If I remember properly, it would have been a joint spec (NASA & AF). The
big problem is the commerical spec for LNG is relatively wide. Think a
cryogenic RP-1. Instead of 1000s of similar components there are only 10
to 20.
The issue is the physical properties for the RP-1 components are fairly
similar. Particularly in terms of density, viscosity, & specific enthalpy.
For LNG, component properties range is much greater.
I'm not certain what the implications are for injectors and performance.
Any LNG can be refined to whatever you want but the price goes up
accordingly.
Rick
On Mar 1, 2018 12:55 AM, "Henry Vanderbilt" <hvanderbilt@xxxxxxxxxxxxxx>
wrote:
Was that an AF standard or a NASA one? AF, I dimly recall.
Henry
On 2/28/2018 6:55 PM, Doug Jones (Redacted sender randome for DMARC) wrote:
I was on the committee (in 2005, I think it was) that set the (several)
standards for rocket-grade methane/LNG. I argued for and got a grade that
was (paraphrasing) low sulfur, 99% hydrocarbons under C4. You can tolerate
some C2 and C3 hydrocarbons, but nitrogen is death on performance (helium
doesn't liquefy, of course). I felt that trying to specify the exact
composition was a bad idea.
Citing the hassles of getting RP-1, we made sure that there was the
broadest possible spec for RG LNG. I lost all that correspondence with my
XCOR account, alas, so damifIknow what the current status is.
On 2018-02-28 10:45 AM, Henry Vanderbilt wrote:
On 2/28/2018 8:58 AM, Perry E. Metzger wrote:
On Sun, 25 Feb 2018 20:34:40 -0700 Henry Vanderbilt
<hvanderbilt@xxxxxxxxxxxxxx> wrote:
FWIW, plain-jane US market natgas has mostly been running between
$2.50 and $3 per million btu's (MMBtu) the last few years. There's
~12 gallons of LNG per MMBtu, at ~3.5lb/gallon, so that's 6-7 cents
a pound for the raw natgas feedstock.
Chances are there'll be markups for vehicle grade (high CH4, low
sulfur, from selected wells) natgas, and for liquefaction. But
there's till quite a bit of room for rocket LNG to come in
significantly cheaper than highly refined kero.
If you're liquefying the gas anyway, I would presume that purifying
the mixture by fractional condensation at the same time would be
practical?
I can't speak to details of the liquefaction and refining-to-pure-CH4
processes, beyond saying that a minute's googling indicates they're
typically separate processes conducted on separate equipment.
My initial assumption would be that's for sound economic reasons, and my
first guess would be that R&Ding a new combined process would be a major
distraction from flying rockets, and likely a money-loser as well.
Because regardless of the exact process, if you're buying the result by
the railroad tank-car full, chances are you'll have no trouble finding an
existing refiner happy to set up to do all that for you. And if, at that
sort of purchase volume, your fuel buyer can't get prices down to less than
it'd cost you to develop and set up your own liquefaction/fractionation
plant, you need a new fuel buyer.
Mind, it's not clear that fractionation to pure LCH4 is even useful.
Simply using liquefied "vehicle grade" natgas - as mentioned, from selected
wells that naturally have high CH4 and low sulfur fractions - seems to work
just fine. If it's clean-burning enough not to gunk up an automotive
piston engine, it seems to be fine for rocket motors too.
Admittedly in a limited number of tests so far. But I'd take Blue
Origin's plans to use natgas rather than refined CH4 as a strong hint -
they tend to do their homework quite thoroughly.
Henry
