[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4)

Sonde Lambda, in french...

Marc a écrit:

Sonde Lambda, in french...

Lambda Sonde in german, Lambda sensor in dutch. O2 probe in 'merican because Lambda is too greek (culture overdose) for them  .

Thank you Frits for your precious advice.

no prob Frits, I wasn't expecting that you'd calculate anything, just hoped you could make an estimated guess with all your experience .
guess I'll have to dig in the topics to find your post (if only the search function of the forum was a bit better   )

JanBros a écrit:

...if only the search function of the forum was a bit better.

I know the problem. At the left side of the page, below "Rechercher" you can choose between "Interne" and "Google".
Always select "Google"; it works a lot better.

hi frits i have a question about time*area. i dont really understand how it could be universal if it doesnt take into account how good or bad the ducts are, or case volume, or pipe, or inlet type etc. i can see how a window of X amount of size, can pass X amount of volume, in X amount of time and that seems universal to me. but because nothing else is considered, it isnt making sense to me.

like you said some time ago, a duct designed by jan would be much superior to what most anyone else could do. so if the rsa needed X amount of time*area, it doesnt make sense to me that we could simply use the rsa time*areas in a cr125 for example and expect great results. simply because every part of the rsa is far better than what you would see in the cr125

Hello there,im newbie in the forum!Im a wannabe tuner(!) and I try to learn as much as possible for combustion chamber design,port timings,exhaust design and pressure waves etc....
I'm planning for a new project,tzr125 engine,wr200 3xp cylinder bored to 69mm with 57mm stroke without powervalve,39mm carburetor,cr500 reed valve(the air-cooled)    and handmade exhaust,I'll try to pull out about 45hp from this,for road use
I just want to tell a big thank you to mr Frits and Jan,for their knowledge publishing!
And a question to mr Frits,
I prefer to do comb chambers with wide squish-more than 50% bathtub design like Aprilia's,with big radius and make them as shallow as possible,something like 9 or 8mm depth!
What's your opinion about that?What was the depth of the rsw-rsa's heads?
Cheers!

lef maybe this is what you need [Vous devez être inscrit et connecté pour voir ce lien]

Thank you brokedown,i need to read the previous post but it needs time to reed 150+ posts
Mr Frits can also explain us how different height's work and what excactly is affected from shallow and deep chambers.

brokedown a écrit:

hi frits i have a question about time*area. i dont really understand how it could be universal if it doesnt take into account how good or bad the ducts are, or case volume, or pipe, or inlet type etc. i can see how a window of X amount of size, can pass X amount of volume, in X amount of time and that seems universal to me. but because nothing else is considered, it isnt making sense to me.
like you said some time ago, a duct designed by jan would be much superior to what most anyone else could do. so if the rsa needed X amount of time*area, it doesnt make sense to me that we could simply use the rsa time*areas in a cr125 for example and expect great results. simply because every part of the rsa is far better  than what you would see in the cr125

Brokedown, you are right in assuming that angle.areas are only part of the story. What you need to move mixture from A to B is, in order of importance, a pressure difference, adequate angle.areas, and a good flow coefficient.
If you base your engine on the angle.areas I presented elsewhere, you will be in the right time zone. It does not mean that you will have a great engine. But If you try to correct flow deficiencies by raising port timings beyond the RSA values, you will run into other problems, so I think it is best to stick with those RSA angle.areas.

Lef16 a écrit:

Thank you brokedown,i need to read the previous post but it needs time to reed 150+ posts
Mr Frits can also explain us how different height's work and what excactly is affected from shallow and deep chambers.

maybe its better to read first and ask questions later   

Again I come here with a non RSA related subject but the opportunity to discuss it with someone of the level of Frits and Jan is too precious.
Since long ago when I learnt about 2 and 4 strokes I envisioned that it would be possible to combine the 2 but as I never saw anything like that I didn't give it too much thought
In more recent years I learnt about diesel 2 strokes which is in principle very similar to "my" original idea.

What I mean is a 2 stroke with head valves. Basically a standard engine with reeds or disc, transfers, but without exhaust port.
instead, a valve or valves on the head geared 1:1 to the crank and synchronized to mimic the standard exhaust port timing.

Now just imagine the possibilities- no scavenging dead spots on the cylinder since the transfers are at the base of the cylinder and the exhaust on the top; a full circle ring transfer ports is posssible; and 4! exhaust valves to which is allowed asymmetric or even variable timing like v-tech or so.

In theory all this sound terrific not only for power but also for mileage,pollution and so on.Ressonant exhaust is still very possible.In my mind it would outweigh the extra weight/complexity etc since it eliminates intake dilution and waste dramatically and requires less finesse at aiming transfer tunnels, while is reasonable to think that 4 exhaust ports are at least comparable to the lost standard port

I know there must be something terribly wrong with this concept since I never saw it except in diesel form, where cranckcase induction is not used, but it does work.

So my question to the whole board is : why it sounds so good and it doesn't exist?
what am I missing?

Thank you and excuse my off topic.

motoholic71 a écrit:

Again I come here with a non RSA related subject but the opportunity to discuss it with someone of the level of Frits and Jan is too precious.
Since long ago when I learnt about 2 and 4 strokes I envisioned that it would be possible to combine the 2 but as I never saw anything like that I didn't give it too much thought
In more recent years I learnt about diesel 2 strokes which is in principle very similar to "my" original idea.

What I mean is a 2 stroke with head valves. Basically a standard engine with reeds or disc, transfers, but without exhaust port.
instead, a valve or valves on the head geared 1:1 to the crank and synchronized to mimic the standard exhaust port timing.

Now just imagine the possibilities- no scavenging dead spots on the cylinder since the transfers are at the base of the cylinder and the exhaust on the top; a full circle ring transfer ports is posssible; and 4! exhaust valves to which is allowed asymmetric or even variable timing like v-tech or so.

In theory all this sound terrific not only for power but also for mileage,pollution and so on.Ressonant exhaust is still very possible.In my mind it would outweigh the extra weight/complexity etc since it eliminates intake dilution and waste dramatically and requires less finesse at aiming transfer tunnels, while is reasonable to think that 4 exhaust ports are at least comparable to the lost standard port

I know there must be something terribly wrong with this concept since I never saw it except in diesel form, where cranckcase induction is not used, but it does work.

So my question to the whole board is : why it sounds so good and it doesn't exist?
what am I missing?

Thank you and excuse my off topic.

Like this :

[Vous devez être inscrit et connecté pour voir ce lien]

I said the same thing to Pépé a couple of years ago, he told me that it has already been done, but nothing more.
may be a "brevet" lock that, may be a 2 stroke will run the ohc too fast (twice the speed of a 4 stroke) for the valves ?

i am afraid that the 2 stroke is just politically incorrect...

motoholic71 a écrit:

Again I come here with a non RSA related subject but the opportunity to discuss it with someone of the level of Frits and Jan is too precious.
Since long ago when I learnt about 2 and 4 strokes I envisioned that it would be possible to combine the 2 but as I never saw anything like that I didn't give it too much thought
In more recent years I learnt about diesel 2 strokes which is in principle very similar to "my" original idea.

What I mean is a 2 stroke with head valves. Basically a standard engine with reeds or disc, transfers, but without exhaust port.
instead, a valve or valves on the head geared 1:1 to the crank and synchronized to mimic the standard exhaust port timing.

Now just imagine the possibilities- no scavenging dead spots on the cylinder since the transfers are at the base of the cylinder and the exhaust on the top; a full circle ring transfer ports is posssible; and 4!  exhaust valves to which is allowed asymmetric or even variable timing like v-tech or so.

In theory all this sound terrific not only for power but also for mileage,pollution and so on.Ressonant exhaust is still very possible.In my mind it would outweigh the extra weight/complexity etc since it eliminates intake dilution and waste dramatically and requires less finesse at aiming transfer tunnels, while is reasonable to think that 4 exhaust ports are at least comparable to the lost standard port

I know there must be something terribly wrong with this concept since I never saw it except in diesel form, where cranckcase induction is not used, but it does work.

So my question to the whole board is : why it sounds so good and it doesn't exist?
what am I missing?

Thank you and excuse my off topic.

The acceleration of the valves would be too slow at high speed for good blow down time. Everything is having to work twice as hard in half the time. Also can you imagine the barrier presented to exhaust gas flow by four valve heads in the way.
Perhaps better to run a second piston in the head controlling the exhaust, two pistons, one cylinder. This configuration is being used in heavy fuel twostrokes still. Germans made a very effective diesel aero engine using this layout at one time.

ideal compromise between 2 stroke and 4 stroke engine is wankel engine...no valves, 4 stroke cycle, but 3 ignitions per one piston revolution...
[Vous devez être inscrit et connecté pour voir cette image]

uniflow a écrit:

The acceleration of the valves would be too slow at high speed for good blow down time. Everything is having to work twice as hard in half the time. Also can you imagine the barrier presented to exhaust gas flow by four valve heads in the way.
Perhaps better to run a second piston in the head controlling the exhaust, two pistons, one cylinder. This configuration is being used in heavy fuel twostrokes still. Germans made a very effective diesel aero engine using this layout at one time.

What you referring is the "split single" as used on the DKW 250 gp racer?

I think the point of the mass involved is valid, a prototype design would require  less aggressive cam profiles than those found on 4 strokes and the best up to date technology for the valve gear.

So is the valve stems hampering the flow, and probably dealing with the amount of heat transferred to the valves, this would require some serious engineering but there are ways to deal with this.

Ultimately my guess is that it's impossible to get the same exhaust TA even with 4 valves, but if an under-square bore/stroke ratio is used the bigger head area will allow bigger valves and perhaps match closer the lost TA to an acceptable level to counter balance the handicap.
Remember there's no R&D done on this (as far as I know)
I'm an electronic engineer from the analogic era, these subjects exceed my ability, once in a while people come to me with projects or ideas and some times I'm able to quickly crunch some numbers and see if it's feasible or worthwhile but not with this.
I'm expecting someone will eventually give me a clear cut reason not to pursuit this, but so far it all seems arguably relative.

When one considers all the outlandish designs that have been tried throughout the years (i.e. Gnome Rhone monosoupape and the likes ) what leaves me perplex in not being able to find a working example of this concept in any application, which leads me to believe it simply doesn't run but I don't know why...

If I could I'd build a crude prototype with existing parts just to see if it runs or not. It needn't have to have 4 valves; A single valve version should run.Just seal the exhaust port on an aircooled 2 stroke and then find a suitable bore 4 stroke head...

Thank you

To the other posters:
Yes there are those engines, they do exist; we know what they do and so on.Wankel, Diesel with roots blower and many many others including gas turbines and what not.
So why not a Otto cycle 2 stroke with valves? maybe with rotary valves to whidstand high speed...if some one knows an example please let me know.Maybe I should start new a topic.
Thank you

motoholic71 a écrit:

To the other posters:
Yes there are those engines, they do exist; we know what they do and so on.Wankel, Diesel with roots blower and many many others including gas turbines and what not.
So why not a Otto cycle 2 stroke with valves? maybe with rotary valves to whidstand high speed...if some one knows an example please let me know.Maybe I should start new a topic.
Thank you

Try this....scroll down to see his Maico bottom with special head.

[Vous devez être inscrit et connecté pour voir ce lien]

every moving part needs some power for moving...so when you put another part to the engine you loose some output power...why complicate 2 stroke with exhaust valves...

You run into several les ideal situations.
Opening time exhaust being one of them. If you want to be open as fast as a piston opens the exhaust you need a serious cam profile.

I think its more wise to up the efficiency from the fuel.
Heat recovery can be adapted in many ways and the 20 ish% of work you get now average can easy got to 35%

There is a lot of power in water. You can ask yourself why is/was there so much air in a kettle from the locomotive?
You lose a lot of work there. Let the water become steam only when it does work. Not before.
This is the flaw in almost all powerplants.

S

I found the name of what I'm looking for.It would be called "spark ignition crank case scavenged 2 stroke with over head poppet valves and tuned expansion chamber".
There are lots of studies and publications about similar designs and even a few prototypes.
But none of them retains all the features; most use compressors to clear the cylinder and none of them use a tuned exhaust. Mostly because every single one is only looking for better fuel efficiency and fewer emissions.
I was looking for specific power and wider power band.So only one of the major factories could do such thing since a smaller 2 stroke manufacturer is probably not rigged to develop a hi performance valve train.

an expansion pipe only works when you get a strong pulse right at it's beginning.
valves (closed by springs, opened by cam) can never open fast enough to get a big enough pulse.

uniflow a écrit:

The acceleration of the valves would be too slow at high speed for good blow down time.

motoholic71 a écrit:

Ressonant exhaust is still very possible.

JanBros a écrit:

an expansion pipe only works when you get a strong pulse right at it's beginning. valves (closed by springs, opened by cam) can never open fast enough to get a big enough pulse.

Sanderhoutman a écrit:

You run into several less ideal situations. Opening time exhaust being one of them. If you want to be open as fast as a piston opens the exhaust you need a serious cam profile.

Yes, opening the valves fast enough is a stumbling block (cooling the valves is another one).
The initial opening velocity of a puppet valve is zero: first it is stationary; then it starts to move.
The initial opening velocity of a piston-controlled port just about equals the maximum piston velocity.
No cam profile can even come close to that.

motoholic71 a écrit:

uniflow a écrit:

The acceleration of the valves would be too slow at high speed for good blow down time. Everything is having to work twice as hard in half the time. Also can you imagine the barrier presented to exhaust gas flow by four valve heads in the way.
Perhaps better to run a second piston in the head controlling the exhaust, two pistons, one cylinder. This configuration is being used in heavy fuel twostrokes still. Germans made a very effective diesel aero engine using this layout at one time.

What you referring is the "split single" as used on the DKW 250 gp racer?

I think the point of the mass involved is valid, a prototype design would require  less aggressive cam profiles than those found on 4 strokes and the best up to date technology for the valve gear.

So is the valve stems hampering the flow, and probably dealing with the amount of heat transferred to the valves, this would require some serious engineering but there are ways to deal with this.

Ultimately my guess is that it's impossible to get the same exhaust TA even with 4 valves, but if an under-square bore/stroke ratio is used the bigger head area will allow bigger valves and perhaps match closer the lost TA to an acceptable level to counter balance the handicap.
Remember there's no R&D done on this (as far as I know)
I'm an electronic engineer from the analogic era, these subjects exceed my ability, once in a while people come to me with projects or ideas and some times I'm able to quickly crunch some numbers and see if it's feasible or worthwhile but not with this.
I'm expecting someone will eventually give me a clear cut reason not to pursuit this, but so far it all seems arguably relative.

When one considers all the outlandish designs that have been tried throughout the years (i.e. Gnome Rhone monosoupape and the likes ) what leaves me perplex in not being able to find a working example of this concept in any application, which leads me to believe it simply doesn't run but I don't know why...

If I could I'd build a crude prototype with existing parts just to see if it runs or not. It needn't have to have 4 valves; A single valve version should run.Just seal the exhaust port on an aircooled 2 stroke and then find a suitable bore 4 stroke head...

Thank you

Valve guides I don't think are a problem as such, more the valve heads ( all four of them ) in the cylinder at the same time retricting flow.
German engine I was refering to is the Junkers opposed piston. Very efficent for it's time and I expect it still is.

In the youtube video is a Uniflow crankcase charged two cylinder ( four piston ) twostroke prototype engine under test ( from years ago ). It did a lot of hours in this jet boat, geared to the jet pump, engine 440cc reved to 9200 rpm. Very fuel effficent ( for a crank case charged twostroke ). First video is the first ever start up, second is first time under load, the engine isn't run to full throttle untill near the end of the lake run.