I have been extending my simulation software to add the effect of having a restricter in the inlet as specified by the rules for the WRC engine. I have no way of verifying the results (the power predicted seems right) as I have no access to presure data from a WRC engine. Below is the simulation results. I wonder if some of you might know if this is realistic or whether I am missing the boat. The simulation at each rpm point is steady state so this is not a transient analysis.

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As the rpm value increases the mass flow increases until the restricter comes into play - the compressor inlet is 43mm and the restricter is 33mm. Boost in the plenum is limited to 2.5bar absolute and the sim was done at 1bar atmospheric. From around 6000rpm the flow becomes restricted and even though the compressor delivers at a higher delta P the mass flow increases slowly and the power drops off. This is as reported for the WRC engine but more info would help.

Vannik

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In a perfect Air Control System, you would restrict the air to the turbo with a Camera Shutter type control system on the inlet side of the turbo compressor.
The compressor would never go into surge due to the normal throttle blade slamming shut and there would be no need for a CBV Compressor By-pass (or Blow-off) type valve. But that system is not well defined at the currect time so we deal with a electronically controlled Throttle Body or a basic mechanical throttle system AFTER the compressor.

Tom Vaught

 

Thanks Tom,
The rules in WRC are quite tight - the inlet restricter is 33mm fixed and must be 50mm before the compressor impellor leading edge so no much space for good pressure recovery either.
At low rpm the compressor does go into deep surge if held steady. There is supposed to be electronicly controlled counter measures but all confidential - the top rally teams have 3 or more experts just looking after the turbo side of things!
Do you know if my simulation results from 6250rpm and above is realistic?
Vannik

 

Tom, is that shutter style valve available or is that what you were referring to when you said the system wasn't well defined?

 

The camera Shutter system was a concept idea from a Supercharger Company president/owner. In theory it made sense. In manufacturing feasibility it was way too complicated vs a cheap throttle body blade.

Hope this helps.

Tom Vaught

 

Thanks!