Idea rotating inlet two stroke for smooth riding

[AlexS]

On the back thinking of an two stroke concept engine.

Always interested in 60s two multi cylinder stroke racers of Japan. For example Suzuki RK67 50cc twin cilinder disc valves with 14 gears. Or RP68 V3 cylinder with disc valves 19 hp 19.000 rpm.
http://www.classic50racingclub.co.uk/Suzuki-Works-50cc-Racing-Motorcycle/
Kawasaki I and II 125c 2 and 4 cylinders

Or the prototype square four 750 of Kawasaki https://www.motorcyclespecs.co.za/model/kawasaki/kawasaki_square_four.html



Have a chat with computers.

Rotary discs are back in the day connected directly to the crankshaft. Which result in fast speeding opening and closing time.

What if you let the disc rotate the half the speed of the crankshaft. You need than 2 cut outs at 180 degree phasing. But then you are able to make a banana or tear drop inlet cut out in the disc. Not for race engine, but let say commuting city driving. Smoother running and higher mid range torque. Accurate timing.

When the disc rotate slower and so need longer arch length cut out. Are you able to create an increasing opening area of the inlet port / disc. To gradually opening to reduce intake turbulence. Think of it like a cam lobe the port begins to open slowly, then more rapidly as the disc rotates.

Opening disc would be around 95 bTDC angle (47,5 degree rotary disc). And what I understand most transition. When you aim for torque you need to have a fully opened inlet port area when the piston is at TDC to 30 degrees aTDC. Closing starting at 5 degrees (55 degrees) for fully closed (60 degrees). And closing need also more smooth and not abrupt shutting off. there for the inlet port is eclipse formed and the cut out of the disc has a radius of 3-5 mm.

Looking at disc, might looking at airplane wings.
Opening. The leading edge of the cutout is curved or sloped, starting shallow and deepening gradually.
Closing. The trailing edge of the cutout is less steep, extending the closing point. A gentle taper or rounded edge to avoid sudden cutoff of flow.

Only thing I see. That when having it rotating at half crankshaft speed and setup the need of fully opening 30 degrees aTDC and fully clossed aTDC. You need to set the cut out at a large radius. And so large disc / inlet construction needed.

Have thinking of theoretical

Port timing for low blow down. And shorter exhaust and transfer duration

[Admiral_dk]

I can't see that changing the shape will improve anything - more likely the opposite - especially if you plan on using Carburetors, as they require a Sharp Rise in Pressure (Vacuum) to propper lift the Gasoline into the Air, for mixture ....

Likewise you need to Shut the Port as quickly for pumping efficiency in the Crankcase ...

A Variable Duration makes much more sense - could be done with two counter rotating Disks. One fixed onto the Crank and the other one about 0.5mm away from it - rotating the opposite direction and likely driven from a belt ....

The Problem will be reduced Reliability + much higher Price ....

Per

[BillTodd]

Best get familiar with the equations of motion ;-)

The forces, pressure differential, involved aren't great and the gas mixture aren't massless. To get sufficient mixture past the valve it needs to be open for as long as possible. At higher revs it's probably the moment of the gas column that becomes the significant number .


Interesting gear box. ISTR  Kreidler used a  4 or5 speed plus a 3 speed range changer to get the gear range to fit the ultra low powerband . I remember watching 50s GP racing at Anderstorp in Sweden in 1974  . They were restricted to just 6 gears by then and had to slip the clutch from the start line to the first bend  . They were still accelerating after the first lap .

[Vixen]

Best get familiar with the equations of motion ;-)

The forces, pressure differential, involved aren't great and the gas mixture aren't massless. To get sufficient mixture past the valve it needs to be open for as long as possible. At higher revs it's probably the moment of the gas column that becomes the significant number .

As Bill said 'the moment of the gas column that becomes the significant number'.
So look at this image of a typical disc valve engine. The disc rotates at engine speed to ensure fast opening and closing. Note the wide induction angle of the disc (approx 210* from just open to fully closed). Note also the wide diameter of the induction port, they could not make it any bigger. It's all designed to get the maximum fuel mixture into the engine, in the shortest possible time.
If you need less power, then partially close the throttle.



Hope this helps

Mike

[AlexS]

Thanks for explanations!

Per. As idea for variable duration for second disc, powered by a servo?

[Admiral_dk]

I personally wouldn't bother .... For road use I would only consider Reed-Valves and that goes for anything less than absolute Max. Power in Racing - where I would copy the last Aprilia 125cc singles and 250cc twins. They use Disc-Valves mounted on the Cylinder and rotated 90 degrees to the Crank (Belt driven).

You have HUGE amounts of more power with modern Two-Stroks than those Old-Timers + MUCH broader Power-Band and that mostly to do with much improved Gas-Flow in ALL Ports ....
I'm not underestimating the importance of the Exhaust Chambers - but they can't do their Magic the the max. without optimum Porting 

In case of the Inlet Port - it MUST end up feeding ALL Transfer Port equally well and that COMPLETELY eliminates the Idea of having the Disk-Valve on the Crank.

The Inlet Port feeds all Transfer Ports directly above the Crank - so the Gas don't have to make a Detour when it's on the Pipe (some of it does anyway and lubricates the Bearings).
Really on the Pipe - the Gas goes straight from the Carb, through the Inlet, up the Transfers and out the Exhaust into the Pipe .... for it to be Stuffed back into the Cylinder after the Closing of the Transfers and before closing of the Exhaust (Acoustic Turbo Charging).
That's why I sometimes joke - that a Loud Two-Stroke is a Slow Two-Stroke 

Per

[AlexS]

Interesting!

Never have seen an open RS125 or 250 engine of Aprilia. What I read these have reed valves in the cylinder, not rotary disc inlet valves. But exhaust power valves.

I see the benefit of having reeds in the cylinder to have the shortest way to combustion chamfer.

I agree with you, for modern setup for maximum performance applying the route with reeds and power valves like modern MX engines.

I was only thinking in the head of smooth and broad multi cylinder engine. Well there reed valves is also a better solution.

I have heard of someone that said, the best performing two stroke is a silence one indeed!

[Admiral_dk]

Alex have a look here :
http://www.pit-lane.biz/t117p220-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked

Warning - besides being a VERY big Rabbit Hole - a number of Browsers etc. will try to prevent you from going there .... because off advertising ....

As the Address above mentions - you get the Fact from the Constructors of the Aprillia them selves - Namely Jan Thiel and Frits Overmars        
Part one is locked now - but if you end up reading enough further - they still answer questions (or did last I looked - a while ago).

Per     

[lohring]

This is the way to adjust disk valve timing.
<a href="https://www.youtube.com/watch?v=bhKrRlZxomc" target="_blank">http://www.youtube.com/watch?v=bhKrRlZxomc</a>

Lohring Miller

[Admiral_dk]

Very ingenious Lohring - haven't seen this before and it gives a symmetric adjustment of the timing 

I hope the Bike isn't supposed to still be used in the Mud with this addition 

Per           

[AlexS]

Interesting forum you shared Per! Great that Jan and Frits answer in an public forum and share there knowledge.

Now I understand you about, about the aprilia race engines. I was thinking about stock road bikes 

Two stroke has some magic.

Lohring nice variable inlet timing! Seem not to difficult to make for a smaller engine too.

Edit: seems like he also build an sleeve valve two stroke with two exhaust ports!

[Admiral_dk]

I later realized that the System Lohring showed also is the Throttle - I have never seen any Throttle that also completely changes the Inlet Timing - in many ways Brilliant.

Alex carefull about the Rabit Hole I showed you - you can end up spending EONs thinking about this subject 

Per     

[lohring]

Flettner (Neil Hintz)  Is one of the most imaginative two stroke builders around.  In addition to the sliding gib system he has built opposed piston engines, sleeve valve engines, a fuel injection  system, a twin exhaust engine, and lots of other innovations.  He casts and machines most of all this.  You can see him, Frits, Wobbly (Wayne Wright), and other two stroke tuners at https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner/

Lohring Miller