Sequential turbos: Bypass HP turbo compressor

Ok I will read up on that cycle

I still see it being slow to spool up.

Seems like you would want to leave as much energy as possible in the output from the large compressor, to drive the small turbine harder. I.e. no interstage intercooler

Maybe a fuel/ign/control system and a combustor between the two. Running one as a turbojet to compress the air for the engine and keep it spun up when engine EGTs are low.

What if output of lp would go directly in the comp of the hp, then thourgh intercooler and then throught the hp turbine. This should make for some very cool iat. Even if the HP comp isnt really adding much PR the expansion at turbine will make air below ambient?

Yes but the small compressor wheel on the hp can fail if pushed hard. Air can be like 400+ degrees F there.

Rub87 said:

What if output of lp would go directly in the comp of the hp, then thourgh intercooler and then throught the hp turbine. This should make for some very cool iat. Even if the HP comp isnt really adding much PR the expansion at turbine will make air below ambient?

Click to expand...

Sounds an awful lot like a perpetual motion machine.

Very interesting if you can get results, but until then, I'll just pay the power company (and run a standard intercooler)

You may want to feed hOT air to the turbine.

why? turbine the expands, the cooler the air goes in, the cooler it comes out. the aim is to expand air so it cools to below ambient. the energy that is extracted is used again to compensate (partially) the pressure drop by copressing the air again a bit at the compressor stage.

sound like a nice idea for a big stationairy engine as I have no clue how this will turn out response wise

Yes it just gets down to the actual aerodynamics of the turbine I guess. Either you run the hp turbine on hot air, or the hp compressor on hot air. I think the turbine runs better than the compressor on hot air, i.e. more efficiently. But that is only a guess.

turbo compressor efficiency peaks at like 70-80%, the rest of that energy is heat. Heat being made from the (rotational) energy coming from the turbine through the shaft. I'll bet the turbine's similarly inefficient. Meaning you are better off just tossing a restrictor plate in there right before the intake manifold for the same cooling effect, at least then you've got less moving parts for the same loss in mass flow.

Actually not, imho. This remains a two stage compressor running on energy from exhaust gas. The number of turbines and compressors is the same as regular setup. Perhaps series linked turbines running on exhaust extract more total waste energy from exhaust. But the second turbine creating back pressure reduces the extraction by the first turbine. So you take a turbine out of exhaust series, and plug it into the compressor series. Energy extracted by LP turbo increases, possibly more efficient than two turbines in series. Yes, you lose the compressor efficiency from the low pressure turbo - the drive gas for the small turbine is that much less dense. But if energy recovery by the primary turbine is more efficient, it compensates a bit.

The energy used by the small turbine here would normally be dissipated by the intercooler. Nobody complains about that loss, usually! So basically you are recapturing a bunch of the adiabatic loss from the LP compressor, and using that to drive the second one, in part.

I think it would be fine, but transient response would suffer.

It would be hard to do the math, and figure out how best to limit boost.

The intake air temp could be really low though, so you might be able to run more fuel (diesel) for same egt.

There seems to be no evidence of this setup being used on any pikes peak racer that I can see. You would think it might be on youtube, if it is on here. I called out there to CO but will have to try again.