2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello all.

Back to the PatBam HCCI

The worst drawback of the PPE (Pulling Piston Engine, more at http://www.pattakon.com/pattakonPPE.htm ) was considered the thin (it can be thin because it is heavily loaded only in tension) “piston rod” in the combustion chamber (through this “piston rod” the piston is connected to the wrist pin):



Looking at the big diameter “column / post / pillar” in the combustion chamber of the Cox Design (funded with several millions so far, some from the GB MoD and considered as a promising innovation by the “Ricardo” which took part in the project):



we have to reconsider: a “piston rod” in the center of the combustion chamber is OK.

Bellow are two PatBam HCCI designs using “piston rod” in the combustion chamber.

The PatBam HCCI PPE (spot on the size and location of the reed valve):





and a conventional 2-stroke (say, like the euro4 compliant KTM 250/300EXC/2018) easily modified to PatBam HCCI:



Thanks
Manolis Pattakos

[Pinger]

I hope it is clear now that a 2-stroke can be turbocharged and supercharged heavily, at a degree similar to that of the 4-strokes.

'A very brief period' - in time.

Comparing an engines running at 80 rpm and 4000 rpm is hardly valid when the issue is charging time. The W has 50 times the time available to the Cox.

You also write:
“Until the pistons melt.....”

A Diesel runs from lean to extremely lean.

The temperature of the piston and of the exhaust gas are substantially lower than in a spark ignition / stoichiometric engines.

With the intake cycle pressure and the exhaust cycle pressure shifted by some 20%-30%, the temperatures are not for melting the pistons.

True, combustion is cooler in CI - but then it is much more prolonged and the turbulence (which promotes heat loss) much more pronounced.
Cooler EGT is more due to the greater expansion that lower combustion temp.

[Pinger]

Looking at the big diameter “column / post / pillar” in the combustion chamber of the Cox Design (funded with several millions so far, some from the GB MoD and considered as a promising innovation by the “Ricardo” which took part in the project):

That 'post' running through the chamber wouldn't be my first choice either. But in Cox's defence, they are claiming excellent reliability/durability so presumably it doesn't impinge on those aspects. Also, Ricardo was of the view that the swirl necessary for CI combustion when achieved with a uniflow scavenging pattern left a core of residual exhaust products at the centre of the cylinder at high delivery ratios. The 'post' then is merely occupying what would be a dead zone anyway.

[manolis]

Hello Pinger.

You write:
“'A very brief period' - in time.
Comparing an engines running at 80 rpm and 4000 rpm is hardly valid when the issue is charging time. The W has 50 times the time available to the Cox.”


Since the Wartsila X92 is a slow revving 2-stroke (yet it is not if you consider its piston speed (similarity); at 76rpm the mean piston speed is: 3.468*2*76/60=8.8m/sec),

here is a high revving turbo 2-stroke:



Quote from https://www.youtube.com/watch?v=Oxj_OAb5bqk



125cc Turbo - Original TZR125 twostroke turbocharged by Boostbusters

Comment from Cooknasty300:

So how do you compensate for the scavenging effect of the 2 stroke? The sound wave pushes the unburned fuel back into the cylinder, but with a turbo, there would be a constant one-way vacuum which would disable this necessary effect in theory am I right?

and reply by Tyson James:

The pipe still works fine as the pressure wave is reflected back up the pipe like it is designed. The difference is with the turbo there is more exhaust backpressure as you are pushing a greater volume of air through the same size pipe then using it to drive the turbine wheel. If you watch the dyno pull when it spools up you see the exhaust pipe start stretching the springs at the manifold from the added pressure. So yes the intake charge blows in the chamber at a greater pressure but the exhaust pressure is also higher. 2 strokes love boost

End of Quote


Spot on where the turbocharger is located.

At 11,000rpm, the high revving small (50mm stroke) TZR125 has a mean piston of:
0.05*2*11,400/60=19m/sec, which is only double than the mean piston speed of the low revving Warsila X92 (by the way, at the 8.8m/sec mean piston speed the Wartsila X92 can work continuously at full load for weeks).



You also write:
“That 'post' running through the chamber wouldn't be my first choice either. But in Cox's defence, they are claiming excellent reliability/durability so presumably it doesn't impinge on those aspects.”


Suppose it is so, i.e. the Scotch Yoke of Cox engine offers excellent reliability.

Isn’t it strange that they don’t use it in a conventional 4-stroke engine (as CMC did a decade ago) replacing the typical “connecting-rod / wrist pin” mechanism?

Why to limit it to an unconventional design?

More reasonable is that they try to justify the increased friction and the reliability issues of their Scotch Yoke by the unquestionable compactness of the design. This is their basic advantage: a compact and lightweight design for outboard Diesels (not a design that offers better fuel efficiency).



You also write:

“Ricardo was of the view that the swirl necessary for CI combustion when achieved with a uniflow scavenging pattern left a core of residual exhaust products at the centre of the cylinder at high delivery ratios. The 'post' then is merely occupying what would be a dead zone anyway.”


The question is whether the unavoidable increase of the cylinder wall surface and the added sets of piston rings are justified by the decrease of the core of residual exhaust products "because the post occupies their place". But let me doubt.

In any case, if Ricardo is right, the PPE engine:





can use as thick post as required "to not leave space" for a core of residual gas in the cylinder.



By the way, here is another version of the PatBam HCCI on a 2-stroke:



The “cage” keeps the ring of the auxiliary piston in place all the time, and allows good scavenging everywhere.

Thanks
Manolis Pattakos

[peppo]

Hello.
this is the solution I studied... bearings in the video are not like those which would be on the real engine (haven't patented the bearing solutions so don't show it)... but the whole thing is made to be compact and symmetric, rods encumbrances in scavenging chambers behind pistons may give the right depression to achieve atkinson cycle.
Please let me have your comments... or contact for anybody who could fundraise

https://www.youtube.com/watch?v=MPW1FtV64ac

[manolis]

Hello Peppo.

You write:
“Please let me have your comments.”


A few thoughts / questions / comments on your design:



In the above drawing, at left, they are shown two pairs of conical rollers per piston. The one pair is rotatably mounted on the piston, the other pair is disposed between the immovable casing and the rotating big gearwheels (those with the circular-wave- tracks) to receive the axial loads.

Is the hatching correct? (as it is now, the rotating gearwheel is like being a part of the casing; shouldn’t its hatching be at a different angle or density, to distinguish it from the casing?).

The two conical track-roller-bearings on each piston are cooperating with a pair of facing each other circular-wave-tracks.
What happens when the force between the piston and the circular-wave-tracks changes direction?
Doesn’t each conical track-roller-bearing have to change –instantly- direction of rotation?
Reasonably, each piston should have two pairs of conical-track-roller-bearings (preloaded between the two trackways), the strong one running on the outer circular-wave-track, the other running on the inner. To keep the height low, the second pair of conical-track-roller-bearings can be disposed at, say, 90 degrees from the other pair.

The piston assembly seems lightweight in the drawing.

But the loads are heavy and the revs the conical-track-bearings operate are high. Are there such high-revving and strong track-rollers in the market?

Judging from the size of the cylindrical-track-roller-bearings of the Revetec engine (which, as the Bourke engine, failed to operate reliably for longer than a few minutes because of the extreme local loading at the line-contact between the track-roller-bearings and the track-ways):







it seems that substantially oversized conical-track-roller-bearings are required in your design, which leads to substantially bigger in diameter circular-wave-tracks.

In the Cox Scotch Yoke design (previous posts) they use “surface” contact, which has the highest loading capacity in expense of frictional loss.

In the Revetec design, there is, permanently, a linear contact between the track-roller-bearing and the track-way, while each track-roller-bearing rotates permanently at the same direction (yet, at variable speed, which is still a big problem), allowing rolling without sliding (at least at the lower revs; at the medium - high revs the cylindrical-track-roller-bearings of the Revetec and of the Bourke cannot help sliding (besides rolling) on the track-way; to cure this problem mce-5 used the following solution:

Quote from http://www.mce-5.com:



The synchronized roller is largely responsible for the low-friction performance of the MCE 5 VCRi



The MCE 5 VCRi synchronized roller cooperates with 3 synchronization racks: two of them are on a plate fixed to the crankcase while one is on the back side of the piston rack

End of Quote

despite their synchronized track rollers, and despite the 100 million euros, or so, funded to mce-5 VCRi, they now appear as closed / bankrupted: in their web site the “latest news” are from 2013).


In your design, is it possible to keep permanently at least “linear contact”? (and not turn it, at some parts of the track-ways, to “point-contact”?). To take the combustion loads with “point contact” is highly questionable (from the reliability viewpoint).

To put it differently: how the conical-circular-track-ways are designed?
If the track-way is conical (zero stroke of the piston), then the conical-track-roller-bearing rolls on the track-way without sliding and keeps - permanently - linear contact.
But if you add a significant axial displacement (piston stroke happening into 90 degrees of totation of the track-way) the complete track roller bearing displaces linearly along the cylinder axis, causing the sliding between the cooperating "conical" and "wave conical" surfaces.


Secondary “issues”:

Doesn’t the piston at the exhaust side need a skirt to cover the exhaust ports when the piston is near the TDC? Even if the bottom of the cylinder is closed / sealed, the exhaust hot gas will return at the space underside the exhaust-piston.

Where the power is provided from? The synchronizing shaft, at left, is not extending out of the casing.


Don’t get me wrong.
I am just trying to help.
As an independent third party, I point on possible issues you may find in practice.

If anything I wrote is confusing please let me know to further explain.

Thanks
Manolis Pattakos

[peppo]

Dear Manolis,
I am thankful for your attention and your reply which is pretty keen. The fact is, my patent just protects the kinematic configuration of that engine so that those drawings must depict the motion functions of the main pieces the most simply possible.
As you may see in the attached video, I continuously update its design (double conic rollers and side skirts on pistons are well visible in other pictures I already made), and lately I also figured out some special features likely to be included in a perfecting patent, then I cannot draw them yet.
I made the first calculations and the thing seems just feasible. The problem is just my lack of time because I must work, and of money to keep this patent and make others... So I need partners, but have no good contacts so far.
I am working now, when I have a minute at home I'll attach here other drawings.
Thank you again for your interest.

[manolis]

Hello Peppo.

As always happens,
those who can help do not want to,
and those you want to help have not the means to.


You write:
“I am thankful for your attention and your reply which is pretty keen.”


Here is another issue you may face in practice:
the torsional loads on the piston, how they are received and what it costs in friction.


The lower “plate” of the piston is abutting on sliders made on the part 6.

After the TDC, the support of the piston on the circular wave track pushes the piston to rotate about the cylinder axis.
The torque is as much as the instant torque the engine provides on the rotating circular wave track.
The only who can stop the piston from spinning about the cylinder axis is the part 6 with its slider-ways.
The resulting loads on these slider-ways are stronger than the thrust loads between the conventional piston and the conventional cylinder liner.

The slide-ways on the part 6 are at small eccentricity from the cylinder axis. If they were at a big eccentricity, things would improve (friction wise).


The same problem, but softer, is met in the Revetec engine which also uses sliders at the two sides of each piston column to receive the torsional loads generated by the offset of the counter-rotating trilobe cams. But in the Revetec the offset between the two cylindrical-track-roller-bearings is substantially smaller than in your design.

Here is how Revetec tried to address it:



It is still not the correct arrangement because the piston is not trying to rotate about the axis of rotation of the two counter-rotating tri-lobe cams; the piston tries to rotate about the cylinder axis.
Here is another design of the Revetec wherein the “thrust rollers” of the previous design have been replaced by sliders.



While a basic idea behind your design is to turn the sliding friction (piston skirt to cylinder liner) of the conventional design into pure rolling friction (am I correct?), at the end it creates stronger forces taken by conventional sliders (on the part 6).

Maybe you should add some roller bearings to take the “side loads” without significant frictional losses, say as the following Crankless engine does:







The green part with the eccentric single-lobe cams is a single piece part.
There is no opposite rotating eccentric cam (so there is no need for synchronization gearing).
Spot on the two needle roller bearings (they are not track roller bearings) at the center of the piston.
A second piston can be secured at the “free” end to form a boxer engine.

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



By the way, in the youtube video the pistons should move more “sinusoidally” / harmonically / smoothly. As they are shown, the resulting inertia loads (fast acceleration / deceleration) create additional loads / problems.



You write:
“ The problem is just my lack of time because I must work, and of money to keep this patent and make others...”

As shown in the previous, there are significant technical issues to be addressed in your design.

From the priority date in the WIPO / PCT publication, it seems you are now in the National Phase in various countries (which means patent lawyer expences, translation expenses, maintenance fees, etc, etc).

My advice, if it worth something:

Do find the time to look again at your design and to compare it with existing / tested / failed similar projects (Revetec, CMC, Boorke etc). Focus on the fundamentals (for instance: a new kinematic mechanism has to be similarly reliable and more efficient than the conventional).

Do address all the technical issues (as those I mentioned).
Reasonably, in order to address the basic technical issues, your design will change substantially (size / weight of engine, receiving of loads etc).

Then look again at your final design and decide if it really can beat the competition and if it is worthy the money you spend now. If not, abandon it and start thinking a new project.

Thanks
Manolis Pattakos

[manolis]

Hello all.

The following animation has been added at the bottom of the http://www.pattakon.com/pattakonPatBam.htm web page.



It is a four-stroke PatBam HCCI control.

Exhaust valve: red.
Intake valve: blue.
Auxiliary chamber "anvil": black.

Thanks
Manolis Pattakos

[peppo]

Again, thank you Manolis for your long analysis,
that part 6 and conic rollers I repeat are not matter of the patent I am pursuing, but maybe of later more specific design I am already developing, and will decide how to manage this with eventual partners. What I need is a sponsor (not for millions, little stuff), so if anybody is interested or know some interested experts, here I am to explain any detail under the right deal.
By the way, how the combustion chamber you just posted is supposed to work?
Thank you
Pierfrancesco

[manolis]

Hello Peppo.

You write:
“how the combustion chamber you just posted is supposed to work?”


Here is the color version of the animation you refer to:




In the old UK (1966) patent GB1,156,821 of Ernest Chatterton (click http://www.pattakon.com/tempman/GB1156821.pdf to open it) it is described the basic idea, which is to divide (at an angle f before the TDC) the combustion chamber into a main combustion chamber (wherein the compression ratio is moderate) and an auxiliary combustion chamber (wherein the compression ratio is high).

Due to the high compression ratio into the auxiliary combustion chamber, the air-fuel mixture therein cannot help auto-igniting. The resulting high pressure is not a problem due to the small piston area of the auxiliary combustion chamber.

When the auxiliary combustion chamber reunites with the main combustion chamber (this happens at the same angle f, but this time after the TDC), the pressure and the temperature into the main combustion chamber undergo an impact increase that causes the auto-ignition / combustion of the lean air-fuel mixture.
Without increasing too much the compression ratio (i.e. keeping low the resulting loads on the kinematic mechanism), we can still cause the auto-ignition of the air fuel mixture and run the engine at true HCCI (or, more correctly, LTC: Low Temperature Combustion) mode.

The following plot is explanatory on how the Chatterton engine works:



The same are described in the Nautilus Engineering web site at http://nautilusengineering.com/

In both cases (Chatterton and Nautilus) the two combustion chambers unite some 30 - 40 crankshaft degrees after the TDC, which is a big problem for the fuel efficiency (because the actual expansion ratio nearly halves) and for the stable combustion of the lean air fuel mixture into the main chamber.


The HCCI combustion is so efficient and clean (as regards the NOx and the particulates emissions) because, besides keeping the peak local temperatures substantially lower, it also completes way faster:






With the PatBam HCCI the main and the auxiliary combustion chambers re-unite a few crankshaft degrees before the TDC, allowing full expansion.

According the animation:
some 20 degrees before the TDC the lean air-fuel mixture into the auxiliary combustion chamber is auto-ignited;
some 10 degrees before the TDC the auxiliary combustion chamber and the main combustion chamber unite, and the burnt gas (yellow) in the auxiliary combustion chamber bursts, through the “transfer port”, into the main combustion chamber wherein the lean air-fuel mixture is below, yet near, the auto-ignition threshold.

In a 4-stroke, around the overlap TDC, the auxiliary piston or "anvil" (black in the animation) cleans the auxiliary combustion chamber from the residual gas.

Later, as the compression stroke proceeds, the auxiliary combustion chamber fills with compressed fresh air-fuel mixture until the cylinder to be divided into a main and an auxiliary combustion chambers.

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

Thanks
Manolis Pattakos

[manolis]

Hello all

Here is the youtube video-animation for a PatBam HCCI 4-stroke



Thanks
Manolis Pattakos

[Pinger]

Re earlier discussion on opposed piston engines and the lead given to the exhaust piston over the inlet piston. Previously I quoted Ricardo in saying that the limit for lead is determined by torsional problems - but overlooked something else. The more lead the exhaust piston has the more the working expansion stroke of the inlet piston is sacrificed.

A key (supposed) benefit of OP engines is that by using the full circumference of the cylinder they sacrifice the least stroke to the gas exchange process. With significant lead on the exhaust piston this is no longer true.

[manolis]

Hello Pinger

You write:
“Re earlier discussion on opposed piston engines and the lead given to the exhaust piston over the inlet piston. Previously I quoted Ricardo in saying that the limit for lead is determined by torsional problems - but overlooked something else. The more lead the exhaust piston has the more the working expansion stroke of the inlet piston is sacrificed.”


With the phasing of the two crankshafts, what really happens is that during the first part of the expansion, the intake piston is still moving towards the TDC (which means, the intake crankshaft is not receiving energy, but it provides energy to the high pressure gas!). Later (after the intake piston TDC) the expansion of the intake piston continuous normally.

This way the big part of the power is provided to the exhaust crankshaft (Junkers Jumo 204, 205 etc).



You also write:
“A key (supposed) benefit of OP engines is that by using the full circumference of the cylinder they sacrifice the least stroke to the gas exchange process. With significant lead on the exhaust piston this is no longer true.”


Not exactly.

Because two cylinders are served by the same exhaust ports (so they have to be as tall as in the conventional (non OP) 2-stroke of same stroke) and because two cylinders are served by the same transfer ports (so they have to be tall).

The real advantage is the asymmetric timing (the exhaust opens first and can close, if desired, first) and the through scavenging. But to achieve the asymmetric timing, you have to phase the two crankshafts (Junkers was using some 11 degrees phase difference). A drawback, besides the torsional problems mentioned by Ricardo, is the balancing.


The asymmetric timing is offered by the PatATi Opposed Piston:





without phasing the crankshafts, and without sacrificing the perfect balancing.

Thanks
Manolis Pattakosa

[Pinger]

A couple of questions maybe some here can answer.

In preparation for a small project using a Ryobi strimmer engine, I found stamped on the exhaust ''LOW COST CAT 600822004''. Googled that to try and find if it is a cat - no joy, just some for sale on eBay and from one of those ads, a pic:



When I took apart an exhaust box from a Zenoah engine there was a flimsy strip of steel gauze - to act as spark arrestor I'd guess, but the Ryobi exhaust has a much more substantial gauze element. Is this a genuine catalytic converter?


If you are looking in Uniflow: For your sleeve valve drive, have you any method/mechanism for preventing the sleeve rotating in the cylinder (around the cylinder's axis) or do the duplicated con rods prevent that completely?
Where did you locate, and are they a specific type, the bearings used in the SV con rods? The rolling elements appear small in relation to the diameters involved or, to put it another way, the ID is large for the OD when there is usually a larger difference in diameters on more conventional bearings.

TIA.