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Enthalpy

Pumping Cycles for Rocket Engines

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Hello you all!

 

Rocket engines often pump liquid propellants in their combustion chamber, and many cycles are used to power the pumps, the best known being:

http://en.wikipedia....le_%28rocket%29

http://en.wikipedia....le_%28rocket%29

http://en.wikipedia....le_%28rocket%29

but here I'd like to describe uncommon cycles, which may be new and of my invention.

 

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The first sketched cycle cracks in a pre-chamber a hydrocarbon or an amine with hydrogen, which produces methane (chemists call this hydrogenolysis), some excess hydrogen, and enough heat that the following turbine powers all pumps that achieve for instance 440b in the pre-chamber and some 200b in the combustion chamber.

post-53915-0-19226700-1317342159_thumb.png

Logically, fuel density and specific impulse are between methane-oxygen and hydrogen-oxygen, thus filling the gap between kerosene and hydrogen engines, as the diagram shows (click to magnify).

post-53915-0-69474800-1317342201_thumb.png

The pre-chamber and turbine run with fuel-rich hot gas, far easier than the oxygen-rich staged combustion cycle which was needed to avoid soot with hydrocarbon fuels.

Or if one oxygen-rich pre-chamber is kept, hydrogen pumping can go through a separate cycle like the one just described, in a kind of full-flow cycle that achieves a higher pressure but would not soot with hydrocarbons. Maybe an adaptation from existing engines like the RD-180. More details to come, as well as other cycles.

 

More lengthy details, in a less ordered fashion, at an earlier thread there:

http://saposjoint.ne...start=60#p34195 and followings, on

Sat Sep 24, 2011 7:05 pm and Sat Sep 24, 2011 8:09 pm and Wed Sep 28, 2011 10:43 pm

 

Marc Schaefer, aka Enthalpy

 

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Now, this other cycle shall decompose an endothermic oxidizer in a pre-chamber to obtain hot gas for the turbine:

post-53915-0-38729800-1317344007_thumb.png

 

It shall be simple and reliable:

- No mix is required at the pre-chamber, which runs at a safe fixed temperature (but in oxidizing gas, true)

- Pump and turbine speed is moderate

- If you have some limited pressure in the tanks, opening two valves starts the engine, and the attitude control can be pressure-fed

- The oxidizing gas lights the fuel by its mere temperature

- The moderate decomposition temperature permits a sort of glow-plug igniter

post-53915-0-43749500-1317344491_thumb.png

 

This cycle burns storable propellants and is more efficient than tetroxide and toxic hydrazine, like 350s with a good expansion, and its tanks are lighter.

 

One oxidizer is Mon-33, or 33% NO dissolved in 67% N2O4. It freezes at -107°C, so if paired for instance with 2,4,6-trimethyl-tridecane (freezes at -102°C), they stay indefinitely on Mars or an asteroid or a Moon just in white tanks. Less NO lowers the vapour pressure at terrestrial temperatures, lowers the pre-chamber temperature, and loses little performance.

 

Again, a messy earlier thread contains more details:

http://saposjoint.ne...6&t=2272#p27535 Mon Jul 05, 2010 2:39 am (cycle description)

http://saposjoint.ne...start=40#p30642 Sat Feb 19, 2011 3:04 am (improved cycle figures)

http://saposjoint.ne...start=20#p28807 Sat Sep 18, 2010 9:48 pm and Sun Sep 12, 2010 5:28 pm (igniter)

 

I had considered hydrogen peroxide H2O2 as the endothermic oxidizer, but the RD-161P uses it already, what a shame:

http://esamultimedia...ocs/EMO/LPE.pdf

so here are the reasons that make this choice bad:

- It's less efficient than oxygen-kerosene

- But peroxide isn't storable neither

- And peroxide is seriously dangerous

HandlingPeroxide

 

Marc Schaefer, aka Enthalpy

 

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And that other cycle recomposes in a pre-chamber a mix of amines to produce methane, nitrogen, little hydrogen, and heat:

post-53915-0-33124500-1317347314_thumb.png

 

Few amine mixes don't soot. I consider Ethylenediamine dissolving 358:1000 of Guanidine. The pre-chamber, turbine and pumps work then at comfortable temperature and speed, and the hot gas is fuel-rich.

 

The sketch suggests an optional pressure-fed attitude control, but since only oxygen gives good performance here and is more difficult to store, this cycle would rather fit some launcher's lower stages. Attitude control uses to gimbal engines there, and booster pumps accepting a low input pressure save tank mass. This cycle is as good as oxygen-kerosene in a staged combustion but far simpler.

 

Previous description, less ordered but more complete:

http://saposjoint.ne...6&t=2272#p27477 Sat Jul 03, 2010 4:45 am

http://saposjoint.ne...start=40#p30666 Tue Feb 22, 2011 1:02 am

 

Marc Schaefer, aka Enthalpy

 

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A few rocket engines decompose a third propellant just to power the turbo-pump for the main propellants. Slightly old-fashioned (hi Wernher) but well-proven, for instance by Soyuz.

http://www.lpre.de/e...D-107/index.htm

 

The standard choice here is hydrogen peroxide, which is dangerous (link above).

 

My suggestion is to recompose an amine instead, to produce hot methane, nitrogen and possibly soot.

The previous Ethylenediamine - Guanidine solution would work, but I believe soot is acceptable here, and then very safe amines are good:

DETA (diethylene triamine NH2-C2H4-NH-C2H4-NH2)

TETA (triethylene tetramine NH2-C2H4-NH-C2H4-NH-C2H4-NH2)

TEPA (tetraethylene pentamine NH2-C2H4-NH-C2H4-NH-C2H4-NH-C2H4-NH2)

 

Gas temperature is mild and constant. Expansion speed is better than 82% peroxide, without the dangers of peroxide or hydrazines.

 

More details there

http://saposjoint.ne...start=60#p34071 Thu Sep 15, 2011 9:09 pm

 

Marc Schaefer, aka Enthalpy

Edited by Enthalpy

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You've been hitting on this one repeatedly for a while and I'll be honest, I'm not about to wade through it all and do the math but...

 

If you're half as convinced that it's cheap/easy as you've been saying, why not just build the damned thing?

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Enthalpy, although I am really interested in rockets, and specifically in the engines, your posts is a little too long. I'm risking being rude, but could you provide us with a summary, so that the lazy people like me have something to discuss?

 

It's just too much of a (time-)investment to read your entire post without knowing (beforehand) what point you're trying to make. Posts like this really need an abstract / introduction.

 

If we have something to discuss, then perhaps we will eventually read your entire post while we're trying to form our own opinions on something.

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A hydrogen staged combustion cycle is simpler than a gas generator cycle for the same moderate pressure and performance:

 

post-53915-0-77869500-1320328435_thumb.png

 

A single stage hydrogen pump after the (not represented) 20b booster pump achieves 123b in the pre-chamber, and the smaller pumping power leaves 103b in the main chamber, which gives the same performance as a gas generator cycle.

 

The hot gas' maximum expansion speed can be shared as 691m/s and 421m/s in the single-stage turbines that power pumps with 528m/s and 141m/s tip speed.

 

Single stages simplify turbines and pumps. Gas generator cycles exploit much faster hot gas through several stages.

We can also accept some liquid leaking into the hot gas if this flows in the drawn direction, which makes seals easier.

 

More details there

http://saposjoint.ne...start=60#p34927

 

Marc Schaefer, aka Enthalpy

Edited by Enthalpy

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