Hi Cole,
We did methane engines at Armadillo for the Nasa Morpheus/M project. I made
a 4000 lbf engine with pintle injector and film cooling that I uncreatively
named "CH4K". All aluminum injector head, except the copper pintle tip and
stainless hardware to retain the tip, stainless film cooled chamber and
nozzle. Short video of it here: https://www.youtube.com/watch?v=JcDSn_qIwrM
The safety protocols around methane were not hugely different from other
fuels, but I'm saying this off the top of my head and may come back with
more. Randall or one of the other ex-XCOR folks could also speak to their
methane experience, and I know Masten is doing methane now as well, a 5k
engine for their suborbital reusable rocket.
* We did not do flare stacks. It's good to have upward pointing vents so
that the cold gas has a chance to disperse and not settle to the ground.
* Everyone was wearing nomex jumpsuits, but that was our normal gear for
LOX/alcohol as well. The anti-fire things you do for normal liquid rockets
should be doubled/fastidious; no sources of ignition, no smoking nearby, no
one wearing synthetic clothes that will melt. If you don't have nomex then
everything should be cotton. Appropriate fire extinguishers positioned
well. Safety glasses, face shields, and hearing protection in case of
inadvertent ignition.
* Test only outdoors. Might seem obvious, but I've done a lot of indoor
engine tests and it would require vastly more stringent controls to test an
easily vaporized fuel indoors, to a level that is probably not worth the
hassle.
* Store LOX and fuel dewars separately. Most states have specific rules for
distances. 100+ feet.
* The propellants are miscible in a way that most other LOX propellants
aren't (aside from a few fuels like propane that are rarely used). This
means that any liquid spills once both propellants are loaded should be
assumed to be sensitive high explosives and allowed to boil off completely
until there is no sign of frost before anyone gets near it. Even with just
LOX it's good practice to never step in frost spots, and don't go walking
around in places where you can't see the ground due to cryo fog.
* That also means that horizontal testing is more dangerous than usual;
I've started an engine half full of alcohol with a LOX lead, but things
will go very badly if you try that with methane. Vertical testing is
preferred, canted downward is better than horizontal. Purges need to be
vigorous for anything horizontal.
* Pre-chilling the plumbing and injector (sometimes called priming) is also
much more dangerous. Injector architectures where it is unnecessary are
ideal; or only chilling one side. Having a somewhat ragged startup is
better than having mixed propellants on the ground. But if that goes too
far it is totally possible to hard start the engine,
https://www.youtube.com/watch?v=CRfAESmUu_c
* Think about how leaks will burn. A small leak in a mostly sealed area can
cause damage because the fire will be contained. Wires and sensors should
be fire shielded. It's not very useful to say "things will be burnier than
a non-methane engine" if this is your first engine, but, well, things will
be burnier than a non-methane engine. Presumably less burny than a hydrogen
engine.
One test anecdote: we were firing the engine Nasa had designed. At one
point the company owner John wandered downstairs, watched a test, and then
asked why the test stand was on fire. The fuel run valve had developed a
stem seal leak. On any other propellant it would have been a drip, on
methane it would get ignited by the engine and there'd be a bit of a
fireball around the valves, but it would go out when the valve was closed.
It was gradually getting worse after each run, but we wanted to finish up
the set rather than detanking and fixing it. We explained that and he
understood and we continued. You could do the same thing at FAR, but
probably not the same thing at larger, more uptight organizations that feel
like their stands shouldn't be on fire.
I know a lot of people are talking about methane and that it's the hot new
propellant, but I somewhat feel that it's been unfortunate to push it down
into student/amateur projects. It's kind of annoying to get and work with.
It makes more sense in high performance stages, possibly even a lot of
sense for things like expander cycle. But in regen you likely want to be
operating at ~1000 psi Pc, something you'd never do in a pressure fed
rocket. 90% of the process of building and testing a rocket has nothing to
do with what fuel you're using.
As I said, this is off the top of my head, so feel free to ask any
questions, and I'll see if any other thoughts come to mind.
Ben
On Sun, Jan 30, 2022 at 9:56 AM Cole Evans <coleevans@xxxxxxxx> wrote:
All,
Long time listener and first-time caller here; I'm currently in the final
stages of design for my LOX/LCH4 rocket project and am looking for some
advice on how to safely dispose of methane from GSE during and after fill
operations. I'm leaning towards a flare stack right now, but I've found it
hard to find information on the proper design of these (notably flashback
protection) and was hoping someone here might have advice/recommendations
of what the best approach would be. Additionally, any tips on general
methane system best practices and cleaning would be greatly appreciated.
- Cole
