[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked)

Hello ,

Avec moins de lumières d'échappement , il y a un SAE paper 2006-32-0061 qui montre un cylindre comme ceci :
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L'auteur assure qu' après un peu de développement et sur un banc de controle de balayage uniquement , les performances avaient atteint +/- celles d'un Honda RS125.

Mais il n'a jamais tourné , alors ?....

Slts

With the design shown by 2T4T, you obtain more angle-area for the transfer ports, but less for the exhaust... You really must utilize both sides of the cylinder for exhausts if you want to raise the maximum rpm for optimal scavenging. And with opposite exhausts you need symmetrical transfers that create a stable central scavenging column, otherwise a great deal of the fresh charge will short-circuit into one of these exhausts.

The pictures below show the effective port areas and the angle-areas for the Aprilia RSA-125 with conventional ports and for the FOS-125 with symmetrical ports.
The ratio between the two transfer angle-areas gives an impression of the rpm that should be attainable...

The transfer timing is about the same for both cylinders and the exhaust timing of the FOS is lower than that of the RSA; the RSA-exhaust timing is a compromise between a timing that is too high for optimum resonance and an angle-area that is too small for the rpm that the transfer ports permit.

With the FOS-system I do not need to compromise because I have 23 % more exhaust blowdown area and 33 % more blowdown angle-area, even with the lower timing. And all of the exhaust area is above the transfer ports, contrary to the RSA where 1/3 of the exhaust area is situated too low to be of any use for the exhaust blowdown phase.

Another advantage: because the cylinder is symmetrical, it will not distort under temperature influences. This makes the piston very happy .
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le bruit n'as pas changé, c'est déjà bon signe

pierre a écrit:

le bruit n'as pas changé, c'est déjà bon signe

C'est le genre de truc à se cuire les jambons !

But to be serious, it's a really nice system with the 2 exhaust.

Just 1 question : if there are 2 exhaust on each side, is it working with 1 or 2 intake and with 1 or 2 carburators to be symetric and fill the volume as much as possible ?

Frits Overmars a écrit:

I could ask Jan Thiel about the aiming of the transfer ducts, but I suppose he is watching this forum so there is no need to pass your questions on to him; he reads everything but doesn't react very often.

One thing you do not want in the scavenging flow is turbulence. You want to expel the exhaust gases, not mix them with the fresh charge. What you are looking for in the transfer streams, is that they collide in the center of the cylinder, slow each other down and form a single column with a high density and a low velocity, that rises to the head and at the same time expands in diameter and pushes burnt gas into the exhaust ducts.

There is hardly an optimal ratio of duct area to port window. I generally try to obtain a value of 1,5 but when you look at the B-transfers of an Aprilia (A is the set nearest the exhaust; then come the B-ports, then the C-port opposite the exhaust) you will see that the entry at the cylinder base is almost a rectangle, with a width of 19mm and a 'length' (in riding direction) of 16 mm; that gives 304 mm².
The B-window in the cylinder wall has a width of 25 mm, a height of 13,2 mm and an upward angle of 10°; the effective port area is 325 mm²; it's bigger than the entry area 8).
That may seem strange, but remember that the entry area is open all the time and the port is not...

Below are some pics of a cylinder layout with FOS-scavenging. The two exhaust ducts point sideways.

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Merci Fritz,
Thanks for sharing that information. How important is duct shape to enable the intake transfer streams to slow enough to form the central rising column?

Regarding the FOS cylinder what will be the best method of induction ? Would triple exhaust ports be an improvement on the bridge port?


Merci de partage que l'information. Comment est l'importance gaine forme pour permettre l'admission transfert les flux de ralentir assez pour former les hausse centrale colonne? En ce qui concerne la FOS cylindre quelle sera la meilleure méthode de l'induction ? Serait triple échappement être une amélioration sur le pont port?

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They make good lampshades

Institute of TwoStrokes a écrit:

How important is duct shape to enable the intake transfer streams to slow enough to form the central rising column?

The ducts should provide an easy path for the fresh charge with as little pressure loss as possible. Not only the cross-section and the radii, especially the inner radius, but also the duct length plays a role. On a flow bench with a constant stream of air you cannot measure this; you need a pulsating air stream to establish the effect of the length.
The ducts should deliver the charge in dense jets, in the desired direction into the cylinder. Here too the inner radius of the ducts is important.
The slowing down of the charge jets is not a job for the ducts; the jets should slow each other down when they collide in the cylinder.

Citation :

Regarding the FOS cylinder what will be the best method of induction ?

The best method of induction, when you consider the conventional solutions, is a rotary valve. But there are also unconventional possibilities; I am working on a system that I call the 24/7-inlet. I will explain later.

Citation :

Would triple exhaust ports be an improvement on the bridge port?

A bridge port like in a Honda RS has two disadvantages. It is relatively long which hinders the heat transport to the surrounding metal, and it is in the thrust face of the piston, which is all the more undesirable because any lubricating oil is blasted off by the hot exhaust gases.
In my cylinder the bridges are much shorter, and they are on the sides, not in the thrust areas.
Apart from the problems with a conventional central bridge it is desirable to have as few bridges as possible, because each bridge is a heat exchanger: it absorbs heat from the exhaust gases and passes this heat on to the fresh charge that has entered the exhaust duct and is subsequently pushed back into the cylinder by the exhaust pulse. This charge should be as cold as possible when the exhaust closes and compression starts.

Hello, interesting !!
Your system looks like in a certain amount, to the big 2T Diesels with the exhaust valves are rond in the head and the inlets ports are all rond in the bottom wall (there is a turbo there...)
I think you are int the good way to improve the cycle , go on

putain!!!!!Si j'avais un peu travailler en cours d'anglais,je ne serais pas comme un con devant mon écran

@ tzpagnol, tu prends le traducteur de google et c'est tout de suite plus claire

cristogrr a écrit:

Your system looks like in a certain amount, to the big 2T Diesels with the exhaust valves are rond in the head and the inlets ports are all rond in the bottom wall.

Yes, with a couple of differences
The big diesels that you mention, have their scavenging ports aimed tangential so that the incoming charge gets a swirling motion. That helps the mixing of air and fuel droplets when the diesel fuel is injected. But in my engine the fuel is already in the charge when it enters the cylinder, and then a rotating motion would have two big drawbacks.
Firstly, fuel droplets that are not already evaporated, are centrifuged against the cylinder wall. There they do not take part in the combustion but instead wash the lubricating oil from the wall.
Secondly, as the incoming charge is much cooler and denser than the burnt exhaust gases in the cylinder, the centrifugal effect separates the two: the fresh charge flings to the outside where it would immediately escape through the exhaust ports, and the burnt gases get trapped in the cylinder center, with nowhere to go.

Another difference is the valves: they open and close too slowly. Even with four exhaust valves their combined angle-area would be far too small for the high rpm that I hope to realise. Remember that in a two-stroke the valves must open and close with every crankshaft revolution. And valves open with an initial speed of zero, in contrast to cylinder exhaust ports that are opened by a piston at near its maximum speed.
Anyway, who wants a two-stroke with double overhead camshafts?

tzpagnol a écrit:

putain!!!!!Si j'avais un peu travailler en cours d'anglais,je ne serais pas comme un con devant mon écran.

Sorry, TZ. If I would write in French, nobody would understand. I hope someone will post a decent translation.

Merci Emmanuel.Thank you fritz

tzpagnol a écrit:

Merci Emmanuel.Thank you fritz

You made me curious, so I entered my last piece of text into the Google translator and had it translated into dutch and into french.
Boy, that required some imaginative reading! You might get some totally new ideas that I never thought of...
But I fear that the things I really wanted to say, might get lost in translation. It would probably be better if the translation was taken care of by somebody with a grasp of english and french, and a bit more understanding of two-strokes than Google has..

Frits Overmars a écrit:

You might get some totally new ideas that I never thought of...

Dear Frits, i'ts real fun moment to speak wis you my friend.
Promis je prendrai des cours d'Anglais dans une prochaine vie

Hello ,

Dans le simulateur MOTA , j'avais chargé les données de ce nouveau concept de cylindre :
Exhaust opening = 85.87°ATDC (Honda = 81.96) Ouv Ech
Full opening = 115.15 Plein ouv ech
width limited to 31mm due to piston configuration. 3D model above take care of this in final design largeur lum ech

Transfer opening all except "new" = 120.6 (Honda = 111.56) - 123.5 at final test (same as additional ports)
angle up main = 0 - width = 22.0 to flow direction (net) angle sortie transf principal
angle up secondary = 15 - width = 18.0 to flow direction (net) angle sortie second
angle up rear = 40 - width = 12.0 to flow direction (net) angle sortie tr AR
angle additional = 22.5 (final test) - width = 22.0 to flow direction (net)
2mm bridge between ports

Le calcul de la section nette des lumières echappement du "Novel concept" etait de 34.9mm contre 38.0 pour le RS Honda.
J'avais calculé le Time-Area de bouffée (blowdown) dans Excel et il était bien plus important.
Le Time-Area des transferts etait sensiblement identique malgre le temps d'ouverture moindre du "Novel concept".
MOTA avait trouvé +3Hp à 12500tmn mais la precision est relative.

J'en avais déduit que le Time-Area de bouffée etait plus important que le Time-Area total echappement ou en cas que la bouffée prévalait sur le total.
Les 2 boosters echappement du RSW/RSA sont très importants aussi et la lumière principale semble relativement plus faible comparativement.
Jusqu'ou aller encore plus loin...

A+

I do not expect my engine to be fully developed in time for the 125 cc GP-season of 2011, and it will certainly not be allowed to make the 250 cc four-strokes look ridiculous in 2012, so there is no need for secrecy anymore .

Well 2T4T, here are some data for comparison with your Novel Concept to keep you and Mota busy:

Exhaust timing = 192°, exhaust floor = 105° below TDC.
Exhaust port width = 4 * 65° (this is the angle measured from the center of the cylinder bore).
With 54 mm bore this gives port widths of 4 * 29,0 mm
(why should the exhaust port width in your Novel Concept be limited by piston configuration??)

Transfer timing = 130°.
There are no main, secondary or rear transfers; all six transfer ports are identical.
As you can see in the 3D-drawings on the previous page, an upward angle of 0° or 15° would be impossible in combination with my port timings; the upward angle is 25°.
Transfer port width = 6 * 50° (= 6 * 22,8 mm).

2T4T a écrit:

J'en avais déduit que le Time-Area de bouffée etait plus important que le Time-Area total echappement.

You are absolutely right.
I quoted my port areas and angle-areas on the previous page (in the red-and-yellow pictures); you can compare those with your Mota results.

It was interesting to see +3 HP @12500 rpm, but I am more interested in Mota's prediction @16000 rpm...

Frits Overmars a écrit:

I do not expect my engine to be fully developed in time for the 125 cc GP-season of 2011, and it will certainly not be allowed to make the 250 cc four-strokes look ridiculous in 2012, so there is no need for secrecy anymore

Very sad!
I can't believe that such a sophiticated engine will have no place to race...
I guess Spain will be the last 2strokes heaven, at least in 125 or 80cc.

Marc a écrit:

Frits Overmars a écrit:

I do not expect my engine to be fully developed in time for the 125 cc GP-season of 2011, and it will certainly not be allowed to make the 250 cc four-strokes look ridiculous in 2012, so there is no need for secrecy anymore

Very sad!
I can't believe that such a sophiticated engine will have no place to race...
I guess Spain will be the last 2strokes heaven, at least in 125 or 80cc.

Spain with Germany too I think. In IDM, they had not interest for Moto2 in 2011, so I hope they will continue with 125 !

Frits Overmars a écrit:

Institute of TwoStrokes a écrit:

How important is duct shape to enable the intake transfer streams to slow enough to form the central rising column?

The ducts should provide an easy path for the fresh charge with as little pressure loss as possible. Not only the cross-section and the radii, especially the inner radius, but also the duct length plays a role. On a flow bench with a constant stream of air you cannot measure this; you need a pulsating air stream to establish the effect of the length.
The ducts should deliver the charge in dense jets, in the desired direction into the cylinder. Here too the inner radius of the ducts is important.
The slowing down of the charge jets is not a job for the ducts; the jets should slow each other down when they collide in the cylinder.

Citation :

Regarding the FOS cylinder what will be the best method of induction ?

The best method of induction, when you consider the conventional solutions, is a rotary valve. But there are also unconventional possibilities; I am working on a system that I call the 24/7-inlet. I will explain later.

Citation :

Would triple exhaust ports be an improvement on the bridge port?

A bridge port like in a Honda RS has two disadvantages. It is relatively long which hinders the heat transport to the surrounding metal, and it is in the thrust face of the piston, which is all the more undesirable because any lubricating oil is blasted off by the hot exhaust gases.
In my cylinder the bridges are much shorter, and they are on the sides, not in the thrust areas.
Apart from the problems with a conventional central bridge it is desirable to have as few bridges as possible, because each bridge is a heat exchanger: it absorbs heat from the exhaust gases and passes this heat on to the fresh charge that has entered the exhaust duct and is subsequently pushed back into the cylinder by the exhaust pulse. This charge should be as cold as possible when the exhaust closes and compression starts.

Thanks again Fritz for your information, are you willing to share any information on your pulsed flow bench (is it similar to the Yamaha SAE paper on anometric testing?) ? Have you found a larger raduis on the inner wall entry increases duct velocity?
I always thought transfer streams were to 'smash' into each other to slow down, but 'collide' sounds much more controlled. :-) I wasn't sure if my old principle was past it use-by date.
Is there any reliable way of gauging if you have to much turbulence in the rising column? I'll term it cylinder purity ?


Encore merci Fritz pour votre information, êtes vous disposé à partager des informations sur votre flux pulsé banc (est similaire à la Yamaha SAE papier sur anometric essais?) ? Avez-vous trouvé un plus grand’sur la paroi intérieure l'entrée augmente gaine vitesse? J'ai toujours pensé que transférer les flux ont été «écraser» dans chaque autre à ralentir, mais «entrent en collision» semble beaucoup plus contrôlée. :-) je n'était pas sûr que si ce vieux principe a été passé, il use-par date.

Est-il moyen fiable pour mesurer si vous avez beaucoup turbulence dans l'augmentation colonne? Je vais terme il cylindre pureté ?

I will not reveal too much about pulsed flow benches (because you keep spelling my first name as Fritz instead of Frits ). In its simplest form it is a normal flow bench with a rotating disc or drum that interrupts the flow. But because of the pulsation it is advisable to put a large buffer volume between pump and interruptor.

A large inner radius in a duct helps to avoid flow separation from the inner wall (the Coanda effect), thus limiting turbulence and pressure loss. This promotes the flow velocity, the density of the charge and the coherence of the flow to the geometrical direction of the duct. In other words: the flow goes where you want it to go.

There is a reliable way of measuring turbulence: laser doppler anemometry. It has only one drawback: $$$$$....
But there is also a cheaper way: put the cylinder on a static flow bench (a pulsating flow bench makes a hell of a lot of noise) and listen to the flow. If you hear flutter, there's turbulence.

To be honest there is always turbulence. But it can be microscopic or macroscopic, and that makes a lot of difference.
And turbulence is not necessarily bad; in the crankcase it improves the mixture of fuel and air, and at the end of the compression phase it speeds up combustion. You just do not want turbulence during flow...

OOPS sorry about that my mistake

Hello,.
MOTA n est un simulateur tres precis : aucune valeur reglable au niveau de la combustion.
J utilise maintenant EngMod2t qui permet ces reglages mais sans donnee relative pas facile.
Je scrute les SAE papers pour trouver des informations sur la combustion et avoir plus de precision a tres haut regime.
Idem pour la carburation.
Et nos 2T vont disparaitre et je n aurai surement jamais assez d informations sur ces sujets.
A+

2T4T a écrit:

..nos 2T vont disparaitre et je n aurai surement jamais assez d informations sur ces sujets.

Yes, it is sad that people who understand incredibly little about motorcycle racing (Dorna - Espeleta) are blinded by the big money that goes around in Formula 1, and try to 'improve' the motorcycle GPs in the same direction.
First the 500-class had to give way to 990 cc four-strokes because the average street rider would be able to 'relate better to that kind of machine' (and because a lot of TV-money was going to World Superbikes).

Then the 250-class was sacrified because 'it was becoming a one-brand class and the Aprilia's were so expensive' (and to launch an attack on World Supersport).
Was it Aprilia's fault that KTM, Honda and all the other manufacturers did no longer offer competitive machines? Now we have Moto2, a real one-brand class, just with various frame builders.

And what about safety? The 600 cc four-cylinder Hondas would be 'much more reliable and much safer' than the 250 cc two-strokes. Yeah, right! Earlier this year a little oil leakage (a blown engine) caused nine riders to crash in the same corner. I've never seen that happen in any two-stroke class...

Next, the 125-class has to go. Why?
We have seen exactly the same thing happen in 125 cc motocross: 250 cc four-strokes would be 'more reliable and more economical'. Now we have experienced that the opposite is true, and a lot of motocross riders would love to have their two-strokes back...
I fear that Moto3 will be a still-born class. But that may be exactly Dorna's goal: to keep 'improving' the racing until there is only one class left (with a little help from their friends at Honda).
I have a lot of respect for Honda's technical achievements but I despise these politics.

EDIT:
@moderator: if you think this text is too controversial, please remove it. I try not to get angry about this MotoGP-Moto2-Moto3-disgrace, but sometimes I need to vent my feelings.

that 's really true

Aprilia lease costs were a scapegoat for scrapping the 250(and subsequently 125cc classes) the real reason for the 'murder in the night' of the classes was Aprilia's withdrawl from MotoGP and taking up WSBK racing while Aprilia Corse continued to make money and prestige from GP racing.
Which is why the offers from KTM to provide a spec FRR 250 at a fixed lease cost and Aprilia's offer to scrap the LE versions, fell on deaf ears.

Though a little off topic , has anyone ever managed to see the factory Red Bull KTM's (both 125 and 250) with the fairings off? One of the few reed valve engines to match the disc valve Aprilia's for top end power

Aprilia bail coûts étaient un bouc émissaire pour la démolition des 250(et par la suite 125cc classes) la véritable raison pour l'«meurtre dans la nuit» des classes a été Aprilia de retrait de MotoGP et prenant WRC racing tout Aprilia Corse a continué à faire l'argent et de prestige de GP racing.

C'est pourquoi les offres de KTM de fournir un spec ERREURS 250 à un coût fixe bail et Aprilia l'offre de débris LE versions, fait la sourde oreille.

Quoique un peu hors sujet , quelqu'un a jamais réussi à voir l'usine Red Bull KTM (deux 125 et 250) avec les carénages off? Un des rares reed valve moteurs d'égaler les disc valve Aprilia pour haut débit.(does this say 'broadband')