The 4A3 400 lbf LOX-IPA engines that powered the Ez-Rocket were regen
cooled with no water added to the fuel, no bias, no film cooling. We tried
multiple transpiration geometries in a 50 lbf engine with poor results.
Regen when done right just _works_. I don't really understand why people
seem so averse to it.
The 3N22 40 lbf engine was also regen cooled, albeit by using
nitromethane-methanol fuel at O:F of 0.3:1, which made the task a lot
easier. I really don't think that the secret was that I was a superior
designer, just that we didn't use the wrong materials and shapes.
Transpiration cooling makes for thick, heavy walls, low Isp, and
complicated machining. Why bother?
On Thu, Aug 13, 2020 at 12:41 PM roxanna Mason <rocketmaster.ken@xxxxxxxxx>
wrote:
Is "transpiration cooling" really necessary? The coolant generally
doesn't get burned so lowers ISP/c* and we've seen with proper design that
a pure regen engine can be built. Granted transpiration cooling would be
advantageous in small,<1KLbF engines where straight regen is not possible.
K
On Thu, Aug 13, 2020 at 12:09 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Wed, 12 Aug 2020, Brian Feeney wrote:
Would 3D metal printing of the injector head / holes help with the Burr
problem. Do post printing cleaning up of the hole walls, injector face.
In principle, yes -- if you don't put the burrs in, they aren't there.
The price is the possibility of other issues with passage shape, e.g.
rough walls. (Post-printing cleanup conceivably could create its own
burrs, depending on how you do it.)
There would be several other benefits to 3D printing the whole engine,
even in a few pieces, as in the saddle jacket over traditional methods.
Appealing in principle. The question is whether the flexibility in
things
like passage geometry pays for the hassles added by the printing; I think
the jury's still out on that. (When looking at the number of people
doing
it, you have to correct for the fact that it's new and sexy and people
don't always appreciate that it adds its own complications, so it has
undeservedly-high investor appeal right now -- which will decline to more
realistic levels as it becomes more routine and people understand it
better.)
To my mind, the long-term appeal of 3D-printed engines is the ability to
do transpiration cooling with precisely-defined passage networks -- the
big problem of transpiration right now is making the wall materials
behave
themselves. All the problems of thermal expansion and such go away if
you
don't let the walls get hot in the first place. But it needs higher
resolution and better quality than today's cheap printing can deliver.
(Some of the older, pre-modern-hype 3D-printing methods can do it, but
they're expensive and can have their own quality problems.)
Henry
