This chapter focuses on the use of biofuels in spark-ignition and compression-ignition engines. The use of biodiesel in the form of fatty acid methyl ester and hydrogenated vegetable oil is discussed briefly before centring on the use of low carbon- number alcohols, methanol and ethanol; the use of butanol is also discussed. The physicochemical properties of these pure fuels are described and the variation of these properties as the alcohols are blended with gasoline is quantified. The chapter also reviews the technologies that enable the operation of flexible-fuel vehicles, alcohol–gasoline bi-fuel vehicles, and tri-flex fuel vehicles. The concept of isostoichiometric ternary blends is introduced as a means of providing a more fungible platform for renewable liquid fuels.
