2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

Thanks for the reply Manolis.

It is interesting that your calculations support the basis of your rotary valve design
being capable of supporting the gas flow required by running on a 2T basis.

Toyota tried this, via converting one of their 4T DOHC 4V mills - to run as an (externally blown) 2T..
..but quickly ran into the inherent poppet valve limitations of flow capacity/mechanical recip' capability..

Best wishes with getting your bold 2T ideas into metal & operating as intended..

Re: fueling-intake/exhaust systems - can you show what you have planned, for your 'Flyer' machine?

[manolis]

Hello J.A.W.

You write:
“Re: fueling-intake/exhaust systems - can you show what you have planned, for your 'Flyer' machine?”

OPRE Tilting 2-stroke / Portable Flyer:

Premixed, with port injection in the intake opening of the crankcase.

Note: the crankcase (i.e. the space inside the piston wherein the crankshaft rotates) is not pressurized (in the conventional 2-strokes the crankcase is pressurized and needs good sealing of the crankshaft bearings), however this space inside the piston is the busiest.



The “tuning” is based more on the intake than on the exhaust.

The transfer ports open, and the scavenging starts with the exhaust ports already open, but earlier than in the conventional 2-stroke.

The pressure into the “scavenge pump” (sealed by the opposite to the “combustion chamber end” of the piston) allows such timing.

Later the tilting valve opens and the scavenging continues based on the inertia of the gas column formed: open tilting-valve-port on the piston, space into the scavenge pump, transfer passageways, transfer ports, combustion chamber, exhaust ports, exhaust.

Air-fuel-oil-mixture from the “crankcase” feeds this “inertia” column, while the “crankcase” is fed, through the intake port, with air-fuel-oil-mixture.

When the piston finally closes the transfer ports, the suction of air-fuel-oil-mixture from the intake port into the “crankcase” continues due to the subpressure created into the “scavenge pump” as the piston moves towards the TDC with the tilting valve wide-open. After the TDC the tilting valve closes and the air-fuel-oil-mixture trapped inside the “scavenge pump” is compressed waiting the transfer ports to open by the piston.

And so on.

If the previous are confusing, I can further explain.


An interesting question is how much less lubricant oil is required than in a conventional 2-stroke: because the OPRE Tilting takes the thrust loads away from the hot exhaust ports, at the “scavenge pump side” (or wrist pin side, or cool side) of the piston skirt.

Thanks
Manolis Pattakos

[gambler]

I've been experimenting with indexing the spark plug on a 2 stroke. It appears to keep the plug cleaner if the electrode is pointed toward the intake side(opposite of the exhaust), It's like the heat of the exhaust burns the oil residue off better. Any other thoughts on what is going on in there?

[J.A.W.]

I've been experimenting with indexing the spark plug on a 2 stroke. It appears to keep the plug cleaner if the electrode is pointed toward the intake side(opposite of the exhaust), It's like the heat of the exhaust burns the oil residue off better. Any other thoughts on what is going on in there?

Have you tried an annular discharge type plug, which does not have a ground strap?

Or an expensive rare metal thin electrode type, & seen any difference?

The combustion chamber design & mixture intake pattern may indicate a favourable index point..
.. for ignition kernel/flame front propagation..

& a freshly built top-end with polished components can be inspected after a brief running period to show tell-tale patterns in
the carbon residues left on the combustion chamber & piston crown..

There may well be some research documentation which shows high speed video of the process - on the test bench.

[gruntguru]

More likely the electrode is shielding the insulator from the incoming charge with its fuel and oil droplets. These would vaporize when striking the insulator, leaving a solid residue.

[gambler]

I've been experimenting with indexing the spark plug on a 2 stroke. It appears to keep the plug cleaner if the electrode is pointed toward the intake side(opposite of the exhaust), It's like the heat of the exhaust burns the oil residue off better. Any other thoughts on what is going on in there?

Have you tried an annular discharge type plug, which does not have a ground strap?

Or an expensive rare metal thin electrode type, & seen any difference?

The combustion chamber design & mixture intake pattern may indicate a favourable index point..
.. for ignition kernel/flame front propagation..

& a freshly built top-end with polished components can be inspected after a brief running period to show tell-tale patterns in
the carbon residues left on the combustion chamber & piston crown..

There may well be some research documentation which shows high speed video of the process - on the test bench.

Ill try one of those plugs, and Ill let you know. Thanks

[Brian Coat]

Hi

There's plenty of talk about HCCI in the threads above.

Time for some of that "occasional relevance" to F1?

Wasn't the first HCCI engine in volume production a 2-Stroke Honda the CRM250AR about 20 years ago?

(I'm not suggesting it's anything like what one would consider for F1in 2016!).

[uniflow]

Brian, it would seem there has been a lot of development by Honda and others on HCCI. Also it would seem that Ryger (if it were real) uses some kind of HCCI. The benefits are real, but all I've seen is part throttle HCCI use (apart from Ryger).
I'm sure I've posted it here before but I've had a go at building an HCCI engine myself, runs, a little hairy but it runs at full throttle with fuel only to regulate load (like a diesel), fuel is squirted into the inlet where the carb once was. It is a twostroke. It does not need recirculated exhaust gas as it just relies on sudden compression rise to ignite the mixture @ approx five to seven degrees ATDC on the working piston. My little engine uses a small piston in the combustion chamber, 38 x 16 bore and stroke, running at twice engine speed, to raise the compression to 21 to one at just the right time. At this pressure and temperature anything will "go off" in the combustion chamber. Simple but also not so simple mechanically. With a variable drive to this little piston I can control ultimate combustion point. This engine has no spark plug at all.
Subsequent runs now fitted with an exhaust pipe and now have some control with the fuel, I can modulate the engine with the spray gun. After this video clip I've rebuilt the top end with a much more robust two ring small piston as it only had a single ring weed eater piston, with a lot of blowby. Thats what killed it in the video.
https://youtu.be/TOHKls3Cxjs

[FW17]

Awesome

As usual 2 stroke proves to be extremely simple.

[manolis]

Hello.

Here is a Radial Cross 4-cylinder 2-stroke for small airplanes / helicopters, paragliding, etc:



It is better balanced than the best V-8 4-strokes.

The crankcase is not pressurized. A conventional turbocharger is used for the scavenging and the supercharging of the engine.

Plain bearings (actually a common plain bearing for the big ends of all the connecting rods).and pressurized lubrication in the crankcase.

The lower piston ring is a conventional oil scrapper -ring that never passes over ports.

When the piston is at its BDC, its lower compression ring abuts on the cylinder liner whereon the oil-scrapper ring of the piston was abutting at the previous TDC.

The lower side of the cylinder liner (wherein the piston skirt abuts and wherein the thrust loads are taken) is over-lubricated (as in the 4-strokes) with the oil scraper ring of the piston scraping the surplus oil back to the oil pan / crankcase.

The timing is asymmetric: the transfer extends substantially after the closing of the exhaust port providing additional time to the turbocharger to fill well the cylinder with pressurized air (and preventing the escape of this air to the exhaust).

Today they are in the market 2,000cc 4-stroke turbo Diesels having a power output of nearly 200PS.

With 80mm stroke and 90mm bore the Cross-Radial PatAT has a capacity of 2,000cc. The calculated weight (short crankshaft, no cylinder heads, air cooled etc) is around 35Kp(75lb).
Is a power output of 300PS too much for this 2-stroke?

For more: http://www.pattakon.com/pattakonPatAT.htm

Thoughts?

Objections?

Thanks
Manolis Pattakos

[tok-tokkie]

Why 4 connecting rods with big ends? Why not the usual master con rod with big end & the other 3 to knuckles on the master?

[Andres125sx]

Thoughts?

Objections?

Only admiration =D>

[manolis]

Hello Tok-Tokkie

You write:
“Why 4 connecting rods with big ends? Why not the usual master con rod with big end & the other 3 to knuckles on the master?”

Because the master-rod architecture causes several significant problems.


Quote from http://www.pattakon.com/pattakonPatAT.htm :

In comparison to the convetional Radial engine:



the Cross-Radial with the four cylinders and with the forked connecting rods is a true "vibration free" engine (better balanced than the "master-slave-rods" Radial regardless of the number of cylinders of the later), it is also a true "symmetrical" engine: all the four cylinders run under the same conditions: same piston stroke, same piston motion profile, same connecting rod leaning (thrust loads), etc.”

End of quote


As the above animation demonstrates, a typical Radial (master rod / slave rods) cannot help running with substantially different piston strokes in different cylinders.

If you look carefully at the above animation, you can see that the side pistons (at left and right) perform an about 10% longer stroke than the top and bottom pistons.
You can also check the leaning angles (relative to the axis of the respective cylinder) of the “slave” connecting rods.
The piston motion “profile” (defined as the piston travel (or displacement) versus the crank angle) is different for different cylinders around the engine. In the top cylinder (above animation) the piston motion profile is symmetrical. In the side cylinders the piston motion profile is highly asymmetric: at the one side of the engine the cylinders have slow compression and fast expansion, at the other side of the engine the cylinders have fast compression and slow expansion.

There are inertia vibrations in the conventional Radial engines (master rod – slave rods); in some cases there were used external balancing shafts to cancel them (a lightweight frame of an airplane is intolerable to vibrations).


Imagine trying to optimize a 4-in-line engine having a 100mm stroke for the two pistons and 110mm stroke for the other two pistons.


In order to achieve the vibration-free quality of the Cross-Radial 4-cylinder PatAT, you need an 8-cylinder 90-degrees-Vee 4-stroke with cross-plane crankshaft). Just compare the weight of the two crankshafts.

I hope it is now clear why the “master rod – slave rods” architecture is not better.

Thanks
Manolis Pattakos

[tok-tokkie]

Thanks for that reply. Makes me look at them differently from now on.

[Tommy Cookers]

master&slave rods worked rather well with the usual 9 or 7 cylinders per bank
the geometrical discrepancies being relatively less uneven

4 cylinders was rather unfavoured as un-symmetric (3,5,7,9, and 11 cylinders have been used, many engines without balancers)
the (liquid-cooled) 24 cylinder Rolls-Royce Vulture had 4 coplanar-cylinder banks and so asymmetric master+3 slave rods
4 cylinders might attract consideration of non-coplanar cylinders to allow rod arrangements more attractive in some ways
there is in current or recent Russian origin production a 7-bank liquid-cooled 42/56 cylinder turbocompounded CI engine

no doubt MP has considered many factors