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Power-to-weight ratio (PWR, also called specific power, or power-to-mass ratio) is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power source.
Engine power is the power that an engine can put out. It can be expressed in power units, most commonly kilowatt, pferdestärke (metric horsepower), 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 ISO 1585.
Two of the four modelling metholodogies in the shootout, one from North Carolina State University and one internal to the EPA, used vehicle-specific power metrics. [3] [4] MOVES was eventually implemented using vehicle-specific power as its primary metric. [4] (See Koupal et al. 2002, § 7.1.3.1 for the EPA MOVES draft VSP specification.)
It applies to reciprocating internal combustion engines for land, rail and marine use excluding engines of motor vehicles primarily designed for road use. [42] ISO 1585 is an engine net power test code intended for road vehicles. [43] ISO 2534 is an engine gross power test code intended for road vehicles. [44]
For vehicles where the above formula cannot be applied (e.g. electric vehicles), the tax horsepower is derived from the effective engine power (which is defined by law as the maximum power that the engine can provide after being used at full power from 30 minutes, which is normally lower than the rated engine power).
Now, if this motor is fed with current of 2 A and assuming that back-EMF is exactly 2 V, it is rotating at 7200 rpm and the mechanical power is 4 W, and the force on rotor is = N or 0.0053 N. The torque on shaft is 0.0053 N⋅m at 2 A because of the assumed radius of the rotor (exactly 1 m).
In Japan, the engine displacement is one of the factors (along with overall vehicle size and power output) used to determine the vehicle size class and therefore the cost of road tax for the vehicle. In France and some other EU countries, mopeds with a displacement of less than 50 cc (3.1 cu in) can be driven with minimum qualifications.
Mean effective pressure is also useful for initial design calculations; that is, given a torque, standard MEP values can be used to estimate the required engine displacement. However, mean effective pressure does not reflect the actual pressures inside an individual combustion chamber – although the two are certainly related – and serves ...