Brake Specific Fuel Consumption (BSFC) Calculator

Background.

Brake specific fuel consumption is fuel mass flow divided by brake power at a measured engine operating point. EPA describes BSFC as engine fuel consumption divided by engine power output, reported in grams per kilowatt-hour or pounds mass per brake-horsepower-hour. A lower value means less fuel mass was used for each unit of delivered shaft work at that point.

Enter mass flow, not gallons per hour. Converting a volume flow would require the measured fuel density for the actual fuel and temperature, so this page does not guess a gasoline or diesel density. Enter brake power measured over the same interval and condition as the flow.

For 100 lb/h at 250 bhp, BSFC is 0.4 lb/(hp·h), equivalent to about 243.29 g/kWh. The conversion uses exactly 453.59237 grams per pound and 0.74569987158227022 kW per mechanical horsepower. BSFC varies across speed, load, temperature, calibration and transient operation; one point is not an entire fuel map or vehicle MPG prediction.

What is brake specific fuel consumption calculator?

BSFC normalizes fuel mass rate by delivered brake power so engine operating points can be compared on a mass-per-work basis.

How to use this calculator.

1. 01Measure fuel mass flow and brake power over the same stable interval.
2. 02Enter pounds per hour and brake horsepower.
3. 03Compare results only across compatible fuels, procedures and operating conditions.

The formula.

The imperial ratio is direct division. Metric conversion changes pounds to grams and mechanical horsepower to kilowatts without introducing a fuel-density assumption.

A worked example.

Frequently asked questions.

References& sources.

1. [1]U.S. EPA. CleanBoost test and quality-assurance plan; defines BSFC as fuel consumption divided by engine power with units g/kWh or lb/bhp-h.