| [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) | |
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+110ROSSIGRM Daniel A. Haufen wax GtG001 noppie7 Aleph Fügner Brian Callahan Howard Gifford roost t2 190mech ettoiffi lesolexeur Mic Hakkelaar Makr pierre95 GrahamB XpTpSMTT julien #41 rgdavid le vieux docteur romeuh80 SB07 Sabijator ghg02 tz_37 gromono72 Tomi titi rg250 EMOTracing David Matech Solutions zilo bic1983 JoeHännes Riley Will MANETON Jan Thiel bengui LDA Jordan75 tht44 mickie pfpraider cocco83 granjoie Shining jenne smit Michael Burgard nasone32 Camus14 tzpagnol cristogrr 2T4T Alfred Kleis Pickup zelos Institute of TwoStrokes MacPepR 2stroke zeze Emmanuel Laurentz Toop pit Frits Overmars jmdonnat lougassi mike Fonfon #155 pierre Charly phil yanapu bitza32 drt67 superkart eric² Jarno fpayart Team MLR Fabien fab evospeed Ricco#6 Pignool Yonel DAD#21 rs69 Seb4LO ridley 50cc dooky remix31 nsfman philou janpol84 aerophil i-greck Polo les gazs freddy Stephane Inspecteur Harry Thirob jerem-aye mecanik svtce l'occitan Martine Eric Marc 114 participants |
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Jan Thiel
Nombre de messages : 517 Age : 83 Localisation : Bangkok Date d'inscription : 12/10/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 9:07 | |
| Sure, but with a variable timing I would like to have more than 3° variation! |
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Frits Overmars
Nombre de messages : 2614 Age : 75 Localisation : Raalte, Holland Date d'inscription : 12/10/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 9:08 | |
| - Jan Thiel a écrit:
- A small diameter and long tract would destroy power.
But you never tried it in combination with 360° inlet timing, did you?
Dernière édition par Frits Overmars le Jeu 23 Fév 2012 - 9:12, édité 2 fois |
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Jan Thiel
Nombre de messages : 517 Age : 83 Localisation : Bangkok Date d'inscription : 12/10/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 9:10 | |
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Frits Overmars
Nombre de messages : 2614 Age : 75 Localisation : Raalte, Holland Date d'inscription : 12/10/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 9:12 | |
| Anyway, small is relative. I might use a 38mm carburetter on a 125 cc engine in combination with a very large crankcase volume. |
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XpTpSMTT
Nombre de messages : 37 Localisation : Hellas Date d'inscription : 08/02/2012
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 9:15 | |
| - Jan Thiel a écrit:
- Sure, but with a variable timing I would like to have more than 3° variation!
So something based on the beauty of the rotary valve and the luxury of a simple form of variable timing is something you would have tried? |
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GrahamB
Nombre de messages : 3456 Age : 62 Localisation : Lyon Date d'inscription : 19/08/2011
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 10:26 | |
| - Frits Overmars a écrit:
- Anyway, small is relative. I might use a 38mm carburetter on a 125 cc engine in combination with a very large crankcase volume.
Funny, makes me think of the other Thiel(*)... who gave his name to the Thiel-Small parameters for parameters for loud-speaker design... including oscillation of bass-reflex ports. Wouldn't a long tract and large crankcase volume both tend towards lowering the resonant frequency to the point where you would end up with a sharply-peaked interaction with engine rpm? (*)... just checked, spelling was different: Neville Thiele... |
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Frits Overmars
Nombre de messages : 2614 Age : 75 Localisation : Raalte, Holland Date d'inscription : 12/10/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 10:45 | |
| - GrahamB a écrit:
- Wouldn't a long tract and large crankcase volume both tend towards lowering the resonant frequency to the point where you would end up with a sharply-peaked interaction with engine rpm?
They would both lower the resonant frequency, ideally to the point where the inlet flow would never come to a full stop. But being a Helmholtz resonance, there would not be any sharp peaks, just a lazy fundamental sine. |
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GrahamB
Nombre de messages : 3456 Age : 62 Localisation : Lyon Date d'inscription : 19/08/2011
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 13:38 | |
| - Frits Overmars a écrit:
- But being a Helmholtz resonance, there would not be any sharp peaks, just a lazy fundamental sine.
A sinewave is a very sharp peak viewed in frequency domain... the width of the peak is determined by the amount of damping (1/Q), which I'd expect to be less for a long than a short tract: mostly it comes from where the ends of the oscillating column of gas flow into the outside atmosphere... which would stay roughly constant with the length and hence smaller relative to the oscillating mass in a longer tube. |
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lesolexeur
Nombre de messages : 4 Localisation : mazamet Date d'inscription : 20/09/2011
| Sujet: helmotz Jeu 23 Fév 2012 - 14:14 | |
| bonjour tous le monde
Mr frits. pour votre système de boite a clapet 24/7 Comment pourrait t' on calculer une résonance avec un carter moteur qui voit son volume modifier constamment par le déplacement du piston? Ou prendrait on une moyenne du volume carter, ou encore un moment précis dans le temps moteur qui donnerait un volume carter Il faudrait aussi calculer avec la section de passage du carburateur au moment donner (encore une autre variable). Enfin est ce que lorsque les conditions le permettent le "phénomène" se déclenche instantanément ou il y a t' il un délai de déclenchement?
Si vous pouviez éclairer ma lanterne. edit: et aussi la pression dudit carter qui change non seulement avec le déplacement du piston mais aussi avec les phase d'admission et échappement. Merci
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Hakkelaar
Nombre de messages : 9 Localisation : The Netherlands Date d'inscription : 03/02/2011
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 14:39 | |
| If the inlet tract is open 360 degrees, smooth and free of obstructions, the diameter shouldn't have to be too large I guess. Almost 10 years ago, I was in the Formula Student competition and we were restricted to a max. displacement of 610 cc and an intake restrictor of 20mm The white thing pointing up in the picture. Using CFD, we and other teams tried to maximize the flow. Some (turbocharged) teams claimed up to 90 hp at the crankshaft (Yamaha R6 engine). The turbo had to be placed down stream of the restrictor. Of course we could use an intake plenum and we had to use fuel injection. We also mounted a supercharger as you can see in the pciture below. [Vous devez être inscrit et connecté pour voir cette image]To get back on topic.... In theory the intake diameter doesn't need to be very large when a high velocity can be reached. I was day dreaming about the effect of supercharging combined with the 24/7 system to reduce possible back flow and to increase the total intertia of the intake system, so to speak... Or would this just increase the crankcase pressure in the same ratio as the intake pressure is raised and the effect will be cancelled...? |
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Frits Overmars
Nombre de messages : 2614 Age : 75 Localisation : Raalte, Holland Date d'inscription : 12/10/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 17:23 | |
| - Hakkelaar a écrit:
- ...I was day dreaming about the effect of supercharging combined with the 24/7 system to reduce possible back flow and to increase the total intertia of the intake system, so to speak... Or would this just increase the crankcase pressure in the same ratio as the intake pressure is raised and the effect will be cancelled...?
Supercharging would offer a lot of additional possibilities, but has one major drawback: it is forbidden in the types of motorsport that I am interested in. If it were allowed, I would not need any form of inlet flow control, but then I would not use the crankcase either; I would blow directly into the transfer ports. And yes, if you do blow into the crankcase, you just raise the pressures and the backflow behaviour will remain the same. |
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Frits Overmars
Nombre de messages : 2614 Age : 75 Localisation : Raalte, Holland Date d'inscription : 12/10/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 17:39 | |
| - lesolexeur a écrit:
- bonjour tous le monde
Mr frits. pour votre système de boite a clapet 24/7. Comment pourrait t' on calculer une résonance avec un carter moteur qui voit son volume modifier constamment par le déplacement du piston? Ou prendrait on une moyenne du volume carter, ou encore un moment précis dans le temps moteur qui donnerait un volume carter. Il faudrait aussi calculer avec la section de passage du carburateur au moment donner (encore une autre variable). Enfin est ce que lorsque les conditions le permettent le "phénomène" se déclenche instantanément ou il y a t' il un délai de déclenchement? Si vous pouviez éclairer ma lanterne. edit: et aussi la pression dudit carter qui change non seulement avec le déplacement du piston mais aussi avec les phase d'admission et échappement. Bonjour Mr. Lesolexeur, You are right; it is not easy to calculate inlet resonance when so many factors are constantly changing. In fact is is too complicated to explain it here in the forum. It made me write a simple story, called: Helmholtz blues"A Helmholtz resonator consists of a volume connected to a duct". That is what Wikipedia tries to tell you. But that is a Helmholtz resonator in its simplest form; one that you won't find anywhere in an engine. What you do find in an engine is an intake tract with a variable cross-sectional area. This tract is from time to time connected to a variable volume (the crankcase) through a very variable window (the intake port / reed valve / rotary inlet). The crankcase is connected to a number of transfer ducts with variable cross-sectional areas, which are from time to time connected to a very variable volume (the cylinder) through a number of very variable windows (the transfer ports). The cylinder is from time to time, through a very variable window (the exhaust port), connected to an exhaust pipe with a very variable cross-sectional area who at the same time doubles as a volume. This pipe volume is constantly connected to a big volume (the outside world) through a tailpipe with a constant cross-sectional area and constant entry and exit windows (thank God, finally someting that's not variable). We call this a compound Helmholtz resonator . The various papers also tell us how to calculate the resonator's frequency: " frequency = speed of sound / (2*pi)* Sqr ( cross-sectional area of the neck / ( volume of the resonator * effective neck length ) ) ". O yes, the speed of sound... It is dependent on temperature, which is not really constant in the intake tract and the crankcase, rather variable in the transfer ducts and very variable in the cylinder and the exhaust pipe. Now the above frequency formula is not exact; it is an approximation that is usable as long as the volume of 'the' tract is very small compared to the resonator's volume. So when engines are concerned, that formula goes very far out the window. Who said gas dynamics is simple dull? PS: It's a similar story with acoustics. That is a sub-branch of gas dynamics, simplified with a lot of assumptions that are acceptable as long as the sound pressure does not exceed a certain limit. The wave pressures in a two-stoke exhaust exceed that limit by a factor of thousand. Bye bye, acoustics... |
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cristogrr
Nombre de messages : 1761 Age : 60 Localisation : sirault belgique Date d'inscription : 26/04/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 19:03 | |
| Some times, some car manufacturers and motorbikes (yamaha) put a derivative duct attached to the main flow pipe, to smooth the resonance; I think it can be usefull to explore this combination with 24/7 system rather than to play with the other dimensions(lenght-diam size). The exhaust is a resonator , why don't put another in the entrance and trying to optimise with avoiding putting some complicated moving parts.... |
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Frits Overmars
Nombre de messages : 2614 Age : 75 Localisation : Raalte, Holland Date d'inscription : 12/10/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Jeu 23 Fév 2012 - 20:30 | |
| - cristogrr a écrit:
- Some times, some car manufacturers and motorbikes (yamaha) put a derivative duct attached to the main flow pipe, to smooth the resonance; I think it can be usefull to explore this combination with 24/7 system rather than to play with the other dimensions(lenght-diam size).
The exhaust is a resonator , why don't put another in the entrance and trying to optimise with avoiding putting some complicated moving parts.... The 24/7-system has no moving parts, except for a very simple reed that is only there to start the engine; once the engine is running in the power band, the reed is swung aside and does not move at all any more. And like the exhaust, the inlet system is also a resonator; no need to complicate it with additional ducts or volumes. |
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XpTpSMTT
Nombre de messages : 37 Localisation : Hellas Date d'inscription : 08/02/2012
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Ven 24 Fév 2012 - 8:34 | |
| - Jan Thiel a écrit:
- ............
At high rpm there is some reverse flow, the transfer ducts becoming black, and even the crankcase and carburetter bellmouth because of the entering burned gasses. This happens because with raising rpm. the pre-exhaust flow becomes insufficient. When rpm raises still more there is no more transfer flow and the engine stops completely. So transfer flow depends completely from what is 'allowed' by the exhaust flow!
. Also yesterday stated the need of a flow diode with in a sense is a reed valve but meaning without the restrictions of one i assume... So GrahamB a full 360 inlet port will have serious practical drawbacks Or else to build two stroke engine based on the theoretics of a pulse jet engine will have us with a motor running at example .13000 rpm....but we will need a starter motor to reach that speed... and never close the throttle again...(or with the 24/7 principle) Anyway thats my(theoretical)opinion... if i had the resources maybe I could test them too,and prove myself wrong... And yes it says transfer flow but can we separate them that "easily"(transfer/exhaust -inlet tract/crankcase)? have i got somethin totaly wrong? edit.about the pulse jet:I havent got deep on how it works and i dont intend to either. im just using it as an example to state the differences of application and needs. |
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GrahamB
Nombre de messages : 3456 Age : 62 Localisation : Lyon Date d'inscription : 19/08/2011
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Mer 14 Mar 2012 - 20:54 | |
| - Frits Overmars a écrit:
(The Cagiva was cured by inserting 1 mm strips between the reed casing and the reeds, so the reeds did not really close anymore. It cost more than 10 hp, but the laptimes improved...) I was reading this famous thread again and came across this. Frits, do you understand why it would have lost so much power? I'd have thought it was a little way towards a 24/7 system, so it might work slightly better near peak torque? Or does having the reeds almost closed mean they start resonating? |
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ettoiffi
Nombre de messages : 10 Localisation : italie Date d'inscription : 14/03/2012
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Mer 14 Mar 2012 - 22:08 | |
| - l'occitan a écrit:
- Voila une des rares photos de son moteur
En 50 on comprimé à 11/1, ça marché bien quand on le prenais pas dans la gueule !!! @+ L’occitan
[Vous devez être inscrit et connecté pour voir cette image] motore bbft |
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Frits Overmars
Nombre de messages : 2614 Age : 75 Localisation : Raalte, Holland Date d'inscription : 12/10/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Mer 14 Mar 2012 - 22:44 | |
| - GrahamB a écrit:
- Frits Overmars a écrit:
(The Cagiva was cured by inserting 1 mm strips between the reed casing and the reeds, so the reeds did not really close anymore. It cost more than 10 hp, but the laptimes improved...) I was reading this famous thread again and came across this. Frits, do you understand why it would have lost so much power? I'd have thought it was a little way towards a 24/7 system, so it might work slightly better near peak torque? Or does having the reeds almost closed mean they start resonating? The 24/7-system has the 'mechanical' advantage that there is no reed hindering the flow, and the gasdynamical advantage that the flow does not need to be accelerated from a complete standstill with every revolution, provided that the inlet system's resonance matches the rpm. The Cagiva had neither of these advantages. Moreover, soft reeds, and to an even greater extent reeds that do not close sufficiently, mess up the carburation: the suction signal to the needle jet will be weak. So it is not surprising that Cagiva became one of the pioneers of injecting a two-stroke. Reed resonance can become a problem if the reed's root frequency falls somewhere in the engine's power band instead of well above it. That can happen with too much free length of the reeds and / or with reeds that are too soft. To my knowledge Caviva did not alter the reed's dimensions so I don't think reed resonance was an issue. |
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Frits Overmars
Nombre de messages : 2614 Age : 75 Localisation : Raalte, Holland Date d'inscription : 12/10/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Dim 18 Mar 2012 - 13:46 | |
| Good news: BMW predicts the return of the two-stroke. [Vous devez être inscrit et connecté pour voir ce lien]Rasputin, you were in the middle of it. Would you care to comment? Or are you still sworn to secrecy? |
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Toop
Nombre de messages : 3902 Age : 17 Localisation : Tours Date d'inscription : 02/01/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Dim 18 Mar 2012 - 13:57 | |
| and he argument are full of sense, contrary to policies liar |
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nasone32
Nombre de messages : 26 Localisation : italy Date d'inscription : 24/11/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Sam 31 Mar 2012 - 12:21 | |
| I would like to show the scooter engine we are building in the Italian machining factory FTM - (we produce the CVT FR4 variator if anybody knows...) It is much inspired from RSA, but reed valved to speed up development and cut costs, power will be enough even with reeds i hope. It is made by welding a new aluminium block in place of the original 50cc crankcase, and then machining it. engine is thought to be "not very expensive" so I had to choose some compromises. [Vous devez être inscrit et connecté pour voir cette image]cylinder is a small RSA replica aswell (50mm bore 48mm stroke, due to available pistons and capacity limitations). bridged exhaust because we are keeping it small (95% bore, no piston plug caps) [Vous devez être inscrit et connecté pour voir cette image]crankcase volume is high and I have a 2-stroke fuel injection kit running around, so 24/7 is OK to be tested here. (but i have much work to do before that...) I went directly for high inertia cranks, because rubber belt CVT suffers much the crankshaft speed fluctuation, I feel high inertia improves power transmission. Also the engine speed will be almost steady (thanks to CVT) so a quick revving engine is not that important. here the (unfinished) crank webs (next to original 50cc Piaggio ones) [Vous devez être inscrit et connecté pour voir cette image]We are going with 100mm conrod, 18mm crank pin and 14mm piston pin. Exhaust will be tuned for max power around 14.6k rpm, or approx. 23 m/s with 48mm stroke. Much informations comes from this topic, so thanks everybody, and also I feel the need to personally thank Frits and Martijn (Emot) the ignition side of the case will be machined from full block in these days... 40hp are possible with 13 bar bmep @ 23m/s, I think is possible to reach this target, what do you think? If i remember Jan Thiel's words, Aprilia did 14.8 bar. but we don't have that technology... |
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Invité Invité
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Sam 31 Mar 2012 - 21:47 | |
| C est un post de folie, domage qu il soit en anglais; C est comme si on essayait de converser avec une très jolie fille qui ne parle pas la même langue; Frustration!!! Moi y en a vouloir comprendre quoi Jan Thiel veut dire. |
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pierre
Nombre de messages : 126 Age : 61 Localisation : HLR-Belgique Date d'inscription : 23/09/2009
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Lun 2 Avr 2012 - 19:14 | |
| @nasone32 |
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Frits Overmars
Nombre de messages : 2614 Age : 75 Localisation : Raalte, Holland Date d'inscription : 12/10/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Ven 6 Avr 2012 - 11:51 | |
| Something to think about while the rest of the family occupy themselves with boiling, hiding, finding and eating easter eggs: a couple of recent videos from the Dutch 50 cc scene. [Vous devez être inscrit et connecté pour voir ce lien] |
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nasone32
Nombre de messages : 26 Localisation : italy Date d'inscription : 24/11/2010
| Sujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) Ven 6 Avr 2012 - 13:25 | |
| very nice, great work there.
the exhaust variaton looks very long to me, from my (small) experience on kart engines there are 2-3 centimeters on the muffler that make quite a difference, but after that you don't gain that much.
maybe they can trade off lenght variation for precision and faster exhaust response?
the "conrod actuator" looks promising and reliable! a stepper motor can provide high torque and position accuracy. (do they use a stepper?) |
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| [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) | |
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