Charge pressure limit

[henry]

Mercedes admit to a maximum drain of 200kW, with the MGU-K taking 120 that would leave 80 for the MGU-H which would probably not be enough to drive the compressor at the sort of boost levels being run.

Perhaps, although, why would they publish accurate data at this time regarding this system?

With turbines open the turbine still delivers power from blow down energy, bringing the compressor power up to the 100 plus kW needed.

I have another pet untested hypothesis that says a MGU-driven-compressor-speed turbine will create too much backpressure to permit exhaust flow through it during WGO.

The Mercedes 200kW figure is unlikely to be “accurate”, but they have a habit of publicising close ballpark figures. In the same source video they show ES efficiency at 95% which works quite nicely with calculations of ES consumption over a race distance.

If your hypothesis is correct and there is sufficient back pressure to prevent flow across the turbine the MGU-H and ES peak power would rise by 10 to 20%. And the e-boost duration would reduce similarly.

[63l8qrrfy6]

I think I've posted this before.
From my calculations assuming 80% compressor adiabatic efficiency, T1=300K, P3/P1 = 4 you'd need 94 kW to drive the compressor for 0.5 kg/s air massflow (1.22 lambda) and 113 kW for 0.6 kg/s air massflow (1.47 lambda).

It does not seem unreasonable that 80kW from the H plus whatever can be harvested from blow-down can just about add up to the 100 odd kW required.

Transiently, the power requirement could be significantly higher depending on the turbo inertia.

[gruntguru]

Don't forget that massflow is also a function of boost. Back of the napkin calculation gives a massflow of 0.85 kg/s (at 11,000 rpm, D.R. = 4.0 (intercooling to ambient), VE = 1.2.).

That brings compressor power up to 159 kW and lambda to 2.1.

Sure - intercooling won't be to ambient but it's in the ballpark.

VE (including trapped mass and scavenge) will be higher in electric supercharger (ES) mode.

@ roon. Turbine backpressure will be high - similar to MAP although not as high in ES mode due to reduced massflow. Blowdown pulses will probably still be high enough to impact the turbine if the plumbing is clever enough.