If the Aluminium has too much thermal expansion, at least in a blueprinted, all-out, custom build, would a ceramic/metallic composite be a better option? I'm specifically thinking of the Aluminium/Boron Carbide Composite that was developed for attack helicopter armour. I've seen footage of panels much thinner than a rotor being hit with repeated 20mm cannon fire and holding up, so I'm thinking it's plenty tough. The only questions I have are whether Boron Carbide is the proper ceramic to use for this application and whether CerMet can be made in a thick enough slab to form a rotor.

 

I bet its not exactly cheap either.....

Or easy to get or work with for that matter

 

Boron is classed as an extreme health hazard for machining or working with, so...

 

In that case, per http://ceramicrotaryengines.com/ how about zirconia based ceramics? I know the DoD experimented with a zirconia based ceramic engine in a HMMWV with no external cooling (though I imagine that it made it no fun to ride in under cold weather conditions).

I still think there is merit in a cermet composite rotor to reduce weight without increasing thermal expansion to a dangerous point.

 

^^if money is no cost then the sky's the limit, remember you are on a forum where people think $5k for a rotary keg is expensive (which it's not)

 

Do the math on the density of TZP zirconia. It's fractionally lighter than cast iron. CRE's engine is something like 1 inch around. TZP just isn't cost effective enough to be useful is large scale. I did a lot of researching into making some rotors / parts out of TZP and it wasn't pretty. Honestly, Aluminum is probably your best bet economically, and weight wise, but it will require better oil cooling.

Also material defects would be a major concern in a cast ceramic part. You'd want to cast them in green state and machine them as close to perfect as possible before sintering them. Once they're fired, it takes diamond bit tooling to work with the material making machining it ridiculously expensive.

I've heard that Cermet's been known to flake, so not a good idea IMO if there's even a hint from anyone if this is actually the case...

The ONLY advantage of ceramic engines is not so much weight as it is thermal efficiency. Due to the extreme heat capacity of TZP, you could in essence have a self catalyzing since you could let the engine run at 1600+ deg F. Problem then is the fuel spontaneously combustion and or melting out your exhaust manifold.

Think of it this way, if you're reflecting the heat from the rotor and not into the oil cooling, then where's the heat going? you'll be heating the liner more which means your water cooling will have to work harder, and the housing will warp / deform more. If something like the lip of the spark plug holes curls up, then you're going to have some problems. There's a lot to think about.

 

aluminum can be great but of what REAL benefit will aluminum rotor make? Weight reduction---so what?
How will the seal groves hold up?
how will the gear mount be done and how strong will it be?
How will expansion/contraction be tolerated within the engine and the seal clearances
yall know all the usual quiestions.............

 

My thinking with an aluminum rotor is that it would likely have to have hardened inserts for the seal grooves, like the ones that Mazda experimented with; but I was thinking that it might be less prone to hot spot build up, making it more tolerant of either boost or static compression (or some combination thereof).

 

it really doesn't matter as the most critical aspect of all is keeping it cool enough so as to not to lose it's heat treating temper, once that happens even an insert will eventually wallow out too

 

Please forgive my newb-ness with regard to metallurgy; but around what temperature would that be? I think that would make the difference between whether aluminum rotors can be used in either a daily driver or an endurance racer, as opposed to a drag racer where the engine might well be torn down immediately after race day.

 

Quite the opposite of what you think actually. I remember in a physics class that the teacher measured a piece of metal with a hole cut in it. Everything got larger as it was heated, even the hole.

Even found a page! Yay evidence (wanted to make sure I wasn't remembering wrong info)!

http://www.newton.dep.anl.gov/askasc...0/phy00741.htm

 

Also, there is such a thing as "too light" in a street driven engine. The more you lighten the rotating assembly, the higher you have to rev and more you have to slip the clutch to launch the car. You're talking like a 4lb rotor if it was made exactly like the factory Mazda rotor. That's 10lb of rotating mass off the crank. I think 6lb would be more realistic since you'd have to make the walls a little thicker. I'm not sure that a 6lb rotor is a good idea for anything other than a race car (drag/ high RPM track), and that being the case, you're not going to sell enough to make it worth manufacturing.

I do think that a lighter rotor could be helpful, but between the thermal properties of aluminum, and the extreme weight loss, I think that it may effect drive-ability too much to be worth the high cost especially if you put a lightened flywheel behind that. The BHR flywheel alone makes the car very quick revving.

 

While I agree that too light a rotating assembly can negatively impact drivability, in Wankel engines where the rotor housings are stationary, there is an eccentricity of mass in rotation (a wobble, if you will) that makes me think that lighter rotors and a lighter balance weight in combination with whatever is the appropriate weight flywheel for the application would be desirable from the standpoint of reduced strain on the E-shaft, reduced wobble of the rotors (esp. at high rpm), and reduction of hot spots, allowing either higher static compression, more boost, or a combination thereof.

 

given how silent the subject has gone since the initial buzz you can pretty much sum it up as being more difficult to accomplish than it appears ...

 

Indeed. Then, even if achievable, the market is very small, production costs high, and potential for profit, approximately zero.