MoTeC M1 Software Tutorial: VE-Based Fuel Model
VE-Based Fuel Model
A VE based fuel model, unlike a millisecond based fuel model actually defines the engine’s volumetric efficiency, or how effectively it is able to fill its cylinders with air at each combination of RPM and load.
Using this type of fuel model, the ECU is calculating the actual mass of air entering the engine and this gives the ECU a lot more control over the fuel delivery as we will see.
With a VE-based fuel model, the ECU starts by looking at manifold pressure, ambient pressure and engine speed to define where in the efficiency table the engine is operating.
Once it knows the engine efficiency, the ECU then takes looks at the engine displacement and number of cylinders to calculate the mass of air entering the engine.
The next step is to look at the mixture aim table for the desired air fuel ratio.
Now using the stoichiometric AFR and density of the particular fuel, the ECU can calculate the required fuel volume to achieve the desired air fuel ratio.
Lastly the ECU will look at the injector linearisation tables to decide on the final injector pulsewidth.
With a VE based fuel model, we are tuning the efficiency table rather than the fuel table.
This efficiency table will have a similar shape to the fuel table in a conventional millisecond based fuel model, but with numbers slightly higher than 100 around the area of peak torque.
The shape of the efficiency table however will be unaffected by fuel pressure or desired air fuel ratio.
With a VE based fuel model, changing the injectors or fuel pressure requires these new parameters to be entered correctly, but once this is done, the tune will not be effected.