Henry,
On Thu, Dec 31, 2015 at 1:37 PM, Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Thu, 31 Dec 2015, Richard Garcia wrote:
Of course, the ways to fend off hot gas, like film cooling, all come at a
price; it may be worth it.
Most LPREs have film cooling, and my previous comments where made
assuming there would be at least some film cooling involved.
I prefer to observe a distinction of terminology: the usual (although not
quite universal) practice of adjusting the injector design to put a
fuel-rich layer near the wall is "curtain cooling", while "film cooling" is
reserved for concepts that put a low-velocity *liquid* layer on the wall,
typically by angled orifices in the wall itself (e.g., the V-2 engine did
this).
P&W's SSME proposal used transpiration cooling
It's my understanding that transpiration cooling, while successful in a
laboratory setting, ultimately proved to difficult to build flight weight
versions that was reliable enough.
It has problems, both passage clogging and flow instabilities, but people
have made it work. If memory serves, P&W had used it extensively in an
experimental high-pressure engine, and thought it entirely feasible for the
SSME. Reportedly, MSFC dismissed it as unworkable without paying any
attention to the details of the P&W experience.
Beware of assuming that the design space has been thoroughly explored --
often it hasn't! There is a particular problem with people trying
something once, having trouble, and concluding that the whole idea is
infeasible.
Along similar lines, quite by chance today I ran across NASA CR-185257,
aka AIAA 90-2116, Quentmeyer, "Rocket Combustion Chamber Life-Enhancing
Design Concepts", which discusses half a dozen different concepts for
making channel-wall chambers more durable. Some seem like long shots, some
look workable.
(Sorry, don't have a URL for that because I ran across it in my own files,
but it ought to be findable...)