A substance or any material that can be used to provide power for an engine or which can be burned in air to release energy.

Fuels; such as, gasoline are made mostly of hydrocarbons (carbon and hydogen molecules).

A vehicle designed to operate on an alternative fuel; for example, compressed natural gas, methane blend, and electricity.

The vehicle could be either a dedicated vehicle designed to operate exclusively on alternative fuel or a nondedicated vehicle designed to operate on alternative fuel and/or a traditional fuel.

A motor vehicle that operates on two different fuels, but not on a mixture of the fuels.

Each fuel is stored in a separate tank.

Any liquid biofuel suitable as a diesel fuel substitute or diesel fuel additive or extender.

Biodiesel fuels are typically made from oils; such as, soybeans, rapeseed, or sunflowers, or from animal tallow.

Biodiesel fuel can also be made from hydrocarbons derived from agricultural products: such as, rice hulls.

Any solid, gaseous, or liquid fuel obtained from biomass; this may be in its natural form (wood, peat) or a commercially produced form (ethanol from sugarcane residue, diesel fuel from waste vegetable oils).

An electrical device powered by fuel from a tank that makes energy through a chemical reaction.

A fuel cell is similar to a large battery, but where a battery gradually runs down, a fuel cell runs continuously for as long as there is fuel in the tank.

A fuel delivery system whereby gasoline is pumped to one or more fuel injectors under high pressure.

The fuel injectors are valves that, at the appropriate times, open to allow fuel to be sprayed or atomized into a throttle bore or into the intake manifold ports.

The fuel injectors are usually solenoid operated valves under the control of the vehicle's on-board computer resulting in "electronic fuel injection".

The fuel efficiency of fuel injection systems is less temperature-dependent than carburetor systems. Diesel engines always use injectors.

A fuel cell is a type of battery which converts the chemicals hydrogen and oxygen into water, and in the process produces electricity.

Hydrogen is pumped into the cell from an on board tank, while the oxygen is taken from the air outside. Together they form steam, which is emitted through the car's exhaust.

Some car makers are putting a lot of time and effort into developing hybrid cars where the electric motors are powered by fuel cells.

Hydrogen is the most abundant element in the universe, but it is highly flammable; that is, it bursts into flames easily and as the lightest gas, it just floats away. Even so, it can be extracted from water, fossil fuels, and other substances.

The problem is to compress, or squeeze, hydrogen into a tank small enough to fit in a car. The tank can be topped off with hydrogen at refueling stations, but there are very few of such places available at this time.

The advantages and disadvantages of fuel-cell cars

In theory, electric-fuel-cell cars could be the answer for clean cars of the future:

• Fuel cells are reliable and make little noise since they have no moving parts.
• Water is the only thing emitted through the exhaust.

There are a number of challenges still to be overcome:

• Increasing the amount of electricity produced so the car has more power.
• Compressing and safely storing enough hydrogen into a small tank for hundreds of miles of driving.
• Making affordable cars which are now very expensive in that a fuel-cell system costs ten times more to make than a conventional engine.

A fuel cell technology that uses metals; such as, zinc, aluminum, and magnesium in place of hydrogen to provide electrical power in order to overcome certain disadvantages that are associated with hydrogen as a fuel.