[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)

Dear Frits,

Thank you very much for the very detailed answer. It's very kind of you to take the time to satisfy the board members' thirst for knowledge, despite your project being a time-consuming task.

However, until now I had the extremely naive hope of being able to lure you to Cologne with something other than what was probably a rather bad cup of coffee, or perhaps with some skill.
But as I'm slowly realizing, you are in the very best hands in absolutely all areas.
It's a pity - but fantastic for you  [Vous devez être inscrit et connecté pour voir cette image]

You seem to be one of the few extremely privileged people who can say that you are following a path in life that allows you to discover the world of your passions like we once did as curious children and ultimately make a living with a lot of fun and satisfaction can earn.
An absolute dream...

OK - but allow me one last try...... [Vous devez être inscrit et connecté pour voir cette image]
If you and your two-stroke friend ever need a material analysis or a metallurgical investigation... Maybe I can help out a little.
It would make me very proud and filled with great joy to perhaps contribute a small piece of the puzzle to your project.

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Hartelijke groeten,

Oliver

Oliver Oettel a écrit:

If you and your two-stroke friend ever need a material analysis or a metallurgical investigation... Maybe I can help out a little.
It would make me very proud and filled with great joy to perhaps contribute a small piece of the puzzle to your project.
[Vous devez être inscrit et connecté pour voir ce lien]
Hartelijke groeten,
Oliver

Vielen Dank Oliver. I will certainly keep your offer in mind.

Dear Frits,

Understandably, more and more questions arise.

1. “Piston Plug”

By overlaying the piston pin with the side exhaust channel and port A
apparently there is not only a loss of scavenging but also a short-term loss of pre-compression and the mixture flowing into the outlet channel before it and the actual scavenging channels open.
Has the impact (power) of these effects of the overlay been measurable?

With regard to the partial flow through the piston pin although not for the performance, does it perhaps even have a positive effect on the temperature of the piston pin?


2. Radius of the piston dome

I saw the radius of the piston dome at R190mm somewhere in your RSA data, unfortunately I can't find it anymore...
I think it was due to the dynamic behavior of the connecting rod on the squish area...

In my measurements of the ASSO RSW pistons at the time, I determined a radius around ~160mm.
Why have you become flatter with this contour? Was the smaller radius less favorable for the turbulence towards the center of the combustion chamber?


3. FOS “diode”

It seems to be a combination of the Tesla valve. I've been lurking around this ingenious principle for a long time and thinking about where I could use it in my areas.
Where do you plan to use it in terms of the engine?

To be continued...

Oliver

Oliver Oettel a écrit:

1. “Piston Plug” By overlaying the piston pin with the side exhaust channel and port A apparently there is not only a loss of scavenging but also a short-term loss of pre-compression and the mixture flowing into the outlet channel before it and the actual scavenging channels open. Has the impact (power) of these effects of the overlay been measurable?

There may or may not be a loss of precompression; it depends on the pressure differentials between the auxiliary exhaust ducts and the A-transfers during the two overlap phases per crankshaft revolution. The drawing below shows the point of maximum overlap in an RSW engine. As you can see, it can be influenced by the position of the piston pin: close to the piston dome, or lower in the piston.
Jan Thiel has measured the effects of plugging the piston pin bores; if I remember correctly they were in the order of 1 HP.
That may not sound like much, until you realize that a gain of 1 HP on average equals a full year of development.
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Citation :

With regard to the partial flow through the piston pin although not for the performance, does it perhaps even have a positive effect on the temperature of the piston pin?

Why should there be any flow through the piston pin at all? There is never any pressure difference between the right and left sides of the pin.

Citation :

2. Radius of the piston dome: I saw the radius of the piston dome at R190mm somewhere in your RSA data... In my measurements of the ASSO RSW pistons at the time, I determined a radius around ~160mm. Why have you become flatter with this contour? Was the smaller radius less favorable for the turbulence towards the center of the combustion chamber?

I do not recall any differences in piston dome radius. As our former prime minister used to say:" I have no active memory of this"

Citation :

3. FOS “diode”: It seems to be a combination of the Tesla valve. I've been lurking around this ingenious principle for a long time and thinking about where I could use it in my areas.Where do you plan to use it in terms of the engine?

Yes, it is a Tesla valve, or a stack of valve elements, to be precise.
I designed so it can be produced on a conventional lathe, and the diode elements can be stacked in series, just like electronic diodes.
The obvious place to use them would be in the inlet tract, but some of the flow influencing principles, for example the sharp edges and turns, might also be applied in transfer ducts.
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Oliver Oettel a écrit:

To be continued...

O, please, gimme a break Oliver.
Your questions are to the point and they may also be of interest to other forum members, so I don't mind putting in the time.
But I haven't got the time

Oh, I definitely didn't realize that I was overusing something....... big SORRY for that  

Citation :

Why should there be any flow through the piston pin at all? There is never any pressure difference between the right and left sides of the pin.

yes..... not from one side to the other......
But I would definitely expect that if the piston pin passes over the additional exhaust channel and at this moment there is a negative wave in the exhaust, then the bolt could also fill up when it passes over the scavenging channels.....But nevermind...forget the nonsense.

Dear Frits, even though it's very hart for me   ,   I'll keep my feet still and then ask the next question at the end of October?

Until then, I wish you much progress and success with your project.

Good morning Frits, good morning gays, in your opinion is a situation like this with the bursts staggered by 90 degrees constructive for the resonance? Thank you

Architito2002 a écrit:

Good morning Frits, good morning gays, in your opinion is a situation like this with the bursts staggered by 90 degrees constructive for the resonance? Thank you

"gays" or "guys" ???

Oliver Oettel a écrit:

Architito2002 a écrit:

Good morning Frits, good morning gays, in your opinion is a situation like this with the bursts staggered by 90 degrees constructive for the resonance? Thank you

"gays" or "guys" ???

everyone

Architito2002 a écrit:

Oliver Oettel a écrit:

Architito2002 a écrit:

Good morning Frits, good morning gays, in your opinion is a situation like this with the bursts staggered by 90 degrees constructive for the resonance? Thank you

"gays" or "guys" ???

everyone

A beautiful answer. And to answer your question: a phase difference of 90 crankshaft degrees will kill the resonance. 0° would be OK.
180° might also work, depending on the exhaust timing, which should be huge, and the distance between the exhaust ports of the cylinders.

Frits Overmars a écrit:

Architito2002 a écrit:

Oliver Oettel a écrit:

Architito2002 a écrit:

Good morning Frits, good morning gays, in your opinion is a situation like this with the bursts staggered by 90 degrees constructive for the resonance? Thank you

"gays" or "guys" ???

everyone

A beautiful answer. And to answer your question: a phase difference of 90 crankshaft degrees will kill the resonance. 0° would be OK.
180° might also work, depending on the exhaust timing, which should be huge, and the distance between the exhaust ports of the cylinders.

Thanks Frits, but in this case where there are two entire collectors that converge on opposite sides of the belly of the expansion wouldn't there be a constructive resonance? I imagine the swing when I think of expansion, which is pushed by the first cylinder and then when it has reached the opposite side it is pushed by the other. Assuming that the frequency of the swing is double that of the motor. Did I miss any pieces? Thank you

Architito2002 a écrit:

Frits Overmars a écrit:

a phase difference of 90 crankshaft degrees will kill the resonance. 0° would be OK.
180° might also work, depending on the exhaust timing, which should be huge, and the distance between the exhaust ports of the cylinders.

Thanks Frits, but in this case where there are two entire collectors that converge on opposite sides of the belly of the expansion wouldn't there be a constructive resonance? I imagine the swing when I think of expansion, which is pushed by the first cylinder and then when it has reached the opposite side it is pushed by the other. Assuming that the frequency of the swing is double that of the motor. Did I miss any pieces? Thank you

The resonance frequency in a two-stroke pipe is always double that of the engine. And the swing, as you call it, from C1 could arrive at C2 just when the C2-exhaust port opens 90° later, but what about the 270° phase difference between C2 and C1?

Frits Overmars a écrit:

Architito2002 a écrit:

Frits Overmars a écrit:

a phase difference of 90 crankshaft degrees will kill the resonance. 0° would be OK.
180° might also work, depending on the exhaust timing, which should be huge, and the distance between the exhaust ports of the cylinders.

Thanks Frits, but in this case where there are two entire collectors that converge on opposite sides of the belly of the expansion wouldn't there be a constructive resonance? I imagine the swing when I think of expansion, which is pushed by the first cylinder and then when it has reached the opposite side it is pushed by the other. Assuming that the frequency of the swing is double that of the motor. Did I miss any pieces? Thank you

The resonance frequency in a two-stroke pipe is always double that of the engine. And the swing, as you call it, from C1 could arrive at C2 just when the C2-exhaust port opens 90° later, but what about the 270° phase difference between C2 and C1?

good evening Frits, I made a diagram to understand how things could go.

What do you think ? Thank you

Ciao Frits,
thank you for all informations you shared in this topic started almost 10 years ago!

RSA125 power is still unbeaten despite his develop finished in 2007. If we wanna achieve greater power we cannot stuck in 5 transfer port layout; nobody will be able to overtake Jan work for quality and quantity.

Your idea of simmetrical layout gives for sure the maximum blowdown and more breath at high revs. Do you have an update on how is working this concept? I started designing an engine with this layout (I have not so much free time in this period, but I'm preparing to cast the cylinder in Christmas), I will keep you updated. For sure the biggest trouble I had in the first flow trials was to avoid shortcut between transfer ports and exhaust.

Ciao
Gabriele

on paper Frits's FOS concept looks great, but I trully wonder how that central mixture column won't mix with the outside ring-column of exhaust gases, both moving in opposite directions.
I know this also happens in a standard 2stroke cylinder, but in it the seperation is much clearer : a center devider where it may happen, but front and back of the cylinder are "turbulence-free"

Jan, I think with the huge blowdown we can reach there won't be so many exhaust gas left to mix whit fresh charge.
For what I saw, the problem is to avoid fresh charge to immediately escape from exhaust ports; this phenomena can help pushing out exhausted gas, and maybe playing with exhaust back wave is possible to bring back a good quantity of the fresh one....

Arcigno a écrit:

Jan, I think with the huge blowdown we can reach there won't be so many exhaust gas left to mix whit fresh charge.

true, bad thinking of my part

This system has never actually worked...
The engine starts, but doesn't rev
No power curve has ever been made......
I think the fresh charge IMMEDIATELY enters the exhaust!

Thanks for sharing your experience, Jan !

Thank you Jan, I saw the same during my first flow trials with this design.
Anyway, I wanna try. Otherwise we will never beat your hp record

Arcigno a écrit:

Thank you Jan, I saw the same during my first flow trials with this design.
Anyway, I wanna try. Otherwise we will never beat your hp record

This is NOT the way to beat my power record.
THAT will be very difficult!!!

Jan Thiel a écrit:

Arcigno a écrit:

Thank you Jan, I saw the same during my first flow trials with this design.
Anyway, I wanna try. Otherwise we will never beat your hp record

This is NOT the way to beat my power record.
THAT will be very difficult!!!

oh yes and who are you, the engineer of the Aprilia 125?

I was, until 2008, after that my record was never broken...