Using Unmodified Vegetable Oils as a Diesel Fuel Extender

Vegetable Oil, Diesel Blends as Potential Fuel Sources 1/2

Engelman et al. (1978) presented data for 10% to 50% soybean oil fuel blends used in diesel engines. The initial results were encouraging. They reported at the conclusion of a 50-hour test that carbon build-up in the combustion chamber was minimal. For the fuel blends studied, it was generally observed that vegetable oils could be used as a fuel source in low concentrations. The BSFC and power measurements for the fuel blends only differed slightly from 100% diesel fuel. Fuel blends containing 60% or higher concentrations of vegetable oil caused the engine to sputter. Engine sputtering was attributed to fuel filter plugging. They concluded that waste soybean oil could be used as a diesel fuel extender with no engine modifications.
Studies in New Zealand by Sims et al. (1981) indicated that vegetable oils, particularly rapeseed oil, could be used as a replacement for diesel fuel. Their initial short-term engine tests showed that a 50% vegetable oil fuel blend had no adverse effects. While in long-term tests they encountered injector pump failure and cold starting problems. Carbon deposits on combustion chamber components was found to be approximately the same as that found in engines operated on 100% diesel fuel. These researchers concluded that rapeseed oil had great potential as a fuel substitute, but that further testing was required.
Caterpillar (Bartholomew, 1981) reported that vegetable oils mixed with diesel fuel in small amounts did not cause engine failure. Short-term research showed that blends using 50/50 were successful, but that 20% vegetable oil fuel blends were better.
Deere and Company (Barsic and Humke, 1981) studied the effects of mixing peanut oil and sunflower oil with Number 2 diesel fuel in a single cylinder engine. The vegetable oil blends were observed to increase the amount of carbon deposits on the combustion side of the injector tip when compared with 100% diesel fuel. The vegetable oil fuel blends were found to have a lower mass-based heating value than that of diesel fuel. Fuel filter plugging was noted to be a problem when using crude vegetable oils as diesel fuel extenders.
International Harvester Company (Fort et al. 1982) reported that cottonseed oil, diesel fuel blends behaved like petroleum-based fuels in short-term performance and emissions tests. The experimental fuels performed reasonably well when standards of judgment were power, fuel consumption, emissions, etc. However engine durability was an issue during extended use of these fuel blends because of carbon deposits and fueling system problems.
Other research at International Harvest Company (Baranescu and Lusco, 1982) was done using three blends of sunflower oil and diesel fuel. Results indicated that the sunflower oil caused premature engine failure due to carbon buildup. It was noted that cold weather operation caused fuel system malfunctions.
Worgetter (1981) analyzed the effects of using rapeseed oil as a fuel in a 43-kW tractor. The goal of running the tractor for 1000 hours on a blend of 50% rapeseed oil and 50% diesel was never achieved as the test was aborted at about 400-hours due to unfavorable operating conditions. The use of rapeseed oil in the fuel resulted in heavy carbon deposits on the injector tips and pistons, which would have caused catastrophic engine failure if the tests had not been aborted. Upon engine tear down, it was found that the heavy carbon deposits on the pistons was the cause of the noted power loss and not the fuel injectors.
Wagner and Peterson (1982) reported mixed results when using rapeseed oil as a substitute fuel. Attempts to heat the oil fuel mixture prior to combustion exhibited no measurable improvement in fuel injection. Severe engine damage was noted during short-term engine testing due to the use of rapeseed oil. A long-term test using a 70% rapeseed, diesel fuel blend was successful for 850 hours with no apparent signs of wear, contamination of lubricating oil, or loss of power.
Van der Walt and Hugo (1981) examined the long-term effects of using sunflower oil as a diesel fuel replacement in direct and indirect injected diesel engines. Indirect injected diesel engines were run for over 2000 hours using de-gummed, filtered sunflower oil with no adverse effects. The direct injected engines were not able to complete even 400 hours of operation on the 20% sunflower oil, 80% diesel fuel mixture without a power loss. Further analysis of the direct injected engines showed that the power loss was due to severely coked injectors, carbon buildup in the combustion chamber, and stuck piston rings. Lubricating oil analysis also showed high piston, liner, and bearing wear.