Using Unmodified Vegetable Oils as a Diesel Fuel Extender
100 Per Cent Vegetable Oil as Potential Fuel Sources 2/2
Bettis et al. (1982) evaluated sunflower, safflower, and rapeseed oils were evaluated as possible sources for liquid fuels. The vegetable oils were found to contain 94% to 95% of the energy content of diesel fuel, and to be approximately 15 times as viscous. Short-term engine tests indicated that for the vegetable oils power output was nearly equivalent to that of diesel fuel, but long-term durability tests indicated severe problems due to carbonization of the combustion chamber.
Engler et al. (1983) found that engine performance tests using raw sunflower and cottonseed vegetable oils as alternative fuels gave poor results. Engine performance tests for processed vegetable oils produced results slightly better than similar tests for diesel fuel. However, carbon deposits and lubricating oil contamination problems were noted, indicating that these oils are acceptable only for short-term use as a fuel source.
Pryor et al. (1983) conducted short and long-term engine performance tests using 100% soybean oil in a small diesel engine. Short-term test results indicated the soybean performance was equivalent to that of diesel fuel. However, long-term engine testing was aborted due to power loss and carbon buildup on the injectors.
Yarbrough et al. (1981) experienced similar results when testing six sunflower oils as diesel fuel replacements. Raw sunflower oils were found to be unsuitable fuels, while refined sunflower oil was found to be satisfactory. Degumming and dewaxing the vegetable oils were required to prevent engine failure even if the vegetable oils were blended with diesel fuel.
Over 30 different vegetable oils have been used to operate compression engines since the 1900’s (Quick, 1980). Initial engine performance suggests that these oil-based fuels have great potential as fuel substitutes. Extended operation indicated that carbonization of critical engine components resulted from the use of raw vegetable oil fuels, which can lead to premature engine failure. Blending vegetable oil with diesel fuel was found to be a method to reduce coking and extend engine life.
Pryde (1982) reviewed the reported successes and shortcomings for alternative fuel research. This article stated that short-term engine tests using vegetable oils as a fuel source was very promising. However, long-term engine test results showed that durability problems were encountered with vegetable oils because of carbon buildup and lubricating oil contamination. Thus, it was concluded that vegetable oils must either be chemically altered or blended with diesel fuel to prevent premature engine failure.
Studies involving the use of raw vegetable oils as a replacement fuel for diesel fuel indicate that a diesel engine can be successfully fuel with 100% vegetable oil on a short-term basis. However, long-term engine durability studies show that fueling diesel engines with 100% vegetable oil causes engine failure due to engine oil contamination, stuck piston rings, and excessive carbon build-up on internal engine components.
Therefore 100% unmodified vegetable oils are not reasonable diesel fuel replacements.