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The efficiency of internal combustion engines depends on several factors, the most important of which is the expansion ratio. For any heat engine the work which can be extracted from it is proportional to the difference between the starting pressure and the ending pressure during the expansion phase.
The inverse of power-to-weight, weight-to-power ratio (power loading) is a calculation commonly applied to aircraft, cars, and vehicles in general, to enable the comparison of one vehicle's performance to another. Power-to-weight ratio is equal to thrust per unit mass multiplied by the velocity of any vehicle.
Engine power is the power that an engine can develop. It can be expressed in power units, most commonly kilowatt, metric horsepower (often abbreviated PS), or horsepower.In terms of internal combustion engines, the engine power usually describes the rated power, which is a power output that the engine can maintain over a long period of time according to a certain testing method, for example ...
Since the power equals thrust times speed, the efficiency is given by η = V / ( S F C × h ) {\displaystyle \eta =V/(SFC\times h)} where V is speed and h is the energy content per unit mass of fuel (the higher heating value is used here, and at higher speeds the kinetic energy of the fuel or propellant becomes substantial and must be included).
In the example provided by the US DoE in its final rule, an electric car with an energy consumption of 265 Watt hour per mile in urban driving, and 220 Watt hour per mile in highway driving, results in a petroleum-equivalent fuel economy of 335.24 miles per gallon, based on a driving schedule factor of 55 percent urban, and 45 percent highway ...
For the purpose of manageability, this list is limited to production cars that have at least 600 kilowatts. Car models with higher-powered variants are listed only in their most powerful incarnation (for example, the Agera RS would be listed in place of the standard Agera, although the Agera makes over 600 kW).
This is around 1 ⁄ 5 (20%) of what is needed to power a standard upright bicycle without aerodynamic cladding at same speed, and 1 ⁄ 50 (2%) of that which is consumed by an average fossil fuel or electric car (the velomobile efficiency corresponds to 4700 miles per US gallon, 2000 km/L, or 0.05 L/100 km). [22]
The efficiency often reported for a particular engine, however, is not its maximum efficiency but a fuel economy cycle statistical average. For example, the cycle average value of BSFC for a gasoline engine is 322 g/(kW⋅h), translating to an efficiency of 25% (1/(322 × 0.0122225) = 0.2540).
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