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Fully electric cars such as the Tesla Model S and the Nissan Leaf are quickly becoming affordable alternatives to cars that operate on internal combustion engines. This page explores the consequences that would accompany a national transition from internal combustion cars to fully electric cars. == Efficiency == Thermal efficiency, , of a heat engine is determined by the ratio between the useful output of work, , and the input of energy, . Some heat engines' efficiency is determined by specific equations. For instance, internal combustion engines follow the Otto cycle. The Otto cycle considers the compression ratio of the engine, , and the specific heat ratio of the gas in the combustion chamber, . In modern internal combustion cars, the compression ratio is between 6 and 10, and the specific heat of the air and gas mixture is 1.28. Given these values, the maximum efficiency of an internal combustion engine is around 44%. An additional 20% is lost to various contributing factors, but mostly friction. As such, the effective efficiency of an internal combustion engine in ideal conditions is around 25%.〔 An electric car is powered by an electric motor. The motor converts electrical work to mechanical work. Due to the fact the motor operates by converting one type of work to another, the motor has a theoretical efficiency of 100%. In practice, an electric car suffers the same friction losses as an internal combustion engine, so the effective efficiency is around 80%. Well-to-wheel efficiency considers the ratio between the output of useful work and the energy content of the fuel, before it has been processed. For internal combustion engines, the well-to-wheel efficiency follows the equation for the efficiency of a heat engine. In this case, is the original energy content of the fuel. A barrel (42 gallons) of crude oil contains, on average, 1694.44 kilowatt-hours of energy. This barrel will produce 19 gallons of gasoline, giving an unrefined original energy content of 40.13 kilowatt-hours per gallon. In 2014, The United States consumed 136.78 billion gallons of gasoline,〔 giving a total of 5.48 trillion kilowatt-hours. The total work done by all of the cars in The United States in 2014 (see Energy Requirements) is 1.15 trillion kilowatt-hours. This results in a well-to-wheel efficiency of 20.9%. To determine the well-to-wheel efficiency for electric cars we must consider the same efficiency equation above. We will use natural gas as the original fuel source. It takes 10.1 cubic feet of natural gas to produce 1 kilowatt-hour of electricity at a power plant. The energy requirement to perform the mechanical work of all US cars, assuming 80% efficient electric cars, is 1.437 trillion kilowatt-hours. The product of the two gives 14.5 trillion cubic feet of natural gas required to produce enough electricity to power a total transition to electric cars. The original energy content of natural gas is 0.305 kilowatt-hours per cubic foot.〔 The product of the energy content and required volume of natural gas gives a total of 4.428 trillion kilowatt-hours. Finally, to determine the overall well-to-wheel efficiency we divide the total work, 1.15 trillion kilowatt-hours by the total of 4.428 trillion kilowatt-hours. The result is an overall well-to-wheel efficiency of 26%. As shown above, a total transition to electric cars in The United States would raise the overall efficiency of the system. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「US transition to electric cars」の詳細全文を読む スポンサード リンク
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