The automobile fuel called e85 consists of 85% ethanol and 15% gasoline. e85 can be used in so-called flex-fuel vehicles (ffvs), which can use gasoline, ethanol, or a mix as fuels. assume that gasoline consists of a mixture of octanes (different isomers of c8h18), that the average heat of combustion of c8h18(l) is 5400 kj/mol, and that gasoline has an average density of 0.70 g/ml. the density of ethanol is 0.79 g/ml.