I am sure you have heard using vegetable oils as a replacement for diesel fuel. The term vegetable oils which have not been modified by transesterification or similar processes to
form what is called biodiesel. The oils studied include virgin and used oils of various
types including soy, grape seed, canola, sunflower, cottonseed and similar oils. In general,
raw vegetable oils can be used successfully in short term performance tests in nearly any
percentage as a replacement for diesel fuel.
When tested in long term tests blends above 20 percent nearly always result in engine damage or maintenance problems. Some have reported success in using vegetable oils as diesel fuel extenders in blends less than 20 percent even in long term durability studies.
Many studies have been done involving vegetable oils as a primary source of energy. Particularly, during the early 1980’s,
studies were completed that tested the possibility of using unmodified vegetable oils as a
replacement for diesel fuel.
There is no question that vegetable oil can be placed in the tank of a diesel
powered vehicle and the engine will continue to run and deliver acceptable performance.
Some vegetable oils, such as grape seed oil, have very high viscosity and thus may starve
the engine for fuel when operated at 100 percent. Most studies show that power and fuel
economy, when compared to operation on diesel, are proportional to the reduced heat of
combustion of the vegetable oil fuel.
Despite the success when diesel engines are operated on vegetable oil for short
term performance tests, the real measure of success when using vegetable oil as a diesel
fuel extender or replacement depends primarily on the performance of vegetable oils in
engines over a long period of time. Thus many researchers have been involved in testing
programs designed to evaluate long term performance characteristics. Results of these
studies indicated that potential hazards such as stuck piston rings, carbon buildup on
injectors, fuel system failure, and lubricating oil contamination,this effect diminishes as the blend
of vegetable oil in diesel is decreased.
Many studies involving use of unmodifed vegetable oils in blend ratios with
diesel fuel exceeding 20 percent were conducted in the early 1980’s. Short-term engine
testing indicates that vegetable oils can readily be used as a fuel source when the
vegetable oils are used alone or are blended with diesel fuel. Long-term engine research
shows that engine durability is questionable when fuel blends contain more than 20%
vegetable oil by volume. More work is needed to determine if fuel blends containing less
than 20% vegetable oil can be used successfully as diesel fuel extenders.