Bio Diesel

Post by: TheYachtMarket News
09 November 2008

Bio Diesel

If your diesel engine has an indirect fuel system, like most yachts and motorboats, you could be running it on pure vegetable oil also known as biodiesel.

What are Biofuels?

Biofuels for diesel engines are made from any organic matter which can be pressed to make oil. It is important to distinguish between pure plant oil (PPO) and biodiesel. PPO, which includes filtered waste vegetable oil, is a more viscous fuel than refined diesel. Diesel engines with indirect fuel systems can be modified to run on PPO. Engines with common rail and more modern fuel injection systems cannot be modified to run on PPO, as it damages the injectors.

How does it work?

PPO is viscous at normal temperatures, making it difficult to start an engine from cold. To run on PPO, an indirect fuel injection system must have a second fuel tank filled with less viscous normal diesel for use in starting the engine. One the system is warmed up, the operator switches over to the main vegetable oil tank until just before the end of the journey.

Alternatively, the main tank can be modified to preheat the oil to around 70 degrees before starting the engine. Conversion kits are available for diesel car engines and could be adapted to marine engines.

Where to buy it

Pure biodiesel can be bought at filling stations around the country. There are no waterside facilities as yet for boat owners. However, Portland Marina's new fuel berth is making plans for a biofuel tank if demand continues to grow.

The cost of biodiesel

The price of pure vegetable oil has doubled in recent years, due to the growing biodiesel industry. The cost varies, depending on the material used to produce it. Fuel made from pure virgin plaint oil is around the same price as standard diesel, despite a lower rate of duty. Fuel made from cooking oil, and other waste source, is normally cheaper.

PPO is considered a fuel substitute and is taxed at the same rate. Using store bought PPO is uneconomical, but cheaper sources, such as wholesale suppliers, could save money.


Pure biodiesel is a strong solvent, and old fuel tanks can be stripped of sediment from the tank and clog the filter. Biodiesel can also attack rubber hoses and gaskets.

Biodiesel creates 10% higher levels of nitrogen oxide emissions than standard diesel, although its carbon emissions and sulphur levels are much lower. International Maritime Organisation emissions regulations set maximum levels for all vessels emissions. Engine manufacturers modify combustion parameters in order to meet the emissions standards. Boat owners are not required to maintain these standards but for environmental reasons, catalectic convertors can be fitted to lower emissions.


Biodiesel can be stored in the same way as normal diesel, using closed containers with as little free space at the top as possible. Biodiesel can also be contaminated by fuel bug, just like other diesel, so avoid half-fuel tanks where condensation can collect. Containers should be protected from direct sunlight and low temperatures.

The pros and cons of Biodiesel

Aside from the lack of supply at waterside, there are doubts over the reliability of using biofuels. Home production is really only viable for boat owners with high fuel use and those willing to sell their excess. Plus, emissions are a concern. However, biodiesel can save you money.

Biofuel production requires some technological improvement before it can be used globally without causing damaging the environment. Watch this space for further developments.