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2-stroke uniflow with 4-stroke lubrication and scuffing resistance


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#51 cheapracer

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Posted 03 April 2012 - 06:11

Wouldn't it be likely those were oil scavenge pumps to reduce windage losses like those used in F1 for ages? I suppose running the crankcases at a significant partial vacuum would reduce fmeps due to air drag, but would the benefit outweigh the power cost of evacuating the crankcase chambers beyond what was necessary to scavenge the oil?.


Was basically discovered by the drag racers in the 1960's where they used intake and exhaust flow pressures to reduce the crankase pressure. They were getting such low pressures they need to reverse their crankshaft oil seals to stop air being drawn into the crankcase.


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#52 Nev

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Posted 03 April 2012 - 06:18

Why do most threads on this forum descend into bouts of willy-waving? :(

#53 cheapracer

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Posted 03 April 2012 - 06:55

For those who would like to understand more, I drew a picture!

The first picture will help to understand the crankcase PIV issue, cylinder 'a' is going up and has robbed cylinder 'b's intake volume ("charge robbing" is the general term). So you can see there is no change in the crankcase PIV volume or pressure other than what is being supplied from the turbo ... you could literally seal this engines intake and turn the engine over and over and all that would happen is the intake volume would merely transfer from one cylinder to the next

Posted Image


In the next picture we have added valves, reed valves in this case, and you can see that cylinder 'a' is being fed only from the turbo while cylinder 'b' has trapped it's volume (green is compressed air) and has compressed it ready for the intake valve to open.

Posted Image

If you sealed off this engine you would experience the pumping losses Wolf is referring too (I think), similar to putting your thumb over the end of a bicycle pump as you did as a kid - you feel the resistance as well as the heat (the energy used compressing air)

Interesting to note that the engine with valves can run as you see it here because the cylinders can create their own air pressure whereas the engine with no valves can not and must rely on an outside source of air pressure ie; supercharging.

Edited by cheapracer, 03 April 2012 - 07:09.


#54 cheapracer

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Posted 03 April 2012 - 07:02

Why do most threads on this forum descend into bouts of willy-waving?


Doesn't matter, in the Racing Comments Forum for example it's all opinions, often unprovable, whereas here it comes down to fact at the end of the day.


#55 manolis

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Posted 03 April 2012 - 07:42

Cheapracer,

The space below the piston crown is different than the crankcase.

The crankcase is completely isolated from the space underside the piston crown.
The connecting rod, the crankshaft and the wrist pin move exclusively inside the crankcase.
Between the crankcase and the space underside the piston crown there is a separator “shell” ( the pants ) that seals / separates the crankcase from the space underside the piston crown.
The air in the pant-legs cannot see the crankcase neither the oil mist or the oil droplets in the crankcase; and the pressure inside the crankcase has no relation to the pressure in the space underside the piston crown.

As for your comment:

“And just for the record, your engine technically is "crankcase induction".”,

when the PatMar operates without one-way valves (as the giant 2-stroke marine engines) it is not,
when it operates with one way valves, at or near the pants, it depends (it still has nothing to do with the crankcase).

By the way, does anybody care how it is “technically” classified?
What matters is: “does it make what it promises without significant side effects, cost and complication?”


Manolis wrote:
If the PatAir is to run without turbo-charging, instead of an additional mechanical compressorm one-way valve(s) can be used to trap the air inside the pants and inside the space underside the piston crown for the next scavenging. Depending on where the one-way valve(s) is (are) located, the “dead volume” of the built-in no-cost piston-type volumetric scavenging pump is defined.

Cheapracer aswered:
Yeah, well this is now appearing in this thread and your website after I, then Wolf, schooled you on it.

What do you understand from the following text and animation quote from the pattakon web site:

"The PatMar fits to smaller strokes, too.

Posted Image

Two reed valves (one per pant-leg) form a built-in zero-cost supercharger."

The above were published in the http://www.pattakon.com web site before some six months.

Well, what is the new thing you think you proposed? That with one way valves the engine becomes self scavenging?


Cheapracer:
“There's been a number of engines with the same premise ie; 2 stroke with isolated 4 stroke lubrication.”

If you don’t mean those with the intake and exhaust valves on the cylinder head and the “loop” scavenging (actually normal 4-stroke engines mofified to 2-stroke), please let me know about them. Compare the valve-time area of the first category (say with two intake valves and two exhaust valves on the cylinder head) to the PatPortLess arrangement

Posted Image

For some reason you appear angry.
Please allow me to remind you:

This is just a technical discussion.
If you have good technical arguments, you win.
"It costs nothing to be polite", as says the match-maker in the "fiddler on the roof".

Thank you
Manolis Pattakos

#56 cheapracer

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Posted 03 April 2012 - 08:40

Cheapracer,

The space below the piston crown is different than the crankcase.


No, it's actually a part of the crankcase, but you call it or describe it as you please, it's not importsnt, it's just semantics and not relevant to the effect of use or non use of individual valves to isolate individual cylinder's charge. On the PatPortLess (which appears to require ports btw), intake is via the cylinder head but still makes no difference.


Cheapracer:
There's been a number of engines with the same premise ie; 2 stroke with isolated 4 stroke lubrication.”[/i]


Google is your friend.

Well, what is the new thing you think you proposed?


Not proposing anything new at all, just having a bit of fun, offering suggestions and help for people who don't understand what's going on but would like to.


For some reason you appear angry.


That would go against how much I enjoy/laugh my way through these threads.



Edited by cheapracer, 03 April 2012 - 09:26.


#57 gruntguru

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Posted 03 April 2012 - 09:28

Hmmm. So where is the apology?

#58 cheapracer

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Posted 03 April 2012 - 10:19

Hmmm. So where is the apology?


I owe you nothing Mate, where's mine for your blatant lie?

Man has nominated that existing systems be used for scavenge.



#59 gruntguru

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Posted 03 April 2012 - 10:56

I don't quite know what your line is Mate

Well mate from where I sit, I observed Manny discussing another well-thought-out development, demonstrating a COMPLETE understanding of the relevant principles then watched you charge in half cocked and tell him how to suck eggs.

but if you want to play this silly ego game then please refer to the "Wankel Compression Ratio" thread posts 18, 19, 20 and 21 where I schooled you on modern 2 strokes, a subject far more complicated and more technical than this engine ever will be.

You mean where I acknowledged your greater knowledge of the subject and thanked you for enlightening me?

Yes, I will have to admit defeat there. You win the ego game. :up:

I suggest that Manny doesn't have a handle on his own engine either, specifically the self balancing effect of the (valveless) crankcase PIV.
Adoration seems to be blinding you.

A totally incorrect assessment as subsequently proven. You have demonstrated a superiority complex so big as to render you unable to recognise when somebody else actually has a better understanding of the topic.

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#60 gruntguru

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Posted 03 April 2012 - 11:04

I owe you nothing Mate,

You accused Manny of claiming and publishing your idea as his own. When he proved you wrong, your response (post # 56) criticised several points in his post yet made no mention of your error.

Racing ahead in the ego stakes. Two - Zip.

where's mine for your blatant lie?

A blatant lie? If that's what it was -I'm sorry mate.

It was pretty obvious to me. Manny designed a system to solve a lubrication issue by replacing the scavenge ports with a poppet valve. No mention of the air charging system means that wasn't part of the redesign.


Edited by gruntguru, 03 April 2012 - 11:15.


#61 manolis

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Posted 03 April 2012 - 13:02

Desmo,

This thread initially started when I got into a discussion wherein the “Holy Inquisition” was judging “24gerrard”.

I don’t know what finally happened, because that thread “disappeared”.

But it was really sad to see members of a forum to accuse another member who was not allowed to defend himself.
Even in the boxing, when the one guy falls, the other stops hitting.

And it was your mistake, because you are the moderator and you allowed it to happen.

The best thing with the Forums is that everything is written (a bad thing is that editing is allowed).

Desmo,

I think it is time for you, as the moderator, to make a good reading of this thread from the beginning to the end, in order to explain to the rest members and to Cheapracer who is right and who is wrong, and why.

I do not ask Cheapracer’s apology or banning. These are nonsense.
If he cannot recognize his mistakes in this thread, his problem.

What I ask you is to cancel 24gerrard's banning.

Thanks
Manolis Pattakos


#62 Kelpiecross

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Posted 03 April 2012 - 13:03

Why do most threads on this forum descend into bouts of willy-waving? :(


You are not incorrect there Nev.

#63 Wolf

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Posted 03 April 2012 - 13:46

Wouldn't it be likely those were oil scavenge pumps to reduce windage losses like those used in F1 for ages? I suppose running the crankcases at a significant partial vacuum would reduce fmeps due to air drag, but would the benefit outweigh the power cost of evacuating the crankcase chambers beyond what was necessary to scavenge the oil?. Hmmm is there a any significant change in volumes below the pistons in a V as the crankshaft rotates? Wouldn't the crank geometry determine that? Do racing bikes run segmented crankcases?

OK, I'll stop with the silly questions.


I don't think so- just pumping out air. And I don't think it has much, if anything, with drag- the way I see it GruntGuru was right when saying that the crankcase pressure increase would work adversely during piston downward motion and to advantage when it moves upwards... But I would argue that those two effects would not cancel each other out, because the disadvantage would be greater than the advantage (on account that inertia of rotating masses, as well as other pistons is already doing that work when piston moves upwards). Back to crankcase pumps- the way I see it they get clear and measurable advantage when the piston is moving down, whereas the loss when the piston is going upwards would have to be* compensated by increasing flywheel inertia by a fraction.

As for crankcase volume change, I don't think it would be to any effect significant, and I'm guessing that it could safely be assumed to be constant in multi-cylinder engines, as Cheapracer was illustrating above (I think my car would be an exception to that- it has I2 engine with single crank :lol: and as a matter of curiosity, its 2nd generation has done away with distributor, firing on all cylinders each revolution, despite being 4-stroke :p). But still, I think the pressure would play a role- maybe one could draw reasonable conclusions from a comparison with a damper (PatMar would IMHO be most suited for comparison because both volumes above and below piston are isolated from atmospheric pressure). :confused:

* if the flywheel was already as light as could be made, that increase would be necessary, otherwise I'd think it wouldn't be called for

#64 cheapracer

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Posted 03 April 2012 - 16:45

You accused Manny ..


Not your business. If you have a concern follow forum rules and report it to a moderator.


claiming and publishing your idea as his own.


WTHell? You mean the idea that I have mentioned many times in multiple threads noting that it has been used in multi millions of engines since the 1970's (and owned by Yamaha)? You mean that idea of mine? :rotfl:


The best thing with the Forums is that everything is written (a bad thing is that editing is allowed).


Firstly, editing is time recorded so people can't go back after the fact without it being obvious.

Secondly, neither "one way valves" nor "type of scavenging" used is mentioned in this thread before firstly I then another member suggested various ways to accomplish those, as you say it's all on record above. Comments are based on information made available, you were lacking.

I especially refer you to this post about one way valves ....

Cheapracer (said),

"I also presume you are using positive displacement of intake on the down-stroke via a one-way valve?"

No, this is not necessary.
In the state-of-the-art giant marine 2-stroke engines, the turbocharger provides compressed air to a plenum surrounding the intake ports at the bottom of the cylinder. In the PatMar the plenum surrounds the bottom end of the pant-legs.


With this information made available your engine will not work, that is a technical fact. Because you and your fan club are not capable of providing the required information rather taking a stance that "I don't understand", is your poor forum reporting ability, not my problem.

I do not ask Cheapracer’s apology or banning.


:lol:

As I do not request yours for your constant spamming - but at least some of your website is technical and interesting among the junk.

If he cannot recognize his mistakes in this thread, his problem.


Not adoring you and actually questioning your technical methods, you might be surprised to learn, is not against forum rules. In fact I hold the belief that technical debate is encouraged here - of course I mention again that debate can only be based on parameters offered.



Anyway, I'm finished here, not fun anymore.

Edited by cheapracer, 03 April 2012 - 17:39.


#65 manolis

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Posted 03 April 2012 - 18:32

So I have, once again, to prove I am not an elephant.

Here is the copy from the pattakon web site, the patmar directory:

Posted Image

It shows the date of the last update of each file.
On March 30, 2012 they were added, as I write in the forum, four drawings explaining the actuation mechanism of the intake valve.

From November 7, 2011 they were published and open to everybody the PatMar_short.gif and the PatMar_short.exe.

Desmo, if you want the password to check by yourself, let me know.


Here are the statistics for the patmar_short.exe file (it is the windows exe program of the gif animation shown in the forum.

Posted Image

Posted Image

Posted Image

Posted Image


Desmo, congratulations for your moderation.

Manolis Pattakos

#66 NTSOS

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Posted 03 April 2012 - 18:58

Anyway, I'm finished here, not fun anymore.


Wait a minute, you have the brazen audacity and unmitigated gall to just quit?

You can't quit....there are forum rules and regulations in place that state "no one is allowed to quit and/or be banned from a potentially contentious debate after only two pages"......you guys are just getting warmed up for christ's sake!

John


Edited by NTSOS, 03 April 2012 - 19:00.


#67 gruntguru

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Posted 03 April 2012 - 23:04

Not your business. If you have a concern follow forum rules and report it to a moderator.

Thanks for the advice but I will do it my way. I asked a simple question - learned a lot.

#68 gruntguru

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Posted 03 April 2012 - 23:13

I don't think so- just pumping out air. And I don't think it has much, if anything, with drag- the way I see it GruntGuru was right when saying that the crankcase pressure increase would work adversely during piston downward motion and to advantage when it moves upwards... But I would argue that those two effects would not cancel each other out,

They near enough cancel. Don't forget all piston engines see the same effect whether the crankcase pressure is 1 bar or 3. If there are multiple cylinders sharing a common crankcase (or interconnected pants) the compression-expansion will be minimal - replaced by a rush of air from the underside of one piston to another.

#69 gruntguru

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Posted 03 April 2012 - 23:30

WTHell? You mean the idea that I have mentioned many times in multiple threads noting that it has been used in multi millions of engines since the 1970's (and owned by Yamaha)? You mean that idea of mine?

Yeah that's it. Imagine my surprise when you posted this . . . .

Yeah, well this is now appearing in this thread and your website after I, then Wolf, schooled you on it.



#70 desmo

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Posted 04 April 2012 - 00:18

With the ban precedent still minty fresh I'd ask that the members here conduct their disagreements here in an agreeable manner or find somewhere else to play. Calling other posters derogatory names- even if true- will at some point result in a ban without any further warning. Strong disagreement is fine but it must be enunciated in a civil manner. I have no remaining problem removing people who cannot do so.

#71 gruntguru

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Posted 04 April 2012 - 02:53

I owe you nothing Mate, where's mine for your blatant lie?

So here is the "Blatant lie".

Man has nominated that existing systems be used for scavenge.

And here is where Manny nominated the existing system for scavenge.

"I also presume you are using positive displacement of intake on the down-stroke via a one-way valve?" (Cheapracer)

No, this is not necessary. In the state-of-the-art giant marine 2-stroke engines, the turbocharger provides compressed air to a plenum surrounding the intake ports at the bottom of the cylinder. In the PatMar the plenum surrounds the bottom end of the pant-legs.


Edited by gruntguru, 04 April 2012 - 02:54.


#72 Kelpiecross

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Posted 08 April 2012 - 03:27


I have to confess to reading the Eng-Tips forum - even though I would never post there due to the excess of know-all dickheads that seem to inhabit the place.

I thought this recent post was interesting:


http://www.eng-tips.....cfm?qid=319676

Why aren't two-stroke diesels ever arranged like this? It would appear to me to be a better way to arrange the engine.
Would this arrangement allow traditional four-stroke oiling methods?


#73 Catalina Park

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Posted 08 April 2012 - 04:30

Would this arrangement allow traditional four-stroke oiling methods?


What oiling methods do you think two stroke diesels have?

Not all two stroke diesels have inlet valves.


#74 Kelpiecross

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Posted 08 April 2012 - 04:54

What oiling methods do you think two stroke diesels have?

Not all two stroke diesels have inlet valves.


Isn't that what this whole thread from Manolis is about?

As far as I know there are no 2-stroke diesels with the inlet controlled by poppet valves and exhausting through ports in the cylinder wall.

The question is - why isn't there any?

#75 manolis

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Posted 08 April 2012 - 05:10

I have to confess to reading the Eng-Tips forum - even though I would never post there due to the excess of know-all dickheads that seem to inhabit the place.
I thought this recent post was interesting:
http://www.eng-tips.....cfm?qid=319676
Why aren't two-stroke diesels ever arranged like this? It would appear to me to be a better way to arrange the engine.
Would this arrangement allow traditional four-stroke oiling methods?


From Eng-tips:
Two-Stroke diesels typically have exhaust valves, using their pistons to uncover intake ports. Why not reverse that, with exhaust ports and intake valves?
In the standard design, doesn't the exhaust valve have to open too early in the power stroke, before the gas is fully expanded, to let the exhaust start going out before the intake port gets uncovered? Wouldn't you get more power if the piston went further down, uncovering exhaust ports, before an intake valve opened in the head? Wouldn't you also gain exhaust efficiency because the momentum of the gas is downward in the power stroke, helping push it out of exhaust ports?
This arrangement would also allow engine designs with variable (intake) valve timing. If you close the intake later, the mechanical compression is delayed; the compression ratio becomes smaller relative to the expansion ratio, extracting more work and reducing exhaust pressure, effectively creating an Atkinson cycle. A digital engine control could employ the variable timing at low and medium power for max efficiency but phase it out for maximum power situations.

My initial thought was that slow-revving diesels would need awkwardly long exhausts for exhaust-tuning (to return escaped air), and moreover could prove to be a bit of problem anyway if the engine was, as is the wont with diesels, turbo- or supercharged... Not that I'm an expert in the field, so I might be completely off the base.


With the ports on the cylinder liner being exhaust ports and with the poppet valves on the cylinder head being intake valves, things get worse.

In the case of the trunk piston arrangement (the piston skirt covers and uncovers the ports, like in the Detroit Diesel engines), the piston skirt has to thrusts heavily onto the hot cylinder wall around the exhaust port area, wherein the openings restrict the available surface, making necessary more lube to prevents metal-to-metal contact and to cool the piston skirt. The lube specific consumption increases and the quality of the lubricating oil degrades sooner (runs hotter and comes in contact to the exhaust gas).

In the case of the cross-head arrangement (as the MAN S35 at the beginning of this thread) the underside the piston crown space fills with hot exhaust gas as the piston moves upwards, which worsens a lot the conditions the piston, the piston rings and the lubricating oil operate. The lower part of the cylinder liner runs almost “red-hot”. The specific lube consumption increases.

Timing:
With the exhaust timing symmetrical (unless a significant crankshaft offset is used), the intake valve timing defines the “asymmetry”. If the exhaust ports open at the same crankshaft angle at which the exhaust valve opens in the conventional arrangement (exhaust valve, intake ports) in order to provide the necessary time for the pressure inside the cylinder to drop before the intake valve opens, then the intake valve must close substantially later than the crankshaft angle wherein the intake ports close in the conventional arrangement. This is also a drawback, unless the engine runs at partial load (Miller cycle).

While there are several severe drawbacks, I can’t see a single advantage of the arrangement with exhaust ports and intake valves as compared to the conventional arrangement (intake ports - exhaust poppet valve, cool cylinder liner, cleaner and cool lubricant, more efficient timing etc).

Thanks
Manolis Pattakos

#76 gruntguru

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Posted 08 April 2012 - 07:21

In addition, you end up with cylinder temperatures the opposite of what is needed for thermal efficiency. The top of the cylinder is exposed to the combustion process for the entire power stroke. The cooler the chamber walls, the more heat is lost and unavailable to maintain cylinder pressure to do work during the power stroke. Putting the intake valves in the cylinder head makes this critical area run cooler while the exhaust ports at the bottom of the cylinder are busily overheating the lubricant.

In a uniflow scavenged engine the heat flows from the intake end towards the exhaust end and the way it is done now is the right way (as usual).

#77 Kelpiecross

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Posted 08 April 2012 - 07:49

[quote name='manolis' date='Apr 8 2012, 16:10' post='5646967']

With the ports on the cylinder liner being exhaust ports and with the poppet valves on the cylinder head being intake valves, things get worse.

In the case of the trunk piston arrangement (the piston skirt covers and uncovers the ports, like in the Detroit Diesel engines), the piston skirt has to thrusts heavily onto the hot cylinder wall around the exhaust port area, wherein the openings restrict the available surface, making necessary more lube to prevents metal-to-metal contact and to cool the piston skirt. The lube specific consumption increases and the quality of the lubricating oil degrades sooner (runs hotter and comes in contact to the exhaust gas).

In the case of the cross-head arrangement (as the MAN S35 at the beginning of this thread) the underside the piston crown space fills with hot exhaust gas as the piston moves upwards, which worsens a lot the conditions the piston, the piston rings and the lubricating oil operate. The lower part of the cylinder liner runs almost “red-hot”. The specific lube consumption increases.



I presume you are not saying that a Detroit Diesel has its exhaust ports in the cylinder liner - even though the above tends to read that way.

For those that don't know (and I didn't know) a "trunk" engine is a non-crosshead engine - like a normal piston engine.

Another question - why are ship 2-stroke diesels of crosshead layout? Why not just a giant version of a Detroit Diesel? Ship 4-stroke diesels are "trunk" and appear to be just like giant automotive and truck diesel engines.

#78 manolis

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Posted 08 April 2012 - 09:56

Kelpiecross,

“I presume you are not saying that a Detroit Diesel has its exhaust ports in the cylinder liner - even though the above tends to read that way.”

The Detroit Diesels have the intake ports on the cylinder liner and the exhaust poppet vales on the cylinder head.
In case the Detroit Diesel is to operate with the arrangement proposed by the guy in Eng-Tips (i.e. in case of a modified Detroit Diesel having exhaust ports and intake poppet valves), the piston skirt has to thrust not onto the cold side of the cylinder, but onto the hot exhaust ports, etc.

“Another question - why are ship 2-stroke diesels of crosshead layout? Why not just a giant version of a Detroit Diesel? Ship 4-stroke diesels are "trunk" and appear to be just like giant automotive and truck diesel engines.”

A few reasons:

The stroke to bore ratio can be as high as you like in a cross head engine, giving a way smaller surface to volume ratio for the combustion chamber during combustion. In a 4-stroke, if the stroke to bore ratio is over a limit they are necessary cuts on the lower end of the cylinder liner to avoid connecting rod to cylinder liner collision (the Hanshin GEL44 is a big 4-stroke having stroke to bore ratio 2).
From Taylor’s “The internal combustion engine in theory and practice” for the Hanshin GEL44: The Bore is small to allow very high bmep (294 psi) with consequent high mechanical efficiency resulting in remarkable fuel efficiency…”

The best efficiency is at a mean piston speed about 7.5m/sec. For direct drive of the propeller (the big ones have best point somewhere between 80 to 160 rpm) of a big ship , the resulting stroke is from 2.8m to 1.4m, otherwise you need revs reduction (gearbox), the overall efficiency (brake thermal efficiency of the engine multiplied by the efficiency of the gearbox) drops, the cost increases.

The two stroke running on the same bmep as a 4-stroke of same displacement and same revs, makes double power.

The cross head takes the thrust loads away from the cylinder liner. With the heavy supercharging used, the thrust loads is difficult to be taken at the piston skirt to cylinder "contact" without deformation (the sealing of the combustion chamber degrades if the piston rings are abutting onto a deformed cylinder). And if the necessary quantity of lubricating oil exceeds the quantity the scapper rings can scrap, a part of the lube gets into the combustion chamber.
The cross head, on the other hand, uses as much lubricant as necessary, has the perfect form for the forces it takes and finally allows short connecting rod to be used, reducing the overall engine height.

The medium speed Wartsila 64 is the most powerful 4-stroke marine (it may also be the biggest: 640mm bore, 900mm stroke). The Wartsila RT96 low-speed 2-stroke has 960mm bore (i.e. 2.25 times the piston area of the biggest(?) 4-stroke) and 2500mm stroke.

The best with the small bore is that the loads are way smaller. This PatMar arrangement :

Posted Image

at http://www.pattakon....takonPatMar.htm matches to heavy truck use (90mm bore, 400mm stroke, straight-four, even firing, balanced as the best V-8, 10lit 2-stroke). Its small bore makes the loads on the piston, on the connecting rod, on the cross head and on the crankshaft similar to those of a small 4-cyliner, 2-liter supercharged direct injection engine.

Thanks
Manolis Pattakos

#79 Kelpiecross

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Posted 08 April 2012 - 12:51

[quote name='manolis' date='Apr 8 2012, 20:56' post='5647065']

Thank you Manolis - that makes sense. Another factor may be that the 4-stroke diesel needs a bigger bore for the extra valve area needed.



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#80 manolis

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Posted 09 April 2012 - 08:31

Another factor may be that the 4-stroke diesel needs a bigger bore for the extra valve area needed.


Kelpiecross,

For the breathing efficiency of an engine the “valve-time area” (not the valve area) is what matters.
The valve-time area takes into account not only the size and the lift of the valve, but also the time for which the valve stays at each lift.

Here is the cylinder head of a 4-stroke marine MAN engine (580mm bore, 640mm stroke):

Posted Image

580mm cylinder bore
640mm piston stroke
1400 KW/cylinder
428 rpm
9.1 m/sec mean piston speed at peak power (2*0.64m*(428/60)/sec= 9.1m/sec)
23.2 bar brake mean effective pressure (bmep)

With a constant pressure equal to the bmep into the combustion chamber, the resulting force onto the piston is the bmep (23.2 Kp/cm^2) multiplied by the piston area (pi*(58cm/2)^2). This is a force of 61296 Kp or 601316 Nt.
Multiplying the force onto the piston (601316 Nt) by the piston stroke (0.64m) it is taken the energy generated during one stroke of the piston. This is 384842 Nt*m, i.e. 384842 Joule.
Multiplying the energy generated during one piston stroke (384842 Joule) by the number of combustions per second per cylinder (0.5*428/60=3.57 combustions per second) it is taken the power per cylinder: 1373604 Joules/sec or 1374 KW (which is rounded to 1400 KW by MAN).

Take the case of an over-square (say 1000mm bore, 400mm stroke) engine and of a sub-square (say 632mm bore, 1000mm stroke) engine of same displacement per cylinder (314 liters in either case).

If both engines run at the same mean piston speed, the valve-time area is the same (for similar design of the two cylinder heads).

For instance, in case the 7.5m/sec is the best fuel-economy mean-piston-speed for both of them (that is: 562 rpm for the first engine and 225 rpm for the second engine), the increased piston area of the over-square engine offers no additional valve-time area.
What changes is the power: for equal bmep, the over-square makes 2.5 times the power of the sub-square. The power ratio equals to the piston area ratio for same bmep and same mean piston speed.

On the other hand, “the small Bore allows very high bmep with consequent high mechanical efficiency resulting in remarkable fuel efficiency…” according Taylor and practice. It is also the better shape of the combustion chamber, the lower thermal loss etc. The fuel economy and the reliability are the most important characteristics of a marine engine. The power density is not significant.

Things are similar for the two stroke engines.
Imagine the above MAN 58/64 cylinder head on a PatMar. All the four valves of the cylinder head become exhaust valves. Four intake valves on the piston crown control the intake.
The PatMar 58/64 has about double valve area.
But its valve-time area is about the same with the MAN 58/64 valve-time area, because the valves of a 2-stroke stay open for about the half crankshaft angle than they stay open in the 4-stroke MAN 58/64.
If the stroke of the above PatMar is multiplied by 3 (from 640mm to 1920mm), and the rpm the engine operates is divided by 3 ( 428 rpm / 3 = 143 rpm, which matches to direct propeller drive) the valve-time area remains the same as before, as well as the power. The displacement of the engine is three times bigger, however the loads inside the engine are the same.

Thanks
Manolis Pattakos

#81 PJGD

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Posted 13 April 2012 - 00:29

I have to say that I can't think off-hand of a non-OPE uniflow 2-stroke diesel with inlets in the head and exhaust ports down the liner, however here is one that got away.

Leyland Motors were responsible for some interesting but under-achieving engines including the L60 OPE tank engine and the fixed head 500 engine. The engine in the attached patent from 1950 looks from the patent drawings as if it was fully detailed and almost ready to go. Perhaps they built some prototypes and discovered the issues that Manolis and others have referred to. Without a doubt low oil consumption would not have been one of its strong points. It has a sleeve valve at the top of the liner to control the inlet ports in the liner, and then the exhaust ports down the liner. Interestingly, like Manolis they recognized the key aspect of large time-integral inlet port area for this engine. The inventor was a German citizen who was responsible for several engine-related patents for Leyland from ~1946 to 1958, so I suspect that he may have been offered a job in the UK immediately following the war.

Edit: OK, so my FTP server is not behaving today, so the best I can do is provide a link to GB696577A such as this: http://worldwide.esp...n...96577A&KC=A

PJGD

Edited by PJGD, 13 April 2012 - 01:51.


#82 Kelpiecross

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Posted 13 April 2012 - 11:31

I have to say that I can't think off-hand of a non-OPE uniflow 2-stroke diesel with inlets in the head and exhaust ports down the liner, however here is one that got away.

Leyland Motors were responsible for some interesting but under-achieving engines including the L60 OPE tank engine and the fixed head 500 engine. The engine in the attached patent from 1950 looks from the patent drawings as if it was fully detailed and almost ready to go. Perhaps they built some prototypes and discovered the issues that Manolis and others have referred to. Without a doubt low oil consumption would not have been one of its strong points. It has a sleeve valve at the top of the liner to control the inlet ports in the liner, and then the exhaust ports down the liner. Interestingly, like Manolis they recognized the key aspect of large time-integral inlet port area for this engine. The inventor was a German citizen who was responsible for several engine-related patents for Leyland from ~1946 to 1958, so I suspect that he may have been offered a job in the UK immediately following the war.

Edit: OK, so my FTP server is not behaving today, so the best I can do is provide a link to GB696577A such as this: http://worldwide.esp...n...96577A&KC=A

PJGD


Good point about opposed piston diesel engines having ported exhausts - this feature doesn't seem to do them any harm.

Manolis has an engine design himself that has a ported exhaust.

#83 manolis

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Posted 13 April 2012 - 12:05

I have to say that I can't think off-hand of a non-OPE uniflow 2-stroke diesel with inlets in the head and exhaust ports down the liner, however
. . . .
PJGD


It seems that besides the increased lube consumption, this Leyland-Motors engine has sealing problems and increased friction.

Posted Image

The second set of immovable rings on the cylinder head, with the sleeve valve sliding over them, is a conventional and reliable solution.

For the lower end of the sleeve valve they use a different approach: it seems they expect that the high pressure inside the combustion chamber increases slightly the external diameter of the sleeve valve, achieving good sealing with the cylinder liner below the intake ports. On the other hand: the sleeve valve has to move along the cylinder liner, even during the combustion of the fuel, making it not a so good solution, of questionable reliability (the Pinnacle Opposed Piston engine uses sleeve valves in a similar way).

Alternatively they could use a third set of rings, outside the lower end of the sleeve valve, sliding over the cylinder liner above the intake ports, for better sealing, lower friction and improved reliability. On the other hand: the use of three sets of rings (the leakage of compressed gas triples as compared to a similar conventional with head gasket and intake poppet valves, the lube consumption increases as compared even to the conventional two stroke etc) is not a great solution.

The problems (side effects) generated by this arrangement of Leyland-Motors are many. Are there any advantages?

Thanks
Manolis Pattakos

#84 manolis

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Posted 13 April 2012 - 12:56

Good point about opposed piston diesel engines having ported exhausts - this feature doesn't seem to do them any harm.
Manolis has an engine design himself that has a ported exhaust.


Kelpiecross,

The ported exhaust is a necessity for the Opposed Piston arrangement (Junkers engines, EcoMotors-OPOC, Achates, PatOP, OPRE).

Things become way better in case the exhaust piston is rid of thrust loads (as with the cross head architecture of the Achates, PatOP and OPRE engines): the exhaust piston runs colder, the necessary quantity of lubricant on the cylinder liner decreases, the specific lubricant consumption lowers a lot (according Achates, the specific lube consumption of their prototype Opposed Piston engine is only 0.1 gr/KWh, i.e. it is comparable, if not better, than many 4-stroke decent diesel engines).

The Detroit Diesel engines use ported intake, with poppet valves at the exhaust.
The giant marine 2-stroke engines also use ported intake, with poppet valve(s) at exhaust.
Is there any advantage of the ported exhaust over the ported inlet?

The next step is to completely avoid the ports, keeping the other good features of the through scavenging engines.
The PatMar engine is a through scavenging engine which is rid of ports.
The PatPortLess engine ( http://www.pattakon....PatPortLess.htm ) :

Posted Image

is also a through scavenging engine which is rid of ports (intake and exhaust).

Thanks
Manolis Pattakos

#85 PJGD

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Posted 05 May 2012 - 02:39

To those interested in opposed piston engines, you will be interested to visit the website created by Martin Flint, one of the authors of the excellent recent SAE-published book on OPE's. This website gives information on many but by no means all of the known OPE's; a brief article where information is available, patents on many that don't fall in that first category, and downloadable technical papers where they exist. I am sure Martin would appreciate information on other OPE's to fill out this great catalog.

The website is here: http://www.opposedpistonengines.com/

It is not a slick production by any means, but it does introduce a lot of unknown engines and put a huge amount of OPE information in one archive for easy access.

PJGD