Vegetable oil is used in several old diesel engines that have indirect injection systems. This oil is also used to create biodiesel, which when mixed with conventional diesel fuel is compatible for most diesel engines. Used vegetable oil is converted into biodiesel. Sometimes, water and particulates are separated from the used vegetable oil and then this is used as a fuel.
Biodiesel is a famous biofuel in Europe. Its composition is just like mineral diesel. When biodiesel is mixed with mineral diesel, the mixture can be used in any diesel engine. It is observed that in several nations, the diesel engines under warranty are converted to 100% biodiesel use. It has also been proved that most people can run their vehicles on biodiesel without any problem. A large number of vehicle manufacturers recommend the use of 15% biodiesel mixed with mineral diesel. In Europe, a 5% biodiesel blend is generally used at gas stations.
Bioalcohols are biologically produced alcohols. Common among these are ethanol and rare among these are propanol and butanol. Biobutanol can be used directly in a gasoline engine and hence is considered a direct replacement for gasoline. The butanol can be burned straight in the existing gasoline engines without any alteration to the engine or car. It is also claimed that this butanol produces more energy. Also, butanol has a less corrosive effect and is less soluble in water than ethanol.
Ethanol fuel is the most commonly used biofuel in the world and particularly in Brazil. Ethanol can be put to use in petrol engines as a substitute for gasoline. Also, it can be mixed with gasoline in any ratio. The contemporary automobile petrol engines can work on mixtures of gasoline and ethanol that have 15% bioethanol. This mixture of gasoline and ethanol has more quantity of octane. This indicates that the engine would burn hotter and more efficiently. In high altitude spots, the mixture of gasoline and ethanol is used as a winter oxidizer and thereby atmospheric pollution is decreased.
The Ethanol fuel has less British Thermal Unit energy content. Thus, to drive the same distance, more fuel is required. Also ethanol has a corrosive effect on combustion chambers, aluminum, rubber hoses and gaskets and fuel systems.
Biogas is created when organic material is anaerobically digested by anaerobes. During production, there is a solid byproduct called digestate. This can be used as a biofuel or fertilizer. Biogas consists of methane. Landfill gas is created in landfills due to natural anaerobic digestion and is a less clean form of biogas. Dried manure, charcoal and wood are examples of Solid biofuels.
The combined processes of gasification, combustion and pyrolyis gives rise to Syngas which is a biofuel. This syngas can be directly burned in internal combustion engines. Syngas can be used to create hydrogen and methanol. By using the Fischer-Tropsch process, it can be transformed to a synthetic petroleum substitute.
Some second generation biofuels that are being developed are Fischer-Tropsch diesel, bio-DME, DMF, biomethanol, biohydrogen, wood diesel, mixed alcohol and biohydrogen diesel. Algae fuel is a third generation biofuel derived from algae. This is also called as oilgae.