Internal Combustion Engines

• The vast majority of modern automobiles are powered by internal combustion engines. These engines use a fuel, such as gasoline, which is ignited to produce the power stroke that drives the vehicle. The internal combustion engine essentially creates a series of small explosions and transfers their power to the driveshaft via the transmission. Most internal combustion engines are four-stroke engines, with four distinct procedures: intake, compression, ignition and exhaust.
  
  

Diesel Engines

• Diesel engines are internal combustion engines that use diesel fuel rather than gasoline. Diesel fuel may be distilled from petroleum or a number of other sources. Some modern biodiesel fuel comes from vegetable or animal fats. Diesel engines ignite the diesel fuel by mixing it with hot air, rather than a spark plug as used in gasoline engines. Diesel engines are more efficient than comparable gasoline engines and also produce less carbon emissions.
  
  

Rotary Engines

• The rotary engine is an internal combustion engine developed in the early-20th century as an alternative to the standard reciprocating piston engine. Instead of the up-and-down motion of a piston, the rotary engine uses a rotating plate inside the engine to seal off sections of the engine, which serve as the compression or combustion chambers. The rotary engine weighs less than a piston engine with a similar volume. Rotary engines are uncommon today, but are still notably used on Mazda's RX series of sports cars.
  
  

Hybrid Vehicle Engines

• Some modern hybrid electric vehicles use an electric motor to produce forward motion. The electric motor is powered by either an on-board gasoline engine or by storing energy during braking or when driving downhill. These electric engines must be supplied by battery packs, which add to the cost and complexity of hybrid electric vehicles. However, cars using primarily electric power produce few emissions and can achieve fuel economy far above even the most modest gasoline or diesel engine.
  
  

Other Alternative Fuel Engines

• Most other alternative fuel cars, some of which are no more than prototypes, use a different type of fuel to power the same sort of electric engine as used in gasoline-electric hybrids. This is true of solar cars, hydrogen fuel cell cars, so-called plug-in hybrids and fully electric vehicles. These electric motors have the advantage of providing their full power at all vehicle speeds, instead of needing to be "revved up" to produce peak power as with an internal combustion engine. They are also flexible, being able to receive their fuel from a variety of sources.