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Shiv,
Can you go into a bit more detail about how the amount of fuel fed to the HPFP is controlled?
The HPFP is an engine driven positive displacement pump, unlike the LPFP which is centrifugal and variable speed. Fuel is incompressible so the HPFP should be pumping an amount that is proportional to rpm (since it's engine driven) all the time. I don't really understand how a valve can affect the amount of fuel "gulped" by the HPFP.
Even if it reduces the pressure of the fuel, pressure has a negligible effect of fuel density so the HPFP would gulp the same amount that would only really change with engine speed.
Is the displacement of the HPFP pistons variable somehow? What am I missing?
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2009 Spacegrau 335i |