ESE's works engine tuner

[Pursang]

Here is a nice overview article from 1994.
https://www.thefreelibrary.com/Engin...ns.-a015497837

NASA still has patents over most of this stuff, from around 20 years ago
Perhaps when they lapse, there might be some more progress.

cheers, Daryl

[wobbly]

Now that might be achievable - 30,000 rpm 70Hp coffee machine .
Be a go on Kickstarter for sure.

[yatasaki]

Would be nice to see colour of deto-combustion

[F5 Dave]

Somewhere in the Emerald isles Paddy is working on a Whiskey augmented version.
72.5hp at a reduced 28790 rpm.

[Michael Moore]

Is there a performance reason why 2T exhaust port manifolds generally are placed at an angle to the cylinder axis instead of perpendicular to it? On 4T generally the closer the alignment of the port to the valve stem the better.

I can see the angled manifolds making it easier to get the pipes attached and out of the way/pointed the direction they need to go, and maybe it creates more room above the manifold to fit an exhaust power valve. But if those issues are ignored is there any reason for the angle -- better flow in/out of the port for either escaping exhaust or for reflected waves in the exhaust pushing unburnt mixture back into the cylinder, etc?

I'm not asking about the transition from the port shape to the round exhaust pipe manifold shape, just the angle.

thanks,
Michael

[wax]

Im sorry to bring this up again and yes i have searched for the answer on here and while i can find some information I cant find enough to satisfy me or to make me understand.
Its re the exhaust port actually not going all the way to bdc.
I understand that the exhaust port has done all its or most of its work by the time the transfers open and so its not really doing much. But whats the advantage of not having it go all the way to the bottom. The only thing i am thinking is by keeping it smaller it keeps the velocity up ?

[husaberg]

Is there a performance reason why 2T exhaust port manifolds generally are placed at an angle to the cylinder axis instead of perpendicular to it? On 4T generally the closer the alignment of the port to the valve stem the better.

I can see the angled manifolds making it easier to get the pipes attached and out of the way/pointed the direction they need to go, and maybe it creates more room above the manifold to fit an exhaust power valve. But if those issues are ignored is there any reason for the angle -- better flow in/out of the port for either escaping exhaust or for reflected waves in the exhaust pushing unburnt mixture back into the cylinder, etc?

I'm not asking about the transition from the port shape to the round exhaust pipe manifold shape, just the angle.

thanks,
Michael

Frits and Jan will give a better explanation but as i understand it 25 Degrees downwards exit works best.

The exhaust port isn't canted downward 30°. The flange mounting face is canted downward 30° but the roof of the exhaust duct exits the cylinder at 25°.
The reason is that this angle gives the best flow.

Frits can give a detailed explanation but i suspect it simply due to the fact thats what direction it expanding out to anyway and to make it 90 Degess to the bore would make it change direction

[Michael Moore]

Thanks, I was thinking the downward angle might help control things with the exhaust first starting to exit at the top of the port/roof of the duct, so that makes some sense to me. I hoped that everyone was doing it that way for a reason, not just for "because".

cheers,
Michael

[katinas]

Im sorry to bring this up again and yes i have searched for the answer on here and while i can find some information I cant find enough to satisfy me or to make me understand.
Its re the exhaust port actually not going all the way to bdc.
I understand that the exhaust port has done all its or most of its work by the time the transfers open and so its not really doing much. But whats the advantage of not having it go all the way to the bottom. The only thing i am thinking is by keeping it smaller it keeps the velocity up ?

Maybe, would be very nice that bottom part of exhaust port moving down together with the piston top edge, so exhaust gases flow without step and without sudden pressure and energy drop behind the piston in the first phase of exhaust opening at the beginning of ex port.
But as this is impossible, so little higher exhaust window bottom and port bottom first part, maybe can help reduce, too much pressure drop and at the same time restricts some fresh gas from flow to exhaust port. But as two stroke is holistic process, the balance most important. (Add photo of Honda engine exhaust port bottom part shape typical for they racers).

Some time ago, cant remember correctly, about 1987 1990, two Institutes, one in Tallinn Estonia, worked on mathematical model for two stroke engine process and they ended with integral model that mismatched to real world about 5%, except very hardly calculated, at that time, process in the whole exhaust system, at the phase, when exhaust window is closed.
Estonians was always very keen about road racing, riders was always very fast, as they tuned engines.
https://www.youtube.com/watch?v=7HTNxEAJDO8&t=19s

[Michael Moore]

Here's a link to that HOnda patent document

https://patentimages.storage.googlea.../US6129059.pdf

[F5 Dave]

Now That is a Fabulous photo katinas

[TZ350]

Im sorry to bring this up again and yes i have searched for the answer on here and while i can find some information I cant find enough to satisfy me or to make me understand. Its re the exhaust port actually not going all the way to bdc. I understand that the exhaust port has done all its or most of its work by the time the transfers open and so its not really doing much. But whats the advantage of not having it go all the way to the bottom. The only thing i am thinking is by keeping it smaller it keeps the velocity up ?

Yes. That is my understanding too, that keeping the velocity up and reduced short circuiting is the benefit. Radiusing the leading edge also showed a benefit.

[Haufen]

Im sorry to bring this up again and yes i have searched for the answer on here and while i can find some information I cant find enough to satisfy me or to make me understand.
Its re the exhaust port actually not going all the way to bdc.
I understand that the exhaust port has done all its or most of its work by the time the transfers open and so its not really doing much. But whats the advantage of not having it go all the way to the bottom. The only thing i am thinking is by keeping it smaller it keeps the velocity up ?

Think of it like this:

Not having the exhaust port go to BDC belongs to the category of not having the port be the maximum area possible all the way from exhaust port opens to BDC. Let me try an explanation chain:

Why don't you have an exhaust port of the maximum width (area) all the way to BDC? Easy, because at some point the exhaust port will be too big and power will suffer.
Additionally, blowdown area before the transfers open is most important. So when most of the exhaust flow has already happened by the blowdown, where would you put the rest of the exhaust port area?
How would you shape the port? Well, you'd shape it so that it would be most useful, wouldn't you. And how would it be most useful?
By preventing short circuiting in the best possible way.

So if you know the behaviour of the scavenging column and the area where it reaches the exhaust side of the cylinder wall, you can adjust your exhaust port shape accordingly. On the engine I developed I had access to huge CFD capacities simulating the scavenging behaviour under various conditions. When the exhaust port shape had been adjusted accordingly, the engine had more power and less emissions. Unfortunately, most of us don't have CFD simulations of their engines, I know. As a first start, for modern transfer ports like in karts or GP road racing, I'd start with a V-shape of the exhaust, extending to BDC, but very narrow in that area and only increase width there when the area above has been maxed out.

[wobbly]

" understand that the exhaust port has done all its or most of its work by the time the transfers open and so its not really doing much. But whats the advantage of not having it go all the way to the bottom "

You are only thinking about this in a narrow field of view.
First is Blowdown , that we all know is very critical.
Angling the duct downward helps to reduce the eddies/ turbulence created by the flow exiting the just opened piston/port area , and the reduced area ( x Cosine of the down angle ) keeps the velocity profile higher.
This then increases the diffuser efficiency.

But then at BDC the pipe does most of its " work " ,this is when the depression created by the exiting wave does the job of pulling residual Ex gases out of the cylinder .
And a by product of this is that when the cylinder is over scavenged, we get clean air/fuel sitting in the duct - that then subsequently gets pushed back past the closing piston /port area.
Lifting the floor above BDC and filling in the bottom corner rads , not only reduces the duct area , but also help reduce short circuiting from the A port directly.

Thus we have two vital elements at odds with each other - overscavenging to get clean mixture in the duct Vs short circuiting ruining the scavenging pattern ( Frits leaning tower ) within the cylinder.
Getting the two optimized is still where " black art " is present in this time of computerized everything.

[wax]

Ok right got you i think. Cheers wobbly.
I have read the leaning tower of transfer enough times i can nearly recite it. Awesome piece of work.

So I get the exhaust coming heading down the duct towards the diffuser and over scavenging. Having the exhaust port floor higher than bdc then would in effect create a wall to stop the A ports heading straight out the exhaust. That makes sense. These things get more and more and more complicated the more i learn.
I need to put this engine im doing into enginemod and see what it comes back with for me

Thanks