[SwedishBus]

The fuel flow is calculated from the (injector flow-rate x engine speed x strokes per rev)

For an electronic diesel engine, this is trivial. Injected fuel mass has been used as a basis figure since the early 1990's, all of the early combustion parameter mapping was done with the flow in (mg/stroke) as the "fuel axis" for all the 2D and 3D maps.

For a 5cyl Volvo engine, there are 2.5 strokes/rev.

So the fuel flow at 2000rpm on an engine injecting at 15mg/stroke is;

15 x 2000 x 2.5 = 75,000 mg/min

Divide that through by 1E6 to convert from mg to kg, and then multiply by 60 to go from minutes to hours, and you get;

75,000 x 60 / 1000000 = 4.5 kg/hr of fuel flow

The density of EN590 diesel is around 0.86 kg/litre, so if you divide that figure above by the density factor, you arrive at something like 5.25litres/hr.

The engine controller has this calculation done from second to second, and can pass this to the instrument pack in that form. All the instrument cluster has to do is to divide that figure by the vehicle speed in kph and then multiply the result by 100, and you arrive at a figure on the display of litres / 100km, which is the standardised way of representing fuel consumption in Europe. The iPack has a built-in conversion factor to go from litres/100km to mpg in one easy step, so depending on the display settings of the pack, the driver can see either format.