factory_p wrote: ↑
Wed Oct 07, 2020 3:49 pm
MHR650 wrote: ↑
Tue Oct 06, 2020 9:05 pm
Cool picture but I design turbochargers, the compressor on that turbo is very simple and conventional. That is not bad since it should perform very well, most of the time when the compressors look odd it is because we had to compromise for packaging reasons. The sensor in the compressor is a Hermes7 speed sensor, I can’t tell what the sensor cable with the high temp sleeve is for. The 2 outboard inlets are both for the turbine, I can’t see enough of the turbine to determine it is a dual volute or a twin scroll design.
Garrett did release a dual compressor turbo back in 2010 for the Ford 6.7L Scorpion engine, but it was a huge failure. It performed poorly compared to the nearly identical turbo used by Chevy on the 6.6L Duramax, except using a conventional compressor. Quite quickly the dual compressor was ditched for a conventional single compressor.
I believe it is a dual compressor designed on this picture and the shield you see is actually between the second compressor inlet and the turbine side (which would make sense to insulate the air intake as good as possible).
See in this picture of the assembled engine : https://images.cdn.circlesix.co/image/2 ... 4a8398.jpg
You can clearly see the compressor as shown before and further behind it the exhaust manifolds connect to an assembly containing the by-pass valve between the turbocharger's turbine and the ERS turbine. But clearly, the exhaust manifolds don't connect to any of the pipes seen in the first picture.
I believe the idea behind the use of this unusual dual compressor in the 919 was partly to reduce the diameter of the compressor in order to fit neatly under the engine cover since it sits so high on top of the engine.
Interesting, seeing that picture I change my opinion and I agree that is a dual compressor design. To be clear I was not involved in the design of the 919 turbo and haven’t really investigated the engine design. It looks like the turbine is a simple monoscroll which would make sense for a hybrid race car, although gasoline VTG is a possibility, we are seeing more and more requests for that.
It would be interesting to see if they use a single back to back compressor wheel like they did on Scorpion. It is clear that a smaller compressor will help with aerodynamics, but when you reduce the diameter of the compressor you must increase the RPM to maintain a reasonable tip speed. That is the downside of the back to back compressor wheel, the extra mass makes it hard to spin it as fast as you would like. A clue that they are concerned with turbo speed is that they are racing with a speed sensor, a lot of times you will use one for development and remove it for production. On the other hand, on a hybrid race car the turbo probably operates over a pretty narrow speed range, the thing that killed the Scorpion was lack of altitude margin. When you got up on a mountain pass in Colorado you couldn’t spin the turbo any higher and had to derate.