Pure plant oil as fuel

Pure plant oil (PPO) or straight vegetable oil (SVO) can be used as a (bio)fuel for heating or cooking , and for use in piston steam engines, internal combustion engines (diesel), Stirling engines, steam and fuel-powered turbines.

Use in internal combustion engines

PPO can only be used in a specific type of internal combustion engine, namely the diesel engine, and only if it is heated to 80° Centigrade (176° Fahrenheit), at which point common vegetable oils are no more viscous than cold diesel fuel. When heated, the vegetable oil is then thin enough to get through modern injection pumps and injectors without causing damage.

Besides heating, it is also possible to add additives (ie ethanol, methanol,^[1] to achieve the necessary thinning of the fuel. Another method still to thin the oil is to chemically transform it into biodiesel.

Modifying engines to run on pure plant oil typically requires an extra tank and engine fuel supply modifications. By pre-heating the SVO with a combination of radiator coolant and electric heat, the SVO runs the diesel engine with no problems. The engine is started on biodiesel (or blend, if below freezing) and run until hot, then an electric valve switches the engine to the SVO tank.

Use in diesel engines

Theoretically it is possible to modify any diesel engine to run on pure plant oils (PPO). The modifications necessary to allow reliable operation vary greatly depending on the design of the engine, the type of oil to be burnt and the ambient temperatures in which the engine will be operated.

For reliable operation with PPO it is highly recommended to perform an engine health check before switching fuels as the use of PPO requires the engine to be in good order.

A widely used method for reliable operation is to convert the engine to a bi-fuel system and fit a PPO two tank system. The engine is started on diesel fuel and switched to PPO as the engine warms. Before the engine is stopped for an extended period the fuel supply is switched back to diesel fuel for enough time to allow the fuel system to be purged of PPO. The engine is then ready to be cold started on diesel fuel.

It is possible however to modify the cold start system and fuelling parameters to allow diesel engines to be started on PPO -this is known as a PPO single tank system-.

Advantages and disadvantages

The ethics of burning perfectly good plant oil (from human consumable plants) for transportation purposes are questionable. This isn't the case with pure plant oils that are not consumable by humans though. Waste vegetable oil is a good alternative to SVO for oils that are humanly consumable as this oil is already used for cooking prior to using it as fuel. It however does require a lot of extra hassle (ie pre-filtering and purification).

Cost

Although some^[2] argue that costs of SVO are considerable (more expensive than petrodiesel^W ), this is not always true. Depending on which country you live in, it may be more costly, or a lot cheaper. For example, in Europe, SVO costs 54 pence/liter at most supermarkets and 42 pence/liter when bought in bulk direct from the manufacturers whereas diesel costs atleast 99 pence per liter (in the UK) to well over that (depends on the year, 1.4 euro is the current market price in central Europe).^[3] In the USA, diesel costs about 0,6 $ per liter^[4] and the cheapest SVO costs about the same, with more expensive oils costing more than that (upto 7$ per gallon).

References

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