Alternative fuel sources are used as a way of reducing the operating cost of vehicles, or to reduce pollution from vehicle emissions, or both.
Some alternative fuels can be mixed with gasoline as a fuel additive to reduce the total amount of gasoline used, others are a complete fuel alternative which may require some modifications to the vehicle.
Ethanol is usually derived from an organic process such as the fermentation of sugar cane, and is therefore referred to as a bio-fuel. It is normally used in the ratio of 9:1 or 9 parts gasoline to 1 part ethanol and is primarily used to reduce the negative emission effects of gasoline.
Methanol is produced from wood or other organic materials. Its calorific value, or burn rate, is not as high as that of gasoline fuel and cannot be used in conventional vehicles without significant modifications.
Liquefied Petroleum Gas or LPG is a petroleum derived colorless gas, and has been used for many years to power specially modified gasoline engine vehicles. It is the third most common fuel and emits much fewer harmful emissions than gasoline. It is generally cheaper than gasoline and is non-toxic and non-poisonous with a very small flammability range. It is popular with high-mileage applications such as taxis, where the cost of vehicle modification can be recouped over time more easily through lower fuel costs.
Compressed Natural Gas or CNG is being used as an alternative fuel in vehicles such as light-duty passenger vehicles, delivery trucks and buses. CNG powered vehicles use natural gas stored in cylinders at pressures of 2,000 to 3,500 pounds per square inch or 140 to 240 Bar.
Liquefied Natural Gas or LNG is being used in heavy-duty diesel powered vehicles such as long-haul trucks, delivery trucks and buses. LNG is almost pure methane and has an energy storage density much closer to gasolinethan CNG, but for the gas to become a more compact and easily stored liquid it has to be cooled to an extremely low temperature, minus 263.2 degrees Fahrenheit, or minus 164 degrees Celsius. The need to keep the liquid very cold at all times limits the more widespread use of LNG.
Natural gas, whether liquified or compressed, is less expensive than diesel and natural gas vehicles are substantially cleaner than comparable diesel vehicles.
