I was thinking cluster of gas generators, single nozzle.
Larger fuel/lox engines have multiple injectors. Catalyst pack size and
geometry will limit multiple injectors for large Peroxide engines. Each added
injector could have it's own catalyst pack.
This gas generator/injectors would be smaller than the thrust chamber and
easily machined. A standard size flange could be machined on both ends of the
catanjector, one end bolts to thrust chamber and the other to your plumbing. You
could remove and repack it (new catalyst) without removing the engine, which will
be important on larger engines. You could build the catalyst-injector to minimize
the cost of catalyst screens and optimize for best gas generation without having
to worry thrust chamber nozzle geometry.
The thrust chamber nozzle could be made large enough to use build up
techniques, rolled or forged and welded. The standard size flanges could be welded
on to accept the catanjectors (gas generators), as many as you want (piglets on a
sow, but blowing not suckling).
I just looked in Sutton for the relationship between chamber total length,
width, convergence length, pressure and velocity of the gas. I quickly went beyond
what I can calculate. It did appear that real gains can be made by shaping the
chamber correctly. The correct shape for the chamber might not be the best shape
for the combustion process (or catalyst process).
Optimum geometry for combustion probably changes with what you are combusting
(or catalyzing) so the optimum chamber geometry for oxygen steam acceleration
might not be the best geometry for adding hydrocarbons into the for a further
burn, and each hydrocarbon could have it's own geometry.
Intuitively I was thinking of a pancake shape for the engine, the catanjectors
radial and off center. Inject the alcohol from the bottom of the pancake against
the swirl for good mixing. The pancake shape would give more surface area for
radiative cooling of the chamber and the placing of the alcohol injectors at the
bottom would be where they could exit from a cooling jacket around the nozzle.
John Carmack wrote:
> I may be coming around on the cluster-of-engines concept for economic reasons.
>
> A lot of manufacturing costs (machining and tooling) scale with volume,
> while thrust scales with area, which makes larger engines start to cost
> more than I like. There are lots of variables, but I know that right now,
> I can make eight six inch motors for the price of one twelve inch motor,
> even after tooling costs are amortized. Including the tooling costs more
> than doubles the advantage.
>
> There is a huge benefit to trying to design things that can be done on
> common CNC machining centers.
>
> If you are pushed that way for economics, you might as well use
> differential throttling on the big engines instead of attitude jets, and if
> have eight engines (say, for an X-Prize vehicle) and a 2x T/W at liftoff,
> you might as well set up for full engine-out operation.
>
> Clusters trade against a few other design decisions -- hybrids look worse,
> and radiative cooling may not be workable with multiple hot radiators nearby.
>
> John Carmack
>
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