PatATE: Asymmetric Transfer and Exhaust in two-stroke engines

[manolis]

Hello all.

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

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:

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

Thanks
Manolis Pattakos

 

[manolis]

Hello all.


Instead of the flap valve, a rotary valve can be used for the control of the communication of the hybrid port(s) with the transfer and the exhaust passageways, say like:

In this PatATE design there are two hybrid ports arranged anti-diametrically on the cylinder liner.

Here they are shown the cylinder liner, the rotary valve and a slice from the top end of the casing:

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

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

From another viewpoint:

Disassembled:

With the rotary valve revving at constant angular speed, the rev limit is set by the rest engine (piston – connecting rod – crankshaft – casing).

More at http://www.pattakon.com/pattakonPatATE.htm

Thanks
Manolis Pattakos

 

[manolis]

Hello all.

Two more animations of a PatATE with rotary vave:

and

Thanks
Manolis Pattakos

 

[manolis]

Hello all.


The following plot and animation has been added in the http://www.pattakon.com/pattakonPatATE.htm web page.

They show a possible timing for the PatATE with the rotary valve.

The same animation at slow motion is at http://www.pattakon.com/PatATE/PatATE_Rotary_Timing_slow.gif

Thanks
Manolis Pattakos

 

[manolis]

Hello all.

I hope it is clear that 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:

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

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

Thanks
Manolis Pattakos

 

[manolis]

Hello all.


Here is the port-map of the famous Vespa 125-150 (57mm stroke)

and here is the port-map of the famous TZR, KR1 and RGV two stroke engines:

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:

Quote from the bottom of the http://www.pattakon.com/pattakonPatATE.htm web page:

In the following version of the PatATE the rotary valve spins at half crankshaft speed:

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:

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

 

[manolis]

Hello all.

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

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:

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

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

The exhaust port side:

The intake side:

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

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

 

[manolis]

Hello all.

Here is an Opposed Piston PatATE:

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

 

[manolis]

Hello all

Regarding the power and torque gain when the expansion extends:


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

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.com/pattakonPatATE.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:

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.com/tempman/Yamaha_RD350LC_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.com/tempman/PatATE_vs_RD350LC_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)..

End of Quote



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

Thanks
Manolis Pattakos

 

[manolis]

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:

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:

it results this diagram:

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

 

[lohring]

This principle has been tried many times and in many ways. One of the most recent is the Lotus Omnivore engine. In my opinion all these systems defeat the most important virtue of the small crankcase scavenged two stroke; simplicity and low cost. A simple 26 cc weadeater engine can develop close to 4 hp with a can muffler. Add a tuned pipe with suitable port timing and you can get close to 7 hp. With a better transfer shape between 8 and 10 hp is still possible using a simple piston port intake. An all out racing 125 cc engine has developed 54 hp. These engines use tuned pipes to get better scavenging and a supercharge effect with high and low pressure pulses. Commercial and racing engines have used variable length tuned exhausts and variable exhaust timing (power valves) for a broader power band. In simple engines mechanical sophistication is replaced with dynamic flow sophistication. It's tougher to design, but simpler to build. Modern computer simulations are a great help in the design of simple two strokes.

Lohring Miller

 

[manolis]

Hello Iohring.

Thank you for your response.



Currently in the market there are no 2-stroke engines propelling cars or motorcycles and complying with the current emissions standards (euro4).

The only exemption is the KTM250-300EXC, model 2018.


Qute from http://www.motorcyclenews.com/news/...missions-impossible-what-euro-4-really-means/

Euro 4 affects all new models introduced in 2016, and all new bikes from 2017.

End of quote.


Quote from http://thedirtbikerider.com/ktm-enduro-exc-efi-2018-2-stroke/

“Also KTM had problems with euro 4 and some KTM dealers can’t anymore sell 2017 models in their country’s. But new 2018 model will come with euro 4 and it will easy pass euro 4 with elections fuel injection and lower emissions. But there is new problem for KTM, in 2020 we will have new big problem called euro5. But we all hope KTM will find solution for this and make EXC and XC models legal for street.”

End of Quote.



It seems that during the next two years KTM has to find a better, than the TPi, solution for the emissions of their 2-strokes.



Here is what a third party (he is a mechanical engineer) wrote yesterday, 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.”

Thanks
Manolis Pattakos

 

[lohring]

The catch is that there's a much better solution to the emissions problem; electric vehicles. We'll see how that develops, but I expect that children looking at today's IC engines in museums will marvel at how we ever could build such complex things. In my model boat racing world, electric power is rapidly replacing IC engines. Electric model boats have held the ultimate speed record for years. Nostalgia for the past will keep modelers building wonderful replicas of IC and steam engines, but I don't see how IC engines can compete with electric power in all but the very largest vehicles as battery costs go down. Even your mower, chain saw, and weedeater will have cordless electric power.

Lohring Miller

 

[Nick Hulme]

Didn't some of the three 2-stroke motorcycles with timing details quoted have systems which actually varied effective port timing depending upon revs, load, etc. making the graphs a very incomplete description of their induction?

- Nick

 

[lohring]

Several people are developing a [ame="https://www.youtube.com/watch?v=Hodd8oyiawk"]sliding cylinder two stroke[/ame] that is at least partially throttled by sliding the exhaust and transfer ports. Power valves on the exhaust port are very common.

Lohring Miller

 

[Niels Abildgaard]

The catch is that there's a much better solution to the emissions problem; electric vehicles. We'll see how that develops, but I expect that children looking at today's IC engines in museums will marvel at how we ever could build such complex things. In my model boat racing world, electric power is rapidly replacing IC engines. Electric model boats have held the ultimate speed record for years. Nostalgia for the past will keep modelers building wonderful replicas of IC and steam engines, but I don't see how IC engines can compete with electric power in all but the very largest vehicles as battery costs go down. Even your mower, chain saw, and weedeater will have cordless electric power.

Lohring Miller

man carrying aircrafts for more than one hour fligths will be IC some time yet.

http://www.homemodelenginemachinist.com/showthread.php?t=26218&page=2

 

[manolis]

Hello Niels.


In the following it is further explained the difference the PatATE architecture brings to the 2-strokes.


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):

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:

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

 

[Nick Hulme]

man carrying aircrafts for more than one hour fligths will be IC some time yet.

And furthermore will continue to use tried and tested designs with as few modes of potential failure as possible in order to meet the requirements for aircraft engines.

 

[lohring]

That might be true, but it all depends on battery development. There are some [ame="https://www.youtube.com/watch?v=ohig71bwRUE"]great concepts[/ame] being tested with current batteries. A respected engineer thinks [ame="https://www.youtube.com/watch?v=erjdYiwoYAo"]supersonic intercontinental transports[/ame] are possible with a little better batteries.

Lohring Miller

man carrying aircrafts for more than one hour fligths will be IC some time yet.

http://www.homemodelenginemachinist.com/showthread.php?t=26218&page=2

 

[Niels Abildgaard]

My bid for future 60 to 200 horsepower aircraft engines look more or less like this.

http://i.imgur.com/SOqAT4f.jpg