2 stroke turbo

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Clop
Clop
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Joined: Sun Oct 04, 2020 8:51 pm

2 stroke turbo

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Hi everyone, online I ve seen some images about 2 stroke carbureted turbo (motorcycle derivation engine). Now.. In the past in this forum some members spoke about turbocharging 2 stroke but not in sufficient detail. The intake and the exhaust are open at the same time and there are no valves like a 4 stroke. But if you search online you can find carbureted 2stroke turbo sled or the Am6 turbo. The question is: Is really possible turbocharge a 2 stroke carburated(NOT EFI)petrol engine and make more horsepower with these engine's config. ?? If yes how it can work??
Link I've attached are about the Am6 turbo and a piston port set up on a sled 2 stroke.

Hope to see interesting answers ad learn something about.

TURBO 50CC 2 STROKE
https://www.google.com/search?q=Am6+tur ... 86u6sm92pM

TURBO SLED 2 STROKE
https://www.hardcoresledder.com/attachm ... g.1441226/

Jolle
Jolle
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Re: 2 stroke turbo

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You really need direct injection to make any kind of these modern 2 stroke concepts work with any kind of efficiency. Else you would just flush out to much unburned fuel.

Clop
Clop
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Re: 2 stroke turbo

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Look this.. Carbureted 2 stroke turbocharger 50cc


How it can do this power maybe a fake video?

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Big Tea
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Re: 2 stroke turbo

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Clop wrote:
Sun Oct 04, 2020 9:58 pm
Look this.. Carbureted 2 stroke turbocharger 50cc


How it can do this power maybe a fake video?
Judging by the shots in the vid it is burning a lot of oil (or fuel) to be producing that smoke.
We are standing on the shoulders of Giants. So watch your feet.

uniflow
uniflow
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Re: 2 stroke turbo

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Jolle wrote:
Sun Oct 04, 2020 9:45 pm
You really need direct injection to make any kind of these modern 2 stroke concepts work with any kind of efficiency. Else you would just flush out to much unburned fuel.
No, not necessary.
Opposed Piston twostroke, petrol, in one end of the cylinder, out the other, total control. Id say you could probably have as clean an exhaust or better using carburetors on an OP crankcase scavenge than a loop scavenge DI twostroke.

J.A.W.
J.A.W.
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Re: 2 stroke turbo

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Rodak wrote:
Thu Oct 08, 2020 1:43 am
Pretty funny coaster.....
Then he'll maybe need a turbo to maintain power at altitude,
just as Skidoo currently offer for their Rotax 850 2T snowmobile:

We are standing on the shoulders of Giants. So wash your feet.

Clop
Clop
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Re: 2 stroke turbo

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Please remain on topic! In the start thread I speak about 2 stroke gasoline CARBURETED turbo. And the mainly question is...

How can it work if the exhaust and the fuel port are open at the same time??

No valve, no injectors nobody, just the carb and the turbo. Anyone can explain that?

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coaster
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Joined: Sat Jun 30, 2012 4:10 am

Re: 2 stroke turbo

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It works like a 2 stroke diesel V8?
Compressor wheel replaces crankcase pressurisation with inlet ports at the bottom of stroke.
Question is the starting procedure, an auxillary electric motor on the compressor?

Edit; a dual system, crankcase gas startup and a port switching mechanism after warmup?

J.A.W.
J.A.W.
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Re: 2 stroke turbo

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Clop wrote:
Thu Oct 08, 2020 8:11 am
Please remain on topic! In the start thread I speak about 2 stroke gasoline CARBURETED turbo. And the mainly question is...

How can it work if the exhaust and the fuel port are open at the same time??

No valve, no injectors nobody, just the carb and the turbo. Anyone can explain that?
Did you miss the explanation about ambient pressure sensing (natural, or via boost)?

So actually, it is irrelevant to the issue of turbo-boost how the fuel is fed, whether injected
or not (in fact the Rotax/Skidoo uses a carb-equivalent aux-injection system for WOT use),
& about the only factor to consider (apart from 'suck-through', or 'blow-through' carbs) would
be the method of preventing excess fuel-mixture loss - by very accurate exhaust valve timing,
&/or resonant flows, (or otherwise by design, as Uniflow has already noted previously in this thread).
We are standing on the shoulders of Giants. So wash your feet.

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coaster
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Re: 2 stroke turbo

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Forgiveable, after all the BS in the last 2 stroke thread.

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Bandit1216
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Re: 2 stroke turbo

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I don't really understand what would change with port overlap /timing with a turbo. I think the biggest challenge is to get the exhaust energy work both the resonance pipe AND the turbo. The way I always understood, exhaust pulses have basically 2 waves of energy. First is more or less the pressure left over from the bang, the rest is the piston blowing stuff out. And I think the first has the most energy by far. That is basically why one can make 2 bar turbo pressure while the pressure in exhaust is only 0,5 bar or so. The energy the turbine consumes is for a great deal kinetic, right?

So I think it will be a trade off. Both the resonance pipe AND the turbo need energy to do their thing. And for the carb. Either before the turbo having mixture though the carb, or after the turbo but then your fuel float bowl will have to cope with the turbo pressure, and the fuel pressure needs to be turbo pressure + 0,2, and you need a big ass jet in the carb. And you will probably blow all seals in the carb. It will be very hard to get it right and get more power compared to an well tuned pipe. The turbo might mess up the pipe more then it can bring to the table. A well tuned pipe could be considered as an kinetic energy re-use charger devise.

I think this is basically why Rotax did what they did. And 4 pound of boost is near to nothing. Just enough to compensate for the elevation. Their turbo will not consume much energy relative.

I know the R5 turbo had blow though carbs, while the R5 alpine turbo had a suck though before the turbo. My knowledge is from that era, so don't kill me if I'm wrong.

Always loved this gif, that tells what a well tuned pipe does better than 100 words can:

Image

J.A.W.
J.A.W.
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Re: 2 stroke turbo

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Bandit1216 wrote:
Fri Oct 09, 2020 7:38 am
I don't really understand what would change with port overlap /timing with a turbo. I think the biggest challenge is to get the exhaust energy work both the resonance pipe AND the turbo. The way I always understood, exhaust pulses have basically 2 waves of energy. First is more or less the pressure left over from the bang, the rest is the piston blowing stuff out. And I think the first has the most energy by far. That is basically why one can make 2 bar turbo pressure while the pressure in exhaust is only 0,5 bar or so. The energy the turbine consumes is for a great deal kinetic, right?

So I think it will be a trade off. Both the resonance pipe AND the turbo need energy to do their thing. And for the carb. Either before the turbo having mixture though the carb, or after the turbo but then your fuel float bowl will have to cope with the turbo pressure, and the fuel pressure needs to be turbo pressure + 0,2, and you need a big ass jet in the carb. And you will probably blow all seals in the carb. It will be very hard to get it right and get more power compared to an well tuned pipe. The turbo might mess up the pipe more then it can bring to the table. A well tuned pipe could be considered as an kinetic energy re-use charger devise.

I think this is basically why Rotax did what they did. And 4 pound of boost is near to nothing. Just enough to compensate for the elevation. Their turbo will not consume much energy relative.

I know the R5 turbo had blow though carbs, while the R5 alpine turbo had a suck though before the turbo. My knowledge is from that era, so don't kill me if I'm wrong.

Always loved this gif, that tells what a well tuned pipe does better than 100 words can:

https://www.mopedarmy.com/w/images/5/52 ... eitakt.gif
Good post Bandit 1216, but not quite there..

Consider the gif, that process will still function, ~ regardless of pressure input*
- given that such propagation of sonic/harmonic waves are distinct from terminal
exhaust outflow - which is why the turbo is downstream of an expansion chamber..

* Of course other parameters may rudely intrude, such as mechanical strength,
& heat-rejection - esp' on usually already fairly highly tuned 2T engines - albeit heat issues are
perhaps in general more easily dealt with in snow/watercraft, than for typical ground air temps...
We are standing on the shoulders of Giants. So wash your feet.

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Bandit1216
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Re: 2 stroke turbo

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Oké, good point. Not to mention the smallest turbo from perhaps an 800 cc TDI smart engine, is still quite big for a 50cc 2-stroke. It will only work when there's enough power potential but than all above comes into play.

Clop
Clop
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Joined: Sun Oct 04, 2020 8:51 pm

Re: 2 stroke turbo

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Interesting posts...thanks!!

But anyway in these config port timing is stock.
So the exhaust port is open and close at the same time of the fuel port.

So the mainly question is: how can, under boost, the fresh fuel mixture not be pushed out to the exhaust port directly into the pipe.? A tuned pipe, a perfectly tuned pipe, can't put back into the cylinder the boosted charge! (too much pressure to put back)

Where is the trick?

I really don't understand how can it work. Look also the second picture I've link in the started thread.

Hope someone can understand how it can work and help me to know it!

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Bandit1216
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Re: 2 stroke turbo

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I think it doesn't matter. Yes, the pressure will be bigger in the whole system after the turbo, but relative pressure pulse in the pipe will still be the same. The same is true for normal 4 stroke. The back pressure from a turbo will cause extra pumping loss. So will the extra air though the same inlet. But the turbo will make up for that plenty.

But you will probably have to re-tune the pipe to the new situation. You can't increase the outlet much either. That's why I think it will be hard to get right. Expect a cherry red pipe.