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Old 01-08-2017, 04:18 PM   #1
manolis
 
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Default PatWankel Rotary Engine

I just received this email from your forum:

"manolis,

We have been missing you on Home Model Engine Machinist for some time now.

If you get a chance, please log in and let us know what you've been doing lately.

http://www.homemodelenginemachinist.com"



In response, here is the PatWankel Rotary Engine, the most recent project we are dealing with:



The working surface whereon the seals abut is not a “cylindrical” surface but a 3D curved surface ending smoothly / tangentially on the side flat surfaces of the casing.









The typical “Wankel sealing grid” (wherein: each combustion chamber is sealed by a set of two side seals, two apex seals and four button (or corner) seals) can be replaced by a single piece seal per combustion chamber.



Here is a PatWankel wherein the working surface is on the inner body (say as in the Liquid Piston engine):











One seal per combustion chamber, as in the reciprocating piston engines.



This five “cylinder” PatWankel rotary ( stereoscopic view, as at http://www.pattakon.com/pattakonStereoscopy.htm ) :



has two combustions per rotation of the inner body, i.e. as much as a two-rotor Wankel Rotary (say, Mazda RX-.







Does the oval seal at bottom middle remind the Honda NR750?

Imagine this PatWankel engine at the back of an airplane pushing forwards:





The outer body (that with the cooling fins) spins at 4/5 (80%) of the speed of the inner body:



There is no eccentric shaft.
There are no balancing webs.
However it is perfectly balanced.


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


Thoughts?

Objections?

Thanks
Manolis Pattakos


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Old 01-08-2017, 04:48 PM   #2
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Here we go again,look's like Manolis has invented the Wankel engine this time.


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Old 01-08-2017, 05:14 PM   #3
Charles Lamont
 
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Quote:
Originally Posted by Vixen View Post
Here we go again,look's like Manolis has invented the Wankel engine this time.
But with even more narrow crannies to hide the gases in, and, oh joy, even more diagrams.
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Old 01-08-2017, 05:23 PM   #4
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The main problem:
1. The tools to create the shape of rotor and rotorhouse.
2. Will it last and how to ovehaul the engine?

Manolis is clever in drawings of wankel engine and lack of tools to create the real wankel engine.
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Old 01-09-2017, 05:25 AM   #5
manolis
 
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Hello all.



I think the following analysis and quotes can make clearer the reasoning behind the PatWankel engine.

In the conventional Wankel Rotary the flame sees way bigger surfaces (and has to travel along way longer distances) than in a conventional engine.

The surface to volume ratio during combustion, only partly explains the increased thermal loss and the emissions of the Wankel.

The high surface to volume ratio is one only of the issues of the conventional Wankel.


According the “Liquid Piston” at www.liquidpiston.com, their non-Wankel engine



runs closer to a constant volume combustion than the reciprocating piston engines.

Last year DARPA signed a $1M agreement with Liquid Piston.


Take the five “cylinder” PatWankel shown in the drawings / animation.
At TDC (i.e. wherein the volume of the working chamber is minimised) almost all the air / mixture entered into the working chamber is concentrated in a compact cavity (spherical or semi-spherical etc).

As compared with a Ducati Panigale 1299cc reciprocating piston engine running at the same revs with the revs of the inner body of the PatWankel, the PatWankel provides more than 40% additional time around the TDC (1.15*1.25=1.43)

The 15% longer dwell at the TDC comes from the harmonic (i.e. pure sinusoidal) variation of the combustion chamber volume:



the 1.25 comes from the 225 degrees required in order the chamber to go from its TDC to its BDC (wherein the volume is maximised):



There is plenty of time, lots of squeeze and a very short distance for the flame to travel, enabling the combustion to actually complete inside the compact cavity.

Most of the thermal loss happens during the combustion.

The thermal loss continuous during the expansion, however the rate of thermal loss during the combustion is way higher.

Compare it with the thermal loss in a Ducati Panigale 1299 wherein the flame, during the combustion, sweeps the inner surfaces of a wide (116mm diameter) short (about 5mm height) cylinder (like a coin) having abnormal bottom and top (valve pockets etc).
Reasonably, the thermal loss towards the walls during the combustion will be substantially more than in the above PatWankel.


So, there are reasons for lower thermal loss in the PatWankel, despite the bigger (than in a reciprocating piston over-square engine) area of its wall surfaces.


Quote from:
http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2467298

“Abstract
The Wankel rotary engine offers a greater power density than piston engines, but higher fuel consumption and hydrocarbon emissions, in large part due to poor gas sealing. This paper presents a model for the deformable dynamics of the side seal, which completes a set of modeling tools for the comprehensive assessment of the gas leakage mechanisms in the rotary engine. It is shown that the main leakage mechanisms for the side seals are: (1) opening of the inner flank due to the contact with the trailing corner seal, (2) flow through the gap with the leading corner seal, (3) simultaneous opening of both inner and outer flanks due to body force at high speed, and (4) running face leakage due to nonconformability at high speed. The leakage mechanisms are qualitatively validated at low speed with observed oil patterns on the rotor from laser-induced fluorescence (LIF) experiments. Finally, the predicted total leakage area for all the gas seals ranges from 1.5 mm2/chamber at low speeds to 2 mm2/chamber at high speeds, which is in agreement with the previous experimental studies, and the three gas seal types (side seals, apex seals, and corner seals) each accounts for about 1/3 of the total leakage, with minor variation as a function of speed.”



End of Quote


According the above abstract / plot, the leakage is a major problem / issue of the Wankel rotary engines.

Each cylinder of the Panigale 1299 has a capacity of 650cc, i.e. as much as each chamber of the Wankel RX-8.
Take a drill and make one hole of 1.5mm diameter (1.77mm2 area) on each piston crown of the Ducati Panigale, to allow each combustion chamber to communicate, through the hole, with the crankcase.
No doubt, the Panigale can still work, however a significant amount of high pressure gas will escape reducing the efficiency (a lot of energy is consumed to compress the gas that leaks without giving back any energy) and worsening the emissions.

This is the way the conventional Wankel works till now.
The gaps around each combustion chamber have an equivalent total leakage area of 1.5mm2 at low revs, to 2mm2 at high revs.

Compare the leakage from the “running surfaces” with the rest leakage.


Quote from http://energyresources.asmedigitalcollection.asme.org/article.aspx?articleid=2522107

“Numerical Investigation on the Effects of Flame Propagation in Rotary Engine Performance With Leakage and Different Recess Shapes Using Three-Dimensional Computational Fluid Dynamics”

ABSTRACT

This study was carried out with an objective to develop a 3D simulation methodology for rotary engine combustion study and to investigate the effect of recess shapes on flame travel within the rotating combustion chamber and its effects on engine performance. The relative location of spark plugs with respect to the combustion chamber has significant effect on flame travel, affecting the overall engine performance. The computations were carried out with three different recess shapes using iso-octane (C8H1 fuel, and flame front propagation was studied at different widths from spark location.
Initially, a detailed leakage study was carried out and the flow fields were compared with available experimental results. The results for first recess with compression ratio 9.1 showed that the flow and vortex formations were similar to that of actual model. The capability of the 3D model to predict the combustion reaction rate precisely as that of practical engine is presented with comparison to experimental results. This study showed that the flame propagation is dominant toward the leading apex of the rotor chamber, and the air/fuel mixture region in the engine midplane, between the
two spark plugs, has very low flame propagation compared to the region in the vicinity of spark. The air/fuel mixture in midplane toward the leading apex burns partially and most of the mixture toward the trailing apex is left unburnt. Recommendations have been made for optimal positioning of the spark plugs along the lateral axis of the engine. In the comparison study with different recess shapes, lesser cavity length corresponding to a higher compression ratio (CR) of 9.6 showed faster flame propagation toward leading side. Also, mass trapped in working chamber reduced and developed higher burn rate and peak pressure resulting in better fuel conversion efficiency.
Third recess with lesser CR showed reduced burn rates and lower peak pressure.



End of Quote.


It is more complicated than “surface to volume” ratio.

According the last plot, if the leakage is avoided, the same Wankel increases its power, reducing at the same time its brake specific fuel consumption (g/kWh).

The surface to volume area remains as high as before.

So, if we could reduce substantially the leakage in the conventional Wankel, an significant increase of the power output and a significant decrease of the BSFC are expected.

This is what the following PatWankel:



does: it reduces the gas leakage to levels met in the reciprocating piston engines.

If the plot of ASME is not wrong, the improvement (on the power output and on the mileage) on a Mazda RX-8 when modified to PatWankel would be significant.


But there is more.


The other version of the PatWankel (the PatWankel wherein the seals slide onto the surface of the inner body) besides reducing the leakage it performs another significant “task”: it enables a compact combustion chamber to be formed, wherein almost all the mixture is concentrated and is burnt before the expansion.

This improvement may prove in practice more important than the significant reduction of the gas leakage.


The mechanical friction in a rotary engine like the PatWankel 5-cylinder is substantially lower than in an “equivalent” reciprocating piston engine.
There is no valve train.
There are no piston skirts to thrust on cylinder walls.
The four roller bearings on the frame and the sliding of the seals on the working surface are the only cause of mechanical friction.
All the energy / torque passes directly through the shaft of the inner body to the load.
The outer body receives no torque, at all.


If you count all these together (improved sealing, fast combustion into a compact cavity, reduced mechanical friction, simplicity etc) things get more than interesting.



The following animation may-be useful for timing-check reasons:



The angle step is 10 degrees (as in the conventional engine, 180 degrees separate the TDC (wherein the volume of a working chamber is minimized) to BDC (wherein the volume of the same working chamber is maximized).

Start counting “frames” (and degrees) the moment the inner body is “horizontal” with the ports at right.

The timing shown is conservative.

The “overlap” may seem big, but it is quite small. This is so because during the “overlap” either the intake ports, or the exhaust ports, or both, are almost closed by the inner surface of the outer body.
The overlap in this engine is way different than in a, say, Ducati Panigale:



wherein overlap means, more or less, the “short circuit” between the intake and the exhaust (the area marked by the yellow ellipses) and inevitable loss of unburned mixture,
while in the above PatWankel overlap means a through or uniflow “scavenging” of the chamber by the fresh charge (more or less as in the opposed piston engines) that sweeps / pushes out the burned gas and reducing this way the residual gas.




By the way:


Last month LiquiddPiston received another $2.5 million from DARPA for their rotary engine.
More important: LiquidPiston also received a $25,000 cash prize from Shikorsky along with the opportunity to explore opportunities for LiquidPiston's technology with the Shikorsky product line




Thanks
Manolis Pattakos
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Old 01-10-2017, 02:27 PM   #6
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Fascinating. The problem with the Wankel, Liquid Piston, and similar concepts has always been sealing. Their designs were 2D concepts that could be made accurately with 20th century methods. However, a piston and cylinder was the only way to get a reasonable seal with these methods. Now we can produce complex 3D shapes with high accuracy thanks to digital technology. Maybe for the first time we can seal an engine like this. I am very interested in how you propose to make this engine.

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Old 01-10-2017, 05:40 PM   #7
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Hello Lohring

You write:
“Fascinating. The problem with the Wankel, Liquid Piston, and similar concepts has always been sealing. Their designs were 2D concepts that could be made accurately with 20th century methods. However, a piston and cylinder was the only way to get a reasonable seal with these methods. Now we can produce complex 3D shapes with high accuracy thanks to digital technology. Maybe for the first time we can seal an engine like this. I am very interested in how you propose to make this engine.”


Having the two radiuses (the “crank arm” R1 and the “rotor” radius R2) and the shape of the selected seal (semicircle? oval? Etc), the geometry of the working surface S is fully defined.



A spherical cutting tool is the best for the machining.

Having the radius r of the spherical cutting tool, what is required is a “3-D Offset” by r of the working surface S to a surface S1 whereon the center of the cutting tool will “move” in order to create the S surface. Easier than what it seems initially.

The CNC milling machine is programmed to move the center of the cutting tool on the S1 surface. This will create the S surface on the metal.

If the CNC milling machine has, besides the typical three axes, a fourth axis (rotation about an axis) things get easier. The complete working surface can be made without removing the part.

Otherwise (case without a fourth axis) the working surface will be machined in two (or more) steps.

With the working surface being the external surface of the inner body, the machining is easy. The hollow shaft is ideal for holding the part during the cutting.

The passageways inside the inner body need not accuracy, so the inner body can be mold made of, say, spheroidal graphite iron. Then its external surface is machined as above.


The outer body is to be made of two halves secured to each other. It needs not special accuracy except from the grooves for the seals.


The gearwheels are conventional and easy to be made.


The seals can be cut accurately with a wire EDM machine. After their bending (to fit in the grooves) they need hardening.


If the above are confusing, please let me know to further explanation.


Thanks for asking
Manolis Pattakos
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Old 01-10-2017, 06:58 PM   #8
Buchanan
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I will have to try this new method of bending seals in my next engine, it sounds so easy to make flat strips and then just bend them. No more turning rings, then cutting them, then the heat treatment, this must be a winner.
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Old 01-11-2017, 12:49 PM   #9
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I doubt that milling will leave an accurate and smooth enough surface on the outer case to get good sealing. However, a CNC grinding machine should be able to produce an accurate surface in the same way. An even better surface finish will still be required from some kind of honing or superfinishing method. The inner element can probably be made accurately enough with milling or even advanced 3D printing. Accurate bending of the rings is also tough. NC wire benders might do the job, but I'm not familiar with their accuracy. The first working model will answer a lot of questions and expose the weaknesses of the design. My experience in product development a long time ago found that you never foresaw most of the problems until you actually had them.

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Old 01-11-2017, 05:48 PM   #10
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Hello Lohring.

You write:
“I doubt that milling will leave an accurate and smooth enough surface on the outer case to get good sealing. However, a CNC grinding machine should be able to produce an accurate surface in the same way. An even better surface finish will still be required from some kind of honing or superfinishing method.”

You are right about the finishing.

However, when you built one prototype and the budget is limited, after the milling there are simpler/cheaper ways to finish / to polish the working surface.


You are wrong in that the accurate and smooth enough surface (the working surface whereon the seals abut and slide) is on the outer body / case. It is on the inner (the red) body:



On the external surface of the inner body (red) is whereon the seals abut and slide.

Only the grooves, made on the outer body / case, need high accuracy. The rest inner surface of the outer body (blue) is not a working surface: nothing slides on it; it gets in contact only with the gas.



You also write:
“Accurate bending of the rings is also tough. NC wire benders might do the job, but I'm not familiar with their accuracy.”

It seems what I wrote for the seals was confusing (Hello Buchanan).

Let me explain what I meant:

From a steel sheet (say 1.5mm width) with a wire EDM machine the seal is cut accurately, say, as it appears at bottom – middle in this drawing:



Then the seal is slightly bend to fit in its groove on the external body (as shown at bottom left and bottom right, radius R2). The radius R1 remains unaffected by this smooth bending.

With a nitride surface hardening the dimensions remain unchanged and the seal is ready to be used.

The seal needs a cut somewhere, say as shown here (bottom middle):

.


Worth to be noted: we talk for the manufacturing of one prototype PatWankel engine at low cost. Not for production.

So, the R1 surface does not result from the bending of a metal strip. It comes from the accurate cutting, with a wire EDM machine, of a steel sheet.

I hope it is more clear now.

Thanks
Manolis Pattakos


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