Vegetable oil comes in very many shapes and sizes, with varying properties. The most important consideration is melting

point. The actual vegetable oil molecule is composed of three long carbon chains on a glycerol 'backbone' and it's

properties are determined by the individual 'fatty acid' chains. Rapeseed oil, for example, may be composed of different

combinations of about 6 different fatty acids and each one of these creates a unique molecule, with unique properties.

A very clever man called Rudolf Diesel invented a new type of engine that operated at a higher compression ratio and

didn't have spark plugs. The first thing that he noticed was that it was about 30% more efficient than a petrol engine and,

also, he could run it on vegetable oil! Very quickly, the engine became adapted for use with fossil fuels since they were,

and still are, very much cheaper than vegetable oil and Rudolf's second idea became forgotten.


It can be used as a fuel engine but we have to be careful not to use it in the wrong way otherwise engine damage may occur.

There are two schools of thought, both of which seem to work well. The first is to blend vegetable oil in with diesel or

kerosene up to a ratio of about 20%, depending on what extra additives are used and what the ambient temperature is. The

additive is used to compensate for the loss in ignition properties and to help keep the combustion cylinder parts clean. The

second school of thought is to use a two tank system where the vehicle is started up on a thin, highly combustible fuel such

as fossil diesel and then switched over to a second tank when the engine is nice and hot. Biodiesel is a third alternative

and can be found blended with diesel at 5% in some petrol stations.the vegetable oil can harm the engine. It must be used

within sensible limits and pushing these limits for convenience or cost will cause long term, or even immediate problems.

Some of the conclusions that people have made regarding the use of vegetable oil as a diesel fuel have been contradictory

and so there are no guarantees to be given. Some of the motor industry test labs found that vegetable oil accelerates coking

of the engine, others found it had no detrimental effect in long term trials. One of the problems with this research is that

none of the engines were used with 2 tank systems and so they were started from cold on vegetable 100% vegetable oil, which

is a definite disadvantage. A recent report from Ricardo has shown that older, indirect engines give good performance

statistics when running with a two tank system, with increased fuel efficiency and similar emmisions when compared with

diesel.