Hi, Can anyone suggest where I can purchase glass rods (less than or
equal to 1/4" dia) and lengths of 4 to 5 inches or more that can be cut
to size as desired, that withstand extremely high heats, 1500 deg C or
I am doing research on an engine and want to insert the glass rod
through the wall to get a photo signal of the combustion. So I want to
connect a piece of optical fiber to the free end of the glass rod and
then connect a photo detector to it, just to get a on-off (logic-TTL)
signal out of it.
I am trying to save money for research by not buying expensive
I would be extremely grateful if anyone can suggest where I can source
this high temp glass rod or transparent ceramic rod and also fiber
Are you sure that you need the optical elements to take that temperature?
If the housing of this engine doesn't get too warm, couldn't you sink a hole
in its wall and then bolt down a suitable window on a ductile metal or
silicone gasket? Sensor stays nice and cool (rtp) on the lab side of the
window, looking through at the happy gas within. Take care with signal noise
(shileded cable) and pick nice amplifiers, and all should be well.
Also, what process are you trying to monitor and is optical the best way to
It might be, but depending on the wavelength you're monitoring, sensors and
windows may be v. expensive.
I use the good people at Crystran for all my window needs (200nm and
Lyman-alpha UV in vacuum systems) and would be surprised if you need an
optical rod of the type you describe.
(aka Dr easily-surprised)
On 26 Apr 2005 22:52:56 -0700, firstname.lastname@example.org wrote:
You might like to try Plowden and Thompson,
http://www.plowden-thompson.com/ who may be able to help, although for
that temperature you need something very special, like fused silica or
Like the other responder suggested, a water-cooled window may be
URL: http://www.terry.harper.btinternet.com /
In 1958, when I was but a mere freshman at the univirsity, the
mechanical engineering department had made some photographs or pictoral
representations of the engine combustion front process. I have
forgotten the details, but I am not certain that this was anything like
cutting edge research at the time.
It seems to me that this is likely to be a fairly old technology, and
need not be reinvented.
I think of things like "depth of field", focus and so on as obsticals to
getting meaningful results from peering into the combustion chamber
through a small rod of transparent material (not all transparent rod
materials are glass rods).
I wish you luck in this project.
I have seen similar from comparable dates. When mucking about with car
engines a decade or two ago I (several times) nearly bought a widget that
could be screwed into a spark plug hole to allow the timing to be tweaked so
as to achieve the optimal combustion colour. (pauses) Gunson, that's the
(googles - yep - the colourtune)
Of course, if his 'engine' is somewhat more unusual (might be an external
combustion rig - fun!) then a modified gizmo (sunken hole gasket, stout
window, clamp) would suffice, and certainly wouldn't need long expensive
fragile rods. More info from phillippanicker would be handy (like propellant
nature, engine size, chamber pressure...)
-James (now intrigued)
Hi all, thank you for the replies.
The engine I am working on is actually a shock tunnel with a detonation
driver mode. So a fuel air mixture is detonated in the tunnel, causing
a shock wave and a flame front to travel down the tube. So my job is to
get a 'blip' from the shock wave (using a pressure transducer) and a
'blip' from the flame front so as to see how much one might lag behind
the other. And I want to do this cheaply ofcourse.
Fuel is propane, and although flame temp for propane can go as high as
2800C, with water cooling the transducers manage to survive. I do
intend to provide watercooling for the 'boroscope' that I want to
Since all I want to get is a 'blip' transformed into a TTL signal, high
tech photo analysis is not required. So all I need is the transparent
rod and a few feet of optical cable.
Thanks again in advance for all suggestions.
Our website is not the best, we haven't updated in a long time, but
here it is. This project is not up on the site yet.
How is the pressure transducer coupled to the system?
Is it inside the tube? Can you put the optical transducer
there, too? Then you wouldn't need to conduct the
light to an external sensor.
(And why apologize about watching the shopping network
when you admit to watching Jerry Springer?)
How large a time lag to you expect to see,
or want to be able to detect?
This will affect your optical arrangement.
If your silica rod is flush with the inside surface of
the tube, then it will collect light over a fairly large
field of view. Hence, your detector will see light
from the flame/detonation front both before and
after the front passes the location of the sensor.
A simple way to restrict this angle of view
would be to recess the surface of the rod
from the opening in the wall.
Olin Perry Norton
McMaster.com lists borosilicate rods that'll do the job for you. If you
need better performance than borosilicate, ask some chemistry friends
if they'll give you a bit of fused silica, fused quartz, or Vycor rod.
I'd try to find some water-clear fused silica.
I doubt there'll be much thermal effect on even borosilicate glass if
understand the situation; these are fast transients. The average &
transient materials temperatures will not be very high.
While you now say you don't care about anything more than detecting a
flash of light, I'll bet that sometime in the no-too-distant future
someone will say "why not do some specrtal analysis to get the actual
flame front temperature history?" I know I would. So will you most
I've done things similar to what you propose. An easy way to hook
things together is to use standard compression fittings*. Drill & tap
the cylinder to accept a 1/8" npt - 1/4" compression fitting to hold
the glass rod in place. This is a strong, secure setup that can be
disassembled when needed.
You might think of using a 1/4" x 1/4" compression fitting at the other
end of the glass rod to secure the photodetector or fiber optic bundle
to the end of the glass rod. Use a short rod so optical absorption by
the glass doesn't kill the whole deal.
In fact, you may not need the glass rod at all as others suggest. Let
the photodetector look through a 1/4" stainless tube.
Good luck; it sounds like fun,
*Brass or stainless steel, it probably doesn't matter much.
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