Using Unmodified Vegetable Oils as a Diesel Fuel Extender

Vegetable Oil, Diesel Blends as Potential Fuel Sources 2/2

Engine Testing by Ziejewski and Kaufman (1982) at Allis Chalmers using a 50/50 blend of sunflower oil and diesel was unsuccessful. Carbon buildup on the injectors, intake ports, and piston rings caused engine operating difficulties and eventual catastrophic failure.
Fuls (1983) reported similar findings for indirect and direct injection engines using 20% sunflower oil, diesel fuel blends. Fuls Emphasized that injector coking was the problem with using sunflower oil in direct injected diesel engines.
Caterpillar Tractor Co. (McCutchen, 1981) compared engine performance of direct injection engines to indirect injection engines when fueled with 30% soybean oil, 70% diesel fuel. The results showed that indirect injection could be operated on this fuel blend while the direct injection engine could not without catastrophic engine failure occurring. The direct injection engines showed injector coking and piston ring sticking as a result of using sunflower oil.
An on-farm study using six John Deere and Case tractors by German et al. (1985) averaged 1300-hours of operation. Carbon deposits on the internal engine components were greater for the tractors fueled with 50/50 sunflower oil/diesel than for those fueled with a 25/75 sunflower oil/diesel fuel blend. All the test engines had more carbon buildup than normally seen in an engine fueled with diesel fuel. The results of this study indicated that neither of the fuel blends could be use as a replacement for petroleum based fuels on a permanent basis without shortening engine life.
Peterson et al. (1982) used rapeseed oil as a diesel fuel extender to study the longterm effects of using vegetable oils as a fuel source. Fuel composed of 70% rapeseed oil and 30% Number 1 diesel fuel was successfully used to operate a small single cylinder engine for 850 hours. No adverse operating conditions were reported at the conclusion of this engine study. A short-term performance test using a 100% sunflower oil caused severe piston ring gumming and catastrophic engine failure. This study highlighted the need for significant long-term engine testing before recommendations of using vegetable oil as a fuel could be made.
Nag et al. (1995) did studies involving the use of seed oils grown natively in India. Performance tests using fuel blends as great as 50-50 seed oil from the Indian Amulate plant and diesel fuel exhibited no loss of power. Knock free performance with no observable carbon deposits on the functional parts of the combustion chamber were also observed during these tests. Although this seed oil was not yet commercially available at the time of this study, it was hoped that it soon would be.
Sapaun et al. (1996) reported that studies in Malaysia, with palm oils as diesel fuel substitutes, exhibited encouraging results. Performance tests indicated that power outputs were nearly the same for palm oil, blends of palm oil and diesel fuel, and 100% diesel fuel. Short-term tests using palm oil fuels showed no signs of adverse combustion chamber wear, increase in carbon deposits, or lubricating oil contamination.
Ryan et al. (1984) characterized injection and combustion properties of several vegetable oils. The atomization and injection characteristics of vegetable oils were significantly different from that of diesel fuel due to the higher viscosity of the vegetable oils. Engine performance tests showed that power output slightly decreased when using vegetable oil fuel blends. Injector coking and lubricating oil contamination appeared to be a more dominate problem for oil-based fuels having higher viscosities.
Pestes and Stanislao (1984) used a one to one blend of vegetable oil and diesel fuel to study piston ring deposits. Premature piston ring sticking and carbon build-up due to the use of the one to one fuel blend caused engine failure. The severest carbon deposits were located on the major thrust face of the first piston ring. These investigators suggested that to reduce piston ring deposits a fuel additive or a fuel blend with less vegetable oil was needed.
Other studies by Hofman et al. (1981) and Peterson et al. (1981) indicated that while vegetable oil fuel blends had encouraging results in short term testing, problems occurred in long-term durability tests. They indicated that carbon build-up, ring sticking, and lubricating oil contamination was the cause of engine failure when vegetable oils were used in high percentages (50% or more) as diesel fuel substitutes.
Due to engine durability problems encountered using raw vegetable oils as a fuel in the early 1980's, most researchers opted to use chemically modified vegetable fuels more commonly known as biodiesel in place of unrefined vegetable oils. Thus, in recent years there has been little literature concerning the feasibility of using raw vegetable oils as a fuel additive.
McDonnell et al. (2000) studied the use of a semi-refined rapeseed oil as a diesel fuel extender. Test results indicated that the rapeseed oil could serve as a fuel extender at inclusion rates up to 25%. As a result of using rapeseed oil as a fuel, injector life was shortened due to carbon buildup. However, no signs of internal engine wear or lubricating oil contamination were reported.