Thrust specific fuel consumption (TSFC) or sometimes simply specific fuel consumption, SFC, is an engineering term that is used to describe the fuel efficiency of an engine design with respect to thrust output. It allows the efficiency of different sized engines to be directly compared.
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 thrust engines (e.g. turbojets, turbofans, ramjets, rocket engines, 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.
Specific fuel consumption of air-breathing jet engines at their maximum efficiency vary more or less inversely with speed, which in turn means that the fuel consumption per mile or km can be a more appropriate comparison metric for aircraft that travel at very different speeds.
This figure is inversely proportional to specific impulse.
Read more about Thrust Specific Fuel Consumption: Significance of SFC, Units, Typical Values of SFC For Thrust Engines
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