The biofuel term involves all the organic-based fuels that have been obtained from living or recently dead organisms (biomass) with the intention of using them as an energy source.

Certain liquid biofuels can replace petroleum-derivate hydrocarbon as a power supply for cars due to their similar behaviour in internal combustion vehicles (ICV), in both Otto and Diesel motors. Those studied in this research are bioethanol, biomethanol and biodiesel, because of their higher relevance in the present market and politic context and due to their feasibility and maturity. Besides, experimental or less common alternatives such as biobutanol, bio-oil or biogas had to be discarded in this research since, even being promising, are not as commercially and institutionally promoted as the anterior ones.

The reason that makes the energy industry consider biofuels as an alternative energy source is the fact that they virtually can't be exhausted, since they are produced from a renewable source (as long as they are produced in a sustainable way), besides the fact that they theoretically don't contribute to the atmospheric CO 2 increase, given that the carbon emitted during their combustion has been previously gathered from the air by photosynthetic organisms. Furthermore, they can be produced from agricultural feedstock, even from vegetal waste, which are present in practically every habited zone in the world.