Ceramic Head Buttons?

[BobBonahoom]

Has anyone ever tried machining a head button out of a machinable ceramic material like macor?  I wonder if its thermal insulating properties would make the combustion process more efficient?  Also, it may then be easy to sputter a thin film of Pt/Ir onto the ceramic dome, which may be catalytic to methanol because of the heat retention.  In other words, the button becomes a sort of giant glow plug and you get a more even and efficient burn.  This sounds a bit looney, but just wondering.   I was remembering when people were running engines with 3 glow plugs and just started wondering.  Thoughts?

 

[shoboat]

Bob,

We are working on a ceramic coating system for head buttons,

piston crowns, and pipe surfaces. I will be testing it at Blue Lake in February

on a few new motors.

Happy New Year,

Mark Sholund

 

[dwilfong]

Try ductile iron.

 

[Marty Davis]

Here is a reply from Brian Callahan.

No idea about the catalyst coating, but I do have experience with thermal resistant coatings. Not exactly the same thing as a whole head made of insulating material but close.

Most people fail to think about the compression stroke. Heat saved by the insulator during expansion makes the chamber hotter and the gas to compress also hotter. This drops density which reduces trapped charge mass. In turn power and torque are reduced. Compared to the extra expansion work achieved on the downstroke, there is a small net loss.

Also detonation is aggravated. This means lower compression ratio or higher octane fuel (less nitro) would be required. Both hurt power and torque.

Toyota and a lot of OEMs studied this concept to death in the 80s. The overwhelming consensus is that the concept is fundamentally flawed. I would not waste any time on it.

 

[LohringMiller]

As I pointed out in another post, you want to transfer heat out of the combustion chamber in the squish area but not out of the dome area.  You can do this to some degree with head shape.  You direct cooling water over the squish but not over the dome.  Plug cooling is important as well so a pee hole directed at the plug would work.

I've thought about Zirconium as an engine material.  It's very common in dentistry and the technology to accurately make small parts exists in all modern dental labs.

Lohring Miller

 

[dwilfong]

Dose some one have the figures for thermal transfer of different metals?

I am not seeing trapping of heat in the chamber as dropping the density enough in are small eng to make a difference.

Now having the chamber hot to flash off the Nitro I can see being a +.

Also the squash being cooled down so it is not a tight hot spot for detonation to occur.

Also it will remove heat from the piston. on the outer edge where  is thinnest at the 90 deg corner.

I stopped testing before I tried Ductile iron for a head button.

Would be nice to see some one give it a good try.

I have a feeling if made right it could do all the above .

I will get back to it one day and give it the old Collage try...........................LOL

 

[BobBonahoom]

Here is a reply from Brian Callahan.

No idea about the catalyst coating, but I do have experience with thermal resistant coatings. Not exactly the same thing as a whole head made of insulating material but close.

Most people fail to think about the compression stroke. Heat saved by the insulator during expansion makes the chamber hotter and the gas to compress also hotter. This drops density which reduces trapped charge mass. In turn power and torque are reduced. Compared to the extra expansion work achieved on the downstroke, there is a small net loss.

Also detonation is aggravated. This means lower compression ratio or higher octane fuel (less nitro) would be required. Both hurt power and torque.

Toyota and a lot of OEMs studied this concept to death in the 80s. The overwhelming consensus is that the concept is fundamentally flawed. I would not waste any time on it.

Marty,

Thanks for asking Brian about it.  No sense wasting time and money on it after all the work that was done by Toyota.  Everything seems to point toward cooling the gas charge for more density and lighting it off at just the right time.  Funny, I think that is called a spark plug!  I have always thought what we really need are high performance spark ignition nitro engines.  People say that using spark with nitro is unsafe, but nothing could be further from the truth!  

 

[LohringMiller]

We've run several ignition engines on nitro.  We didn't spend much time optimizing for the fuel.  The engine probably needs a different head button, different ignition timing, and especially a different pipe.  The picture below shows what happened to a Quickdraw's plug on 40% boat fuel.  It ran fine on 15%.  We also did a series of fuel tests on a modified Zenoah.  You can see from the graph that without the changes mentioned, the power didn't change much over non ethanol pump gasoline (87 Otto on the graph).

Besides the head button, the other cooling questions involve the exhaust and transfers.  The principle is keep the incoming charge cool.  The current thinking is to route cooling water over the transfers then around the exhaust duct and finally over the head button.  It may help to separate the transfer flow from the exhaust flow with two cold water intakes.  Cooling the exhaust may remove some heat energy from the pipe, but cooling the charge that is pushed back into the cylinder gives more power.  Ceramic coatings on half or all of the exhaust duct reduced power.

Lohring Miller

 

[Timbo Whalen]

We are delving into the ceramic TBC field and have a good, knowledgeable source who has positive dynomometer validation.

Do your research and make your own determination.

Personally, we were working on an engine program at Pontiac Advanced Vehicle Engineering (GM AVE) back in the early-mid 80's

for the Gen II P-car platform (Fiero) that never came to fruition, as the whole platform was canceled.

The only thing we can offer is the engine indicated used an awful lot of CF, titanium, ceramic components and ceramic TBC's

during development. It was an inline 4 and was an experimental exercise code named 'Manhattan'.

There is a lot of data out there that contradicts some of the statements here.

Again, you be the judge.

http://swaintech.com/why-coat-a-two-stroke-piston/

The following paper substantiates, to a degree, what Brian Callahan is quoted as saying. Of note, fuel type and coating thickness

plays a roll in all of this. However, this paper also offers validated work around's to the issues Brian speaks of for a net gain in 

brake thermal efficiency and brake power output. Of note, the gross losses are mostly a result of using gasoline as the fuel, whereas

the use of methanol turns everything around producing gains- BMEP is significantly higher with the methanol throughout the test

engines rpm range-

https://www.osti.gov/servlets/purl/10194664

The following source offers a wealth of products and technical information regarding various coatings as applied to IC engine technologies-

https://techlinecoatings.com/tech-line-coatings/hi-performance-coatings/internal-engine-coatings/

On a final note, there are plenty of SAE papers out there that validate ceramic TBC's in a positive light.

Hope this intrigues some of you.

 

[Dennis Somers]

Generally speaking, heat ( and therefore expansion ) is power, right up to the point of detonation. If the chamber and piston top are reflecting the heat instead of absorbing it, there will be  more expansion pushing on the piston, and the hotter exh. gases will speed the flow. This can be good for spark ign. on lower RPM engines, where the burn is more controlled, so as to control detonation. But the very small glow engs. operating at 30 to 40+K, it's very possible that the glow plug is simply a constant torch at those RPM, and may be lighting off the fuel as soon as the transfers close. It's a question of whether you want the chamber/piston to cool the charge and use a higher nitro load, or reduce the percentage slightly and use more expansion heat. I don't think there's a good/fits-all answer for glow engs. Like most things; a trade-off.

 

[LohringMiller]

My information comes from the few people who are still trying to get the most power from small two strokes.  Their feeling is that the combustion chamber can be allowed to get hot, but the plug and squish area needs to be cool to postpone detonation and/or preignition.  Detonation is what limits the power of spark ignition engines.  Cooling of the exhaust port and duct area follows similar reasoning.  The above mentioned people have tried coatings and various cooling methods on dynos.  Their conclusion is that cooling of the mixture pushed back into the cylinder by the pipe made more power.  Allowing this returning charge to get hot also promoted detonation. 

Our engines are far from the state of tune that these people are testing.  I doubt that much of the above would make a noticeable difference in our engines.  In any case it would take careful dyno testing to see this.  Other factors tend to overwhelm small changes.  This was made apparent to me when we saw the change due to break in reducing friction and increasing power over a series of tests.  Friction is huge in small engines.

Lohring Miller