ESE's works engine tuner

[jamathi]

i think it was jan that once said blowdown can be improved without enlarging the window but rather by making the passage geometry better. i suppose the rsa windows were as large as they could be and and he found some way to improve more with a change in the passages. alot of people (on other sites) only look at how big they can enlarge the window with little regard to the other small details

One of the ways to improve blowdown was to raise the exhaust port bottom....
I did not find out the limit of this because I stopped working.
But I think the exhaust bottom could eventually have been as high as the transfers top.
All you really need is the blowdown....

[Jannem]

Shit. How wrong I was in my thought process about supersonic exhaust not working in a regular 2-stroke... On the contrary, It's got to be best thing since sliced bread. I'll explain when I get to my computer.

[peewee]

One of the ways to improve blowdown was to raise the exhaust port bottom....
I did not find out the limit of this because I stopped working.
But I think the exhaust bottom could eventually have been as high as the transfers top.
All you really need is the blowdown....

hi jan. maybe im mistaken but i thought the rsa aux ports had a larger sweep than the rsw which gave alittlr more power ?

[Flettner]

I though wobbly said the exhaust couldn't go supersonic.

[Jannem]

I though wobbly said the exhaust couldn't go supersonic.

And he was correct. In a regular exhaust, where the area in the pipe side of the contraction is not shaped like a supersonic nozzle, you will get shockwaves in the contraction when flow speed reaches mach 1, choking the flow to the speed of sound.

If you have the area behind the contraction shaped correctly, the flow speed will break the sound barrier and accelerate to supersonic speeds taking energy from the heat of the fluid, effectively cooling it. The flow speed at the contraction will remain at mach one, but mass flow through it will increase. This is nothing fancy and can be done with pressure ratios much lower than exhaust. The Ford patent I posted previously used that phenomenon in the intake side to atomize fuel in the carburetor.

Now, the reason why I thought SS exhaust would not work for regular 2-stroke was that I initially thought that SS flow after contraction would block the wave action in the pipe. It wont. SS port will actually both magnify wave supercharging effect and keep the pipe in tune for much longer range.

The reason for keeping the pipe in tune is direct result of being able to break the speed of sound in a partial length of the pipe after the contraction, which means the pulse makes the overall back and forth trip faster helping the pipe stay in tune. Edit: speed increasing with the pressure ratio->with power.

The magnified wave tuning comes from the phenomenon that the flow does not stay supersonic forever behind the contraction, but slows down depending on the pipe area changes and the pressure in the cylinder decaying, creating a shockwave (sonic boom when flow is returning to subsonic) in the pipe, which will then reflect back from the reverse cone and will give a remarkable shove back at the exhaust closure.

The whole fun in this is that it's all is achievable from a piece of scrap metal turned in a lathe to fit your exhaust pipe into the cylinder. Can there be any simpler and non-intrusive modification to be tested with better potential?

Area expansion rate vs. distance from contraction is where it's at to make the flow go supersonic. And the shapes and area changes don't need to be anything fancy for speeds for slightly above mach 1 either.

[Jannem]

I'm hoping that I would get critique to this from Frits. It shouldn't be in his NDA with Ryger, as it makes it's power from naturally aspirated intake side, better combustion and reduced losses, not from supersonic exhaust. This is nothing fancy but 2 dollar modification based on public information anyone can try.

[Flettner]

Ok, make one and show us.

[Flettner]

A normal twostroke goes flat as it runs out of blow down time area. So if you have an engine that will apparently bypass this requirement, how?
More exhaust time area can be had if you blocked up the transfers. The blow down phase could continue all the way to BDC, and what a lot of time area we would have there. Now pressure is low enough, open the transfers.
If the crank case is a low volume high pressure unit, transfer will shoot up.into the cylinder, inertia might be such that transfer will continue well past the normal time transfer stops right up until when the transfers shut. Normally wasted stroke as I understand transfer is usually all over by 30 degrees ABDC. We are shifting the phasing around.
How do we shut the transfers off until the pressure equalizes? One way valves (reeds) in the transfers, that's how. We are not dealing with a soft inlet pules like a standard large capacity crank case, the inlet will be much sharper (and powerful) like a fourstroke. Fourstroke don't have extra cylinder capacity to shove the extra fuel air into like a crank case but yet they over fill their cylinders somewhat by the powerful induction inertia.
A short rod will help this.
This was suggested early but for what ever reason didn't stick. With what we know now its more relevant than ever, in my opinion.

[Frits Overmars]

The whole fun in this is that it's all is achievable from a piece of scrap metal turned in a lathe to fit your exhaust pipe into the cylinder.
Can there be any simpler and non-intrusive modification to be tested with better potential?

I'm hoping that I would get critique to this from Frits... This is nothing fancy but 2 dollar modification based on public information anyone can try.

Gimme a break Janne. There's only 37 minutes between your supersonic-post and your 'hoping to get critique' and I'm still trying to get my brain into gear (long night).

Your ss-post contains some remarks that I would have phrased differently, but your 'piece of scrap metal turned in a lathe to fit your exhaust pipe into the cylinder'
is spot-on.
You may have encountered the 50cc-pipe I posted some time ago. Yes, there is that 'piece of scrap metal', locally reducing the exhaust duct cross flow area.

[jamathi]

hi jan. maybe im mistaken but i thought the rsa aux ports had a larger sweep than the rsw which gave alittlr more power ?

No, the sand cores were exactly the same!
There never were different cores for the RSA.
But the water circulation of the RSA was better..
The aux ducts remained the same for some years, 3 or 4 I think.
But the central duct was changed many times!

[Frits Overmars]

A normal twostroke goes flat as it runs out of blow down time area. So if you have an engine that will apparently bypass this requirement, how?
More exhaust time area can be had if you blocked up the transfers. The blow down phase could continue all the way to BDC, and what a lot of time area we would have there.
enough to rev a 125cc engine to 30.000 rpm
Now pressure is low enough, open the transfers. If the crank case is a low volume high pressure unit, transfer will shoot up.into the cylinder, inertia might be such that transfer will continue well past the normal time transfer stops right up until when the transfers shut. Normally wasted stroke as I understand transfer is usually all over by 30 degrees ABDC. We are shifting the phasing around.
Normal transfer reaches its maximum flow velocity some 10° to 20° after BDC. At 30° after BDC; it's slowing down, but still flowing in the desired direction.
How do we shut the transfers off until the pressure equalizes? One way valves (reeds) in the transfers, that's how. We are not dealing with a soft inlet pules like a standard large capacity crank case, the inlet will be much sharper (and powerful) like a fourstroke.
Fourstroke don't have extra cylinder capacity to shove the extra fuel air into like a crank case but yet they over fill their cylinders somewhat by the powerful induction inertia.
Fourstrokes don't have the extra horsepower of an equally-big two-stroke either; not even half of it.
A short rod will help this. This was suggested early but for what ever reason didn't stick. With what we know now its more relevant than ever, in my opinion.

Neil, the Ryger's single exhaust port that wouldn't even provide enough blowdown for 10.000 rpm, seems to have put some wonderful ideas, unhibited by any NDA,
in your mind. Would you consider changing your nickname to Luc 2.0?

[Flettner]

Ok? Luc 0,2 gives in.
I guess I would like to so much believe there is something in it, as many of us would.
It's just hard to let it go. Is there a Rygers Anonymous one might join?

[husaberg]

No, the sand cores were exactly the same!
There never were different cores for the RSA.
But the water circulation of the RSA was better..
The aux ducts remained the same for some years, 3 or 4 I think.
But the central duct was changed many times!

When did the CNC machining of the duct occur?
Also what disc valve did you you on the dyno for the RSW mule i noticed there were many variantions on shape as well as timing.
which i assume were variations for indidual tracks?
https://www.kiwibiker.co.nz/forums/a...8&d=1414826610
https://www.kiwibiker.co.nz/forums/a...4&d=1432538053
https://www.kiwibiker.co.nz/forums/a...8&d=1413017658

[Frits Overmars]

Ok? Luc 0,2 gives in. I guess I would like to so much believe there is something in it, as many of us would. It's just hard to let it go. Is there a Rygers Anomus one might join?

No need to give in or let go, Neil. I was trying to imply, without saying it aloud, that you might be on the right track I was writing between the lines .

[Jannem]

Gimme a break Janne. There's only 37 minutes between your supersonic-post and your 'hoping to get critique' and I'm still trying to get my brain into gear (long night).

I didn't mean immediately, but when you are able to...

A normal twostroke goes flat as it runs out of blow down time area. So if you have an engine that will apparently bypass this requirement, how?

What limits the mass flow capability of blowdown making the area so critical? I'd expect it to be the speed of sound. Although I enjoy thinking about these things, I don't claim expertise, so I may be wrong. I do like the idea of reeds in the transfer ports...

Ok, make one and show us.

I will. Once I get around it, I will post the results, whatever they are. That may take some time with our project though.

In the spirit of this thread however, here's what I intend to try:

Contracting the exhaust area to mach 1 at distance from the bore, where there is room for expansion after it. I'm probably already there with 0.8 exit area with single port. Likely I wont need to shrink the port further.

Starting from contraction increase the area with mild convex shape. At distance of 0,93*diameter of the contraction should be at 1,425*area of the contraction and continue with mild concave shape aiming 1,52*Ac at distance of 1,25 Dc. This area should match the diameter of the header. Errors in the high side with lengths and low side with areas should have less risk of spoiling the results afaik.

Will need to measure and calculate if I can get the contraction and header diameters to match properly while keeping the contraction small enough.

So, anyone willing to have fun in my expense before I get there is welcome to do so. It's foil hat or chocolate fish. Although I have no idea where that chocolate fish thing comes from.

I'm a bit worried though. Nothing more fun than ww public embarrasment.

Edit: Whether the nozzle should be closer to the cylinder and way smaller to actually help blowdown, I don't know... Doing that would allow bigger area ratios for higher speeds though, so it shouldn't take away from the total mass flow.