Actually the fuel consumption is calculated solely from "Engine Thrust" which is a function of both speed and engine throttle.
You can examine this by trying any of the demo aircrafts.
1. Turn on the engines and don't release the parking brakes
2. Increase the throttle and observe the engine burn rate increase with the increasing engine RPM and Thrust... Despite the aircraft being completely stationary.
Oh Lemme guess...the Throttle was reading 0%?
This does not necessarily mean the engine is off, infact it might be that the engine is at "Theoretical idle power".
The function that does all the engine calculations/ fuel consumption is only set to update if "engineOn == true". So once the engine is turned off either by the user, fuel exhaustion or some other condition, thrust is no longer generated and other conditions including fuel consumption stops.
