Contents 1 History 2 Calculating power 3 Definitions 3.1 Mechanical horsepower 3.2 Metric horsepower (PS, cv, hk, pk, ks, ch) 3.3 Tax horsepower 3.4 Electrical horsepower 3.5 Hydraulic horsepower 3.6 Boiler horsepower 3.7 Drawbar horsepower 3.8 RAC horsepower (taxable horsepower) 3.9 Compressed air horsepower 4 Measurement 4.1 Nominal (or rated) horsepower 4.2 Indicated horsepower 4.3 Brake horsepower 4.4 Shaft horsepower 4.5 Wheel horsepower 5 Engine power test standards 5.1 Society of Automotive Engineers/SAE International 5.1.1 Early "SAE horsepower" (see RAC horsepower) 5.1.2 SAE gross power 5.1.3 SAE net power 5.1.4 SAE certified power 5.2
6 See also 7 References 8 External links History[edit] One metric horsepower is needed to lift 75 kilograms by 1 metre in 1 second The development of the steam engine provided a reason to compare the
output of horses with that of the engines that could replace them. In
1702,
So that an engine which will raise as much water as two horses, working together at one time in such a work, can do, and for which there must be constantly kept ten or twelve horses for doing the same. Then I say, such an engine may be made large enough to do the work required in employing eight, ten, fifteen, or twenty horses to be constantly maintained and kept for doing such a work…[4] The idea was later used by James
P = W t = F d t = 180 l b f × 2.4 × 2 π × 12 f t 1 m i n = 32 , 572 f t ⋅ l b f m i n . displaystyle P= frac W t = frac Fd t = frac 180,mathrm lbf times 2.4times 2,pi times 12,mathrm ft 1,mathrm min =32,572 frac mathrm ft cdot mathrm lbf mathrm min .
T displaystyle T is in pound-foot units, rotational speed ( N ) displaystyle (N) is in rpm and power is required in horsepower: P / hp = T / ( ft ⋅ lbf ) × N / rpm 5252 displaystyle P/ text hp = frac T/( text ft cdot text lbf )times N/ text rpm 5252 The constant 5252 is the rounded value of (33,000 ft⋅lbf/min)/(2π rad/rev). When torque T displaystyle T is in inch pounds: P / hp = T / ( in ⋅ lbf ) × N / rpm 63,025 displaystyle P/ text hp = frac T/( text in cdot text lbf )times N/ text rpm 63 , 025 The constant 63,025 is the approximation of 33,000 ft ⋅ lbf min ⋅ 12 in ft 2 π rad ≈ 63,025 displaystyle 33 , 000, frac text ft cdot text lbf text min cdot frac 12, frac text in text ft 2pi ~ text rad approx 63 , 025 . If torque and rotational speed are expressed in coherent SI units, the power is calculated by ; P = τ ⋅ ω displaystyle P=tau cdot omega where P displaystyle P is power in watts when τ displaystyle tau is torque in newton-metres, and ω displaystyle omega is angular speed in radians per second. When using other units or if the speed is in revolutions per unit time rather than radians, a conversion factor has to be included. Definitions[edit] The following definitions have been or are widely used: Mechanical horsepower hp(I) ≡ 33,000 ft lbf/min = 550 ft⋅lbf/s ≈ 17696 lb⋅ft2/s3 = 745.69987158227022 W Metric horsepower hp(M) - also PS, cv, hk, pk, ks or ch ≡ 75 kgf⋅m/s ≡ 75 kg ⋅ 9.80665 m/s2 ⋅ 1 m/s ≡ 735.49875 W Electrical horsepower hp(E) ≡ 746 W Boiler horsepower hp(S) ≡ 33,475 BTU/h = 9,812.5 W Hydraulic horsepower = flow rate (US gal/min) × pressure (psi) × 7/12,000 or = flow rate (US gal/min) × pressure (psi) / 1714 = 550 ft⋅lbf/s = 745.69987158227022 W Air horsepower = flow rate ( cubic feet / minute) × pressure (inches water column) / 6,356 or = 550 ft⋅lbf/s = 745.69987158227022 W In certain situations it is necessary to distinguish between the various definitions of horsepower and thus a suffix is added: hp(I) for mechanical (or imperial) horsepower, hp(M) for metric horsepower, hp(S) for boiler (or steam) horsepower and hp(E) for electrical horsepower. Hydraulic horsepower is equivalent to mechanical horsepower.[citation needed] The formula given above is for conversion to mechanical horsepower from the factors acting on a hydraulic system. Mechanical horsepower[edit] Assuming the third CGPM (1901, CR 70) definition of standard gravity, gn=9.80665 m/s2, is used to define the pound-force as well as the kilogram force, and the international avoirdupois pound (1959), one mechanical horsepower is: 1 hp ≡ 33,000 ft-lbf/min by definition = 550 ft⋅lbf/s since 1 min = 60 s = 550×0.3048×0.45359237 m⋅kgf/s since 1 ft = 0.3048 m and 1 lb = 0.45359237 kg = 76.0402249068 kgf⋅m/s = 76.0402249068×9.80665 kg⋅m2/s3 since g = 9.80665 m/s2 = 745.69987158227022 W since 1 W ≡ 1 J/s = 1 N⋅m/s = 1 (kg⋅m/s2)⋅(m/s) Or given that 1 hp = 550 ft⋅lbf/s, 1 ft =
0.3048 m, 1 lbf ≈ 4.448 N, 1 J =
1 N⋅m, 1 W = 1 J/s: 1 hp ≈ 746 W
Metric horsepower (PS, cv, hk, pk, ks, ch)[edit]
The various units used to indicate this definition (PS, cv, hk, pk, ks
and ch) all translate to horse power in English, so it is common to
see these values referred to as horsepower or hp in the press releases
or media coverage of the German, French, Italian, and Japanese
automobile companies. British manufacturers often intermix metric
horsepower and mechanical horsepower depending on the origin of the
engine in question. Sometimes the metric horsepower rating of an
engine is conservative enough so that the same figure can be used for
both 80/1269/EEC with metric hp and SAE J1349 with imperial hp.
( P 40 ) 1.6 + U 45 displaystyle scriptstyle left( tfrac P 40 right)^ 1.6 + tfrac U 45 , where P is the maximum power in kilowatts and U is the amount of carbon dioxide (CO2) emitted in grams per kilometre. The term for CO2 measurements has been included in the definition only since 1998, so older ratings in CV are not directly comparable. The fiscal power has found its way into naming of automobile models, such as the popular Citroën deux-chevaux. The cheval-vapeur (ch) unit should not be confused with the French cheval fiscal (CV). Electrical horsepower[edit] The horsepower used for electrical machines is defined as exactly 746 W.[21] In the US, nameplates on electrical motors show their power output in hp, not their power input. Outside the United States watts or kilowatts are generally used for electric motor ratings and in such usage it is the output power that is stated. Hydraulic horsepower[edit] Hydraulic horsepower can represent the power available within hydraulic machinery, power through the down-hole nozzle of a drilling rig,[22] or can be used to estimate the mechanical power needed to generate a known hydraulic flow rate. It may be calculated as[22] hydraulic horsepower = pressure × flow rate 1714 , displaystyle text hydraulic horsepower = frac text pressure times text flow rate 1714 , where pressure is in psi, and flow rate is in US gallons per minute.
Drilling rigs are powered mechanically by rotating the drill pipe from
above. Hydraulic power is still needed though, as between 2 and
7 hp are required to push mud through the drill bit in order to
clear waste rock. This hydraulic power, considerably more than this,
may also be used to drive a down-hole mud motor to power directional
drilling.[22]
Boiler horsepower[edit]
Boiler horsepower is a boiler's capacity to deliver steam to a steam
engine and is not the same unit of power as the 550 ft-lb/s
definition. One boiler horsepower is equal to the thermal energy rate
required to evaporate 34.5 lb of fresh water at 212 °F in
one hour. In the early days of steam use, the boiler horsepower was
roughly comparable to the horsepower of engines fed by the boiler.[23]
The term "boiler horsepower" was originally developed at the
F displaystyle F ) is measured in pounds-force (lbf) and speed ( v displaystyle v ) is measured in miles per hour (mph), then the drawbar power ( P displaystyle P ) in horsepower (hp) is: P / h p = ( F / l b f ) ( v / m p h ) 375 displaystyle P/ rm hp = (F/ rm lbf )(v/ rm mph ) over 375 Example: How much power is needed to pull a drawbar load of 2,025 pounds-force at 5 miles per hour? P / h p = 2025 × 5 375 = 27 displaystyle P/ rm hp = 2025times 5 over 375 =27 The constant 375 is because 1 hp = 375 lbf⋅mph. If other units are used, the constant is different. When using coherent SI units (watts, newtons, and metres per second), no constant is needed, and the formula becomes P = F v displaystyle P=Fv . This formula may also be used to calculate the horsepower of a jet engine, using the speed of the jet and the thrust required to maintain that speed. Example: How much power is generated with a thrust of 4,000 pounds at 400 miles per hour? P / h p = 4000 × 400 375 = 4266.7 displaystyle P/ rm hp = 4000times 400 over 375 =4266.7 RAC horsepower (taxable horsepower)[edit]
See also: Tax horsepower
This measure was instituted by the
RAC h.p. = 2 5 D 2 n displaystyle text RAC h.p. = frac 2 5 D^ 2 n where D is the diameter (or bore) of the cylinder in inches n is the number of cylinders[24] This is equal to the engine displacement in cubic inches divided by 0.625π then divided again by the stroke in inches. Since taxable horsepower was computed based on bore and number of cylinders, not based on actual displacement, it gave rise to engines with 'undersquare' dimensions (bore smaller than stroke) this tended to impose an artificially low limit on rotational speed (rpm), hampering the potential power output and efficiency of the engine. The situation persisted for several generations of four- and six-cylinder British engines: for example, Jaguar's 3.4-litre XK engine of the 1950s had six cylinders with a bore of 83 mm (3.27 in) and a stroke of 106 mm (4.17 in),[25] where most American automakers had long since moved to oversquare (large bore, short stroke) V-8s (see, for example, the early Chrysler Hemi). Compressed air horsepower[edit] Compressed air is commonly referred to in terms of horsepower. This refers to the horsepower required to produce any given amount of compressed air. It also refers to the gross amount of compressed air required for large applications or plant wide requirements. Chart showing horsepower required to compress air Measurement[edit] The power of an engine may be measured or estimated at several points in the transmission of the power from its generation to its application. A number of names are used for the power developed at various stages in this process, but none is a clear indicator of either the measurement system or definition used. In the case of an engine dynamometer, power is measured at the engine's flywheel.[citation needed] Also, with a chassis dynamometer or rolling road, power output is measured at the driving wheels. This accounts for energy or power loss through the drive train inefficiencies and weight thereof as well as gravitational force placed upon components therein. In general: Nominal or rated horsepower is derived from the size of the engine and the piston speed and is only accurate at a steam pressure of 48 kPa (7 psi).[26] Indicated or gross horsepower (theoretical capability of the engine) [ PLAN/ 33000] minus frictional losses within the engine (bearing drag, rod and crankshaft windage losses, oil film drag, etc.), equals Brake / net / crankshaft horsepower (power delivered directly to and measured at the engine's crankshaft) minus frictional losses in the transmission (bearings, gears, oil drag, windage, etc.), equals Shaft horsepower (power delivered to and measured at the output shaft of the transmission, when present in the system) minus frictional losses in the universal joint/s, differential, wheel bearings, tire and chain, (if present), equals Effective, True (thp) or commonly referred to as wheel horsepower (whp) All the above assumes that no power inflation factors have been applied to any of the readings. Engine designers use expressions other than horsepower to denote objective targets or performance, such as brake mean effective pressure (BMEP). This is a coefficient of theoretical brake horsepower and cylinder pressures during combustion. Nominal (or rated) horsepower[edit] Nominal horsepower (nhp) is an early 19th-century rule of thumb used to estimate the power of steam engines.[26] It assumed a steam pressure of 7 psi (48 kPa).[27] nhp = 7 × area of piston × equivalent piston speed/33,000 For paddle ships, the Admiralty rule was that the piston speed in feet per minute was taken as 129.7 × (stroke)1/3.38.[26][27] For screw steamers, the intended piston speed was used.[27] The stroke (or length of stroke) was the distance moved by the piston measured in feet. For the nominal horsepower to equal the actual power it would be necessary for the mean steam pressure in the cylinder during the stroke to be 7 psi (48 kPa) and for the piston speed to be that generated by the assumed relationship for paddle ships.[26] The French Navy used the same definition of nominal horse power as the Royal Navy.[26] Comparison of nominal and indicated horse power Ship Indicated horse power (ihp) Nominal horse power (nhp) Ratio of ihp to nhp Source Dee 272 200 1.36 [26] Locust 157 100 1.57 [26] Rhadamanthus 400 220 1.82 [26] Albacore 109 60 1.82 [27] Porcupine 285 132 2.16 [26] Harpy 520 200 2.60 [26] Spitfire 380 140 2.70 [26] Spiteful 796 280 2.85 [27] Jackal 455 150 3.03 [26] Supply 265 80 3.31 [27] Simoom 1,576 400 3.94 [27] Hector 3,256 800 4.07 [27] Agincourt 6,867 1,350 5.08 [27] Bellerophon 6,521 1,000 6.52 [27] Monarch 7,842 1,100 7.13 [27] Penelope 4,703 600 7.84 [27] Indicated horsepower[edit]
Indicated horsepower (ihp) is the theoretical power of a reciprocating
engine if it is completely frictionless in converting the expanding
gas energy (piston pressure × displacement) in the cylinders. It is
calculated from the pressures developed in the cylinders, measured by
a device called an engine indicator – hence indicated horsepower. As
the piston advances throughout its stroke, the pressure against the
piston generally decreases, and the indicator device usually generates
a graph of pressure vs stroke within the working cylinder. From this
graph the amount of work performed during the piston stroke may be
calculated.
Indicated horsepower was a better measure of engine power than nominal
horsepower (nhp) because it took account of steam pressure. But unlike
later measures such as shaft horsepower (shp) and brake horsepower
(bhp), it did not take into account power losses due to the machinery
internal frictional losses, such as a piston sliding within the
cylinder, plus bearing friction, transmission and gear box friction,
etc.
Brake horsepower[edit]
Brake horsepower (bhp) is the power measured at the crankshaft just
outside the engine, before the losses of power caused by the gearbox
and drive train.
In Europe, the
Japanese Industrial Standard D 1001[edit] JIS D 1001 is a Japanese net, and gross, engine power test code for automobiles or trucks having a spark ignition, diesel engine, or fuel injection engine.[43] See also[edit] Brake specific fuel consumption—how much fuel an engine consumes per
unit energy output
References[edit] ^ "Horsepower", Encyclopædia Britannica Online. Retrieved 2012-06-24.
^ "International System of Units" (SI), Encyclopædia Britannica
Online. Retrieved 2012-06-24.
^ "Directive 2009/3/EC of the European Parliament and of the Council
of 11 March 2009", Official Journal of the European Union. Retrieved
2013-02-15.
^ "The miner's friend". Rochester history department website:.
Archived from the original on May 11, 2009. Retrieved July 21,
2011.
^ "Math Words — horsepower". pballew.net. Retrieved
2007-08-11.
^ Hart-Davis, Adam, Engineers, pub Dorling Kindersley, 2012, p121.
^ Tully, Jim (September 2002). "Philadelphia Chapter Newsletter".
American Society of Mechanical Engineers. Archived from the original
on 2007-08-13. Retrieved 2007-08-11.
^ Coon, Brett A. Handley, David M. Marshall, Craig (2012). Principles
of engineering. Clifton Park, N.Y.: Delmar Cengage Learning.
p. 202. ISBN 978-1-435-42836-2.
^ Marshall, Brian. "How
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