2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

On the production unit, the turbine entry has always been at the end of the expansion chamber,
the drawing (which I'd posted earlier) refers to a patent, & may be for future use, or perhaps
packaging considerations took precedence, with a compartmentalized requirement for by-pass
inlet flow at low engine speeds, & a more compactly tucked-in muffler system?

[Pinger]

I suspect they found - or surmised - that the expansion chamber was half as effective with half of the initial pulse being swallowed by the turbo never to be seen again. The conservation of pulse energy prioritised over thermal energy to the turbo being more effective than the converse.

[vorticism]

Both stingers and turbines are restrictive; this would be factored into the expansion chamber design. Edit - the patent file image and the photos might be for two different engine concepts.

[Pinger]

It could though, be taken as the turbo being mounted at the manifold and the expansion chamber operating as a resonant chamber only - not a conduit of exhaust gas.
It is a viable set-up but with pros and cons over what was productionised.

[vorticism]

Good point. Any link to the patent filing? Maybe it was for a different concept than what's depicted in the photo.

[Pinger]

What's going on with that?
The bit after the expansion chamber? And the two connections to the EC?

edit PS. Googled it and it's a turbo. But why so different looking from the other photo?

editPPS Just realised it's the same engine viewed from the other side - with the weirdest turbine housing in existence.

[vorticism]

Yeah, the heat shielding has an unusual shape.

-Two exhaust ports to EC on one end
-Wastegate and turbine entry on the other
-the compressor outlet is visible in that last image; this is not part of the exhaust system though

In the previous photo you posted you can see that there's both an atmospheric and a compressor charge entry into the intake plenum. I'm not sure why. Reed valve?

[gruntguru]

One has to assume the "pipe" is an expansion chamber and wont work if you put a turbine between it and the engine.

[johnny comelately]

Hybrid at Jerez tests

[Pinger]

One has to assume the "pipe" is an expansion chamber and wont work if you put a turbine between it and the engine.

In series it wouldn't work, in parallel it would.

[Pinger]

In the previous photo you posted you can see that there's both an atmospheric and a compressor charge entry into the intake plenum. I'm not sure why. Reed valve?

Improves off-boost throttle response - more direct route for air without having to pass through the compressor. Once boost builds, that air path is closed.

More puzzling is that the system is without an intercooler. I guess the reason why is the difficulty with preventing radiators/heat exchangers clogging with snow and a purely liquid system would add too much weight. I suppose the low ambient temps (and relatively low boost) it will operate in help but still strange to see a turbo set-up without intercooling to regain air density.

[Tommy Cookers]

One has to assume the "pipe" is an expansion chamber and wont work if you put a turbine between it and the engine.

In series it wouldn't work, in parallel it would.

what I think that I think is that I think that .....
it would (ie could) work in series
tuned length effects of expansion chamber are boosted ie proportionate to mean exhaust pressure ahead of turbine ?

unless ex chamber tailpipe is sized so mean exhaust pressure in chamber is above ambient even when ambient is 1 atm ?
(never found conformation or denial of that one)

[Pinger]

what I think that I think is that I think that .....
it would (ie could) work in series
tuned length effects of expansion chamber are boosted ie proportionate to mean exhaust pressure ahead of turbine ?

To work in series the pulses would have to be able to travel through the turbine housing in both directions - which may or may not be possible.
The first positive pulse would have to pass through cleanly but as the turbine housing likely presents a change in cross-sectional area, the pulse will react to that and reflect back towards the cylinder - polarity unknown.

Despite my asking, no one has ever been able to answer the question of pulse behaviour entering a turbo - not even turbo specialists.

[Tommy Cookers]

if the expansion chamber freely exhausted into a large enclosed mass of exhaust gas upstream of the turbine entry ? ....
ie wouldn't it be isolated from whatever behaviour might be caused by subsequent entry to the turbine casing ?

ok maybe that's not what is being done with this engine shown

[Pinger]

Pretty much it is, yes. Except more likely the velocity through the tail of the expansion chamber is kept high to maximise the pulse energy remaining in the exhaust stream. That pulse energy if greater than with 4Ts may be why Rotax developed its own turbo.

My comments were in relation to the turbo and EC being in series and the turbo upstream of the EC. With the turbo downstream of the EC (as Rotax have configured it) however, what the pulse 'sees' when it enters the turbo doesn't matter. As a divergent volume it would be as exiting an EC to atmosphere and as a convergent volume it would be replicating the stinger. I suspect the pulse 'sees' the turbo differently depending on prevailing back pressure - but pure conjecture on my part.