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In the area of alternatives to regular diesel, there are two options. Both can be very cheap, and both are renewable fuels with environmental benefits over diesel. The word "biodiesel" has become common, as some gas stations are beginning to offer biodiesel mixes, but unrefined, straight vegetable oil can also be used as a fuel in a diesel engine. This article will summarize the key points in the biodiesel versus SVO debate.

What is the difference between biodiesel and SVO?

Rudolph Diesel designed his first engine to run on peanut oil; hence, before there was such a thing as "diesel fuel," the engine it was made to fuel was already compatible with unrefined vegetable oil. This "straight vegetable oil," given the acronym SVO, is nothing but the same vegetable oil used for cooking. Any variety of vegetable oil is suitable, even used cooking oil (provided that it has been filtered).

Biodiesel, on the other hand, is a chemical ester derived from vegetable oil, but refined for lower viscosity.  

What are the functional differences between biodiesel and SVO?

An obvious difference between the fuels you would notice if you held a container of each side-by-side is that SVO is far more viscous than either biodiesel or petroleum-derived diesel (i.e., it does not flow as easily). The foremost functional difference is that while biodiesel can run well in an unmodified diesel engine, modifications should be made to a diesel engine Making Biodiesel to allow it to run off vegetable oil effectively and safely over the long term. This is largely a consequence of the higher viscosity of vegetable oil, though vegetable oil also has different combustion properties than diesel fuel.

Problems arise from the viscosity ("thickness") of SVO in the fuel injection system of the engine, where the viscous substance creates far more wear than the relatively free-flowing diesel/biodiesel. Over time, the fuel injectors can become choked with deposits from using vegetable oil. Another problem arises in cold weather, where vegetable oil will become several times more viscous yet, and become virtually impossible to feed into the engine.  

Engine modification

The most significant modification made to a diesel engine to allow it to accept vegetable oil is the addition of an oil preheater. Not only will this resolve the difficulties of starting the engine in cold weather, it will also help to make the oil more pliable and reduce the stress on the injection system by lowering the viscosity of the oil. Further modifications may include the addition of a second tank for SVO to allow for dual-fuel use, or the use of specially designed fuel injectors with higher injection pressures.  

Fuel mixtures

While biodiesel is commonly and easily mixed with petroleum-derived diesel fuel and many SVO enthusiasts do mix other additives into SVO to reduce its viscosity, it is more advisable to make mixtures with biodiesel rather than vegetable oil. The reason is that beyond the difference in viscosity which is the most apparent difference between the fuels, straight vegetable oil also has different combustion characteristics than either biodiesel or regular diesel. Biodiesel, on the other hand, is much more mixable because its combustion characteristics are much more similar to petroleum diesel.  

Ease of Use

The fact that SVO can be fed into a suitably modified engine without having to go through a chemical conversion is the greatest factor in its favor. Though the conversion process is simple and there is not much that is very complicated about the use of a biodiesel processor at home, the very fact that additional chemicals are needed as well as the time needed to operate the processor makes SVO simpler to implement over the long run -- once your engine has been appropriately modified. The only step that may be needed to use SVO is to filter it, if you are using used cooking oil.  

Conclusions

Of course, we cannot answer the question posed in the title for you, but merely inform you as to the pros and cons of either choice. In either case, there is a modification to be made: in the case of SVO, a modification to the engine, and in the other case, a chemical modification of oil to make biodiesel. Either choice can save you a lot of money over the skyrocketing price of diesel, while both provide similar environmental benefits.