Specific Fuel Consumption

The fuel economy of an engine design in terms of thrust output is known as thrust-specific fuel consumption (TSFC). TSFC is also known as fuel consumption per unit of thrust (grams/second) (kilonewtons, or kN).

The mass of fuel required to provide net thrust for a given period (e.g. lb/(hlbf) (pounds of fuel per hour-pound of thrust) or g/(skN) for thrust engines (e.g. turbojets, turbofans, ramjets, rocket engines, etc.) is referred to as TSFC or SFC for thrust engines (e.g. turbojets, turbofans, ramjets, rocket engines, etc (grams of fuel per second-kilonewton). Because fuel mass is unaffected by temperature, it is utilised instead of volume (gallons or litres) for the fuel measurement.

At maximal efficiency, the specific fuel consumption of air-breathing jet engines is roughly proportional to exhaust speed. For aeroplanes that move at extremely different speeds, the fuel consumption per mile or per kilometre is a better comparison. There’s also power-specific fuel consumption, which is calculated by dividing thrust-specific fuel consumption by speed. It can be expressed in pound-per-hour-per-horsepower units.

Examples of Specific Fuel Consumption:

Engineers employ the TSFC factor in a variety of ways. When the TSFC of two engines is compared, the engine with the lower TSFC is the more fuel efficient. Consider the following two scenarios:

1. Assume we have two engines, A and B, both of which create the same amount of thrust. Assume that Engine A consumes half as much fuel per hour as Engine B. As a result, we can argue that Engine A consumes less fuel than Engine B. When we compare the TSFC of Engines A and B, we find that Engine A’s TSFC is half that of Engine B’s.
2. To put it another way, imagine we had two Engines, C and D, and we fed each of them the same amount of fuel per hour. Let’s pretend Engine C has twice the thrust of Engine D. Then, because Engine C produces higher thrust for the same quantity of fuel, we may argue that Engine C is more fuel efficient. When we calculate the TSFC for Engines C and D, we find that Engine C’s TSFC is half that of Engine D’s.

Significance of Specific Fuel Consumption:

SFC is influenced by engine design, however differences in SFC between engines based on the same underlying technology are often minor. On jet engines, increasing the overall pressure ratio tends to lower SFC.

Other elements are usually quite important in determining the fuel economy of a particular engine design in a certain application in practice. In aircraft, for example, turbine (jet and turboprop) engines are often significantly smaller and lighter than equivalently powerful piston engine designs, both of which reduce drag on the plane and the amount of power required to move it. As a result, turbines are more efficient for aeroplane propulsion than a cursory glance at the table below might suggest.

SFC changes depending on throttle position, altitude, and climate. Air flight speed is also a significant factor for jet engines. The jet’s exhaust speed is counteracted by air flight speed. (One can easily see why the jet’s net thrust should be near zero in an artificial and extreme example with the airplane flying exactly at the exhaust speed.) Furthermore, mechanical power is force times speed, because work is force (i.e., push) times distance. Although the nominal SFC is a helpful metric of fuel efficiency, when comparing engines at different speeds, it should be divided by speed.

Conclusion:

It is calculated by dividing the rate of fuel consumption by the amount of energy produced. It measures fuel usage in pounds per hour divided by brake horsepower in traditional figures. The fuel economy of an engine design in terms of thrust output is known as thrust-specific fuel consumption (TSFC). TSFC is also known as fuel consumption per unit of thrust. 

At maximal efficiency, the specific fuel consumption of air-breathing jet engines is roughly proportional to exhaust speed. For aero planes that move at extremely different speeds, the fuel consumption per mile or per kilometre is a better comparison. Engineers employ the TSFC factor in a variety of ways. When the TSFC of two engines is compared, the engine with the lower TSFC is the more fuel efficient. SFC is influenced by engine design, however differences in SFC between engines based on the same underlying technology are often minor.

Other elements are usually quite important in determining the fuel economy of a particular engine design in a certain application in practice. SFC changes depending on throttle position, altitude, and climate. Air flight speed is also a significant factor for jet engines.

Furthermore, mechanical power is force times speed, because work is force (i.e., push) times distance. Although the nominal SFC is a helpful metric of fuel efficiency, when comparing engines at different speeds, it should be divided by speed.