Ceramic engines?

[FYRHWK1]

Originally posted by 454Casull
What is your definition of rust?

the metal oxidizing and breaking apart.

[454Casull]

Sorry, I'm talking out of my ass again.

However, aluminum DOES oxidize - but does not break apart.

[SaabJohan]

On that page they really seemed to overrate ceramic engines.

As I remember Renault had tried with ceramic pistons (just the pistons) in F1, but without any good results. The basic problem is the ceramics sensetivity, yes they're strong and hard, but hard usually also means sensitive.

Ceramics are difficult to machine, almost impossible, instead they are usually sintered (or similary).

Ceramics, just like metals expand in heat, this is a limitation of the tolerances.

Also, ceramics like all materials have friction (which we should be happy for) when they get in contact with another material. No wear.. good joke.

Ceramics can't oxidize, this is because they already have.

A higher combustion temperature means that much more can burn (just like mentioned on that page), but this isn't always a good thing. Since air contains about 70% nitrogen, NOx can easily be formed, this is one of the problems in todays lean burn engines.

It is easy to got carried away with the talk about ceramics, but it should not be forgotten that ceramics isn't always the best construction material, in engine applications it's probably metals that is the best material.

Take a look on aero engines, you don't find so many ceramics huh, and here is money usually no problem (since an engine can cost $3M).
Today, many of the "supermaterials" used in cars come from aero or space technology... so if they will get these type of materials to work that is probably the place where we'll find it first.

[FYRHWK1]

Originally posted by 454Casull
Sorry, I'm talking out of my ass again.

However, aluminum DOES oxidize - but does not break apart.

ahh, didnt know that part, i was under the impression it couldnt be rusted/corroded by other materials, like water,oils, etc, save for acidic substances of course

[TheChivalrist]

A number of ceramics were tried for engines, one being Sialon for Si Al O N or silicon, aluminum, oxygen, nitrogen which is the original silicon nitride dope (small amount added) with aluminum oxide. This ceramic had the hardness and flexibility to make some parts but ceramic has to be made in pieces to allow for heat expansion. Sialon has an excellent thermal shock resistance (resists strength of material objectit when one piece changes size and another doesn't) and glass for instance has little. Glass is essentially a solution of silicon doped with many different other elements and is actually a liquid. Silicon has to be almost totally pure to crystallize and thus not change shape. The tiny amount of doping in silicon solid state materials are just enough to creat holes in anb actual crystal while glass is very impure. Silicon, if pure, will take a lot as long as it is heated throughout but engines is not one of its uses.
If thin enough, its flexibility might approach its strength such as in exotic deposition (ion transfer in a vacuum making films of several atoms thickness) which are not brittle because the displacement of bonds across that distance are too small to matter. The only ceramic engine available would be some ceramic made up of bubbles that had walls very thin so the flexibility would exceed the strength.

[454Casull]

Sialon is silicon aluminum oxynitride - I feel nitpicky.

Glass is not a liquid (at room temp), but rather an amorphous solid.

... What did you resurrect this thread for, anyway?

[icon]

Check out Ford's SHO's, the newer ones have ceramic parts. It's lighter and runs cooler, I guess, makes me wonder why we still have cars that are under 100 miles per gallon, I mean come on, we're in outer space (not well, but we're there) for Gods' sake. It's all about the money.

[Michael_S]

(This is stuff I remember from college physics. If anyone can point out errors in my logic, please feel free to do so.)

Assume a 3000 pound car gets 25 mpg and is 10% efficient (worse case scenario). That means that 10% of the energy in the fuel system is used to move the car, and 90% is lost due to incomplete fuel burning, friction in the drive train, and heat.

For that car to get 250 mpg, it would need 100% efficiency. 100% of the gas would have to be vaporized and burned. The shifts of the transmission (where gas is wasted while the engine runs but no gear is engaged) would have to be instantaneous and friction free. You couldn't possibly use cylinders in the engine itself, because energy is lost in the constant up-stop-down-stop cycling. You couldn't possibly use valves in the engine itself, because the up-stop-down-stup movement of the valves saps energy too. Bigger valves, which permit more air and fuel into the cylinders and increase power, also burn more power because they are heavier. The pollutant control systems in the exhaust would have to work without slowing exhaust fumes at all, because that reduces efficiency. The exhaust would have to leave the car the same temperature it was in intake, and all of the heat energy it contained would need to be recycled. Now, heat energy can be converted to electrical energy, so that adds efficiency to the car. However, the conversion process would sap power by slowing the exhaust and adding mass to the car. The wheels would have to weigh nothing, because the energy from the engine pushes the car by spinning the wheels, and a lot of the energy is lost fighting the angular momentum of the wheels. 100% of the energy from braking would have to be recovered by the engine. The engine would be off whenever the car wasn't moving.

I think a 50% efficiency vehicle would represent positively amazing technology.

[454Casull]

Some marine diesels approach 50% in total efficiency.

[Michael_S]

Originally Posted by 454Casull

Some marine diesels approach 50% in total efficiency.

Marine diesels don't have drivetrains, transmissions and/or torque converters, complicated exhaust systems, tires to spin, idling at a stop light, or braking to worry about. I would think that makes a big difference in total efficiency.

Still, that's an impressive percentage. I didn't realize they worked that well.