Special fuel consumption is defined as the amount of fuel in pounds per hour consumed by an engine per brake horsepower or per pound of thrust.

• A. The ratio of fuel to air mass
• B. The maximum fuel capacity
• C. The minimum fuel grade
• D. The amount of fuel in pounds per hour consumed by an engine per brake horsepower or per pound of thrust

Answer: (D)

Specific fuel consumption is a measure of how much fuel an engine uses to produce a given amount of useful output. It is defined as the pounds of fuel consumed per hour for each unit of power or thrust—per brake horsepower for piston engines or per pound of thrust for jet engines. This makes it a direct efficiency metric: the smaller the SFC, the more efficiently the engine converts fuel into useful work.

So the statement that describes fuel flow in pounds per hour per brake horsepower or per pound of thrust is the correct description, because it captures exactly how SFC expresses fuel efficiency relative to output. It’s not about the fuel-air ratio, fuel capacity, or fuel grade, which are different concepts.