With high gasoline prices and a focus on energy independence, alternatives to petroleum based fuels are gaining popularity. Biodiesel and recycled vegetable oil fuel are often presented as environmentally preferred alternatives to petroleum fuels, but what are they and how do they compare with each other?
Biodiesel refers to a vegetable oil or animal fat-based diesel fuel typically made by chemically reacting lipids such as animal fat or vegetable oil with an alcohol to produce fatty acid esters. Biodiesel can be used in standard diesel engines, alone or blended with petroleum diesel and can also be used as a lower carbon alternative to heating oil.
Vegetable oil can be used as an alternative fuel for diesel engines and heating oil burners. Most diesel car engines are suitable for the use of straight vegetable oil with appropriate modifications otherwise poor atomization and combustion of the oil will create carbon buildup that will ultimately damage the engine. Either new, clean vegetable oil or reclaimed vegetable oil can be used but recycled vegetable oil is perceived as a more environmentally responsible alternative.
The sustainability of biodiesel fuels is under debate as the land devoted to bio diesel crops results in a net loss of food crops and there is some argument about the ratio of energy used in growing biodiesel crops compared to the amount of energy received once those crops have been refined into biodiesel fuel. Straight vegetable oil fuel can lay claim to higher sustainability because recycled vegetable oil can be recovered from businesses and industry that use the oil for cooking in deep fryers, snack food factories and restaurants.
In 2009 ConsumerReports.org performed a test of biodiesel and vegetable oil fuels using a 2002 Volkswagon Jetta TDI and compared fuel consumption and accelerations, emissions, and ease of use. Biodiesel yielded marginally better mileage and acceleration and produced almost 20% less hydrocarbons (3ppm compared to 14ppm). Vegetable oil produced less particulates and NOx emissions. There is no difference in the amount of carbon dioxide produced no matter what liquid fuel an engine burns.
Consumer Reports determined that biodiesel is significantly easier and more convenient to use as an engine fuel than vegetable oil. Vegetable oil requires engine modifications, sacrificing trunk space to carry an auxiliary tank, personal time and effort locating fuel sources as well as time and labor picking up the vegetable oil, filtering and storing it. In addition, even if you use vegetable oil fuel you still need to start the engine using diesel fuel after every drive and cleaning the system before shutting it down.
At first glance, the idea of powering your car with recycled vegetable oil may appear as if there are no negatives, but the positives of using a recycled fuel and exhaust that smells like potato chips may not outweigh the significant personal time investment that is involved. If your primary concern is air quality and carbon pollution, the minimal differences in emissions and the zero difference in carbon dioxide production may affect your decision.