UNIVERSITY PARK, Pa. – Recently people have been using the terms “soy-diesel” and “biodiesel” interchangeably, but there is a major difference between the fuels.
Failing to recognize that difference will spell disaster for diesel engines if run on soy-diesel, said Dennis Buffington, an ag engineer at Penn State University.
Soy-diesel is a 20/80 blend of filtered and clarified crude soybean oil and diesel fuel.
“According to the U. S. National Renewable Energy Laboratory in Colorado,” Buffington said, “no one should be mixing any crude vegetable oils into fuels for vehicle use.”
What happens. The glycerin in soybean oil acts like sugar in the fuel tank and will eventually ruin fuel injectors, according to the laboratory. Engine durability also is poor.
The laboratory points out that no long-term studies exist on engine performance and maintenance requirements because the engines don’t last long if run on soy-diesel fuel.
“The NREL states that even if crude soybean oil is first filtered and clarified, it’s still a vegetable oil,” Buffington explains. “It should not go into a compression ignition engine until it has been refined to the point where it meets American Society for Testing and Materials minimum standards for diesel fuel.”
Works at first. Buffington said diesel engine owners may initially be misled if they try to use the soy-diesel fuel.
“The engines will run on soy-diesel for the short term until the fuel injectors foul,” he said. “You may be lulled into a false sense of comfort when burning soy-diesel because everything appears to be fine for a while.”
Most, if not all, engine manufacturers will void the engine warranty if soy-diesel (or any blend of crude vegetable or animal oil) is burned in an engine, Buffington added.
“A company representative,” he said, “can easily document if an engine has been fueled by a crude oil/diesel blend by examining internal engine parts.”
Biodiesel. By contrast, a process called transesterification is used to prepare soybean oil for blending with diesel fuel to make biodiesel. Alcohol is added to soybean oil with a catalyst and stirred vigorously. The ester (biodiesel) will rise to the top and glycerol and alcohol will settle on the bottom. After several washings, the biodiesel then can be marketed as a fuel.
Penn State’s Energy Institute is conducting both short-term and long-term research to determine if filtered and clarified soybean oil can be used as a diesel fuel supplement.
Until the long-term results are analyzed and replicated, Buffington said soy-diesel blends should not be burned in diesel engines.