Power-to-weight ratio

From Wikipedia, the free encyclopedia

Power-to-weight ratio (specific power) is a calculation commonly applied to engines and other 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 sources. It is also used a measure of performance of a vehicle as a whole, with the engine's power output being divided by the curb weight of the car, to give an idea of the vehicle's acceleration.

Contents 1 Power to weight (specific power) 2 Examples 2.1 Engines 2.2 Vehicles 2.3 Batteries 2.4 Fuel cells 3 See also 4 References

[edit] Power to weight (specific power)

The power-to-weight ratio (Specific Power) formula for an engine (power plant) is the power generated by the engine divided by weight of the engine as follows:

A typical turbocharged V-8 diesel engine might have an engine power of 250 horsepower (190 kW) and a weight of 450 kilograms (1,000 lb), giving it a power to weight ratio of 0.56 kW/kg (0.25 hp/lb).

Examples of high power to weight ratios can often be found in turbines. This is because of their ability to operate at very high speeds. For example, the Space Shuttle's main engines use turbopumps (machines consisting of a pump driven by a turbine engine) to feed the propellants (liquid oxygen and liquid hydrogen) into the engine's combustion chamber. The liquid hydrogen turbopump is slightly larger than an automobile engine (weighing approximately 320 kilograms (700 lb)) and produces nearly 70,000 hp (52.2 MW) for a power to weight ratio of 160 kW/kg (100 hp/lb).

[edit] Examples

[edit] Engines

Engine	Power to weight ratio
Turbocharged V-8 diesel engine	0.25 hp/lb / 410 W/Kg[1]
Space shuttle turbopump	100 hp/lb / 164120 W/Kg[2]

[edit] Vehicles

Vehicle	Power	Weight	Power to weight ratio
Subaru R2 type S 2003[3]	47 kW / 63 bhp	830 kg	57 W/Kg
Subaru Legacy 2.0R 2005[4]	121 kW / 162.3 bhp	1370 kg	88 W/Kg
Subaru Outback 2.5i 2008[5]	130.5 kW / 175 bhp	1430 kg	91 W/Kg
Ford Focus 2.0 auto 2007[6]	104.4kW / 140 bhp	1198 kg	94 W/Kg
Artega GT[7]	220 kW / 300 bhp	1100 kg	200 W/Kg
Lotus Exige GT3 2006[8]	202.1 kW / 271 bhp	980 kg [9]	206 W/Kg
Chevrolet Corvette C6[10]	321 kW / 430 bhp	1441 kg	223 W/Kg
Chevrolet Corvette C6 Z06[11]	337 kW / 505 bhp	1421 kg	265 W/Kg
McLaren F1 GT 1997[12]	467.6 kW / 627 bhp	1220 kg	403 W/Kg
Ultima GTR GTR720 2000[13]	257.3 kW / 345 bhp	1048 kg	480 W/Kg

[edit] Batteries

Battery type	Power to weight ratio
Nickel hydrogen battery	75 Wh/kg
Nickel-cadmium battery	150 W/kg
Lead acid battery	180 W/kg
Nickel metal hydride	250[14] (market) –980 W/kg[15] (lab)
Lithium ion battery	1700 W/kg (lab)[16]

[edit] Fuel cells

Fuel cell type	Power to weight ratio
PEMFC	967 W/kg (market) - 1,500 W/kg (lab)[17]

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 performance to another. Weight-to-Power ratio is a measurement of the acceleration capability (potential) of any land vehicle or climb performance of any aircraft or space vehicle.

[edit] See also

• Vehicle metrics

[edit] References