27.04 How is fuel consumption measured?

Fuel consumption measurement for diesel engines ins complicated by the fact that the engine consumes only about 1 / 3 of the fuel flow. There are 2 common methods of determining consumption: (a) measure the fuel flow into a day tank or reservoir tank and compensate for start volume, end volume, and temperature, (b) use 2 meters one on the engine fuel supply plus one on the engine fuel return, compensate for temperature and net the difference.

The second method of measuring inflows and outflows can be subject to inaccuracy because a very small measurement error is multiplied by many times with repeated flow. Highly accurate mass flow meters are preferred for this method.