Straight Vegetable Oil as a Diesel Fuel?

Straight Vegetable Oil as a Diesel Fuel?

Concerns about U.S. reliance on imported petroleum and fluctuating fuel prices have led to growing interest in using biodiesel, an alternative fuel made from vegetable oils. Some people have expressed interest in using straight vegetable oil (SVO), or waste oils from cooking and other processes, as fuel. These oils seem to be appealing because they are obtainable from U.S. agricultural or industrial sources without intermediate processing. However, SVO and other waste oils are generally not considered acceptable vehicle fuels for large-scale or long-term use.

Straight vegetable oil is not the same

as biodiesel and is generally not recommended for long-term vehicle use.

the problems to some degree, but do not eliminate them entirely. Studies show that carbon buildup continues over time, resulting in higher engine maintenance costs and/or shorter engine life. Figure 1 shows how the tendency to form carbon deposits increases when blending vegetable oil into a diesel fuel.2

Another issue that is particularly critical for use of SVO is fuel viscosity. As Figure 2 (see back) indicates, the viscosity of pure SVO is much higher than that of diesel fuel at normal operating temperatures.3 This can cause premature wear of fuel pumps and injectors and can also dramatically alter the structure of the fuel spray coming out of the injectors to increase droplet size, decrease spray angle,

1 Babu, A.K.; Devaradjane, G. “Vegetable Oils

and Their Derivatives as Fuels For CI Engines: An Overview.” SAE Technical Paper No. 2003-01-0767.

2 Jones, Samuel T.; Peterson, Charles L.; Thompson, Joseph C. Biological and Agricultural Engineering Department, University of Idaho, Moscow, Idaho. “Used Vegetable Oil Fuel Blend Comparisons Using Injector