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Specific fuel consumption

Article by: Layton, J. Preston Formerly, Conceptual Design Division, RCA Astro­Electronics, Princeton, New Jersey. Publication year: 2014 DOI: http://dx.doi.org/10.1036/1097­8542.641600 (http://dx.doi.org/10.1036/1097­8542.641600)

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Bibliography Additional Readings

The ratio of the fuel mass flow of an aircraft engine to its output power, in specified units. Specific fuel consumption (abbreviated sfc or SFC) is a widely used measure of atmospheric engine performance. For reciprocating engines it is usually given in U.S. Customary units of pound­mass per hour per horsepower [(lbm/h)/hp or lbm/(hp·h)], and International System (SI) units of kilograms per hour per kilowatt [(kg/h)/kW]. See also: Reciprocating aircraft engine (/content/reciprocating­aircraft­engine/575300)

For the gas turbine family of atmospheric aircraft engines, and for ramjets, performance is usually given in terms of thrust specific fuel consumption (abbreviated tsfc or TSFC) expressed as fuel mass flow per unit thrust output with Customary units of pound­mass per hour per pound­force [(lbm/h)/lbf] or SI units of kilograms per hour per newton [(kg/h)/N; 1 N equals approximately 0.225 lbf]. For high­supersonic and hypersonic ramjets, specific fuel consumption is sometimes given in pound­mass per second per pound­force [(lbm/s)/lbf] or kilograms per second per newton [(kg/s)/N]. Specific thrust (or specific impulse), which is the inverse of specific fuel consumption, is often used especially for supersonic combustion ramjet (scramjet) performance at Mach numbers above 6 (the Mach number

NMa equals 1.0 at the local speed of sound). See also: Aircraft propulsion (/content/aircraft­propulsion/019200); Turbine engine subsystems (/content/turbine­engine­subsystems/359200); Mach number (/content/mach­ number/394700); Propulsion (/content/propulsion/549100); Specific impulse (/content/specific­ impulse/642000); Turbine propulsion (/content/turbine­propulsion/716300); Turbofan (/content/turbofan/716500); Turbojet (/content/turbojet/716600)

Since the combustion process in atmospheric aircraft engines is supported by oxygen in the ambient air, only the hydrocarbon fuel (gasoline for reciprocating engines and kerosine for turbine engines and ramjets), which must be carried on board the aircraft, needs to be accounted for in determining engine performance. Methane and hydrogen may be used in the future as fuels for atmospheric engines. To obtain a low specific fuel consumption, the fuel should have both a high heat of combustion (that is, energy content per unit mass of fuel) and high cycle efficiency. The cycle efficiency is related to the operating compression ratio of the engine. See also: Aircraft fuel (/content/aircraft­ fuel/018800); Gasoline (/content/gasoline/281900); Kerosine (/content/kerosine/363400) A typical specific fuel consumption value for reciprocating engines and turboprops (in terms of equivalent shaft horsepower) is approximately 0.5 (lbm/h)/hp [0.3 (kg/h)/kW]. Gas turbines range between 0.6 (lbm/h)/lbf [0.06 (kg/h)/N] for turbofans and 0.8 (lbm/h)/lbf [0.08 (kg/h)/N] for turbojets. Ramjet engines with hydrocarbon fuel range upward from a minimum of about 2.0 (lbm/h)/lbf [0.20 (kg/h)/N] at flight speeds between Mach numbers 2 and 4. Values of specific fuel consumption for ramjets and scramjets with hydrogen fuel beginning at Mach 4 trend from approximately 0.9 to 2.4 (lbm/h)/lbf [0.09 to 0.24 (kg/h)/N] at Mach 16 and beyond.

J. Preston Layton

Bibliography

D. G. Shepherd, Aerospace Propulsion, 1972

Additional Readings

M. Ehsani, Y. Gao, and A. Emadi, Modern Electric, Hybrid Electric, and Fuel Cell Vehicles: Fundamentals, Theory, and Design, 2d ed., CRC Press, Boca Raton, FL, 2010

A. Maiboom et al., Experimental study of an LP EGR system on an automotive diesel engine, compared to HP EGR with respect to PM and NOx emissions and specific fuel consumption, SAE Int. J. Engines, 2(2):597–610, 2010 DOI: 10.4271/2009­24­0138 (http://dx.doi.org/10.4271/2009­24­0138)

P. M. Sforza, Theory of Aerospace Propulsion, Butterworth­Heinemann, Waltham, MA, 2012

T. A. Ward, Aerospace Propulsion Systems, John Wiley & Sons, Singapore, 2010