These fuels are derived from the treatment of biomass. They belong to the alcohol and oil families.
The most important liquid fuels are:
oils obtained from oleaginous cultures.
Alcohols, which are used in explosion engines, decrease CO operating
temperatures and emissions. Specific consumption (in volume) increases by
Their use as a gasoline additive causes an increase in the octane number (e.g., the addition of 25% ethanol volume increases the index from 90 to 98).
Carburetors require modifications; for example, with 20% mixtures, flow rates have to be increased by approximately 10% (increase in specific consumption: 9%).
There may be problems related to miscibility (and stability of the mixture) because of the alcohol's water content (generally 2–5%). Its use in Diesel engines as a supplementary fuel is also possible (e.g., with the dual-fuel system).
Oils of vegetables origin are characterized by heating powers approaching those of light oils for Diesel engines. Their use does not present problems, as long as precombustion engines are employed. The most serious problems are connected with:
clouding at relatively high temperatures (from -5 to -10°C).
Possible consequences are:
increased sensitivity to climatic conditions. The quality of the oils should make it possible to use 3–μm filters.