Opposing Piston Engines 10

[Painterman]

Hello to all,

I keep on noticing favorable comments about opposing piston engines, i.e., Junkers and Napier Deltics. If they are so good, then why aren't they used more widely? That is to say, these engines must have a problem or a shortfall. Can anybody say what the problem is? Also, what about their efficiencies?

Any other would be appreciated.
Kind thanks & best regards
Painterman (DFD)

 

[ivymike]

The good thing about them is they shake less.

The list of bad things might include: they cost more to make, they don't fit as nicely in a car, the pistons "wear funny" compared to vertical ones, they can consume more oil, they're harder to properly lubricate.

The thermo efficiency shouldn't be much affected by the orientation of the pistons (may be minor effects).

 

[Painterman]

To ivymike fm painterman/DFD

Thanks for your reply. What makes them more expensive to make?

Thanks, DFD

PS: read on your posting resume, quiet impressive
Regards DFD

 

[SomptingGuy]

If wacky opposed piston engines float your boat, check out what those mad scientists at Achates Power are up to.

- Steve

 

[ivymike]

regarding expense, instead of having all of your cylinders in a neat little row, you have some going this way and some going that way, like a v engine with a 180deg V-angle. For a 4- or 6- cylinder (vs inline), that means an extra head and more material to make the block. vs a vee configuration at a smaller angle, you have to put material all the way around the crankshaft to hold the halves together, and you have to find a place to put your cams, etc. You can't use common intake (as with Vee), or common intake and common exhaust (as with inline).

 

[ivymike]

hey, they're even hiring guys like me at the moment, thanks for the site (never know where the axe is going next)!

 

[patprimmer]

If opposed piston is like a Commer knocker rather than like a VW then getting the power back to one output shaft adds some cost.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[MikeHalloran]

I've read up on the Deltic, mostly because I was preparing to help somebody put them in a yacht. The project kind of disappeared along the way. Most of the fun projects do that.

The Deltic's big virtue is that there are no valves to mess with, at all. It's a two-stroke, so emissions might be a problem today.

The Deltic's real Achilles heel is oil pooling. When the engines are left idle, the bottom cylinders fill up with lube oil. If they're not barred through a couple of revolutions without fuel, to clear the cylinders of lube oil, then the start will clear the cylinders another way, by breaking something.



Mike Halloran
Pembroke Pines, FL, USA

 

[jmw]

Achates Power fits my scam test quite well (not to say it is, there ain't enough info there yet):
It has a slick web site
It has a nice animation
It has some nice investors listed
The next guess is that a working unit will always be one step away, the directors will be getting big salaries from the investment money.
We're just missing some big name companies who are asking for such and such a demonstration unit to be built (the ones the have or were working on are always the wrong size or colour).
Direct/indirect ratio? well lots of directors, few grease monkeys.

However, there are only three pages at

http://achatespower.com/index.html

and somehow a scam ought to have;lots more pages full of faked up "independent " reports etc.

Be nice to know what they are doing besides recruiting.

JMW

http://www.ViscoAnalyser.com

 

[turbomotor]

I know one of the engineers at Achates Power. He is very sharp. I think the effort is real. There is a high risk of achieving competitive hp/$ and finding a suitable marketplace, but a real effort none-the-less.

My experience with opposed piston diesel engines (Darpa program in early 90s) is that the combustion chamber volume evolution and the location of the injectors is very hard to optimize. No one has developed combustion in an opposed piston engine to work as well as a classic bowl in piston with a central injector.

The engine program referenced above resulted in very good weight specific power, but very bad brake specific air consumption. Combustion was not very good at less than about 1.8 stoichiometric air.

I think modern four stroke piston diesels are achieving very good combustion efficiency at about 1.3 ~ 1.4 stoichiometric air.

jmw - if you have 35 minutes, and you want to view a video about an opposed piston engine that will make your scam test meter buzz like crazy, check out the link below to a youtube video on Dr. Paul's opposed piston engine.

 

[ivymike]

based on the animation on the first page, it looks to me like they're using sleeve valves at opposite ends of a cylinder. I didn't see where the piston was, and I didn't see any compression/expansion going on. Perhaps the "sleeves" were actually pistons. The animation would seem to be a CFD intended to calculate how well they get the charge in/out of the cylinder.

 

[turbomotor]

Ivymike,

I'm pretty sure the Achates engine is a two stroke uniflow scavenged opposed piston diesel, so one piston uncovers the exhaust ports and the other uncovers the intake ports.

We did a CFD analysis on a similar engine with the guys from Sandia NL a few years ago, and the resulting airflow pictures looked very similar to the Achates animation.

 

[ivymike]

I have to admit that when I heard "opposed piston" I was thinking of a conventional "boxer" or horizontally opposed cylinder engine layout. I didn't bother looking up the deltic or junker. I think that the two-per-cylinder idea is unneccesarily complicated, and that the deltic looks like a circus act. They must have had some very talented engineers to make that thing successful.

 

[WGJ]

Mike - I've not seen this in person, but....I gather the Deltics used in the Deltic British Rail traction units were prone to shoot sheets of flame out of the roof exhausts if they were opened up under certain conditions - nice problem to fix on a yacht. It should intimidate other yachtie types in the harbour.

Bill

 

[tbuelna]

turbomotor,

If my memory serves me correctly, the biggest problem with the opposed-piston TRC engine was ring scuffing. Any piston ported engine, whether opposed-piston or with a conventional cylinder head, has the basic issue that the stroke overlap of the oil control ring and the compression ring pack is very limited, due to the fact that the oil control ring can never travel above the lower edge of the cylinder ports. The only reason piston engine compression rings manage to work at all is due to the perfect oil film condition left behind by the oil control ring during each stroke of the piston. Since the oil control ring cannot travel up into the working area of the cylinder bore in a ported two-stroke, the compression rings are deprived of the oil film they so desperately need where it matters most.

The situation in the TRC engine was compounded even further due to the fact that area of the cylinder bore surface exposed to peak combustion pressures and temperatures had a very thick wall and was made of low thermal conductivity alloy steel. So even though it was water cooled on its outside, the heat transfer across that thick liner wall was not sufficient to prevent flashing of whatever oil film managed to make it up to that area around the TDC point of the liner. Every time we tore that engine down, we would see ring chatter marks around the TDC point of the liner.

With regards to the injector location and chamber shape of that opposed-piston TRC engine, I'm pretty sure that was an issue we could have eventually resolved satisfactorily.

By the way, I'm working with the old DTC group on my new diesel project.

Regards,
Terry

 

[dcasto]

The opposed piston is ancient engineering. Railroad engines used them as did pre WWII submaries.

 

[patprimmer]

I think this egine is pre WW1 vintage

http://www.sa.hillman.org.au/TS3.htm

Regards
Pat
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[SomptingGuy]

Next time you guys happen to be wandering through South Kensington (London), check out the engines section in the Science Museum. Nothing is new!

- Steve

 

[catserveng]

When I worked as a mechanic, I worked on both Fairbanks Morse OP engines and on a converted WWII minesweeper with three of the Deltic engines on board.

I'm sure in their day, these were powerhouse engines, but I found them dirty, overly complex and hard to maintain in top running compared to modern diesel engines. Both engines suffered liner cracking around the ports, mostly due to poor operational procedures, such as extended times at low load or idle, improper prestart procedures, and lube oil problems.

We had a competitor underbid us on a major repair of two Fairbanks OP engines, and their mechanics were not familiar with the correct timing procedures between the upper and lower cranks, needless to say a VERY expensive mistake. We had the advantage of a former US Navy man who had experience with that engine, and knew the manuals were not very clear on all of the repair procedures.

When the Deltic engines were running good they were impressive, but a bit scary to stand next to while underway, lots of moving parts, funny noises, and oil slinging everywhere.

I think now days, when we look at all things we ask of a modern diesel engine, like high horsepower to weight and footprint ratios, low fuel consumption, low emission rates and high reliability, they older designs like complex OP engines, especially two stroke, just can't compare. But in their day they sure did push the envelope. I think those engines took real craftsmen and truly dedicated professional operators to assure good performance and reliability, something I don't see much of these days in the engine business.

My two cents worth.

 

[WGJ]

I say Pat - the TS3 pre WW1 indeed!

As a schoolboy, I used to think they made a pretty 'neat' noise when they were in the old Commer Karrier trucks in thr 50's and 60's.

http://rides.webshots.com/photo/2388315590078404180UCDGyH

Bill