Australian Team Working On Engines Without Piston Rings

JabrTheHut writes "An Australian team is seeking funding for bringing an interesting idea to market: cylinder engines without piston rings. The idea is to use small grooves that create a pressure wave that acts as a seal for the piston, eliminating the piston ring and the associated friction. Engines would then run cooler, could be more energy efficient, and might even burn fuel more efficiently, at least according to the article. Mind you, they haven't even built a working prototype yet. If it works I'd love to fit this into an older car."

Why not eliminate the piston too?

[scorp1us]

I thought this was about this article [newscientist.com] which uses a pistonless pressure wave and makes all the same promises.

Re:It won't work - sure about that?

[ridgecritter]

I wouldn't dismiss this right away.

If the physical features on the piston provide resistance to gas flow along the piston/cylinder annulus similar to that provided by piston rings, they wouldn't need a close-fitting piston - therefore no expansion coefficient headaches. It may also be that the hydrodynamics tend to center the piston in the cylinder, which would reduce contact events and scuffing wear.

You could probably get a feasibility go/no check with a few weeks' worth of modeling. The resonance interactions in the piston grooves when the combustion pressure front reaches them would be very interesting to see.

Re:It won't work

[Anonymous Coward]

Trust me, I have a PhD in engineering.

Would you care to expand upon that? Or is this the scenario we are looking at below?

I'm an engineer too, but without PhD. I don't know what he was thinking of (or even if he is an engineer at all), but I can say one major flaw that I noticed. The piston rings serves two functions and they only consider one.

The article deals with combustion, which is on top of the piston. It never mentions what is below, which is the piston rod and the crankshaft. The connection between those two needs to be well lubed, but the construction makes it really tricky to lube a "run away" bearing. The solution is to make an "oil fog", which sticks to everything, including the cylinder below the piston. When the piston moves downwards, the piston rings scrape off the oil from the cylinder and provides a clean surface for the combustion.

When running an engine with cracked piston rings, lube oil will start to enter the combustion. This will produce toxic black and foul smelling exhaust and the engine "will be burning oil". Even worse the oil burns badly and leaves behind soot, which will damage/block the valves. Some of it will stick to the cylinder wall and not be removed by the piston rings, which mean it ends up in the lube oil. The higher the amount of soot in the oil, the worse lubing ability it has. Eventually you have an engine with enough oil, but no lubing.

In short: no piston rings will destroy every valve and bearing in the entire engine and replacing it could be cheaper than repairing it.

I consider this to be a far more serious problem than anything the article mentions and I find it rather shady that they completely avoid this rather serious issue. It isn't like it is an unknown problem. If you run big engines like trains or ships, then you will periodically test the oil for soot (and other stuff related to other defects) to detect faulty piston rings before the engine is wrecked. Anybody working in the engine industry should know this.

This is an old idea

[larwe]

Turbulent obturation rings of this kind (well, technically I guess these are obturation cannelures) have been used in a lot of applications because they have some interesting properties. For instance they are used in mortar shells. When you drop the shell down the mortar barrel, you essentially want it to fall without retardation so the primer gets a good hard strike and the propellant ignites 100% of the time. However you want as much as possible of the propellant gas to do the job of propelling the projectile, without blowing past it in the barrel. You ALSO want it to be as consistent as possible so the CEP of where the projectile lands relative to the target is as small as possible. So this isn't impossible, but it's not easy either.

How about Ceramic Engines ?

[Taco Cowboy]

From the TFA:

"... that an absolute seal isnâ(TM)t that important, and eliminating the friction generated by the rings on the cylinder wall can have far-reaching effects on engine design on the whole "

" ... that the whole thing is blowing a bunch of hot air?"

If they _ CAN _ use that bunch of hot air to form a seal, and achieve a drastic reduce of friction in between the piston ring and the bore itself, I feel that it's time for the return of the ceramic engine.

The chief reason why ceramic engine doesn't make it into the mainstream despite having had under research since the 1970's is that the friction in between the piston ring and the wall of the bore itself result in the wearoff of the ceramic material in the form of a pile up of fine ceramic dust inside the chamber.

If what the vendor said is proven to be true, then we should bring the ceramic engine back to the fore-front.

Re:It won't work

[AK Marc]

One of the reasons for going from 2-stroke to 4-stroke was heat. So the "fix" to your problem is to go to 6-stroke engines, with extra strokes for cooling. Also, water injection was used to fix that issue in other engines as well. There are lots of ways to fix that. No oil in the chamber doesn't mean you can't spray the back of the piston with a cooling agent (oil in today's cars). I can fix that problem easily in any of a hundred ways (finding the most efficient would be the trick), and you've proposed no other solution to the problem fixed by the air seal.

Comment removed

[account_deleted]

Comment removed based on user account deletion

How do you know?

[Firethorn]

When running an engine with cracked piston rings, lube oil will start to enter the combustion. This will produce toxic black and foul smelling exhaust and the engine "will be burning oil".

You mention an engine where a specific feature, specifically the piston rings, has failed, so it's no surprise that it's operation would be undesirable. I will counter with 2 stroke and wankel/rotary engines, which burn oil by design. Burning oil isn't as much of a problem if you design for it.

The Australians are working on a design where the piston rings won't be necessary. It could end up that they need a new lube system for the piston rod/crankshaft, or it could end up being an insurmountable problem(for now). I like that they're looking into it though. It reminds me about how HD platter arms are suspended by air flow from the rotating platters. High enough pressures might cause the air to act more like a liquid.

Re:How about Ceramic Engines ?

[ne0n]

Ceramic would be amazing but what caught my eye in TFA is they're "working on a version for rotary engines". Imagine a Wankel without those shitty apex seals exiting the tailpipe after 100k! Probably still guzzles oil though.

An engine that needs no cooling

[Taco Cowboy]

To add on to what user Firethorn has said, try imagine an engine that needs no cooling.

The very reason we need to COOL our engine because the metal that we use in our engine can withstand heat up to a certain limit, and beyond that, the engine starts to melt.

Ceramics don't have that problem. Some ceramic compounds can withstand thousands of degrees of heat (and for that they have been used as shields for the Space Shuttles) and they are excellent insulators !

Serious research has been carried out on ceramic engines since before 1970's, by almost all the developed countries (America, Europe, Japan) and prototype engines had been developed.

The main problem so far is that, unlike metal, ceramics are not as durable against friction. Very fine ceramic dusts will fall out as a result of the friction, and combined with the fuel, it become "sludge"-like, jamming up the chamber.

There are a lot of places inside an engine where there are frictions, but the MAIN place which friction takes place is in between the piston ring and the bore wall.

If what the TFA says is true - that they can manipulate the air to become a "force" and takes the place of the piston ring, which means, the friction in between the piston ring and the wall of the bore is gone, then, the number one problem facing the ceramic engine is solved !