2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello.

For substantially over-square designs (like, say, the Ducati Panigale 1299 wherein a 60.8mm stroke combines with a 116mm bore), the crankshaft is small relative to the cylinder head.

What if instead of combining two big cylinder heads with a common (and compact) crankshaft / crankcase (as happens in the Ducati Panigale), a unique cylinder head were combined with two crankshafts?

Here is a 4-stroke even-firing Opposed-Piston PatRoVa rotary valve engine, wherein a unique rotary valve serves two cylinders:



With load evenly distributed between the two counter-rotating crankshafts (like, say, two counter-rotating intermeshed propellers) the arrangement appears advantageous for some applications.

For instance, think of the balancing / vibration-free-quality of such a solution.
Or think how much the crankshaft balance webs can be reduced without affecting the balance.
Or think how much simpler the intake and exhaust plenums can be made.



Hello Tommy Cookers.

At http://www.connecticutscorsair.com/page ... istory.htm (about the Pratt & Whitney R-2800 Double Wasp Engine) there is this drawing:



wherein the stroke B of the third piston is shown substantially longer than the stroke A of the master rod piston. Reasonably this means unevenly spaced hinge-pins.

On the other hand, if this photo:



does show a R-2800 master rod, its hinge-pins are evenly spaced.

Either way, the unevenness – irregularity issues mentioned in previous posts remain.

Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis,
Is your PatRoVa system unable to cope with the required flow capacity for 2T function - as an opposed piston machine?
Why else would you want to essentially cripple it, by running it as a 4T?

& FYI, the P & W R-2800 underwent many significant design revisions, as power demands were raised..

[manolis]

Hello J.A.W.

You write:
“Why else would you want to essentially cripple it, by running it as a 4T?”

Because it is a fuel efficient and green 4-stroke engine.
Imagine it driving two counter-rotating electric generators to form a Range Extender Module (REM).
Its long shape makes easy its installation somewhere in an electric car.
Its perfectly vibration free quality fits with electric cars. Etc.


You alsowrite:
“Is your PatRoVa system unable to cope with the required flow capacity for 2T function - as an opposed piston machine?”

It would be useful if you could make a drawing of your “ideal” 2-stroke Opposed Piston with PatRoVa rotary valves controlling the exhaust and the transfer, in order to use it as a basis for discussion.

The PatRoVa is able for flow capacities substantially higher than the conventional poppet valves.


On the other hand, when there are substantially simpler and better solutions like the PatAT turbocharged Opposed Piston Diesel:



( more at http://www.pattakon.com/pattakonPatAT.htm )

why to add complication and cost and weight to the 2-stroke?

For instance, spot on the true spherical combustion chamber which is partly formed on the two piston crowns, and partly formed on the center of the casing (loop scavenging, independently in each cylinder); spot also on the location of the fuel injectors; count the moving parts; see how much asymmetric the transfer can be, while the phase difference of the two crankshaft is zero; spot on the 4-stroke like lubrication of the crankcases and of the lower sides of the cylinder liners.

Why to leave this simplicity and functionality for the sake of poppet valve or rotary valve Opposed Piston 2-strokes?

Thanks
Manolis Pattakos

[Tommy Cookers]

the AEHS article 'No Short Days' seems to say the R2800 had slave rod bigends at different distances from the crankpin centre (but at equal angles ?)
presumably the convention, to give a common TDC height regardless of stroke and much commonality of components

[Brian Coat]

For a hybrid range extender, the crankshaft etc could be dumped to save cost & mass?

What are people's views on best arrangement to drive a linear generator.

Opposed piston? 2/4 stroke?

Key requirements are compactness plus low NVH and high efficiency at a single operating point?

[manolis]

Hello Tommy Cookers.

Both, the angles of the hinge-pins around the master rod’s big end center and the eccentricities of the hinge-pins from the master rod’s center can vary to optimize “something” regarded by the designer as the most important.

As J.A.W. wrote, there were various versions, each with its own “optimization” and asymmetry.

Carl D. Sorensen at http://www.pattakon.com/tempman/Radial_ ... _Slave.pdf “complains” that:
“I have not been able to get TDC position, stroke, and TDC timing errors all
to be very close to zero simultaneously.”

Even if there were a way to eliminate the errors in TDC position, stroke, and TDC timing simultaneously, even then there is an inherent asymmetry in the Radial engines based on master rod / slave rods: the piston motion profile around a row of cylinders varies significantly. Also the compression in some cylinders is substantially faster than in other cylinders (it is like operating some cylinders at higher revs). The same for the expansion. The same for the instant torque provided by each cylinder vs the crank angle. The same for the leaning of the connecting rods and the resulting thrust loads.

Despite all these “issues”, the simple and compact and lightweight structure of the conventional Radials was a great advantage for airplanes.


In comparison, the structure of the Cross-Radial PatAT with the four only pistons:



does eliminate the errors in TDC position, stroke, and TDC timing simultaneously, and does keep identical all piston motion profiles.
It also eliminates all free inertia forces, moments and torques (more vibration free than the best V-8 4-stroke conventional engines).

Thanks
Manolis Pattakos

[manolis]

Hello Brian Coat

A linear generator is neither as efficient, nor as lightweight as a conventional “rotary” generator.

A few posts ago there is the animation of an “Opposed Piston” 4-stroke with a common PatRoVa rotary valve in the middle.

Here is a version with the spark plugs at the same side:



Suppose it is the basis for a REM (Range Extender Module) for electric cars.

Suppose it is made using two CFR250 Honda “crankshaft / connecting rod / piston” assemblies.

It is not only that you don’t need external balancing shafts any longer (the cost of the balance shaft of the CFR250 is about half of the cost of a crankshaft / con-rod assembly, it adds friction, it adds weight, it adds problems),
it is not only that you can grid / remove a big part of the balance webs of the crankshafts (because you have only to counterbalance the big end of the connecting rod and the crankpin), which means lower weight,
it is also that the set of the two oppositely arranged cylinders is perfectly balanced.

With one generator driven by each crankshaft (or with a propeller driven by each crankshaft for a 4-stroke Portable Flyer), the set is perfectly vibration-free. You can’t have a more vibration free gen-set or REM.

With the rotary valve there are not poppet valves landing / hitting on their valve seats, which means quieter operation.

Its long and thin shape makes easy the installation somewhere in the electric car.

Among its key advantages: compactness, lightweight, low NVH, low cost, high fuel efficiency, low emissions, high power to weight ratio etc.

Thanks
Manolis Pattakos

[Brian Coat]

Thanks.

Yes, I saw that post.

I find the free piston linear engine interesting, if challenging.

[J.A.W.]

Hi Manolis,

The reason I was curious about the PatRoVa running as a 2T, was the non-concern about piston ring-crossing of ports.

[manolis]

Hello J.A.W.

You write:
“The reason I was curious about the PatRoVa running as a 2T, was the non-concern about piston ring-crossing of ports.”

Exactly this is what the PatPortLess engine at http://www.pattakon.com/pattakonPatAT.htm does:



Don’t look at the big inlet (transfer?) valve on the piston crown; it can be replaced by four inlet / transfer poppet valves covering all the piston crown, as shown in other animations.

Similarly for the PatMar engine at http://www.pattakon.com/pattakonPatMar.htm

With exhaust poppet valves covering the cylinder head and inlet / transfer poppet valves covering the piston crown, the valve area doubles as compared to the case with valves only on the cylinder head.

The piston rings never pass over ports (no piston ring-crossing of ports).

The scavenging is uniflow: the fresh charge passes from the piston crown and pushes out / expels the burnt gas.

A limitation is that the revs cannot be too high because the poppet valves open and close twice as fast as in a 4-stroke engine. Yet this limit is not too low: a KTM-250cc (78mm bore) with 32.5mm titanium intake valves has the red line at 14,000rpm. A PatPortLess with four such inlet valves on its piston crown would run reliably at, say, 7,000rpm.


With PatRoVa rotary valves on the cylinder head, the inlet valve area and the exhaust valve area are substantially reduced: less than half of the cylinder head can be used for exhaust, less than half of the cylinder head can be used for inlet / transfer.

Does it matter that the valves can now operate at extremely high revs?

Besides, in order to improve the scavenging efficiency, the shape of the combustion chamber worsens.
This is why I asked you to make a drawing of your ideal PatRoVa portless 2-stroke.


On the other hand, the inherent simplicity of the 2-stroke combined with built-in asymmetric transfer, as in the following stereoscopic animation (more about how to see stereoscopically at http://www.pattakon.com/pattakonStereoscopy.htm ) seems interesting for some applications:



Thanks
Manolis Pattakos

[manolis]

Hello all.

Here:



it is a V-90 2-cylinder short-stroke PatRoVa rotary valve engine:


Here:



is the Ducati Panigale V-90 engine.

Here:



it is the one cylinder liner of the Ducati Panigale (look at the deep valve pockets on the piston inside the cylinder liner).

Here, the above cylinder liner is shown alone:



Here, the above cylinder is shown from the side:



And here:



they are shown the parts inside each Panigale Desmodromic cylinder head of Ducati (excluding the camshafts).



Here:



it is shown the above PatRoVa V-90 from various viewpoints for more details.


Conventionally, between (and “above”) the two halves of the Ducati Panigale casing:



they are secured a pair of Ducati cylinder liners and a pair of Ducati Desmodromic cylinder heads to form the Ducati Panigale engine:


Unconventionally, between the two halves of the Ducati Panigalle casing they can be secured a pair of PatRoVa “cylinder liner / cylinder head” (the cylinder liner together with its cylinder head is one piece, eliminating the gasket and improving the cooling), to form a Ducati PatRoVa V-90 engine which, among others, is:

- more Desmodromic than the Ducati Panigale (there are no restoring springs, at all),

- more high revving than the Ducati Panigale (the cylinder head has not rev limit any longer), for substantially higher specific power,

- way simpler and cheaper than the Ducati Panigale (just count the number of parts).

Thoughts?

Objections?

Thanks
Manolis Pattakos

[Brian Coat]

It is difficult to assess the various proposed PatRova *configurations* without the basic concept having being properly tested/developed/proven in an engine lab.

Although the concept testing only requires a different cylinder head with appropriate instrumentation, the *facilities* may be a current constraint?

Idea: This could be installed on a standard single cylinder research engine (e.g. Ricardo Hydra). The advantage would be that some universities and research establishments already have these facilities. Then you need to find one that sees the PatRova work as interesting as a student/research project ... that's where I run out of ideas I'm afraid but you may know of somewhere/one.

[tok-tokkie]

Hello Tommy Cookers.

Both, the angles of the hinge-pins around the master rod’s big end center and the eccentricities of the hinge-pins from the master rod’s center can vary to optimize “something” regarded by the designer as the most important.

As J.A.W. wrote, there were various versions, each with its own “optimization” and asymmetry.

Carl D. Sorensen at http://www.pattakon.com/tempman/Radial_ ... _Slave.pdf “complains” that:
“I have not been able to get TDC position, stroke, and TDC timing errors all
to be very close to zero simultaneously.”

Even if there were a way to eliminate the errors in TDC position, stroke, and TDC timing simultaneously, even then there is an inherent asymmetry in the Radial engines based on master rod / slave rods: the piston motion profile around a row of cylinders varies significantly. Also the compression in some cylinders is substantially faster than in other cylinders (it is like operating some cylinders at higher revs). The same for the expansion. The same for the instant torque provided by each cylinder vs the crank angle. The same for the leaning of the connecting rods and the resulting thrust loads.

Despite all these “issues”, the simple and compact and lightweight structure of the conventional Radials was a great advantage for airplanes.


In comparison, the structure of the Cross-Radial PatAT with the four only pistons:

http://www.pattakon.com/PatAT/PatAT_Cross_Radial_1.gif

does eliminate the errors in TDC position, stroke, and TDC timing simultaneously, and does keep identical all piston motion profiles.
It also eliminates all free inertia forces, moments and torques (more vibration free than the best V-8 4-stroke conventional engines).

Thanks
Manolis Pattakos

Hi,
You state that it 'eliminates all free inertia forces, moments and torques ...'
Four stroke boxer engines have a double throw crank so both pistons reach TDC simultaneously thereby balancing their rocking couple. You cross radial does the converse. You have balancing software but I must say I remain sceptical.
I much appreciate what you have posted on this thread - I have learned much, particularly the WW2 rotary engine differences in stroke.
I don't understand how your PatRoVa overcomes the sealing challenge that all rotary valves come up against. But it certainly makes an elegant alternative to desmodromic valves. I know you have had a demo engine running but it would be graet to see PatRoVa heads on a Ducati bottom end.

[manolis]

Hello Tok-Tokkie.

You write:
“Four stroke boxer engines have a double throw crank so both pistons reach TDC simultaneously thereby balancing their rocking couple. You cross radial does the converse. You have balancing software but I must say I remain sceptical.”

A boxer is not so good, as explained below.

In a conventional boxer (say, BMW R1200GS motorcycle) the two cylinder axes are at a substantial offset from each other:



In the following drawing the cylinder offset is more obvious:



With a, say, 25mm wide web between the two crankpins and with a 20mm wide connecting rod big-end, the overall offset between the two cylinder axes is: 25+2*(20/2)=45mm.

While the inertia force from the one piston is equal and opposite to the inertia force from the other piston, these two forces are at a significant (say 45mm) offset. The result is zero total inertia force plus an unbalanced free inertia moment (or pair of forces). The balance webs on the crankshaft can cancel only a part of this inertia moment. The rest vibrates the engine.

With the two pistons stopping simultaneously at their TDC’s, and being simultaneously at their middle stroke, i.e. near their maximum speed, another kind of vibration results.
It is the inertia torque.
The set of crankshaft / flywheel has to accelerate when the two pistons are approaching their TDC’s (to absorb the kinetic energy of the pistons), and to decelerates when the two pistons are leaving their TDC’s (to provide the required kinetic energy to the pistons).
You can think of it by considering the inertia thrust forces acting on the cylinder liners due to the con-rod leaning, but the energy approach seems simpler. The inertia thrust forces on the two cylinder liners is a pair of forces (a torque, a moment) that tries to vibrate the casing about the crankshaft axis.



Take now the Cross-Radial PatAT engine:



In this PatAT Cross Radial the combustion chambers are formed in the cylinder heads and not on the piston crowns (colder pistons).

All the cylinder axes are coplanar.

Let’s calculate the location of the center of gravity of the four pistons with simple geometry.

The center of gravity C1 of the set of the bottom left and of the top right pistons (driven by the unique crankpin through the green and red connecting rods, respectively) is the projection of the crankpin center K onto the common axis of these two cylinders (note: the triangle formed by the red and green connecting rods is isosceles).

Similarly the center of gravity C2 of the set of the top left and right bottom pistons (driven by the crankpin through the blue and brown connecting rods, respectively) is the projection of the center K of the crankpin onto the common axis of these two cylinders. This axis is normal to the other diagonal axis.

The center of gravity C of all the four pistons is the center of gravity of the abovementioned two sets of pistons, so it is in the middle of the line C1-C2 connecting the above two centers of gravity.

This point C is in the middle of the line K-O from the center K of the crankpin to the center O of the crankshaft (where the two cylinder axes intersect).

So, the center of gravity of all the four pistons is at a constant distance from the center O of the crankshaft and follows the rotation of the crankpin (i.e. it rotates with constant angular velocity). You can make the confirmation by the balance.exe program at http://www.pattakon.com/pattakonEduc.htm

With a pair of balance webs secured on the crankshaft, the inertia force is perfectly balanced, the inertia moment is zero (all cylinder axes are coplanar), as for the inertia torque, it is almost zero (dozens of times smaller than in a Boxer with 2 or 4 cylinders).

In comparison to the best V-8 four-stroke engines, this 4-cylinder 2-stroke Cross Radial PatAT engine is better balanced from any point of view: zero free inertia force instead of a small 4th order unbalanced inertia force in the V8, half inertia torque than the V-8, equal intervals between successive combustions.

If something is unclear, please let me know to further explain.



You also write:
“I don't understand how your PatRoVa overcomes the sealing challenge that all rotary valves come up against.”

When you have to deal with tons of force pressing outwards (relative to the combustion chamber) the rotary valve and its bearings, it is impossible to maintain the required small / tiny clearance in order to achieve good sealing and small leakage.
.
The PatRoVa rotary valve is different than all other rotary valves.

Compare it to, say, the Bishop – Cross rotary valve that came near to success in Formula1 (if the F1 rules were not changed to abandon the rotary valves, it could be the permanent winner now).

The Bishop rotary valve is a thin cylinder with an oblique separator at its middle, with the one side being red-hot and with the other side being cool. During combustion, the two bearings of the Bishop –Cross rotary valve receives a huge force (like 3 tons upwards). The two bearings are at the sides of the cylinder, i.e. at some 100+ mm from each other, with the one bearing running too hot. The valve bends due to the force load due to the high combustion pressure, and distorts due to its highly asymmetric structure and due to its highly asymmetric thermal loading.

It is impossible to keep the required tiny clearance without using sealing means. Sealing means means need for lubrication, extra friction, wear, cost etc.

Despite all these sealing problems, despite the need for cooling the exhaust side / exhaust bearing, despite the side located spark plugs (the “window” between the valve and the combustion chamber covers the central part of the bottom of the cylinder head), despite the added complexity associated with the driving of the Bishop –Cross rotary valves (count how many gearwheels and bearings and space are required):



it came near to success (some 10% more power than the best poppet valve Formula1 engines, according Mercedes and Ilmor)


To put it differently: the minimum required clearance of the big diameter bearings (big diameter because the working medium passes through them) of the Bishop – Cross rotary valve is more than the tiny clearance required for a decent sealing.

In comparison, the symmetric and extremely robust structure of the PatRoVa rotary valve, the zero total force it receives due to the high pressure in the combustion chamber, the independence of its sealing clearance from the clearance of its bearings, its independence from deformations along the two – of the three – dimensions, the from the combustion chamber, etc, etc, distinguish it from the rest rotary valves.



I hope it is now more clear the difference between the PatRoVa rotary valve and the rest rotary valves of the state-of-the-art.

Thanks
Manolis Pattakos

[manolis]

Hello Brian Coat.

You write:
“It is difficult to assess the various proposed PatRova *configurations* without the basic concept having being properly tested/developed/proven in an engine lab.”

You are right.

On the other hand, a few Rotary Valve designs came near to success (Cross, Cross – Bishop, Cross – Ralf Watson, Coates CRSV, etc).
In the hindsight it seems their basic principles were wrong.
They solved the original problem (rotary valves instead of reciprocating poppet valves) by creating other significant (and more difficult to be solved) problems / side effects.


Quote from http://www.douglas-self.com/MUSEUM/POWE ... alveIC.htm

“The basic problem, is that the pressures in the cylinder of an internal combustion engine are high, due to both the compression stroke and the explosion of the fuel-air mixture. This produces large forces on the valve system, however it is contrived; the beauty of the poppet valve is that such forces simply push it harder against its seat, and have no effect at all on the valve-actuating mechanism.

However, the geometry of rotary valve systems is inherently different; in the Aspin concept below, the vertical valve cone is pushed up axially against the cylinder head, while the horizontal Cross valve is pressed up against the top half of the bearing surfaces. In both cases this can cause excessive friction and seizure, the root of the problem being that enormous forces are acting on the valve while it is moving.”

End of Quote.


Theoretically the PatRoVa rotary valve seems to answer the above problems of the rotary valves of the prior art.



You also write:
“Idea: This could be installed on a standard single cylinder research engine (e.g. Ricardo Hydra). The advantage would be that some universities and research establishments already have these facilities. Then you need to find one that sees the PatRova work as interesting as a student/research project ... that's where I run out of ideas I'm afraid but you may know of somewhere/one.”

For an engine maker having the required machinery and staff, the construction and the basic testing of a PatRoVa rotary valve engine is a matter of a few days, not of weeks.

For a University it would take no more than a couple of weeks.

From experience, there is no interest. They prefer the conventional solutions because they make money without risk.

If somebody will ask for our support to make some PatRoVa prototypes for tests / evaluation, we will help.


Till then, the best idea seems to put the PatRoVa directly in practice (on the roads) and challenge the champion.

With a modified to PatRoVa Ducati Panigale on the roads beating the conventional Ducati Panigale, things gets straightforward.



Why a two cylinder V-90 instead of a single cylinder engine?

Because in the single you have to add one or two external balance shafts (weight, cost, additional bearings, friction, extra space, complication etc) to reduce the inertia vibrations, while in the V-90 the second piston besides offering a much better vibration-free quality (think of the elimination of the inertia torque on the rear tire of a motorcycle) it also doubles the power and lowers the specific friction.

To take an idea, the balance shaft for a Honda CFR250 costs about half than what costs the set of crankshaft / connecting rod.

Thanks
Manolis Pattakos