Hybrid cars, regular cars, electric cars, plug-ins, hydrogen fuel cells and even solar--the types of vehicle technologies available today continue to multiply and confuse. To simplify, remember that the basic difference is between the conventional combustion engine and new technologies for powering the engine. "Regular" cars have relied on the internal combustion engine since the automobile was first invented. Recent technologies have combined this engine with an electric engine to create a hybrid. All hybrids tend to greatly increase gas mileage, decrease pollution and save on fuel costs, but not all hybrids are alike.
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Internal Combustion Engine
Regular cars use the internal combustion engine, invented shortly before the turn of the 20th century. These engines, until very recently, used gasoline or diesel fuel made from petroleum, a fossil fuel. The engine works by literally burning the fuel, which creates heat and causes expansion of gases, directly causing movement of pistons in the engine.
A perfect combustion reaction would leave only carbon dioxide and water. However, perfect combustion is impossible, so these engines also emit carbon monoxide, nitrogen oxides and particulate pollution--all of which contribute to air pollution. The reliance of a regular engine on fossil fuels means they emit greenhouse gases, or GHG, contributing to global warming. Even partial or 100 percent biofuels will emit GHG, but since biofuels are produced from rapidly growing plants, the idea is that there is a net recycling of GHG. However, the recycling effect depends on the amount of fossil fuels--in the form of fertilizers, pesticides and fuel--that go into producing the biofuels themselves.
A hybrid engine combines internal combustion engine technology with electric engine technology. The electric half of the engine uses powerful batteries to store energy. The plug-in hybrid requires that a car recharge its electric engine by plugging into a source of electricity from the "grid." The grid is the system of generation that supplies virtually all of our electricity, and the source of that electricity may be fossil fuels--primarily coal--or renewables, such as hydro, wind or solar.
All hybrids greatly increase the fuel efficiency of cars and decrease tailpipe emissions, as well as energy costs, because they allow the electric engine to replace power when the internal combustion engine is least efficient, such as during start up. Some hybrids, such as the GM Volt, will allow sole use of the electric engine in the first 20 miles of driving. However, the source of your electricity greatly affects a plug-in's reduction of GHG. The "green" factor for plug-ins overall relies on an increasing level of renewable energy supplied to the nationwide grid.
A "true" hybrid engine also combines internal combustion and electric engines, but the electric battery is recharged completely by waste heat and energy from the conventional engine when the car is decelerating. This means a true hybrid, such as the Toyota Prius, does not require plug in to an external source of energy at all. Because they do not require plug-in, these cars will not run out of charge and they decrease emissions of pollutants and GHG absolutely. They use no fossil fuels or any other type of fuel from the grid to power the electric half of the engine.
Some hybrids, including some plug-ins, are being developed to also allow the eventual use of diesel, biofuels or hydrogen fuels to power the internal combustion part of the engine.