Measurement Methods

Direct measurement method

The flow meter is installed after the fine filter. Low pressure injection pump pushes fuel from the tank through the coarse filter to the fine filter, after which the fuel under pressure is sent through the flow meter to the high pressure injection pump. Extra fuel returns to the tank through a special inlet valve installed on the fine filter before the flow meter, thus it is not counted. All the connections on the meter and after it are protected by special seals with unique numbers.

Installation scheme:

With this installation scheme the error of measurement equals only 1%. Additional error can be created by "the return flow from nozzles", which in most cases makes up about 1% from general fuel consumption. On some engines it is possible to loop the return flow from nozzles on the inlet of the high pressure injection pump. 

Differential measurement method

In the fuel systems with fuel injectors or Common-Rail a differential flow meter can be installed, which calculates both, the direct («supply») and return («return») flows. The difference between the two flows (consumed fuel) is calculated by the board computer, for example DFM BC, or an onboard control unit of the GPS monitoring system.

Installation scheme:

With the differential installation scheme the error of measurement depends on the construction of the fuel system and the engine operation mode.