2 stroke turbo

[Clop]

Really interesting. So you think turbo made a sort of "balance" between intake pressure and turbo pressure it is what you mean?

[Bandit1216]

No. I mean before turbo the presure will be eg 0,2 and back pulse 0,25 but after turbo 0,5 and 0,55 bar. So the diff is the same.

[Clop]

OK understand. Anyway in a 4 stroke valves open at different time and the overlap time is not so much like the 2 stroke where the ports are ever open! So really I don't understand that. Under boost, the fuel mixture, is blow thorugh exhaust port there is not a closing valve in petrol 2 stroke. The only back pulse can't contain the boost. What about it?

[Bandit1216]

But there is. The piston is the closing valve.

[Clop]

Surely but open and close the ports at the same time. Is like a huge overlap! The question became more difficult if we think that is too rarely find these turbo 2 stroke setup around.

[Bandit1216]

I work for a company that sells plenty 2-stoke turbo’s. 920mm bore, 3468 mm stroke. Only 80 rpm, but plenty off torque 6,6 MNm for the 12 cilinder.

[Clop]

Naval diesel! Different designs!

[J.A.W.]

Surely but open and close the ports at the same time. Is like a huge overlap! The question became more difficult if we think that is too rarely find these turbo 2 stroke setup around.

Clop, you appear to misapprehend the basics of piston-port* 2T gas-flow timing functions.

(Try & conceptualize the idea of a hi-performance resonance-flow 2T piston acting
as the combustion-chamber/timing valve of a pulse-jet - with the reciprocation-to-rotary
power-shaft transmission through to final drive - as analog to a turbo-shaft geared gas turbine).

With a lambda-state air-fuel mixture a 2T will function in the low pressure air found
3km up a mountain, or in a sealed engine test-cell pressurised to +1 bar over sea-level**,
now guess which operating condition - will show more power on the dyno...

*With, or without added inlet/exhaust valve timing control devices.

**Equivalent to what a fair level of turbo-boost will pump.

[Clop]

Ok now it's clare. In the end to conclude this topic: a turbocharged two stroke gasoline engine (like a classical 2 stroke motorcycle engine 250cc 500cc etc. ) can work and do more hp than the same engine naturally aspirated but turbo should be mounted mandatory after the expansion chamber to maintain his function.

Do you all agree??

[Clop]

OT: Bandit1216 I've laughed because you have write 80 rpm and I had imagine this little engine compared to the huge like you say! Not for what you have write in your post don't misunderstand me!!

[Pinger]

OK understand. Anyway in a 4 stroke valves open at different time and the overlap time is not so much like the 2 stroke where the ports are ever open! So really I don't understand that. Under boost, the fuel mixture, is blow thorugh exhaust port there is not a closing valve in petrol 2 stroke. The only back pulse can't contain the boost. What about it?

The additional backpressure in the entire exhaust system created by the turbo's turbine inhibits direct charge loss.
As per J.A.W.'s explanation of low atmospheric pressure or pressurised dyno chamber the turbo recreates the latter as the engine sees elevated pressure at inlet and exhaust ports - just as if atmospheric pressure were raised.

Scavenging effects from pulse tuning are merely overlaid on that with adjustments for the different thermodynamic properties of the exhaust gas at higher density and probably temperature but only so much as they affect the speed of sound in the pipe. And yes, if exploiting that, the turbo is situated downstream from the expansion chamber.

[coaster]

Hello Clop,
The Youtube journey of the 'worlds most powerful 2 stroke' has gone in the direction of supercharging, maybe worth giving this thread a bump and follow his ideas?

[Zynerji]

What about an MGUH on a 2T turbo? Could it help the exhaust turbine in evacuation if it's "boosted" by an electric motor?

[J.A.W.]

What about an MGUH on a 2T turbo? Could it help the exhaust turbine in evacuation if it's "boosted" by an electric motor?

No. Its a needless complication.

Check out the Rotax 2T turbo arrangement shown by the drawing (in the 3rd post down, dated: 27 March,
on page 251 of the '2-stroke...' thread) in the - 'Engine, transmission & controls' - section of this forum.

It depicts the turbine feed gas take-off mounted just down from the 2-1 header manifold - while the
usual 2T expansion chamber is blind-end capped - to the effect of a short run by the exhaust gas efflux
into the turbo, with the advantageous pressure-wave reflection, also still being utilized effectively..

[coaster]

Good idea for a scavenge turbine, cancels out the expansion chamber but a computer controlling all pressures would need research, coupled with direct injection and sliding sleeve port for a variable port timing it could promise much.
This must have been what Pat Symonds was alluding to, the story of 2 stroke is not over yet.