What is specific fuel consumption (SFC)?

• A. SFC is the fuel weight in pounds per hour per horsepower.
• B. SFC is the fuel weight per hour per engine.
• C. SFC is the air-fuel mixture ratio.
• D. SFC is the fuel weight per minute per horsepower.

Answer: (A)

Specific fuel consumption measures how much fuel an engine uses to produce a given amount of power over time. It normalizes fuel flow to the engine’s output, so you can compare efficiency across different engines. The standard unit is pounds of fuel per hour per horsepower (lb/hr per hp). This tells you how many pounds of fuel are needed for one horsepower sustained for one hour. A lower SFC means greater efficiency, since the engine can produce the same power with less fuel.

For example, if an engine develops 600 hp and consumes 180 lb of fuel each hour, the SFC is 180 divided by 600, which equals 0.30 lb/(hp·hr). This concept is about fuel flow relative to power output, not the total fuel flow of the engine, not the air–fuel mixture ratio, and not a per-minute rate.