Biofuels

Unlike petroleum-based products, vegetable oils are biodegradable, nontoxic, and are derived from a renewable resource. When used as a fuel, they produce nearly 100 percent less greenhouse gases than petroleum-based diesel fuels and when used as motor oil they improve gas mileage by more than 3 percent and reduce smog-forming nitrogen oxide emissions by 75 percent, according to Charris Ford,an alternative fuels advocate in Telluride, Colorado who drives a modified diesel truck fueled by used vegetable oil that he collects from local restaurants

Many vegetable oils and some animal oils are 'drying' or 'semi-drying' and this restricts their use as fuels. Drying results from the peroxidation of the unsaturated bonds, leading to its irreversible polymeriization into a plastic-like solid. The process is accelerated in the high temperatures commonly found in internal combustion engines, and the engine can quickly become gummed-up in as little as 20 hours.

The traditional measure of the degree of bonds available for this process is given by the 'Iodine Value' (IV) (See under Quality Parameters.)

While some oils have a low IV - less than about 25 - and are suitable for use as fuel without any further processing other than extraction and filtering, the majority of vegetable and animal oils have an IV, which may cause problems if used as a neat fuel. The table below lists various oils and some of their properties.

Only coconut oil has an Iodine Value (IV) low enough to be used without any potential problems in an unmodified diesel engine. However, with a melting point of 25 deg C, the use of coconut oil in cooler areas would obviously lead to problems. With IVs of 25-50, the effects on engine life are also generally unaffected if a slightly more active maintenance schedule is maintained such as more frequent lubricating oil changes and exhaust system decoking.Palm oil, which is solid at room temperature, is used mainly to produce soaps and cosmetics. The majority of European rapeseed oil production is used to produce biodiesel.

At cold temperatures, oils with low cloud point - more the double bonds, lower the cloud point because they resist solidifying at lower temperatures, and will not plug filters is recommended. Coconut oil, palm oil, tallows and lard is not suitable, rapeseed or canola, soy, sunflower or corn oil are much better. But in a hot climate, cloud points won't bother you and the opposite is true: coconut and palm oil, tallow and lard all have higher cetane numbers than the others, and lower Iodine Values.