VW's 2.3L oval-piston diesel

vwestlife

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I just came across this on Ti Kan's Audi site... in 1990, VW developed a 2.3-liter 4-cylinder diesel engine with oval pistons (well, actually they're elliptical, not oval):



Comparison to a standard 1.6L diesel block:


The bore was 99.49 mm in the long direction, and 76.5 mm (same as the 1.6L diesel) in the short direction. The crank was the same as the 1.9L diesel. The exact displacement was 2343 cc, with 57 kw (76 HP) and 165 Nm (122 lb-ft) torque. No turbo. The pistons were developed by Mahle, and the engine was used in several VW test cars, but obviously never put into production. It was written about in 1990 in Germany's "Auto Motor und Sport" magazine, if anyone cares to look it up and translate.
 

vwestlife

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whitedog said:
More displacement with less engine length?
That was the idea, but it was destined to merely be a curiosity, because around that time VW/Audi introduced their first TDI in Europe, and they were already getting a respectable 80 HP out of the intercooled 1.6L IDI TD.

Also, the oval-piston 2.3L diesel did not have the same kind of gains in power over the 1.9L diesel, as the 1.9L had over the 1.6L. For example, the non-turbo 1.9L has 40% more torque than the 1.6L, but the oval 2.3L only has 22% more torque than the 1.9L. I suppose it's like speakers; an oval 4"x10" speaker may have a larger surface area than a 6" round speaker, but a round 6" speaker will have higher power handling and better frequency response than the oval 4"x10" speaker, because the circle is a more efficient shape for turning the voice coil's vibrations into sound.

p.s. 1990-1991 was also when VW was developing the VR6... obviously it became much more of a success than the oval-piston diesel.
 

Variant TDI

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It's a cool idea, but I'd be concerned about a non circle piston... and even moreso... a non circle bore.

It's probably not a coincidence that both the oval bore and VR were developing at the same time, since both designs are aiming at the same exact end. More engine in less space.

The VR's revolutionary ideas were based primarily on the offset journals between the 2 banks, and not in changes to the basic, and proven cylinder design, making success a slightly easier task.
 

GoFaster

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Honda played with elliptical pistons in motorcycle engines years and years ago. In their case, the ellipse was the other way, and there were 2 con-rods and doubled-up valves - the engine was an elliptical-piston V4 that was laid out like a V8 but with the adjacent cylinders joined. If anyone's curious, the extremely limited-production NR750 was like this.

It was not a good idea.
 

Kiwi_ME

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coachgeo said:
Interesting! Wonder what the advantages to this piston shape is?
Looks more like the result of the drivetrain engineering manager trying to prove a point to the chassis department!

Either that or someone in production spilled coffee on the drawings...
 

Kabin

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GoFaster said:
Honda played with elliptical pistons in motorcycle engines years and years ago. In their case, the ellipse was the other way, and there were 2 con-rods and doubled-up valves - the engine was an elliptical-piston V4 that was laid out like a V8 but with the adjacent cylinders joined. If anyone's curious, the extremely limited-production NR750 was like this.

It was not a good idea.
I remember reading a motorcycle mag article about that when it came out. Somehow they thought it would give them improved valve flow/performance.
 

jasonTDI

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They raced 2 strokes with the same oval design in the 80's (motorcycles)
 

wjdell

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It seems to me the pressure would be displaced in line with the rod. Piston could be lighter and stronger. Rod bearing wear would also change. The cost and complexity probably not justified.
 

10then34

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VW has a habit of developing innovative stuff and either:
- not using it at all
- use it for a couple of years and then revert to a conventional design
 

Volkstraktor

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IIRC the pistons in my 85 Escort Pony were not round- on purpose-. It was the most trouble free and cheapest car I have owned to date. 200K miles and only normal filter/fluid/plug maintanance and a couple of timing belts- non-interference engines rule-, and one set of front pads.
 

Matt-98AHU

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Diesel_Benz said:
Many pistons are not made round. They expand and become round as the heat up.
Holy necropost batman! Thanks for bringing back a thread from 2007!
 

T_D_I_POWER

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It's interesting that the oval head doesn't grow symmetrically w/i the cyl. CL. The evidence is shown from the oval piston picture where the valve cut-outs are offset from the cyl. CL. Therefore, exh. and intake manifolds remain in the same position wrt to cyl. head CL.

Diesel Benz said:
Many pistons are not made round. They expand and become round as the heat up.
Hmmm, this is new to me. How do they seal piston rings gap when the engine is cold, and the pistons are out of round in an almost perfectly round cyl. bore. It must burns some oil, until pistons and rings conform to the cyl. bore shape?
 
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Ski in NC

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Gad- What a nightmare. What kind of rig must it take to bore an eliptic hole, and accurately?? How to measure so you know its right?

Also, the nice thing about a cylinder is that it maintains its roundness under pressure. An elipse will deform under pressure towards more roundness. Blowby must be an issue.

Reminds me of an old quip about engineers: Germans take a stupid idea and refine it to where it works beautifully. Americans take a brillant idea and cheapen it until it sucks. Italians make it beautiful, but might not work. Brits make it ugly, and it might not work. Japanese copy what works.

Glad this idea died early. Whew.
 

nokivasara

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T_D_I_POWER said:
Hmmm, this is new to me. How do they seal piston rings gap when the engine is cold, and the pistons are out of round in an almost perfectly round cyl. bore. It must burns some oil, until pistons and rings conform to the cyl. bore shape?
A perfectly round piston, when cold, will expand more in the direction of the piston pin because there's more material there (thermal expansion).
That piston will be slightly oval when warmed up.
If it's narrower at the pin from the start it will be perfectly round when warmed up.
Great huh? :)
 

Pat Dolan

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T_D_I_POWER said:
It's interesting that the oval head doesn't grow symmetrically w/i the cyl. CL. The evidence is shown from the oval piston picture where the valve cut-outs are offset from the cyl. CL. Therefore, exh. and intake manifolds remain in the same position wrt to cyl. head CL.
which is why the engine had dissappointing performance - didn't use the available area to increase valve size (or number) - result of axis of elipse being in the "wrong" direction.

Hmmm, this is new to me. How do they seal piston rings gap when the engine is cold, and the pistons are out of round in an almost perfectly round cyl. bore. It must burns some oil, until pistons and rings conform to the cyl. bore shape?
Pistons aren't there to seal anything, the rings do that. They in turn seal against the top and bottom of the ring groove, not the round inner surface (which you will note has holes for oil drain). Also, rings are quite flexible.

Only the skirt of the piston has any reason to ever touch the bore. Having the area around the pin do so is just creating more drag/friction/heat and contributing nothing, so "round" pistons are often "cam ground" to reduce that measurement. There is no need or desire for it to become round at operating temperature. In fact, many pistons simply don't HAVE any material out there at all, since it is nothing but dead weight.
 

Pat Dolan

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Ski in NC said:
Gad- What a nightmare. What kind of rig must it take to bore an eliptic hole, and accurately?? How to measure so you know its right?
It would take an eliptical boring tool (one that has a dynamic second prallel axis). Just think of the need to bore epicyclic rotor housings for Dr. Wankel's engines, and you can appreciate that it isn't that hard.

Also, the nice thing about a cylinder is that it maintains its roundness under pressure. An elipse will deform under pressure towards more roundness. Blowby must be an issue.
Rings easily comply and conform. Cylinders don't stay all that round for all that long, nor do cylinders distort very much at BMEP values (but of course, you are right, an elipse will do so trying to become round under pressure).

Reminds me of an old quip about engineers: Germans take a stupid idea and refine it to where it works beautifully. Americans take a brillant idea and cheapen it until it sucks. Italians make it beautiful, but might not work. Brits make it ugly, and it might not work. Japanese copy what works.
I hadn't heard this before. After I stop spitting up all over the keyboard, I would like to adopt that expression, with your kind permission.
 
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Ski in NC

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Pat Dolan said:
I hadn't heard this before. After I stop spitting up all over the keyboard, I would like to adopt that expression, with your kind permission.
Permission granted. At least from me. That quip has existed for a while in the public domain. Can't remember where I first heard it. It was funny at first, then later when dealing with real world engineering, it was often painfully true. MBA's should never be allowed in American manufacturing. At least what is left of American manufacturing.
 

TurbinePower

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Ski in NC said:
Permission granted. At least from me. That quip has existed for a while in the public domain. Can't remember where I first heard it. It was funny at first, then later when dealing with real world engineering, it was often painfully true. MBA's should never be allowed in American manufacturing. At least what is left of American manufacturing.

America still has manufacturing?:eek:
 

Pat Dolan

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TurbinePower said:
America still has manufacturing?:eek:
Yes, it does. It makes parts for buildings for WalMart and Wall Street, port equipment to unload containers from China and supertankers from Saudi, as well as arms and munitions to blow up jerkwater non-countries. It also makes enough drugs to stupify half the planet. I think the hydroponics side is growing closer to the top now, though. We (yes, I am an American corporately) just don't manufacture anything that will create wealth or benefit Americans.
 
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Ski in NC

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Our port here in Wilmington NC just a few years ago installed some really big cranes to unload containers from ships, mostly from China. The cranes were made in China. They were transported on a strange looking ship built just for this purpose. The ship was built in China. A local company owned by a friend was hired to touch up the paint on the cranes. He was glad to get the work.
 

Scott_DeWitt

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I read an article about the Us shipping industry and specifically the containers that goods are transported in. Containers are made in China and shipped over here, where they are shredded then sent back to china as scrap steel to be made into new containers again! Seems it's less expensive to do this than to ship empty containers over there. There's so many excess containers people are turning them into housing.
 
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