Conventional petrol engines may be adapted to function with ethanol in certain proportions. A flex fuel car can run on petrol, ethanol in the amount of 15% (E15) or 85% (E85). These engines use the same storage system, power and injection regardless of the fuel composition.
Among the advantages of flex fuel car can be found: obtaining fuel (ethanol) from agricultural crops (corn, sugar cane), lower emissions and about the same cost of production to that of a gasoline car. The disadvantages are higher fuel consumption and cold starting problems when using predominant ethanol (E85).
The biodiesel is a form of diesel fuel produced from vegetable oils, animal fats or recycled waste oils. Common blends of biodiesel are: B2 (2% biodiesel, 98% diesel), B5 and B20. B2 and B5 biodiesel fuels can be used without problems in most diesel engines.
Compared with diesel fuel, biodiesel has the following advantages: it can be produced from renewable sources, can be used in any diesel engine, the combustion produces fewer emissions and greenhouse, is biodegradable, non-toxic and handling conditions are less dangerous.
However, compared with diesel a composition fuel 100% biodiesel (B100) has the following limitations: fuel consumption is higher and dynamic performances are lower (about 10% to 2% B100 and B20), the price of production is higher and problems occur with combustion at low temperatures, and reliability of engines may be impaired.