View source for Physics:Thrust-specific fuel consumption

{{short description|Fuel efficiency of an engine design with respect to thrust output}}
'''Thrust-specific fuel consumption''' ('''TSFC''') is the [[Physics:Fuel efficiency|fuel efficiency]] of an [[Engineering:Engine|engine]] design with respect to [[Thrust|thrust]] output. TSFC may also be thought of as fuel consumption (grams/second) per unit of thrust (newtons, or N), hence ''thrust-specific''. This figure is inversely proportional to [[Physics:Specific impulse|specific impulse]], which is the amount of thrust produced per unit fuel consumed.

TSFC or SFC for [[Engineering:Reaction engine|thrust engine]]s (e.g. [[Engineering:Turbojet|turbojet]]s, [[Engineering:Turbofan|turbofan]]s, [[Engineering:Ramjet|ramjet]]s, [[Engineering:Rocket engine|rocket]]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 exhaust speed. The fuel consumption ''per mile'' or ''per kilometre'' is a more appropriate comparison for aircraft that travel at very different speeds.{{cn|date=February 2021}} There also exists power-specific fuel consumption, which equals the thrust-specific fuel consumption divided by speed. It can have units of pounds per hour per horsepower.

==Significance of SFC==
SFC is dependent on engine design, but differences in the SFC between different engines using the same underlying technology tend to be quite small. Increasing [[Engineering:Overall pressure ratio|overall pressure ratio]] on jet engines tends to decrease SFC.

In practical applications, other factors are usually highly significant in determining the fuel efficiency of a particular engine design in that particular application. For instance, in aircraft, turbine (jet and turboprop) engines are typically much smaller and lighter than equivalently powerful piston engine designs, both properties reducing the levels of [[Physics:Drag|drag]] on the plane and reducing the amount of power needed to move the aircraft. Therefore, turbines are more efficient for aircraft propulsion than might be indicated by a simplistic look at the table below.

SFC varies with throttle setting, altitude, climate. For jet engines, air flight speed is an important factor too. 
Air flight speed counteracts the jet's exhaust speed. (In an artificial and extreme case with the aircraft flying exactly at the exhaust speed, one can easily imagine why the jet's net thrust should be near zero.)  Moreover, since work is force (''i.e''., thrust) 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 when comparing engines at different speeds.

For example, [[Engineering:Concorde|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 pounds 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 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] {{Webarchive|url=https://web.archive.org/web/20150418181832/http://www.srmuniv.ac.in/downloads/turbofan-2012.pdf |date=2015-04-18 }}", 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"
!
!align="right"|Specific impulse<br/>(by weight)
!align="right"|Specific impulse<br/>(by mass)
!align="right"|Effective<br/>exhaust velocity
!align="right"|Specific fuel consumption
|-
!SI
|=''X'' seconds
|=9.8066 ''X'' N·s/kg
|=9.8066 ''X'' m/s
|=101,972 (1/''X'') g/(kN·s) / {g/(kN·s)=s/m}
|-
!Imperial units
|=''X'' seconds
|=''X'' lbf·s/lb
|=32.16 ''X'' ft/s
|=3,600 (1/''X'') lb/(lbf·h)
|}

==Typical values of SFC for thrust engines==

{| class="wikitable sortable mw-collapsible mw-collapsed"
! colspan="10" |Civil engines<ref>{{cite web |author=Lloyd R. Jenkinson |display-authors=0 |date=30 Jul 1999 |title=Civil Jet Aircraft Design: Engine Data File |url=https://booksite.elsevier.com/9780340741528/appendices/data-b/table-3/default.htm |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}}
! data-sort-type="number" | [[Sea level|SL]] SFC !! data-sort-type="number" | cruise SFC !! data-sort-type="number" | Weight
! Layout !! data-sort-type="number" |cost ($M) !! data-sort-type="date" | Introduction
|-
| GE GE90 || {{cvt|90000|lbf|kN|disp=br}} || 8.4 || 39.3
| || {{cvt|0.545|tsfc|si tsfc|disp=br}} || {{cvt|16644|lb|kg|disp=br}}
| 1+3LP 10HP<br/>2HP 6LP || 11 || 1995
|-
| RR Trent ||	{{cvt|71100-91300|lbf|kN|disp=br}}	 ||	4.89-5.74 ||	36.84-42.7
|		 || {{cvt|0.557-0.565|tsfc|si tsfc|disp=br}} ||	{{cvt|10550-13133|lb|kg|disp=br}}
|	1LP 8IP 6HP<br/>1HP 1IP 4/5LP ||	11-11.7	 || 1995
|-
| PW4000 || {{cvt|52000-84000|lbf|kN|disp=br}} || 4.85-6.41 || 27.5-34.2 
| {{cvt|0.348-0.359|tsfc|si tsfc|disp=br}} || || {{cvt|9400-14350|lb|kg|disp=br}}
| 1+4-6LP 11HP<br/>2HP 4-7LP || 6.15-9.44 || 1986-1994
|-
| RB211 ||	{{cvt|43100-60600|lbf|kN|disp=br}} ||	4.30 ||	25.8-33
|	 ||	{{cvt|0.570-0.598|tsfc|si tsfc|disp=br}} ||	{{cvt|7264-9670|lb|kg|disp=br}}
|	1LP 6/7IP 6HP<br/>1HP 1IP 3LP ||	5.3-6.8  || 1984-1989
|-
| GE CF6 || {{cvt|52500-67500|lbf|kN|disp=br}} || 4.66-5.31 ||	27.1-32.4
| {{cvt|0.32-0.35|tsfc|si tsfc|disp=br}} || {{cvt|0.562-0.623|tsfc|si tsfc|disp=br}} || {{cvt|8496-10726|lb|kg|disp=br}}
| 1+3/4LP 14HP<br/>2HP 4/5LP || 5.9-7 || 1981-1987	
|-
| [[Engineering:Progress D-18T|D-18]]	||	{{cvt|51660|lbf|kN|disp=br}}	||	5.60	||	25.0	
|	||		{{cvt|0.570|tsfc|si tsfc|disp=br}}	||	{{cvt|9039|lb|kg|disp=br}}
|	1LP 7IP 7HP<br/>1HP 1IP 4LP	||	||		1982
|-
| PW2000 || {{cvt|38250|lbf|kN|disp=br}} || 6 || 31.8
| {{cvt|0.33|tsfc|si tsfc|disp=br}} || {{cvt|0.582|tsfc|si tsfc|disp=br}} || {{cvt|7160|lb|kg|disp=br}}
| 1+4LP 11HP<br/>2HP 5LP || 4 || 1983
|-
| PS-90	||	{{cvt|35275|lbf|kN|disp=br}}	||	4.60	||	35.5	
|	||		{{cvt|0.595|tsfc|si tsfc|disp=br}}	||	{{cvt|6503|lb|kg|disp=br}}
|	1+2LP 13HP<br/>2 HP 4LP	||	||		1992
|-
| [[Engineering:IAE V2500|IAE V2500]] || {{cvt|22000-33000|lbf|kN|disp=br}} || 4.60-5.40 || 24.9-33.40
| {{cvt|0.34-0.37|tsfc|si tsfc|disp=br}} || {{cvt|0.574-0.581|tsfc|si tsfc|disp=br}} || {{cvt|5210-5252|lb|kg|disp=br}}
| 1+4LP 10HP<br/>2HP 5LP || || 1989-1994
|-
| CFM56 || {{cvt|20600-31200|lbf|kN|disp=br}} || 4.80-6.40 || 25.70-31.50
| {{cvt|0.32-0.36|tsfc|si tsfc|disp=br}} || {{cvt|0.545-0.667|tsfc|si tsfc|disp=br}} || {{cvt|4301-5700|lb|kg|disp=br}}
| 1+3/4LP 9HP<br/>1HP 4/5LP || 3.20-4.55 || 1986-1997
|-
| [[Engineering:Soloviev D-30|D-30]]	||	{{cvt|23850|lbf|kN|disp=br}}	||	2.42	||	
|	||		{{cvt|0.700|tsfc|si tsfc|disp=br}}	||	{{cvt|5110|lb|kg|disp=br}}
|	1+3LP 11HP<br/>2HP 4LP	||	||		1982
|-
| JT8D || {{cvt|21700|lbf|kN|disp=br}} || 1.77 ||	19.2
| {{cvt|0.519|tsfc|si tsfc|disp=br}} || {{cvt|0.737|tsfc|si tsfc|disp=br}} || {{cvt|4515|lb|kg|disp=br}}
| 1+6LP 7HP<br/>1HP 3LP || 2.99 || 1986
|-
| BR700	||	{{cvt|14845-19883|lbf|kN|disp=br}}	|| 4.00-4.70	||	25.7-32.1	
|	{{cvt|0.370-0.390|tsfc|si tsfc|disp=br}}	||	{{cvt|0.620-0.640|tsfc|si tsfc|disp=br}}	||	{{cvt|3520-4545|lb|kg|disp=br}}
|	1+1/2LP 10HP<br/>2HP 2/3LP	||	||		1996
|-
| [[Engineering:Progress D-436|D-436]]	||	{{cvt|16865|lbf|kN|disp=br}}	||	4.95	||	25.2	
|	||		{{cvt|0.610|tsfc|si tsfc|disp=br}}	||	{{cvt|3197|lb|kg|disp=br}}
|	1+1L 6I 7HP<br/>1HP 1IP 3LP	||	||		1996
|-
| [[Engineering:Rolls-Royce RB.183 Tay|RR Tay]]	||	{{cvt|13850-15400|lbf|kN|disp=br}}	||	3.04-3.07	||	15.8-16.6
|	{{cvt|0.43-0.45|tsfc|si tsfc|disp=br}}	||	{{cvt|0.690|tsfc|si tsfc|disp=br}}	||	{{cvt|2951-3380|lb|kg|disp=br}}
|	1+3LP 12HP<br/>2HP 3LP	||	2.6	|| 1988-1992
|-
| [[Engineering:Rolls-Royce Spey|RR Spey]] ||	{{cvt|9900-11400|lbf|kN|disp=br}} ||	0.64-0.71 ||	15.5-18.4
|	{{cvt|0.56|tsfc|si tsfc|disp=br}} ||	{{cvt|0.800|tsfc|si tsfc|disp=br}} ||	{{cvt|2287-2483|lb|kg|disp=br}}
|	4/5LP 12HP<br/>2HP 2LP ||		 || 1968-1969
|-
| GE CF34 || {{cvt|9220|lbf|kN|disp=br}} || ||21
| {{cvt|0.35|tsfc|si tsfc|disp=br}} || || {{cvt|1670|lb|kg|disp=br}}
| 1F 14HP<br/>2HP 4LP ||  || 1996
|-
| AE3007	||	{{cvt|7150|lbf|kN|disp=br}}	||			||24.0	
|	{{cvt|0.390|tsfc|si tsfc|disp=br}}	||	||		{{cvt|1581|lb|kg|disp=br}}
|	||	||				
|-
| ALF502/LF507	||	{{cvt|6970-7000|lbf|kN|disp=br}}	||	5.60-5.70	||	12.2-13.8	
|	{{cvt|0.406-0.408|tsfc|si tsfc|disp=br}}	||	{{cvt|0.414-0.720|tsfc|si tsfc|disp=br}}	||	{{cvt|1336-1385|lb|kg|disp=br}}
| 1+2L 7+1HP<br/>2HP 2LP	|| 1.66 ||		1982-1991
|-
| CFE738	||	{{cvt|5918|lbf|kN|disp=br}}	||	5.30	||	23.0	
|	{{cvt|0.369|tsfc|si tsfc|disp=br}}	||	{{cvt|0.645|tsfc|si tsfc|disp=br}}	||	{{cvt|1325|lb|kg|disp=br}}
|	1+5LP+1CF<br/>2HP 3LP	||	||		1992
|-
| PW300	||	{{cvt|5266|lbf|kN|disp=br}}	||	4.50	||	23.0	
|	{{cvt|0.391|tsfc|si tsfc|disp=br}}	||	{{cvt|0.675|tsfc|si tsfc|disp=br}}	||	{{cvt|993|lb|kg|disp=br}}
|	1+4LP+1HP<br/>2HP 3LP	||	||	1990
|-
| JT15D	||	{{cvt|3045|lbf|kN|disp=br}}	||	3.30	||	13.1	
|	{{cvt|0.560|tsfc|si tsfc|disp=br}}	||	{{cvt|0.541|tsfc|si tsfc|disp=br}}	||	{{cvt|632|lb|kg|disp=br}}
|	1+1LP+1CF<br/>1HP 2LP	||	||		1983
|-
| [[Engineering:Williams FJ44|WI FJ44-4A]] ||	{{cvt|1900|lbf|kN|disp=br}}	||		||		
|		||	{{cvt|0.456|tsfc|si tsfc|disp=br}}	||	{{cvt|445|lb|kg|disp=br}}
|	1+1L 1C 1H<br/>1HP 2LP	||	||		1992
|-
|[[Engineering:Williams FJ33|WI FJ33-5A]]
|{{cvt|1000-1800|lbf|kN|disp=br}}
|
|
|{{cvt|0.486|tsfc|si tsfc|disp=br}}
|
|{{cvt|300|lb|kg|disp=br}}
|
|
|2016
|}

The following table gives the efficiency for several engines when running at 80% throttle, which is approximately what is used in cruising, giving a minimum SFC. The efficiency is the amount of power propelling the plane divided by the rate of energy consumption. Since the power equals thrust times speed, the efficiency is given by
:<math>\eta=V/(SFC\times h)</math>
where V is speed and h is the energy content per unit mass of fuel (the higher heating value is used here, and at higher speeds the kinetic energy of the fuel or propellant becomes substantial and must be included). 

{| class="wikitable sortable"
|+ typical subsonic cruise, 80% throttle, min SFC<ref>{{cite web |url= http://adg.stanford.edu/aa241/propulsion/sfc.html |title= Specific Fuel Consumption and Overall Efficiency |work= Aircraft Design: Synthesis and Analysis |author= Ilan Kroo |publisher= Stanford University|archive-url=https://web.archive.org/web/20161124123017/http://adg.stanford.edu/aa241/propulsion/sfc.html|archive-date=November 24, 2016}}</ref>
|-
! Turbofan !! efficiency
|-
| GE90 || 36.1%
|-
| PW4000 || 34.8%
|-
| PW2037 || 35.1% (M.87 40K)
|-
| PW2037 || 33.5% (M.80 35K)
|-
| CFM56-2 || 30.5%
|-
| TFE731-2 || 23.4%
|}

==See also==
*{{annotated link|Physics:Specific impulse}}

== Notes ==
{{notelist}}

==References==
{{reflist}}

==External links==
*[http://www.geae.com/engines/commercial/cf6/index.html GE CF6 website] {{Webarchive|url=https://web.archive.org/web/20110904041357/http://www.geae.com/engines/commercial/cf6/index.html |date=2011-09-04 }}
*[http://www.hq.nasa.gov/office/aero/events/encompat/soaeng.pdf NASA Cruise SFC vs. Year]
*[http://www.jet-engine.net/civtfspec.html SFC by Engine/Mfg] {{Webarchive|url=https://web.archive.org/web/20190627155423/http://www.jet-engine.net/civtfspec.html |date=2019-06-27 }}

{{DEFAULTSORT:Thrust Specific Fuel Consumption}}
[[Category:Engine technology]]
[[Category:Power (physics)]]

{{Sourceattribution|Thrust-specific fuel consumption}}