[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked)

I see where you problem lies, Senso. Angle.area is not simply the total blowdown area multiplied by the total blowdown angle. It is the sum of a lot of small area steps, multiplied by the time during which each of these steps is open.

For example, let us assume that the exhaust port is a simple rectangle, 40 mm wide, that it opens 1 mm further for each degree of crankshaft rotation, and that the total blowdown angle is 30°.
Then the first degree of exhaust opening will open an area of 40 mm x 1 mm = 40 mm², and this area will be open during the whole 30° of blowdown period. That first area thus has an angle.area of 40 x 30 = 1200°mm².

When the crankshaft turns 1 degree further, an additional area of 40 mm² is opened. This second area will be open during 29°, so its angle.area is 40 x 29 = 1160°mm².

Repeat this calculation for each crank degree until the end of the blowdown phase, and add all the angle.area values; that will give you the total blowdown angle.area.

In reality this calculation is complicated by the fact that not every degree of crank angle gives the same port height difference, and even more by the fact that the exhaust port is not a simple rectangle. But you will understand the principle of angle.area.
One final remark: my first name is spelled Frits, not Fritz .

I'm so sorry for calling you the wrong name, I will not do it again.

I understand, I need to integrate the area, maths it not really my speciality but I think I can come up with the right numbers, I will open a post in the Technique part of the forum when I have more data and crazy ideas, so to not spam this topic, but thanks for the advices, its all that I need to keep me going in the right direction.
In the case of the italkit cylinder it is a W shaped exhaust port, that might be fun to integrate and arrive to the correct values.

Best regards Mr. Frits

Bonne leçon de logique dynamique, j'ai pris ma dose merci Frits :-) , je voulais revenir sur les temps d'ouvertures et fermeture du distributeur (valve rotative), je post des photos d'un moteur avec la position de la valve au PMH (TDC), la fermeture total du conduit est 86° ATDC

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TDC position

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86° ATDC

Ensuite je cherche à savoir comment relever l'autre valeur angulaire, et quelle méthode utiliser?
Merci pour vos réponses les amies, je me fait ici le porte parole de ceux, qui ne ne comprennent qu'une partie de la distribution rotative.

Je posterais d'autres photos si nécessaire

Emmanuel Laurentz a écrit:

Ensuite je cherche à savoir comment relever l'autre valeur angulaire, et quelle méthode utiliser?

Désolé Manu, je me sens plus bête que d'habitude cet ap. Qu'est-ce tu entends par "l'autre valeur angulaire" ?
C'est par rapport au début d'ouverture, début de ferméture... ou l'aire d'ouverture en fonction d'angle, dans le même sens que les calcules de blow-down ci-dessus ?

Chers amoureux du 2-tps,
Dear 2-stroke lovers,

Je viens de parcourir un nouveau topic qui pourrait vous intéresser, ici :
I just discovered a new topic that might be of interest for you, here :

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Il semble que ce soit seulement une introduction à ce qui sera un topic plus détaillé.
I understand this is only an introduction to what will be a more detailed topic later.


J'en profite pour vous remercier à nouveau de la qualité de vos échanges ici : même un béotien total comme moi prend plaisir à vous lire en apprenant quelques mots nouveaux et quelques débuts de bribes de notions :)

Tu sais les valeurs sont indiqués tel 86/136 (pour l'exemple), donc sur le moteur ci dessus j'ai effectivement 86° depuis le PMH jusqu’à la fermeture de l'admition ok mais que représente cet angle de 136° et à partir de quand ?

J'ai lu dès la page 24 et suivantes des valeurs de 95/150.

Q: 95° avant fermeture admission à partir du PMH ?
Q: 150° à partir de quand ?

j'y vais tout de suite .

Emmanuel Laurentz a écrit:

Tu sais les valeurs sont indiqués tel 86/136 (pour l'exemple), donc sur le moteur ci dessus j'ai effectivement 86° depuis le PMH jusqu’à la fermeture de l'admition ok mais que représente cet angle de 136° et à partir de quand ?

J'ai lu dès la page 24 et suivantes des valeurs de 95/150.

Q: 95° avant fermeture admission à partir du PMH ?
Q: 150° à partir de quand ?

ouvrir 150° avant PMH
fermer 95° apres PMH

Jarno

Merci

senso a écrit:

I'm so sorry for calling you the wrong name, I will not do it again.

I understand, I need to integrate the area, maths it not really my speciality but I think I can come up with the right numbers, I will open a post in the Technique part of the forum when I have more data and crazy ideas, so to not spam this topic, but thanks for the advices, its all that I need to keep me going in the right direction.
In the case of the italkit cylinder it is a W shaped exhaust port, that might be fun to integrate and arrive to the correct values.

Best regards Mr. Frits

I believe you can find a formula either in Bell &/or Blair publications,with described process to tackle odd port shapes and rod length is necessary for calc. I'll post if I find it,very busy today,might b easier?

I think it's actually a double integral, since you need to sum up over angle the area of port open, which is itself the integral of the width of the port over the height...ie

Int(from A to B) [ Int(from h(t) to H) W(y) dy ] (dh/dt) dt

where W(y) is the width of the port at height y above BDC,
h(t) is the height of the piston above BDC at t° after BDC,

h(t)=s*(1-cos(t)) + sqrt(r²-s²*sin²(t)) -r,

where r is rod length and s=stroke/2

and (dh/dt) is the piston speed in mm/degree at a given crank angle, ie the derivative of the expression above,

(dh/dt)(t)=s*sin(t) - [s²*sin(t)*cos(t) / sqrt(r²-s²*sin²(t)) ]

Erk!

Easiest way would be to make up a spreadsheet allowing you to enter the port width at 1mm or 1/2mm steps...

True. Either way seems 1st step should be to roll some mil graph paper and scrib the ports shape

Given the odd W shape of the exhaust port, I will make a port-map of the cylinder, then I will transfer it to some millimetre graphing paper and spent half a day counting little 1mm^2 squares, for some reason I have read the Jennings book some years ago and I got the impression that the time areas where calculated just by multiplying some values, probably I'm mistaken.

I will try also to get some points into Matlab and let it have all the fun doing the dual integral, or pull my hair off trying(I have a love-hate relation with Matlab.)

Thanks for the tips!

Hi Senso,

In Matlab I would creatie a Riemann Sum (Google: Riemann Sum Matlab). Easy to program and if the internationale steps are small enough, the result will be accurate enough for this application.

Cheers, Jacob

I meant integration steps...

D*mn iPhone...

GrahamB a écrit:

(dh/dt)(t)=s*sin(t) - [s²*sin(t)*cos(t) / sqrt(r²-s²*sin²(t)) ]

Oops... forgot that I was working in degrees, not radians. The above should be multiplied by Pi/180...

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With a 41.5mm carb we are going to try and crack the 50HP barrier with this.

Frits, would this pipe be an Aprilia pipe??

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I came upon it while reading this paper 'Correlations for Wiebe function parameters for combustion simulation in two-stroke small engines'
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It looks very much like the RSA pipe design! Expect the first 'flange' part that is missing -they test different lengths.
Test engine is an 125cc rotary valve, 83°ex-113°tfr, which looks weird -maybe it's a honda(??) or kart..

Vagelis a écrit:

Frits, would this pipe be an Aprilia pipe?.....It looks very much like the RSA pipe design!

It does, but it looks even more like an older Aprilia pipe, designated Tubo 55.
I suppose someone has hand-measured a Tubo-55 because the dimensions differ in some places, but only very slightly.
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Frits Overmars a écrit:

Vagelis a écrit:

Frits, would this pipe be an Aprilia pipe?.....It looks very much like the RSA pipe design!

It does, but it looks even more like an older Aprilia pipe, designated Tubo 55.
I suppose someone has hand-measured a Tubo-55 because the dimensions differ in some places, but only very slightly.
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I wonder if those tiny differences could be felt on dyno...

I see... Thanks for the schematic Frits!

About the A-tubo designs (21, 102 and now 55).. Were they part of a 100+ pipe testing procedure over Jan's years at Aprilia? Or they were code named after something?
There are just minor changes between these pipes.
It would be interesting to hear about the pipe development story, if you or Jan have some spare time (and wish to spare it here). :)

I take the liberty to post all three designs together. Hope you don't mind, since they were already in public:

• A-tubo 21
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• A-tubo 55
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• A-tubo 102
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Vagelis a écrit:

About the A-tubo designs (21, 102 and now 55).. Were they part of a 100+ pipe testing procedure over Jan's years at Aprilia? Or they were code named after something?

Just a matter of evolution: after tubo # 1 came tubo #2, and so on.

Citation :

I take the liberty to post all three designs together. Hope you don't mind, since they were already in public

No problem.

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Marc :
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