Alternative fuels which are renewable and eco-friendly reduce the dependency on fossil fuels and they help to preserve the atmosphere by reducing the emission levels. The burning of fossil fuels create higher levels of CO2 and other gases in atmosphere affecting the greenhouse effect. The scarcity of conventional fossil fuels, growing emissions of combustion causing pollutants and their increasing costs will make biomass sources more attractive.

Epidemiological studies have concluded that the long term exposure to diesel exhaust may cause lung cancer and other respiratory diseases. The diesel emission has been classified as human carcinogen. The different kinds of fuels that have been considered as alternative fuels for petroleum based fuel are classified as solid, liquid and gas. The solid fuels are pulverized coal, slurry and charcoal which are not used in IC engines due to their physical properties, handling and storage problems. The liquid fuels are alcohols (ethanol, methanol) and vegetable oils (edible and non-edible). The gaseous fuels are LPG, CNG, H2, biomass and producer gas. Liquid fuels are easy to handle, transport, store and have reasonable calorific values and they are preferred for IC engines.

ALTERNATIVE LIQUID FUELS

There are few techniques by which alcohol fuels can partially or completely displace diesel fuel. Once it was believed that alcohol was suitable for S.I. engine fuels but not suitable for C.I. engine due to its high octane number. In mid-1970, ethanol and methanol were considered as prime alternative to diesel and the most promising techniques are explored for better engine performance namely power output, thermal efficiency, emissions and operability.

The most common alternative fuels for SI engines are ethanol in blends with gasoline as well as compressed natural gas (CNG), liquefied natural gas (LNG), and liquefied petroleum gas (LPG). Biodiesel, synthetic diesel, green diesel, and DME are the most common alternative fuels for CI engines.