GMTA! LN2 is cheap and doesn't go bang; it's an obvious pre-chill for
LCH4 plumbing.
But yeah, Murphy guarantees that bringing the bare minimum of any vital
consumable to an important test will cause you to need more than you
have. (On a good day, that just means you ran out of caffeinated soda
in the cooler.)
On that other matter, yes, I'm pretty sure having a propellant
transitioning from liquid to gas an uncontrolled distance before the
injector can couple chamber pressure back to the transition point and
result in low frequency chamber pressure variations. My
I-was-only-a-manager-the-engineers-would-know-more guess is that once
you get decent quality liquid to both fuel and LOX injectors, that sort
of thing should settle down.
Henry
On 2/22/2018 5:04 PM, Carl Tedesco wrote:
We did have an LN2 chilldown procedure, but due to some holds/recycles, we
ran out of LN2 ☹ Will bring a full dewar next time.
Carl Tedesco
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On
Behalf Of Henry Vanderbilt
Sent: Thursday, February 22, 2018 2:38 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: L* for LOX/methane
Interesting issue there, RE keeping the injected propellant liquid from the
start in a LOX-methane motor intended to run liquid-liquid.
Yes, chilling down the LOX circuit before firing is routine for LOX-whatever
engines, but doing so for both propellant paths on a LOX-methane engine
could get WAY too exciting in terms of pad fires, hard starts, etc.
Maybe set up the LOX and methane circuits in good enough mechanical/thermal
contact so you can slowly pre-chill both with a trickle of LOX?
Or pre-chill the methane path with LN2 from a separate ground supply?
Henry
On 2/22/2018 3:26 PM, Carl Tedesco wrote:
Thanks Doug. That's shorter than I expected.
If C* were less than 18" I assume C*_eff would start to drop off.
Would you expect combustion instability. I'm asking because a LOX/CH4
motor we hot-fired a few weeks ago had a low L* and had a significant
low-frequency sound and obvious "sputtering/chugging". It had co-axial
injectors which were intended to be liquid-liquid, but were likely
gas-gas (or low-quality liquid at best), since the plumbing may not
have reached thermal equilibrium.
--- Carl Tedesco