On Thu, 2004-06-10 at 19:47, John Carmack wrote:
> Doing it with cooling passeges sounds pretty challenging to me, but we are
> planning on fabricating a palte with 16 x 1" nozzles, which should be a
> direct performance comparison with our current 1 x 4" nozzles, if I keep
> the same expansion ratios. I don't expect it to have a significant
> performance loss, and we might even get some aeruospike expansion effect at
> high altitudes if we arrange the nozzles correctly.
You just cool the two plates -- making a flat-plate heat exchanger isn't terribly challenging, and use a material with a nice high heat conductivity to conduct heat away from the throats. If that's not good enough, just bore straight holes through from one side to the other and arrange the flow paths appropriately.
You would have to be a smaller than 1" throat nozzles (several inches tall) to heat sink all the way to the top and bottom, but 1/2" nozzles would probably work. That would be a pretty heavy plate, but you might be able to live with aluminum.
On the performance side, I will be very curious to see your results. There are four types of losses that I see affecting an array of square nozzles much more than a single nozzle. One, the square nozzles aren't as efficient as round ones, due to different flow behavior in the corners. Two, since each nozzle is smaller, the boundary layers take a relatively bigger bite than they do in a larger single nozzle. Three, the oddly shaped combustion chamber probably will not be as efficient. Four, since each flow passage is smaller, manufacturing defects of the same absolute size have a larger effect.
-p
Square nozzles? I was talking about getting 100 little nozzles run off on a CNC lathe. They would have integral shoulders so they fit into holes cut with an abrasive waterjet in stainless plate, then you weld them in. The catalyst / combustion chamber would be exactly the same as on our normal engines.
John Carmack
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