degrade natural rubber gaskets and hoses, although these are uncommon in modern vehicles. Biodiesel can also break down deposits in the fuel lines, clogging fuel filters. Therefore, owners should change the fuel filters after the first tank of biodiesel. Finally, biodiesel sometimes costs more than standard diesel.

But just as the students at the University of Colorado voted to increase fees in support of biodiesel, many vehicle owners are finding that these costs are worth the added benefits. Interest in biodiesel continues to grow, and as of 2011, there are more than 1,000 locations in the United States that distribute biodiesel.

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