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

Honda made a bike with a revolutinal engine with a very nice exhaust valve system. You will find attached some little pictures, unfortunately I've never found more informations.


Frits ?

According the drawings, it seems that the exhaust valve opens only during exhaust times ?
D'après les croquis, la valve d'échappement semble s'ouvrir seulement durant les phases d'échappement?
Dan

Dan probably true, but I haven't any further information and the pictures are too small to appreciate the real functioning.
Only 3 cycle pictures suggest that the valve works at the pace of the piston. And therefore it is only open during the exhaust phase.
Which would produce a lower pollution.
It's hard to realize what would be the gain in thermal efficiency. The shorting of fresh gas to the exhaust being deleted, filling supplement caused by the return of these fresh gas will also be deleted.
What else ?
Must still provide an high frequency alternative operation of this valve.

Probablement vrai Dan, mais je n'ai aucune information complémentaire et les images sont trop petites, pour pouvoir apprécier le fonctionnement réel.
Seules les 3 images du cycle laissent penser que la valve fonctionne au rythme du piston et que donc, elle n'est ouverte que durant la phase d'échappement.
Ce qui serait favorable à une plus faible pollution.
J'ai du mal à me rendre compte quel serait le gain en rendement thermique. Le court-circuit des gaz frais vers l'échappement étant supprimé, le supplément de remplissage provoqué par le retour de ces gaz frais sera supprimé également.
Quoi d'autre ?
Encore faut-il assurer un fonctionnement alternatif, à haute fréquence, de cette valve.

Frits

It was the Honda 400 EXP-2.
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ktuningteam a écrit:

you think of this? rotary valve system for exhaust. With this system, which is able to close the outlet of gas entering cool. I want to do, but I think someone before I would have thought the same, there is something? somebody has tried?
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The late Eyvind Boyesen has tried something similar to the above video that you posted. He did not use a rotary valve in the exhaust port, but a valve that reciprocated at the same frequency as the piston. It was not a success. It could stop the fresh mixture from entering the exhaust duct, but this also meant that the exhaust pipe reflection could not push any fresh mixture back into the cylinder, which is so important for a two-stroke.

Here is another example of a rotary exhaust valve, built by Lorenzo Ghiselli.
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fpayart a écrit:

Only 3 cycle pictures suggest that the valve works at the pace of the piston. And therefore it is only open during the exhaust phase which would produce a lower pollution.
It's hard to realize what would be the gain in thermal efficiency. The shorting of fresh gas to the exhaust being deleted, filling supplement caused by the return of these fresh gas will also be deleted.
Frits

You called, Sir?  
The Honda exhaust valve does not move at the pace of the piston. It only moves at the pace of the rev counter needle, dependent upon rpm and throttle position, and its job is to keep some exhaust gas in the cylinder, as descibed in Maneton's link. Honda called it Active Radical Combustion; nowadays it is more commonly known as HCCI: Homogenous Charge Compression Ignition.
The captured exhaust gas pre-heats the fresh charge in the cylinder, so this will be at the limit of detonation at the end of the compression stroke.
There is no flame front; combustion starts spontaneously and simultaneously everywhere in the combustion chamber.
This way combustion will be very complete and very, very fast. Exhaust gases will contain very little HC and NOx, and the engine will remain cool.


EDIT: I tried to attach an animated gif comparing the burn velocities of HCCI, spark ignition and Diesel, but somehow it will not work...

EDIT2: probably the file is simply too big; it's 5230 KB.

Dank u,
Aside from the reduction in pollution, has there an interest on the mechanical efficiency ?

fpayart a écrit:

Aside from the reduction in pollution, has there an interest on the mechanical efficiency ?

Maybe not on the mechanical efficiency, but certainly on the thermodynamic efficiency. Because combustion is so rapid, it can start later, so there is less pressure on the piston before TDC. There is also less heat transfer from the combustion to the surrounding metal.
In this picture of the Ryger kart you may notice that notwithstanding the elevated engine power the radiator is very small; even too small for a conventional 125 cc engine. And yet the coolant temperature always stays low.
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In fact Honda uses a same way that is in Diesel engines: a part of exhaust gaz is used at the inlet to improve the combustion efficiency at low revs and cold situations.
En fait Honda emploie le même principe qu'utilisé sur les moteurs Diesel: une partie des gaz d'échappement est recyclée à l'admission pour favoriser la combustion à bas régime et à froid ( valve EGR, source souvent de soucis). Ce n'est pas une simple copie, une application particulière au 2T.
Dan

That mean that Ryger engine, use HCCI system ?

We can suppose that!, a common license between Ryger and Honda?
Dan

Dan42 a écrit:

a common license between Ryger and Honda?

Certainly not, Dan. In case you want some literature:
P.M.Najt & D.E.Foster: Compression-Ignited Homogeneous Charge Combustion, SAE Paper 830264
This paper is 32 years old, which solves any HCCI patent questions.
What's more, Homogenous Charge Compression Ignition was first applied in the Lohmanm mopedmotor about 60 years ago

Given it's superior cooling,could a Rygerengine be air cooled?Just thinking how nice it would be to convert an older engine for vintage racing.

yeahhim a écrit:

Given it's  superior cooling,could a Rygerengine be air cooled?Just thinking how nice it would be to convert an older engine for vintage racing.

Yes, it could. Aircooling does not get in the way of the Ryger principle.

Frits Overmars a écrit:

ktuningteam a écrit:
you think of this? rotary valve system for exhaust. With this system, which is able to close the outlet of gas entering cool. I want to do, but I think someone before I would have thought the same, there is something? somebody has tried?
[Vous devez être inscrit et connecté pour voir ce lien]
The late Eyvind Boyesen has tried something similar to the above video that you posted. He did not use a rotary valve in the exhaust port, but a valve that reciprocated at the same frequency as the piston. It was not a success. It could stop the fresh mixture from entering the exhaust duct, but this also meant that the exhaust pipe reflection could not push any fresh mixture back into the cylinder, which is so important for a two-stroke.

Here is another example of a rotary exhaust valve, built by Lorenzo Ghiselli.

Frits Thanks for the information! I searched on Boyesen, and I think there is a difference between what he did and what I thought, this is your system completely blocks the passage of the exhaust gases and makes up and down as in conventional valves a rectilinear motion, however my system is only an aid, closes a little before you make the piston, and also the movement is circular, accompanying fresh gases escaping through the hole up, maybe this could be final to run well.

Jan I have a question about your RSA engine. What connecting rod length did you use and did you try other rod lengths? If so what advantages and disadvantages were there to either shorter or longer rod lengths?
Second question is could you or Fritz tell me approximately what the ignition timing curve worked best?
As you can figure out I am building a 250 parallel twin rotary valve motor using RSA clone cylinders.
I plan to spin it around 12000 rpm

Jan and Frits will give you a good answer for the best rod length, i am sure. Old manuals ( from 1932) indicates concerning the aircraft and automotive engines design: connecting rod length= 2 engine stroke. It's probably a very good data, used today.
Dan

I've seen answers and discussions on it, few pages ago ... Part #2 or #3

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I recall something like "we started at 110 and ended with 120 which gave more power"


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Howard Gifford a écrit:

Jan I have a question about your RSA engine. What connecting rod length did you use and did you try other rod lengths? If so what advantages and disadvantages were there to either shorter or longer rod lengths?
Second question is could you or FritS tell me approximately what the ignition timing curve worked best?
As you can figure out I am building a 250 parallel twin rotary valve motor using RSA clone cylinders.
I plan to spin it around 12000 rpm

The RSA design started with a 115 mm RSW rod but eventually a 120 mm rod was used to make more room for the inlet flow under the cylinder and piston.
Here is the 100% throttle ignition curve for the RSA once more:
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Very interesting curve but one important parameter is missing : the amount of ignition energy delivered to the coil and most of all the amperage and its duration thru the spark plug. In general said timing figures should ALWAYS be accompanied by energy and current values.

I don't understand the secrecy behind the Ryger engine since it's released for sale what prevents anyone from buying one and tear it open to learn the tricks within? Apart from having finances to do so of course.
I still think the figures are astonishing is there a dynamometer curve we can see please?

Dan42 a écrit:

In fact Honda uses a same way that is in Diesel engines: a part of exhaust gaz is used at the inlet to improve the combustion efficiency at low revs and cold situations.
En fait Honda emploie le même principe qu'utilisé sur les moteurs Diesel: une partie des gaz d'échappement est recyclée à l'admission pour favoriser la combustion à bas régime et à froid ( valve EGR, source souvent de soucis). Ce n'est pas une simple copie, une application particulière au 2T.
Dan

Nowadays every car engine petrol or Diesel of any brand any kind will have an EGR valve. This began in the 90's in Europe.
It's not related to the Honda system.

This valve mixes some exhaust gas in the intake to bring down combustion temperature thus reducing NOX emissions. The valves are usually water cooled and are there just because of gas emissions laws, they don't help performance nor promote combustion and actually reduce engine life by completely filling the intake ducts with charred grease gunk.

Just saying this for the sake of knowledge that's all

Frits Overmars a écrit:

Dan42 a écrit:

a common license between Ryger and Honda?

Certainly not, Dan. In case you want some literature:
P.M.Najt & D.E.Foster: Compression-Ignited Homogeneous Charge Combustion, SAE Paper 830264
This paper is 32 years old, which solves any HCCI patent questions.
What's more, Homogenous Charge Compression Ignition was first applied in the Lohmanm mopedmotor about 60 years ago

The glow head engines of Lanz Bulldog type was from 1890 and runs Hcci.They consume diesel oil but the exhaust smell very different

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I worked at the factory 1977

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