Yes I remember :)
https://patents.google.com/patent/US9151246B2
On Wed, Jul 13, 2016 at 1:24 PM, Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Wed, 13 Jul 2016, David Gregory wrote:
It's also unlikely to be worth the trouble, since the turbine exhaust is
pure hydrogen, and reasonably warm, giving decent Isp...
"Expander" doesn't automatically imply "hydrogen". People have run
expander cycles (in fact, modified RL10s!) successfully on methane and
propane.
Remember also that expander turbine exhaust isn't necessarily all that
warm. The RL10 turbine inlet temperature is about -90degC -- yes, that's a
minus sign. There's probably a tradeoff there between higher energy
content and bulkier gas plumbing (since higher temperature means lower gas
density).
and you need a way to cool your giant nozzle anyway.
Why would the nozzle be giant? Or hard to cool? The original RL10
nozzle, sized for vacuum operation, was pure regen (with an expander, more
regen is good); some later models added uncooled refractory extensions.
Henry