Atomic nitrogen for scramjet propulsion?

[Robert Clark]

A problem with scramjets, which attempt to achieve combustion at hypersonic
speeds, is that the high speed means the air is producing so much drag that
it is difficult to achieve net thrust when combusting with just the oxygen
in the air.

So what if we also combusted with the nitrogen? Nitrogen makes up 80% of the
air mass so perhaps this could provide sufficient thrust. The problem is
nitrogen is commonly present in the atmosphere as N2, a molecule that is
very stable, i.e., non-reactive.

But at hypersonic speeds so much heat is produced that the N2 is "cracked",
generating various nitrogen species, such as N, NO, NO2, etc.

So how much energy could be produced by reacting hydrogen fuel with the
various nitrogen species? How much for methane fuel?

The energy density and thus Isp would be less than for reacting with oxygen
but conceivable the thrust could be greater because of the greater mass of
the nitrogen.

Bob Clark

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In fact, contrary to popular belief SSTO's are actually easy.
Just use the most efficient engines and stages at the same time,
and the result will automatically be SSTO.
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[Fred J. McCall]

"Robert Clark" <rgrego...@gmSPAMBLOCKail.com> wrote:

>A problem with scramjets, which attempt to achieve combustion at hypersonic
>speeds, is that the high speed means the air is producing so much drag that
>it is difficult to achieve net thrust when combusting with just the oxygen
>in the air.
>
>So what if we also combusted with the nitrogen? Nitrogen makes up 80% of the
>air mass so perhaps this could provide sufficient thrust. The problem is
>nitrogen is commonly present in the atmosphere as N2, a molecule that is
>very stable, i.e., non-reactive.
>
>But at hypersonic speeds so much heat is produced that the N2 is "cracked",
>generating various nitrogen species, such as N, NO, NO2, etc.
>
>So how much energy could be produced by reacting hydrogen fuel with the
>various nitrogen species? How much for methane fuel?
>
>The energy density and thus Isp would be less than for reacting with oxygen
>but conceivable the thrust could be greater because of the greater mass of
>the nitrogen.
>

Uh, Bob? You don't get to 'pick' what your fuel reacts with when your
oxidizer is ram air. It all reacts. Energy of formation for things
like NH3 is tiny when compared to H20, so that sort of reaction is
going to make your energy lower. The nitrogen in the atmosphere
doesn't just go away. All that mass is still in the exhaust whether
you 'combust' it or not. If you spend a lot of fuel 'combusting' with
nitrogen you are burning more fuel to get less energy; you are burning
50% more fuel to 'combust' nitrogen to NH3 and only getting 12% or so
of the energy you get from combusting with oxygen.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn

[Robert Clark]

Thanks for that. Apparently, with the combination of high pressure you can
crack the nitrogen so that it can react chemically at only moderate
temperatures. And the required temperature is reduced even further with the
use of a catalyst. This is how the famous Haber-Bosch works to produce
ammonia, NH3:

Ammonia.
"Modern ammonia-producing plants depend on industrial hydrogen production to
react with atmospheric nitrogen using a magnetite catalyst or over a
promoted Fe catalyst under high pressure (100 standard atmospheres (10,000
kPa)) and temperature (450 °C) to form anhydrous liquid ammonia. This step
is known as the ammonia synthesis loop (also referred to as the Haber–Bosch
process):[80]

3 H2 + N2 → 2 NH3"
https://en.wikipedia.org/wiki/Ammonia#Synthesis_and_production

Bob Clarkhttps://en.wikipedia.org/wiki/Ammonia#Synthesis_and_production

------------------------------------------------------------------
Single-stage-to-orbit was already shown possible 50 years ago
with the Titan II first stage.
In fact, contrary to popular belief SSTO's are actually easy.
Just use the most efficient engines and stages at the same time,
and the result will automatically be SSTO.
Blog: Http://Exoscientist.blogspot.com
------------------------------------------------------------------

"nu...@bid.nes" wrote in message
news:c6a42afc-9efa-4d75...@googlegroups.com...

Yeah, automobile engines have had the same problem without needing to
operate at ramjet velocities.

It's about combustion temperature. Get the reaction hot enough (above
2500F or so to reliably burn all the fuel you can cram into the combustion
volume with all the available oxidizer in the air, and the nitrogen burns
too, except "burn" doesn't necessarily mean "oxidize".

Look up "NOx emissions".


Mark L. Fergerson

[Fred J. McCall]

"Robert Clark" <rgrego...@gmSPAMBLOCKail.com> wrote:

>
> It's about combustion temperature. Get the reaction hot enough (above
>2500F or so to reliably burn all the fuel you can cram into the combustion
>volume with all the available oxidizer in the air, and the nitrogen burns
>too, except "burn" doesn't necessarily mean "oxidize".
>
>Look up "NOx emissions".
>

Uh, nitrogen to nitrogen oxides is kind of within the definition of
'oxidize'.

>
> Mark L. Fergerson