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Dear EarthTalk: I understanding that you can run a diesel car on used cooking oil. Why would I want to do that and how would I convert such a vehicle to do so? -- Benjamin Crouch, Boston, MA
The use of vegetable oil for diesel fuel has grown in popularity in recent years, thanks to both high fuel prices and ecological concerns. Analysts estimate that some 5,000 North Americans have converted their diesel cars or trucks to run on vegetable oil in the last few years alone.
Those who do so usually make a deal with a local eatery willing to hand over its used cooking oil at the close of the business day.
The idea isn't new. The first diesel engines built in the 1890s were created to run on peanut oil to be used in developing countries where oil reserves didn't exist.
And many of the older diesel cars and trucks still on the road today can use straight vegetable oil, especially in warmer climates where it won't congeal as easily as in the cold.
Many modern diesel engines, though, leave the factory requiring true diesel fuel to run well, as straight vegetable oil can muck up intricately engineered fuel pumps and injectors.
But drivers willing to spend between $400 and $1,000 on a conversion kit from one of two leading vendors, Missouri-based Golden Fuel Systems and Massachusetts-based Greasecar Vegetable Fuel Systems, can make the switch.
And fryer-friendly restaurants are just about the only economical fuel source right now. Buying cooking oils at the supermarket would be costly, and consumers shouldn't expect to find filling stations pumping vegetable oil anytime soon.
The benefits of a conversion are more than economic. Vegetable oil is a renewable resource derived from plants, which by nature absorb carbon dioxide (CO2) during photosynthesis. Vegetable oil is thus carbon neutral--burning it merely releases stored CO2 back into the atmosphere and therefore contributes no new greenhouse gases to the environment.
By contrast, burning gasoline in a traditional engine releases CO2 that had been stored underground in oil, and thus contributes to global warming. Vegetable oil also burns cleaner than regular diesel, spewing no sulfur and much less particulate and carbon monoxide.
The conversion kits are only for diesel vehicles, as gasoline engines do not tolerate vegetable oil as a fuel. Since a conversion entails replacing and moving hoses and leads, as well as adding a separate fuel tank for the vegetable oil, it is best handled by a trained mechanic. Drivers should know that a converted vehicle does need a small amount of regular diesel fuel to get started, because at normal or cold temperatures vegetable oil is too thick to properly ignite.
But the vehicle can switch over to vegetable oil once it is warmed up and the heat inside the engine loosens its thickness so it can run through efficiently.
Another way to use vegetable oil in a diesel engine is to blend it with regular diesel fuel. This blend has become known as biodiesel, and works fine in regular diesel engines with no conversion required. Biodiesel vendors have set up pumping stations across North America, although they tend to be few and far between.
Canadians can locate biodiesel stations at the website of the Canadian Renewable Fuels Association; Americans can consult the website of the National Biodiesel Board.
CONTACTS:
Golden Fuel Systems
Greasecar Vegetable Fuel Systems
Canadian Renewable Fuels Association
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