Thrust-specific fuel consumption: Difference between revisions

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clean explicit et al, gen fixes
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TSFC may also be thought of as fuel consumption (grams/second) per unit of thrust (kilonewtons, or kN). It is thus thrust-specific, meaning that the fuel consumption is divided by the thrust.
 
TSFC or SFC for [[reaction engine|thrust engine]]s (e.g. [[turbojet]]s, [[turbofan]]s, [[ramjet]]s, [[rocket engine]]s, etc.) is the mass of [[fuel]] needed to provide the net thrust for a given period e.g. lb/(h·lbf) (pounds of fuel per hour-pound of thrust) or g/(s·kN) (grams of fuel per second-kilonewton). Mass of fuel is used, rather than volume (gallons or litres) for the fuel measure, since it is independent of temperature.<ref>[http://selair.selkirk.bc.ca/Training/Aerodynamics/range_prop.htm Specific Fuel Consumption<!-- Bot generated title -->]</ref>
 
Specific fuel consumption of air-breathing jet engines at their maximum efficiency is more or less proportional to speed. The fuel consumption ''per mile'' or ''per kilometre'' is a more appropriate comparison for aircraft that travel at very different speeds. There also exists [[power specific fuel consumption]], which equals speed times the thrust specific fuel consumption. It can have units of pounds per hour per horsepower.
SFC varies with throttle setting,altitude and climate. For jet engines, flight speed also has a significant effect upon SFC; SFC is roughly proportional to air speed (actually exhaust velocity), but speed along the ground is also proportional to air speed. Since work done is force times distance, mechanical power is force times speed. Thus, although the nominal SFC is a useful measure of fuel efficiency, it should be divided by speed to get a way to compare engines that fly at different speeds.
 
For example, [[Concorde]] cruised at 1354&nbsp;mph, or 7.15 million feet per hour, with its engines giving an SFC of 1.195&nbsp;lb/(lbf·h) (see below); this means the engines transferred 5.98 million [[foot pound]]s per pound of fuel (17.9 MJ/kg), equivalent to an SFC of 0.50&nbsp;lb/(lbf·h) for a subsonic aircraft flying at 570&nbsp;mph, which would be better than even modern engines; the [[Rolls-Royce/Snecma_Olympus_593Snecma Olympus 593|Olympus 593]] used in the Concorde was the world's most efficient jet engine.<ref>[https://www.pbs.org/wgbh/nova/transcripts/3203_concorde.html Supersonic Dream]</ref><ref>"[http://www.srmuniv.ac.in/downloads/turbofan-2012.pdf The turbofan engine]", page 5. ''[[SRM Institute of Science and Technology]], Department of aerospace engineering''</ref> However, Concorde ultimately has a heavier airframe and, due to being supersonic, is less aerodynamically efficient, i.e., the [[lift to drag ratio]] is far lower. In general, the total fuel burn of a complete aircraft is of far more importance to the customer.
 
==Units==
 
{| class="wikitable sortable"
|+ Civil engines<ref>{{cite web |url= https://booksite.elsevier.com/9780340741528/appendices/data-b/table-3/default.htm |title= Civil Jet Aircraft Design: Engine Data File |author= Lloyd R. Jenkinson et al.|display-authors=etal |date= 30 Jul 1999 |publisher= Elsevier/Butterworth-Heinemann}}</ref>
|-
! Model !! data-sort-type="number" | SL thrust !! data-sort-type="number" | {{abbr|BPR|Bypass ratio}} !! data-sort-type="number" | {{abbr|OPR|Overall Pressure ratio}}