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For nearly a century, the internal combustion engine has been the primary source of power for automobiles. In an internal combustion engine, a mixture of gasoline and air is compressed within a cylinder and ignited, and the expanding gas moves a piston, which in turn rotates the vehicle driveshaft.

However, there are several alternative technologies either currently on the market or in various stages of development.

Hybrid Vehicles

A hybrid vehicle combines two or more methods of propulsion in one vehicle. The primary type of hybrid vehicle is the gasoline-electric hybrid. In this type of vehicle, each of the power plants can directly power the vehicle drive train.

Hybrid vehicles have been on the market in the United States since the debut of the Toyota Prius in 2000. Hybrid vehicles often take advantage of natural power generation cycles in the vehicle, such as using regenerative braking technology to regain some of the energy from the decelerating vehicle.

Plug-In Hybrids

A plug-in hybrid vehicle also has an electric engine and a gasoline engine, but the gasoline engine is only used to recharge the batteries, rather than actually propel the vehicle.

As of now, there are no commercially available plug-in hybrid models on the road, but several models are in production, including a plug-in hybrid version of the Toyota Prius, and the newly developed Chevrolet Volt.

Battery-Electric Vehicles

A battery-electric vehicle (BEV) relies solely on the chemical energy storage of its batteries for electric power. There is no gasoline engine as backup, as would be found in hybrid or plug-in hybrid vehicles. A BEV uses a traditional DC motor to convert the battery energy into mechanical motion. The success of BEVs has generally been limited due to the size, weight, and cost of battery packs.

However, development has continued in niche markets. Tesla Motors set out to create a luxury battery-electric sports car, resulting in the debut of the Tesla Roadster. While the $100,000 price point places the Roadster out of range for most consumers, Tesla is using the proceeds and building on the engineering of the Roadster to develop a more modest sedan version.

Hydrogen Fuel Cell

While hydrogen can be used as a fuel in an internal combustion engine, its use as a fuel is far more efficient in a fuel cell system. A hydrogen fuel cell relies on chemical reactions involving hydrogen and oxygen to generate electricity.

The only by-product of the fuel cell reaction is water, resulting in a completely clean and emission-free process. The operation of the vehicle after the electricity is generated is the same as in a battery-electric vehicle, using a DC motor.

Compressed Natural Gas

Compressed natural gas (CNG) can be used as an alternative fuel in internal combustion engines. While it is still a fossil fuel, CNG produces the smallest amount of carbon dioxide emissions during the combustion process of all other fossil fuels. CNG vehicles are not extensively used in the United States, but can be found widely in South America.

Although the internal combustion engine has dominated the automotive world for 100 years, alternative technologies are making a breakthrough as people are more concerned about the costs of petroleum-based fuels and the effects of the emissions of gasoline-based vehicles on health and environment.