Hagen:
Why not use a metallic shell?
Stainless (309 or 310) is good to around 2000 F (about 1100 C) and Titanium
will handle very high loads (racing engine exhaust valves) at 1350 F (730
C) for hours.
I plasma spray coat the inside of the shell with stabilized Zirconia and
have had no problem with burn times up to 10.5 seconds (the steel shell in
that case reached a maximum of 800-850 F [460 C] based on thermal paint on
the outside of the nozzle extension).
Bill
On Thu, Apr 22, 2021 at 1:18 AM Hagen Hübner <hagen.huebner@xxxxxx> wrote:
Hello everyone,
a few days ago we (Forschungsgemeinschaft Alternative Raumfahrt - FAR
e.V.) tested an O-motor with a nitrate-based fuel. The part of the nozzle
near the combustion chamber was made of graphite and withstood the high
temperatures and the abrasive exhaust without any problems. The nozzle
extension - for weight reasons made of carbon fiber reinforced epoxy resin
(tempered, but otherwise standard resin), material thickness 3 - 7 mm -
however, failed after about one second of burning time (see attached
photos).
Question(s): What can be improved to prevent the extension from burning
through in the future? Is there any chance at all chance to make a
weight-saving nozzle extension made of composite, designed for a burn time
of 5 - 10 seconds? Which more temperature-resistant resin should I use?
Which reinforcing fibers are (more) useful? Do basalt fibers have a
significant advantage over carbon fibers?
Regards,
Hagen