Horsepower

Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors.It was later expanded to include the output power of other power-generating machinery such as piston engines, turbines, and electric motors.In 1702, Thomas Savery wrote in The Miner's Friend:[4] The idea was later used by James Watt to help market his improved steam engine.[7] So: Engineering in History recounts that John Smeaton initially estimated that a horse could produce 22,916 foot-pounds (31,070 J) per minute.[9] In 1993, R. D. Stevenson and R. J. Wassersug published correspondence in Nature summarizing measurements and calculations of peak and sustained work rates of a horse.[15] When torque T is in pound-foot units, rotational speed N is in rpm, the resulting power in horsepower is The constant 5252 is the rounded value of (33,000 ft⋅lbf/min)/(2π rad/rev).When torque T is in inch-pounds, The constant 63,025 is the approximation of 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 imperial horsepower is: 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 ≈ 745.7 W The various units used to indicate this definition (PS, KM, cv, hk, pk, k, ks and ch) all translate to horse power in English.), the Swedish hästkraft (hk), the Finnish hevosvoima (hv), the Estonian hobujõud (hj), the Norwegian and Danish hestekraft (hk), the Hungarian lóerő (LE), the Czech koňská síla and Slovak konská sila (k or ks), the Serbo-Croatian konjska snaga (KS), the Bulgarian конска сила, the Macedonian коњска сила (KC), the Polish koń mechaniczny (KM) (lit.Hydraulic power is still needed though, as 1 500 to 5 000 W are required to push mud through the drill bit to clear waste rock.One boiler horsepower is equal to the thermal energy rate required to evaporate 34.5 pounds (15.6 kg) of fresh water at 212 °F (100 °C) in one hour.[22] The term "boiler horsepower" was originally developed at the Philadelphia Centennial Exhibition in 1876, where the best steam engines of that period were tested.[citation needed] A few years later in 1884, the ASME re-defined the boiler horsepower as the thermal output equal to the evaporation of 34.5 pounds per hour of water "from and at" 212 °F (100 °C).When using coherent SI units (watts, newtons, and metres per second), no constant is needed, and the formula becomes P = Fv.As new engines were designed with ever-increasing efficiency, it was no longer a useful measure, but was kept in use by UK regulations, which used the rating for tax purposes.[25] where 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), which tended to impose an artificially low limit on rotational speed, hampering the potential power output and efficiency of the engine.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.Engine designers use expressions other than horsepower to denote objective targets or performance, such as brake mean effective pressure (BMEP).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.[28] 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.Horsepower was originally measured and calculated by use of the "indicator diagram" (a James Watt invention of the late 18th century), and later by means of a Prony brake connected to the engine's output shaft.[31] Shaft horsepower is a common rating for turboshaft and turboprop engines, industrial turbines, and some marine applications.Correction factors are used to adjust power and torque measurements to standard atmospheric conditions, to provide a more accurate comparison between engines as they are affected by the pressure, humidity, and temperature of ambient air.Prior to the 1972 model year, American automakers rated and advertised their engines in brake horsepower, bhp, which was a version of brake horsepower called SAE gross horsepower because it was measured according to Society of Automotive Engineers (SAE) standards (J245 and J1995) that call for a stock test engine without accessories (such as dynamo/alternator, radiator fan, water pump),[35] and sometimes fitted with long tube test headers in lieu of the OEM exhaust manifolds.This contrasts with both SAE net power and DIN 70020 standards, which account for engine accessories (but not transmission losses).The atmospheric correction standards for barometric pressure, humidity and temperature for SAE gross power testing were relatively idealistic.However, the 2006 rating does not reflect the new SAE testing procedure, as Ford did not opt to incur the extra expense of retesting its existing engines.CUNA prescribed that the engine be tested with all accessories necessary to its running fitted (such as the water pump), while all others – such as alternator/dynamo, radiator fan, and exhaust manifold – could be omitted.