DT wrote:

I
That may be the one (partially) true claim, actually.

Hydrogen remains largely transparent as it burns, so it emits very
little light. Blackbody radiation is called that for a reason --
perfectly reflective or transmissive materials don't emit light when
they're hot; bright yellow flames get that way because soot is black,
which is part of the reason that hot soot glows. So if you looked at
the flame with an infrared pyrometer it would show up as not much warmer
than it's surroundings.



Even that claim is dubious. It's true that a hydrogen flame doesn't emit
much light, but I can assure you it emits plenty of IR radiation.

That's not necessarily inconsistent with their claims though. Sounds like a
selective emitter--that being the case where's the peak and to what
blackbody temperature would that correspond?

I worked many years at NASA's Rocket Engine Test Facility (RETF) at the
(now) Glenn Research Center in Cleveland. One of our continuing programs
was liquid hydrogen cooled nozzles. The hydrogen was run through the
nozzle and skirt to cool the throat and preheat the hydrogen before it was
injected. Since this was a test of the cooling and not the combustion, we
just dumped the warm hydrogen.

It went up a stack about 120 ft high, where it exited a manifold and was
ignited by a pilot flame. The flame was huge (this was about a 20,000 lb
thrust motor), about 50 feet high and 20 feet across. Since the RETF was
right next to Cleveland Hopkins airport, we had to get clearance to allow
this flame so close to the runway. My friend Ken actually flew a small
aircraft above the flame to test for thermals.

You could barely see the flame on overcast days, it surely is invisible.
But, if you went outside, Hole mackeral, it was hot! It was just like a
second sun on the other side of your face, really a strange feeling since
there didn't appear to be anything there to cause it.

Among other neat things about this testing was the fact that the final run
of piping to the engine was not insulated (it was a SS flex line). When
the hydrogen came on at 2000 psi the lines stiffened up and liquid began
'raining' around them. It is liquid air! The non insulated line is so cold
the atmosphere condenses around it. The oxygen rich mixure rained down on
the test stand and if any oil or dirt was present it poofed into flames.

More than once I called into the intercom, "Fire on the stand!" The test
conductor (a half mile away) would always reply with, "Hang on, we need 5
more seconds!"

As the fuel operator I was only 30 feet from the stand, in a foot-thick,
hardened building ominously called the 'Termination Room" (it's where the
instrumentation terminated). I looked out through 40 panes of bullet-proof
glass (totaling 12" thick) with a a thick steel plate that held a mirror
at a 45 degree angle. Above this was another mirror facing the stand, so
it amounted to a periscope.

Near my right hand was the big red abort button, but woe to the tech who
pushed it too early!

Dennis

--
--John
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(was jclarke at eye bee em dot net)