Window in combustion chamber?

[JW]

Hi,

I am new here. You may know my site, www.jetengines.tk. I live in the netherlands, study mechanical engineering, bla bla.

The combustion chamber of my jetengine is a bad design. The engine runs with it but the ignition electrodes are bad and it leaks air, and its a bit too small for the turbo that I am using.

Because I built this engine for a school project, my old teacher is very interested in buying this engine from me.
So before I sell it, I think I want to build a window in the cc to observe the combustion. This would make the engine also a lot more interesting for demonstration purposes at school..



this is my combustion chamber.

I have a lot of old 1 cm thick and new 1.5 cm thick plexiglass that I can use. I want to make a window in the tube of the combustion chamber, parallel to the flame tube. I have ideas about how I can mount it.

Any advice?

thanks,
JW

[Anders Troberg]

Plexi will not last long, it will go soft, melt or burn. I heat it in the oven to shape it, and my oven is probably a much kinder environment. You will probably need something far tougher than plexi.

[Dang911]

At the temperatures these engines run at, I really don't see any materials working "great" for this idea. Plastics are totally out of the "ball park".

Your best bet would be to get some heavy tempered glass. This stuff will be the best heat resistant material. Tempered glass is shatter/heat resistant. It it used in oven baking pans, and more importantly Pyrex lab equitement, beakers/test tubes.......etc.

The highest working temperature of tempered glass is around 1400-1500 degrees Celsius (2500-2700 degrees Fahrenheit)

If that doesn't work, your last resort it Quartz. Quartz has a working temperature of up to 1650 degrees Celsius (3000 degrees Fahrenheit).

[JW]

Ok, thanks...

I doubt* that the outside if the combustion chamber gets too hot for plexiglass. My engine is running at 5 PSI so the compressor discharge air is not very hot. The outside of the cc can be touched when the engine is running. maybe it gets 100 degrees C. I can search/calculate the strength of plexiglass at that temp.

* but the heat the red hot flame tube radiates could be too much....

I've read that more people have put plexiglass windows in their cc's, maybe it works, I am not sure..

[Dang911]

Well if you say the temperatures are that low, I will take your word for it.

Instead of using Plexiglas which is acrylic, use polycarbonate. It holds up better to radiant heat, and has an overall higher melting temperature (also 10x stronger).

At the same time, there are laminates much like window tinting which you could place on the inside of the "plastic" window. They are clear on one side, buy almost mirror like on the other. These laminates usually will withstand high temperatures, and are meant to reflect radiant heat. You probably could pick up some scraps at a local auto shop, because you won't be needing very much.

There is an alternative to using a sheeted material. High temperature resins, (phenolic) could work if you were to make a mold and poured into it. This could be a mounting method in itself, and in the end save time! You would have to make sure it was a clear resin though......

You say the your running low pressure, but is there any chance a lick of flame could touch the window? If so it will bubble anything but glass.

[JW]

thanks for the tips, I was thinking of some heat shielding etc but the foil is a really good idea!
I am not sure of the material I have, I assumed it is plexiglass, but thst just a guess. Its a clear material, it is from a local car dealer, they threw away all the brochure stands, and I took them home :wink:

I'll post my design for mounting it soon..

[Dang911]

THATS 100% CRAP!!!!!!! :-(

Those display stands are made out of the worst quality, lowest grade, non structural/heat resistant acrylic!!!!!!!!

Its good for looks, but literally if you were to drop a piece it would crack. Take a piece of polycarbonate, and I bet you, you could throw that at the ground all day, as hard as you can, and it would never crack.

In the right thickness, polycarbonate is what they call bullet-proof-glass. About 1/2" will stop a small hand gun, with 1.5" stopping most* rifles. Its a pretty common material, and im sure lowes and home depot has some. 1/4" should be thick enough for your application. Any thicker and it becomes hard to find, and a little costly....

[Anders Troberg]

Perhaps having double layers of glass / plastic with some space between and blowing cool air between them would help somewhat.

Still, even if it doesn't melt, it will probably get soft and deform or fall out.

I have som pieces of lexan which I use to make replacement parts for my pinball machine, and even that becomes soft and shapeable with only moderate heat.

Try putting some of it in the oven first and see how it reacts. If it doesn't remain hard there, it will not survive looking into the CC.

And whatever you do, don't put your face anywhere near the window while it is running. Use a camera.

[Fricke]

Hi JW -

There are some sightglass for boilers, Look at Mark Nyes site... He had a pair mounted to his CC so he could look in the flameholder when it was running...

//FK

[JW]

sorry I forgot to mention, the display stands are indeed pretty low quality, the other 1.5 cm thick piece is a much better material.
Boiler glasses are indeed a good choice, but cutting glass is pretty difficult I guess, and I don't have the glass.

I think that I just make the hole in the cc and a flange to fit a window to it, and then try my materials, and if/when it doen't work I'll buy some good stuff.

this thread is giving me a lot of useful information, thanks!

[Dang911]

Tempered glass and Pyrex are two entirely different things. Tempered glass is just normal glass that's been heat treated in a specific way that sets up internal stresses that strengthens the glass. Pyrex is a trademark for borosilicate glass, a glass with a low coefficient of expansion, making it ideal for situations with differential temperatures, like lab or cooking use. Or combustor windows.

HYMM..... Glass is a general term, so although Pyrex and regular glass are different chemically, they are both glass. I realize the differences as I work with Pyrex on a daily basis. Ok so we can agree that Pyrex is glass. Now is Pyrex tempered? Indeed it is. So generally saying Pyrex is tempered glass IS A CORRECT STATEMENT. Looking aside, there are over 200 different types of glass!!!

The problem you will face if you uses glass, double pane or not, is forming. You will not be able to find a rectangle of "glass" bent to the proper curve to fit around the circumference of the CC. Using glass, or plastic, will intail a softening to bend it. With plastic that is a very easy job. With glass it requires a lot of care/know how, and then the glass needs to be control cooled, to prevent the temper from being lost. All in all, honesty, the resin sounds like the easiest way out. It will mold itself to the curve, and mount itself in a seal, and then harden heat resistant and perfect.

[Dang911]

FIND ME PYREX "glass" THAT IS NOT TEMMPERED!!!

In the process of making Pyrex brand glass, it is always tempered. Every piece with the Pyrex label has been tempered........

[Dang911]

Damn your good.....

Although it didn't say weather the rod was tempered of not, I agree, it couldn't be tempered, to be worked with in such a manor.

Let me rephrase my original statement. All Pyrex final products, not raw materials are tempered. These would include all of the lab and cooking equipment. It is what originally made Pyrex well known for the "plates" that supposedly could be dropped and would not brake.

[marksteamnz]

Hehehe. If we stick with borosilicate glass as a definition vast quantities are not tempered. It's used in glass wool insulation. Trust me on this one (18 longggggggggggggg months as a glass wool plant chemist many years ago)
Back to the problem.
The glass used in wood fire enclosed heater windows is a pyro ceramic. No idea of formulation but it is much tougher than borosilicate. If you can find a wood heater installer they often have offcuts and spares. It's the best. Forget curving it, just make a cunning holder / window location.

Pyrex is tough but it does shatter, just depends how "hard" you hit it

Damn your good.....

Although it didn't say weather the rod was tempered of not, I agree, it couldn't be tempered, to be worked with in such a manor.

Let me rephrase my original statement. All Pyrex final products, not raw materials are tempered. These would include all of the lab and cooking equipment. It is what originally made Pyrex well known for the "plates" that supposedly could be dropped and would not brake.

[Mark]

http://www.qsiquartz.com/techinfo.htm
http://www.skutt.com/glass/accessories/window.php