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

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 :

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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...
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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.

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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.

There was an engine in the 1930s called the Petter Harmonic engine. A low rpm engine that had the exhaust valves in the head and a long resonant length pipe. Can be seen via Google.

To me there are 2 options for the next quantum power jump in performance 2 strokes:

1. A ring of exhaust ports around the bore with valves in the head, maybe even passive reed valves, cooled each time during induction

2. Go with a RSA type port layout, but have a diversion valve, say in the B ports that allows this to be connected to a short (throttled?) duct from atmosphere, ie direct inlet to the cylinder, bypassing the crankcase. Even the diversion valve could be eliminated by simply dedicating the B port to external air (& fuel?) only, leaving the A & C ports to provide sufficient flow for starting and getting up to the tuned speed when the B port passage could be opened

Ken Seeber a écrit:

To me there are 2 options for the next quantum power jump in performance 2 strokes:
1. A ring of exhaust ports around the bore with valves in the head, maybe even passive reed valves, cooled each time during induction

Hi Ken, long time no see. Been doing anything interesting lately?
A reed valve in the head must be able to cope with combustion temperature and pressure. Do you think you can make something sturdy enough that will also be light and flexible enough to function as a suction reed valve?

Citation :

2. Go with a RSA type port layout, but have a diversion valve, say in the B ports that allows this to be connected to a short (throttled?) duct from atmosphere, ie direct inlet to the cylinder, bypassing the crankcase.  Even the diversion valve could be eliminated by simply dedicating the B port to external air  (& fuel?) only, leaving the A & C ports to provide sufficient flow for starting and getting up to the tuned speed when the B port passage could be opened

Been there done that. Well, sort of. I once attached carburetters to the sides of a two-stroke cylinder, bypassing the crankcase. It could be made to run but the con rod bearing didn't like it.

I think that any design that wont allow an effective squish head with a central spark plug will prevent high power because detonation will occur.
Probably the next evolution we would see on the tracks is fuel injection. There is a DIY kit available on the market but the electric fuel pump power draw will require a powerful generator and hence a weight penalty on the flywheel. Ideally it should have a mechanical pump.

motoholic71 a écrit:

Probably the next evolution we would see on the tracks is fuel injection.

For sure, although the ideal, direct injection, may not be within reach for high-revving two-strokes just yet.

Citation :

There is a DIY kit available on the market but the electric fuel pump power draw will require a powerful generator and hence a weight penalty on the flywheel. Ideally it should have a mechanical pump.

There are lots of DIY injection kits on the market, and have been for years. But don't ask me to name the best; there are people more qualified than me on this forum to answer that question.
I never got the impression that an electricfuel pump requires that much energy. And don't you think starting might become difficult with a mechanical pump?

A standard 3bar injection pump runs on about 2.5A. My street bike gets by with an internal-rotor generator designed for race use, which has lower MoI than the external rotor type on my TZ.... and it also drives a headlight :-) It doesn't charge below 4000rpm, but with modern Li-ion batteries this is not really a problem unless you spend a lot of time idling in traffic.
So I don't think the pump is really an issue.

For the next leap forward in 2T development (ie more power /cc displacement) you must analyze just what it would take to create the power. In order to make more power you must burn more optimal fuel/air mixture and achieve a higher BMEP. Fuel injection is good but has it's limitations, that being achieving complete combustion at all operating parameters. I believe there are some power gains here but mostly it would be in fuel efficiency not greater output. Pipe technology is another scope of power improvements but there is no big magic here to discover either. The pipe is basically a supercharger with no moving parts that uses residual energy in the form of exhaust waves to increase the amount of trapped charge, but it is where most of the performance of a 2T engine is currently achieved. Even the mighty RSA would barely pull it's own weight without a pipe. So the next step in development I feel is to find a method of supercharging the cylinder that works better than a conical pipe.. Perhaps a small poppet inlet valve in the head coupled to a direct injection high pressure compressor that injects a fuel air mixture after the exhaust port has closed. Even if the valve injected 12cc charge more per revolution to the combustion chamber it would be a substantial increase on a 125 engine.

Maybe I have too much time on my hands but I want to try to cobble something together to try it.

Frits Since I have a modified street engine I have a blanked oil injection drive but it's no doubt hard to find a suitable fuel pump and set the gear ratio. Besides the injection needs pressure before the engine is running, I would either have to spin the engine very fast or fit an electric pump as a start up aid that would then be switched off...I'll stick to carbs for now but will look into it later.

My generator puts out a little over 5 amps; the fuel system with sensors, injectors ,ecu etc should draw close to 5A...I still have 2X EGT,DET,lambdas and a DC CDI. although the plan is to keep only the det. after dialing the carbs.
The draw back of fuel injection to me is about generator weight/bulkiness so please Graham, is there a site where I can check out your internal rotor, or does it have a brand that I can investigate?
Thanks

Howard I'm with you, it's firstly about rising the volumetric efficiency. The pipe uses part of the fuel energy to create back pressure. I think Jan has reached close to the limit of this
So how can this energy be increased without being at the expense of port timing?
As an electronic eng. I tend to discard solutions that revolve around electromechanic  devices to actively supercharge the engine because the amount of power is often staggering and usually not very reliable.And heavy and overcomplicated.

How about injecting fuel directly in the pipe? A la afterburner? That should be funny!

a spark plug and a nozzle placed where a second syncronized explosion would cram the mix back in after the transfers close.A single transistor would switch an automotive di nozzle and a 12V ign.coil simultaneous, coil would spark upon trans. switch off after injection time... Driven of a basic hall sensor on the crank,timing to be found depending on pipe.
I wonder if such thing could kill you... Kabumm
Just one problem-no O2 to burn!(I think) maybe with the Cal. RZ350 catalist exhaust with reeds on the header pipes to suck fresh air for the cat system. probably NLA hardware though


Or a synchro sleeve valve at the tip of the pipe, instead of a chamber. The port would only open after the sleeve closed so the back pressure would go from nought at exhaust open to very high right after, ideally after transfer period. Then port closes and sleeve open bleeding out exhaust gas.
But it would still require a tuned length of pipe in order to have the back pressure arrive on the right time. and to have variable timing to stay open during blowdown below the powerband or it wouldn't run there.
This is harder to do since it requires balanced parts.
honestly I don't have much faith in it
I prefer the after burner.

I think any improvement modification made will have to retain all the features present on todays high power engines to be taken seriously.



Isn't there a government fun fund to apply to exploit this stuff?

motoholic71 a écrit:

Isn't there a government fun fund to apply to exploit this stuff?

The other day I visited an army museum and an airforce museum.
Man, the things we could have done with the money that got spent by the military....

+1 Mr frits. I agree with you;