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PatATE: Asymmetric Transfer and Exhaust in two-stroke engines


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#1 manolis

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Posted 24 June 2017 - 15:45

Hello all.

 

Here is an unconventional two-stroke (the PatATE) in comparison to a conventional two-stroke:

 

PatATE_1.gif

 

The main difference is that the exhaust port is now a "hybrid" port (the 4): at the end of the expansion the valve 7 connects the hubrid port with the exhaust passageway 5, and the exhaust starts the conventional way.

 

Later the valve 7 opens the transfer passageway 6 and seals the exhaust passageway 5; the exhaust continues through auxiliary (and "lower") exhaust ports 8; the transfer uses the conventional (symmetrical) transfer port 9 and the hybrid port 4.

 

Later the piston closes the conventional transfer port 9 and the auxiliary exhaust ports 8. 

 

In the conventional two-stroke the exhaust remains open for several degrees (while the transfer is closed). In the PatATE the transfer continous (while the exhaust is closed). Regarding the operation of the engine, it looks like a significant difference.

 

Here are some more drawings / graphs:

 

PatATE_2.gif

 

PatATE_3.gif

 

PatATE_4.gif

 

PatATE_5.gif

 

PatATE_6.gif

 

 

For more: http://www.pattakon....takonPatATE.htm

 

Thanks

Manolis Pattakos



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#2 gruntguru

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Posted 24 June 2017 - 22:04

How is it actuated?



#3 manolis

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Posted 27 June 2017 - 03:40

Hello Gruntguru.

 

Depending on the engine, the valve can be activated either mechanically (a cam lobe on the crankshaft and a linkage), or electro-magnetically (as shown in the last drawing of my previous post), or . . .

 

For high revving, an option is the use of a rotary valve for the control of the communication of the hybrid port(s) with the transfer and the exhaust passageways, say like:

 

PatATE_Rotary_2.gif

 

PatATE_Rotary_3.gif

 

PatATE_Rotary_1.gif

 

There are two hybrid ports arranged anti-diametrically on the cylinder liner.

 

The timing plot reminds “4-stroke” timing plots:

 

PatATE_Rotary_Timing.gif

 

In the specific case, but not necessarily, the rotary valve rotates at crankshaft speed:

 

PatATE_Rotary_Anim_2.gif

 

PatATE_Rotary_Anim_3.gif

 

PatATE_Rotary_Anim_5.gif

 

More at http://www.pattakon....takonPatATE.htm

 

Thanks

Manolis Pattakos



#4 manolis

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Posted 30 June 2017 - 12:02

Hello all.
 
 
In the following two animations, besides the exhaust and transfer it is also shown the asymmetric intake port:
 
PatATE_Rotary_Anim_7.gif
 
PatATE_Rotary_Anim_8.gif
 
 
 
The following plot and animation has been added in the http://www.pattakon....takonPatATE.htm web page.
 
They show a possible timing for the PatATE with the rotary valve.
 
PatATE_Rotary_Timing_Plot.png
 
PatATE_Rotary_Timing_fast.gif
 
The same animation at slow motion is at http://www.pattakon....Timing_slow.gif
 
Thanks
Manolis Pattakos


#5 Kelpiecross

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Posted 01 July 2017 - 03:12

Flap valves never seem to work all that well - maybe use a conventional poppet valve? And maybe a poppet valve for the intake as well? - but keeping the exhaust valve in the side position to get a "uniflow" effect. Any mechanically-operated valve is going to have speed of operation problems in a two-stroke.

A rotary valve is going to have the usual rotary sealing problems. There have been very successful model plane two-strokes with rotary valve action but in this case the whole cylinder revolved. Maybe a revolving cylinder liner (and head?) similar to a sleeve valve 4-stroke engine?

Edited by Kelpiecross, 01 July 2017 - 03:14.


#6 manolis

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Posted 01 July 2017 - 11:29

Hello Kelpiecross.

 

The rotary valve is not dealing with the sealing of the combustion chamber.

 

The piston with the piston rings that slide on the (stationary) cylinder liner do the sealing, as in the conventional two-strokes.

 

The rotary valve is arranged outside the cylinder liner, around the hybrid ports, and needs not tight sealing. 

It just controls the flow of the exiting gas and of the entering gas.

 

In the following animation the rotary valve and the casing are sliced to show how the exhaust and transfer passageways formed in the rotary valve cooperate with the hybrid ports to give asymmetrical exhaust and transfer:

 

PatATE_Rotary_Timing_2.gif

 

And looking from the cylinder head (the exhaust passageways are shown by purple color):

 

PatATE_Rotary_Timing_3.gif

 

 

If it is not yet clear how it works, please let me know to further explain.

 

Thanks

Manolis Pattakos


Edited by manolis, 01 July 2017 - 11:33.


#7 manolis

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Posted 06 July 2017 - 03:18

Hello all.
 

 
Here is the port-map of the famous Vespa 125-150 (57mm stroke)
 
Vespa_PX125_150_portmap.jpg
 
and here is the port-map of the famous TZR, KR1 and RGV two stroke engines:
 
TZR_KR1_RGV_portmap.gif
 
 
The height of the exhaust port is more than double than the height of the transfer ports in all cases.
 
The timing is symmetrical, say as in the plot in the middle:
 
Two-Stroke+SI+Engine+EPO+%E2%80%93+exhau
 
The necessary early opening of the exhaust ends up with an exhaust remaining open for several crankshaft degrees after the end of the transfer.
 
 
 
Quote from the bottom of the http://www.pattakon....takonPatATE.htm web page:
 
In the following version of the PatATE the rotary valve spins at half crankshaft speed:
 
PatATE_Rotary_Anim_6_Half_Speed.gif
 
The width (along the periphery of the cylinder) of each hybrid port (there are two) is 90 degrees. 
 
The duration of the hybrid ports is 180 crank degrees (the piston starts opening the hybrid ports at 90 degrees before the BDC and closes them at 90 degrees after the BDC). 
 
There are two intake ports. 
 
In the following graph it is shown the Exhaust Ports area and the Transfer Ports area versus the crank angle:
 
PatATE_Rotary_Porting.png
 
End of Quote.
 
 
Compare the heavily asymmetrical port timing plot of the PatATE with the previously presented symmetrical port timing of the typical 2-stroke.
 
Thanks
Manolis Pattakos

Edited by manolis, 06 July 2017 - 04:41.


#8 manolis

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Posted 07 July 2017 - 17:11

Hello all.

 

The following version of the PatATE seems the fittest for realization in metal.

 

PatATE_Rotary_Single_Around_3.gif

 

It has the typical arrangement, with one only hybrid port “looking” forwards and one intake port at the back of the engine.

 

The width of the hybrid port along the periphery of the cylinder liner is nearly 180 degrees.

The duration of the hybrid port is 180 crankshaft degrees:

 

PatATE_Rotary_Single_Around_2.gif

 

The port at the lower side of the (red) rotary valve, in cooperation with the (blue) piston, controls the intake port of the engine:

 

PatATE_Rotary_Single_Around_1.gif

 

 

The rotary valve (red) rotates at crankshaft speed (1:1).

 

The exhaust port side:

 

PatATE_Rotary_Single_Anim_1.gif

 

The intake side:

 

PatATE_Rotary_Single_Anim_2.gif

 

 

The Exhaust Ports area and the Transfer Ports area versus the crank angle:

 

PatATE_Rotary_Porting.png

 

Is as in the version with the half-speed rotary valve and the “double” ports.

 

 

According this plot, the variable exhaust and intake of the conventional two-strokes seem as not necessary for the PatATE because it separates the cycle in a “4-stroke-like” way:

 

after the expansion it follows a rapid opening of the exhaust port and the pressure drops quickly,

 

then the transfer opens progressively with the exhaust still opening,

 

then the exhaust starts progressively to close with the transfer opening more and more,

 

then the exhaust closes with the transfer being still widely open,

 

finally the transfer closes and the compression starts.

 

Its operation is closer to a 4-stroke with extreme valve overlap (say, as the Cosworth DFV with the 116 crank degrees valve overlap) than to a conventional 2-stroke.

 

Thanks

Manolis Pattakos



#9 Kelpiecross

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Posted 10 July 2017 - 02:50


You mention that the operation of the engine is in some ways similar to a 4-stroke - would 4-stroke operation be possible in a layout similar to yours with piston porting and a rotary valve etc.? It always seems to me that 2-strokes really just don't have enough time for decent induction and exhaust etc. no matter what you do.

#10 manolis

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Posted 10 July 2017 - 05:39

Hello Kelpiecross.

 

 

Judjing from the extreme revs the 2-strokes can run, it seems the two stroke engines have plenty of time for the exhaust and the transfer.

Sometimes they have more time than what is really necessary.

 

 

For instance, the OS.18TZ miniature (model / RC) engine (more at http://www.pattakon....est-rcnitro.pdf ) makes its peak power at 30,500rpm and has the red line at 42,500rpm 

 

OS18TZ_moving_parts.jpg

 

OS018Z_spec.png

 

OS018Z_ports_dyno.png

 

PatATi_OS18TZ_timing.gif

 

Spot on the height of the exhaust port.
It is about double as compared to the height of the transfer ports
Why? 
Because the conventional 2-stroke has to give time to the cylinder pressure to drop before the beginning of the transfer.

 

 

The early opening of the exhaust port is a requirement in all high revving 2-stroke engines.
 
 
For instance, in the RD350LC the exhaust port opens before the middle stroke:
 
 
RZ-RD-Ports.jpg
 
 
It is strange: according the port-map at bottom right, the exhaust port of the Yamaha RD350LC opens 100 degrees before the BDC (only 47% of the piston stroke is given to expansion). This is 200 degrees exhaust port duration. The transfer duration, according the same port-map, is only 125 crankshaft degrees.
 
 
Note: the height of the exhaust port is 29mm, while the height of the transfer port(s) is only 12mm (42% of the exhaust port height).
 
 
 
For higher revving the PatATE needs a long hybrid port duration, too.
 
However there is a significant difference between the PatATE and a conventional 2-stroke (like the RD350LC): the conventional needs the long exhaust duration not for the exhaust itself, but in order to enable a significant duration (and height of the ports) for the transfer, while in the PatATE the height of the transfer is the same as the height of the exhaust (it is the height of the hybrid port).
 
On this reasoning, the PatATE can extend the expansion for several crankshaft degrees (say, 15 or 20) to milk more energy from the fuel without loosing breathing efficiency or revving capacity.
 
 
Based on the port-plan of the RD350LC of ’86, they were added, in the plot at the bottom of the http://www.pattakon....takonPatATE.htm web page, the curves of the RD350LC:
 
 
PatATE_vs_RD350LC_porting.png
 
 
The green curve is the exhaust port area (versus the crankshaft angle), while the yellow curve is the transfer port area.
 
The duration of the hybrid port of the PatATE is only 180 degrees, while the duration of the exhaust port of the Yamaha RD350LC is 200 degrees (which means the PatATE has an about 18% longer (measured as piston travel) expansion, and additional mechanical energy on the crankshaft).
 
Despite the shorter duration of the hybrid port of the PatATE, the rhythm (or rate) of the exhaust opening in the PatATE is almost double as compared to the rate of the exhaust opening of the RD350LC.
 
While the exhaust port of the RD350LC opens 10 degrees earlier (at 80 degrees after the TDC), 
40 degrees later (i.e. at 120 degrees after the TDC or at 60 degrees before the BDC) the exhaust port area of the PatATE (which started opening 10 degrees later) is more than 50% larger.
 
 
The differences are even larger as regards the transfer (see the plot).
 
 
The previous “say” that the PatATE can use way more conservative timing than a conventional 2-stroke (i.e. less time for the exhaust and transfer) without loosing anything in breathing and high revving capacity. 
 
 
It is strange: the PatATE idea started as a way to clean the exhaust of the 2-stroke engine.
 
Thanks
Manolis Pattakos

Edited by manolis, 10 July 2017 - 05:52.


#11 Kelpiecross

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Posted 10 July 2017 - 06:00


I am always amazed that 2-strokes run at all let alone at very high RPM with plenty of power - I have Cox TD .010 that is good for 30,000RPM or so. But I don't think that with having the exhaust opening 100 degrees before BDC you can expect a very good TE - even at 90BDC (which I think your engine is) it must giving away a lot of TE through insufficient expansion.

#12 manolis

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Posted 10 July 2017 - 15:03

Hello Kelpiecross.

 

The 90 degrees exhaust opening before the BDC is for a racing engine wherein the power output is above all.

 

 

Here is an Opposed Piston PatATE:

 

PatATE_Rotary_OP_1.gif

 

PatATE_Rotary_OP_2.gif

 

In case of divided load (Portable Flyers with two intermeshed counter-rotating propellers, Electric Power sets with two counter-rotating generators, Marine Outboard engines driving two counter-rotating screws etc) the synchronization gearing (not shown) runs unloaded and the basis of the engine is perfectly rid of vibrations. 

The compact combustion chamber is shared between the two opposed pistons (the instant pressure on the two piston crowns is the same). 

The scavenging is not of the through or uniflow type. 

 

Thanks

Manolis Pattakos


Edited by manolis, 10 July 2017 - 15:04.


#13 manolis

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Posted 11 July 2017 - 06:39

But I don't think that with having the exhaust opening 100 degrees before BDC you can expect a very good TE - even at 90BDC (which I think your engine is) it must giving away a lot of TE through insufficient expansion.

 

 

Hello Kelpiecross.

 

 

Regarding the power and torque gain (as well as the BTE (Brake Thermal Efficiency) gain) when the expansion extends:

 

 

Here is the pressure (and the torque) versus the crankshaft angle of a typical 4-stroke engine:

 

Taylor_Torque_vs_Crankangle.jpg

 

It is from Taylor’s book “The Internal Combustion Engine in Theory and Practice”.

 

After the closing of the ports a 2-stroke gives a quite similar plot.

 

 

Spot on the pressure at 90 crank degrees. It is about 1/6 of the peak pressure.

 

Spot on the torque at 90 degrees.

 

While at 90 degrees after the TDC the pressure is several times lower than the peak pressure, at the same 90 degrees the eccentricity of the connecting rod from the crankshaft axis maximizes, explaining how, with six times lower pressure, the torque at 90 degrees is only two times lower than the peak torque.

 

The mechanical energy provided by the engine during the rotation of the crankshaft from an angle f to an angle f+df equals to the torque (at the angle f) times the angle differential df.

 

The total mechanical energy provided to the crankshaft from 0 degrees to 180 degrees equals to the area underside the torque curve, which is about equal to the torque at 90 degrees times 180 degrees (according the plot of Taylor, the torque at 90 degrees is about the mean torque during the expansion stroke).

About one quarter of this mechanical energy is consumed during the compression stroke (torque curve before the TDC).

 

According the previous, extending the expansion from 80 degrees after the TDC (RD350LC) to 90 degrees after the TDC (PatATE), another 6% of mechanical energy arrives to the crankshaft during the expansion stroke.

And because the compression is already "paid", this 6% is "clean", which means the mechanical energy to the crankshaft (as well as the power of the engine) increases by some 8%.

 

An 8% increase of the power and of the torque (and of the mileage etc) cannot be considered as insignificant.

 

As for the above rough calculations, they favor the conventional, not the PatATE.

 

 

 

 

Regarding the exhaust opening and the transfer closing:

 

 

It is not the valve that opens the hybrid port.

 

Several degrees before the piston starts opening the hybrid port, the rotary valve has uncovered the outer side of the hybrid port.

 

See the following animation.

Spot on the hybrid port and on the rotary valve when the piston is around the TDC: the piston keeps the hybrid port closed, however the rotary valve keeps rotating to get at the right angle / position when the piston will start opening the hybrid port.

 

 

Quote from http://www.pattakon....takonPatATE.htm (near the end of the web page):

 

 

Rate of Exhaust Opening and of Transfer Closing

 

In the following graph it is shown the Exhaust Port area and the Transfer Port area versus the crank angle:

 

PatATE_Rotary_Porting.png

 

In the following animation it can be seen the position of the rotary valve of the PatATE just before the opening of the hybrid port by the piston.

 

During the compression and the expansion the rotary valve keeps rotating.

 

At the beginning of the exhaust the outer side of the hybrid port is fully "uncovered" by the rotary valve, so that the complete hybrid port is dedicated to the exhaust.

 

The rate of the exhaust opening is about double as compared to the rate of the exhaust opening in a similar conventional 2-stroke.

 

According the Yamaha RD350LC port-map (click http://www.pattakon....LC_port_map.jpg to download), the exhaust port extends on the periphery of the cylinder liner for some 80 degrees while the hybrid port of a similar PatATE extends along the periphery of the cylinder liner for nearly 180 degrees.

 

The graph at http://www.pattakon....0LC_porting.png shows the difference.

 

With similar timing with a conventional, the blow down of the PatATE is substantially faster.

 

For similar blow down, the PatATE needs substantially more conservative timing (which also means longer expansion, more power and torque, better fuel efficiency etc)..

 

PatATE_Rotary_Port_Opening_Slow.gif

 

End of Quote

 

 

 

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

 

Thanks

Manolis Pattakos



#14 MatsNorway

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Posted 11 July 2017 - 16:45

A sealing nightmare with extra friction. I would not waste too much time on this one i feel. But it looks cool tho.



#15 gruntguru

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Posted 12 July 2017 - 06:02

Sealing is low pressure only.

 

Friction area could be reduced substantially compared to the simplified model in the animation.



#16 manolis

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Posted 12 July 2017 - 06:14

Hello MatsNorway.

 

You write:

A sealing nightmare with extra friction. I would not waste too much time on this one i feel.”

 

 

No.

 

 

The sealing of the high pressure is realized exclusively by the piston rings sliding on the cylinder liner (i.e. as in any four-stroke or two-stroke conventional engine).

 

Only after the opening of the “hybrid port” by the piston, and only then, the working gas finds the exhaust wide open, it also finds the top end of the (red) rotary valve.

 

The main “duty” of the rotary valve is to prevent the slightly compressed, inside the crankcase, air or air fuel mixture to escape to the exhaust.

 

The rotary valve has a second “duty” to accomplish: to close the intake port on the casing in synchronization with the piston (providing, this way, a highly asymmetrical intake and ridding the engine from reed valves).

 

 

All you need is a small clearance between the cooperating surfaces (no mechanical friction involved).

 

 

In any case, the rotary valve does add some mechanical friction (cooperation of the two bevel gears, support of the rotary valve on the casing).

 

The question is whether the added mechanical friction justifies the radical change the PatATE design brings to the two-stroke engines.

 

 

Worth to mention here:

the basic two-stroke has substantially lower mechanical friction than a four-stroke,

and (as Gruntguru wrote):

A lot of the mating surfaces shown in the animation could be removed, relieved or run with large clearances.

 

 

Now compare the straight / simple way the PatATE operates (red and blue curves) reminding four-stroke engines:

 

PatATE_vs_RD350LC_porting.png

 

with the mess / confusion / chaos during the gas exchange in a conventional like the Yamaha RD350LC (green and yellow curves) two-stroke.

 

In the conventional,

after the scavenging is over (scavenging: when transfer and exhaust are both open),

the exhaust keeps being wide open for several crankshaft degrees.

 

Can you see any reasoning behind it, except that keeping the exhaust port wide open after the closing of the transfer port is an unavoidable drawback / a heavy-side-effect of the simple 2-stroke design?

 

Thanks

Manolis Pattakos



#17 manolis

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Posted 15 July 2017 - 04:51

Hello all.
 
In another forum someone wrote:
 
“When 2T runs the same compression ratio as 4T then it runs with the same expansion ratio. Only the start and end points are different.
View the 2T from a different perspective. It is an engine that uses half of its cylinder for gas exchange and the upper, other half for power production. It uses the same compression and expansion ratios as its 4T competitor (of the same capacity and rpm range) but each cycle utilises half the mass charge of the 4T - but does so twice as often. Really, there is no loss of expansion - just fewer pumping strokes.”
 
 
 
Here is the valve lift versus the crankshaft angle of several older 4-stroke Ducati engines:
 
4stroke_Ducati_timing.png
 
For each of the above 4-stroke Ducati engines, the exhaust valve opens at 90, or so, degrees before the BDC. 
Similarly for their intake valves: they close at 90 degrees, or so, after the BDC.
 
 
According the above reasoning / understanding of the 2-stroke engines,
 
i.e. that the stroke is divided into an upper half for power production and into a lower half for gas exchange, 
 
each of the above 4-stroke Ducati engines “uses half of its cylinder for gas exchange and the upper, other, half for power production”.
 
 
On this reasoning, these engines should provide half power and torque as compared to 4-strokes having exhaust valve(s) opening at the BDC and intake valve(s) closing at the next BDC. 
 
In practice the opposite happens. The above Ducati 4-stroke engines had top specific power and torque.
 
 
The theory of the "two cylinder halves" needs reconsideration / amendment.
 
 
Back to the 2-stroke engines:
 
 
Adding to the previous graph the curves from the following plot:
 
PatATE_vs_RD350LC_porting.png
 
it results this diagram:
 
2stoke_vs_4stroke_timing.png
 
 
Compare the pair of the red and blue curves (drawn by bold line) at left (2-stroke PatATE, exhaust and transfer opening versus the crankshaft angle) with, say, the pair of curves “G Corsa EX” (thin cyan line at left) and “G CORSA IN” (thin dark-cyan line at right) of the Ducati “G-Corsa”.
 
 
Then spot on the left pair of curves for the Yamaha RD350LC conventional 2-stroke: dark-green bold line for the exhaust, yellow bold line for the transfer, with the exhaust closing more than 30 crankshaft degrees after the transfer.
 
Aren’t the PatATE curves quite different than those of the conventional RD350LC 2-stroke?
 
 
Aren’t the PatATE curves similar to those of the 4-stroke Ducati G-Corsa? 
 
This is what the PatATE brings to the 2-stroke engines: a completely different (and relatively similar to 4-stroke) way for the gas exchange.
 
Thanks
Manolis Pattakos


#18 Kelpiecross

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Posted 15 July 2017 - 05:10


Thank you Manny - this latest post and graphs etc. does tend to explain why you think that the PatATE should be a good idea - time to make a running prototype and find out.

#19 manolis

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Posted 18 July 2017 - 03:32

Hello Kelpiecross.

 
 
Here is what a third party wrote a couple of days ago, answering to another member in a discussion in the F1 Technical Forum:
 
 
“I think you are missing the clear advantages of a system which can achieve what Manolis is trying to do.
 
1. The ability to separate the phasing of the exhaust and transfer events can only be beneficial. Remember that the degree of such separation in the PatATE is a design variable which can be optimised to suit the intended application. The conventional two stroke is limited to zero separation - should we assume that this is optimal for every application? Many of the characteristics (exhaust emissions in particular) that make two strokes unsuitable for the applications where four strokes dominate, could be suppressed in the PatATE.
2. A large increase in port width permits larger ports for better flow and faster open/close rates.
3. Shared exhaust/transfer function of the hybrid port provides cooling for the otherwise problematic exhaust port.
4. Cooler exhaust port should allow reduced lube rate.
5. Exhaust reversion could be dramatically reduced - again less stress on the lube and reduced lube consumption.
 
The goal is not a simple engine to compete in the weed-whacker market - it is a more sophisticated two stroke with all the advantages (other simplicity) without the disadvantages.”
 
 
 
The point in a strictly techncal discussion like this is to point / to find / to show the weak points of something new before making prototypes.
 
Thanks
Manolis Pattakos


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#20 Kelpiecross

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Posted 18 July 2017 - 05:15


What "third party"?

#21 manolis

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Posted 18 July 2017 - 07:48

Hello Kelpiecross.

 

 

It is easy to find who the third party is.

 

 

 

 

Strictly Technical:

 

 

 
Here is the port map of the famous Aprilia RS250 of 1999 (two cylinders in V90, oversquare design with 56mm bore and 50.6mm stroke):
 
Aprilia_RS250_1999_port_map.jpg
 
The porting is focused on the faster blowdown: the “peak” (?) exhaust duration is 209.3 degrees and the “typical” (?) exhaust duration is 193.4 degrees, while the duration for the side transfer ports is only 129.6 degrees and the duration for the boost port is only 127.3 degrees.
 
The transfer is not only 64 degrees narrower than the exhaust, but its maximum (at the BDC) is not bigger than the maximum of the exhaust.
 
 
The above way of presenting the porting of a 2-stroke does not fit with the asymmetrical porting of the PatATE.
 
 
Here is a different presentation of the porting of a, say, modified to PatATE Aprilia RS 250:
 
Aprilia_RS250_vs_PatATE_port_map.png
 
The ports of the Aprilia RS250 are shown by black line.
 
The red triangular is the exhaust of the PatATE RS250, the blue triangular is the transfer of the PatATE RS250.
 
 
Going from top to bottom:
 
The exhaust of the PatATE starts opening substantially later (at, say, 87 degrees before the BDC) than the exhaust of the original RS250 (which opens at 105 / 97 degrees before the BDC).
 
The (red) exhaust opens at a higher rate than in the RS250. 
Soon the exhaust area of the PatATE gets larger than the exhaust area of the RS250 (and as mentioned before, the Aprilia RS250 is focused on a larger exhaust area for the sake of a faster blowdown). 
 
Some 20 degrees later the transfer (blue) of the PatATE starts opening at a very slow rate, giving time to the blowdown to complete. At the angle wherein all the transfer ports of the original RS250 open, the area of the transfer of the PatATE is still quite small, with a substantially smaller rate of increase.
 
At the BDC the rate of exhaust closing and the rate of transfer opening of the “PatATE” are about the same. 
At the BDC the area of the exhaust port is still larger than the area of the original RS250 exhaust port.
 
As the piston moves towards the next (lower in the diagram, see the beige arrows) TDC, the transfer of the PatATE strengthens and the exhaust weakens / reduces until it closes completely.
 
For another 20, or so, degrees the transfer of the PatATE remains open to complete the transfer, while the exhaust is closed. 
 
According the plot, the transfer remains open several degrees later than the transfer of the original RS250; also the exhaust of the RS250 remains open several degrees after the closing of the transfer of the PatATE.
 
 
 
On the same diagram, going from left to right is like moving along the periphery of the cylinder, with the zero angle being at the center / middle of the exhaust ports.
 
The exhaust of the RS250 covers, at maximum, about 120 degrees on the periphery of the cylinder, the transfer of the RS250 covers the rest cylinder but has, necessarily, substantially shorter height.
 
The exhaust and the transfer of the PatATE extend, each, for some 180 degrees along the periphery of the cylinder, but they are substantially asymmetrical relative to the BDC: the exhaust is significant before the BDC (blowdown, upped half of the plot) while the transfer is significant after the BDC (filling of the cylinder by the compressed gas in the crankcase, lower half of the plot). 
The height of the transfer and the height of the exhaust are equal.
 
 
 
It is a long post.
 
However this is a different and useful way to present the porting (and not only) of a 2-stroke engine.
 
Even for the conventional 2-strokes, in a diagram like this one can put the relative pressures (or temperatures, or gas velocities etc) without the need to explain whether they refer to the downwards motion of the piston (expansion stroke) or to the upwards motion of the piston (compression stroke). 
 
Thanks
Manolis Pattakos

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