Apollo Discussions > The Reality of Apollo

It really is rocket science

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cjameshuff:

--- Quote from: ka9q on March 15, 2012, 08:34:50 PM ---I would think that the atomic oxygen released by the decomposition of H2O2 would be at least as corrosive as any oxidizer, but maybe not.
--- End quote ---

HTP's been used as a monopropellant in numerous rockets (not often...performance is poor and it's expensive, hazardous, prone to decomposition in the presence of any contamination, etc). Any atomic oxygen has probably recombined to molecular hydrogen by the time it mixes with the kerosene and burns, so you're basically using a mixture of steam and oxygen as your oxidizer, which is probably a good bit cooler burning and less of a corrosion issue than injecting pure liquid oxygen.

Bob B.:
I seem to recall reading somewhere that the Black Arrow used 85% hydrogen peroxide, though I don't know the mixture ratio of oxidizer to fuel.  That's going to produce a great deal of water in the exhaust.  The temperature is also much lower than when LOX is used.  A LOX/RP-1 engine might have a combustion chamber temperature of around 3300o C, while a HTP/RP-1 (HTP=high test peroxide) engine might operate at about 2400o C.  I'm by no means an expert of the incandescence of carbon, but I have to believe the lower temperature would decrease the effect.

Bob B.:

--- Quote from: ka9q on March 15, 2012, 08:34:50 PM ---... it was also my understanding that most rockets are run fuel-rich to avoid an oxidizing environment that could erode the combustion chamber and nozzle
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Reducing corrosion might be part of the reason, but I've always understood the reason for operating fuel-rich is to lower the molecular weight of the exhaust gas.  Oxidizing the fuel creates heavy molecules -- CO2 is heavier than CO, and H2O is heavier than H2 or H -- which results in a lower exhaust gas velocity.  The downside of running fuel-rich is that the temperature is less, which also reduces exhaust velocity.  There's a happy medium where we supply adequate oxygen to burn enough of the fuel to get a high temperature, but not too much oxygen that we drive the molecular weight too high.  The optimum mixture that achieves the highest exhaust velocity is on the fuel-rich side of a stoichiometric ratio.

By the way, the Russians operate many of their engines oxidizer-rich in the preburner and turbines.  I haven't studied their designs enough to know how they've overcome the corrosion issue, but they've apparently figured it out.  I think their N2O4/UDMH staged-combustion engines operate oxidizer-rich, though the main combustion chamber is still burning a fuel-rich mixture.  They route the oxidizer along with a small amount of fuel to the preburner, and then the oxygen rich gas is routed to the turbines.  The turbine exhaust then goes to the combustion chamber where it is combined with the remaining fuel and burned.

Glom:
What's the problem with a lower exhaust velocity?

What's the problem with high mass lowering exhaust velocity?  That would mean you could get the same thrust for a reduced power.

ka9q:

--- Quote from: cjameshuff on March 15, 2012, 09:07:09 PM ---so you're basically using a mixture of steam and oxygen as your oxidizer, which is probably a good bit cooler burning and less of a corrosion issue
--- End quote ---
Steam can be notoriously corrosive, as any power plant operator can tell you.

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