[AR] Re: Thoughts on low pressure fuels...

  • From: Paul Breed <paul@xxxxxxxxxx>
  • To: arocket@xxxxxxxxxxxxx
  • Date: Tue, 26 May 2015 10:25:39 -0700

This what I get in RPA 200 psi chamber 50:1 expansion to vac.

[image: Inline image 1]




On Tue, May 26, 2015 at 9:45 AM, Henry Vanderbilt <
hvanderbilt@xxxxxxxxxxxxxx> wrote:

DME does look interesting. There's a decent FAQ at
http://www.aboutdme.org/index.asp?bid=234

Briefly, it's C2H6O, handling and storage are similar to propane, toxicity
very low (it's been used as a spray-can propellant for a while now),
increasingly available as a cheap way to make natural gas CH4 more easily
transportable, and at prices in the same ballpark as other common fuels.

It's usable as a motor fuel - directly in diesels, in a propane mix in
gasoline engines - which means it's likely to be more available over time.

The 365 seconds @ 200 psi chamber, 25x vac expansion result for DME/LOX
looks very interesting, given the RP-1/LOX number of 331 under similar
conditions. Given DME density of around .67, this could make for a useful
LOX/kero replacement.

Also, could someone run the comparable numbers for DME/peroxide at 80%,
90%, and 100% peroxide? Given some improvement on the 70% peroxide number
of 317 seconds, this could make for a good in-space non-toxic storable
combination. (Michael Carden of XLSpace mentioned making 100% peroxide
commercially available at Space Access; it seems he has a new process.)

Henry


On 5/25/2015 12:49 AM, Keith and Mary Stormo wrote:

Some interesting thoughts have been bouncing around. I used
propane/nylon for my nitrous hybrid but looked at propylene and others
as well. I entered Dimethyl ether (DME) into propep and it has quite
high performance with LOX, H2O2 and N2O. If you want the data for
adding it to the PEPCODED.DAT: Dimethylether (LIQUID) 2C 6H
1O 0 0 0 -49 .0266

It is denser than propane .67 g/cc, readily available, inexpensive, high
purity, can handle 7% water before it separates into two phases,boils at
-24 deg C, freezes at -142 deg C, 5 bar vapor pressure at 20 deg C, very
low surface tension, very low human health risks, used as an aerosol
propellent in hair spray and others, and lots of other good properties.

Vacuum Impulse at 200 psi chamber pressure with an expansion ratio of 25
43% DME and 57% LOX is 365
16% DME and 84% H2O2 (70%) is 317
18% DME and 82% N2O is 313
for comparison:
27% RP-1 and 73% LOX is 331
80% nitromethane and 20% LOX is 321

I would be interested if someone who has Clark's Ignition could see if
it was tested and reported. It is a fairly recent commodity fuel
developed as a means to easily convert methane to a transportable fuel.

Keith

At 10:46 PM 5/24/2015, David Weinshenker wrote:

Monroe L. King Jr. wrote:
Methyltetrahydrofuran ? Perhaps with a little Nitromethane?

Nitromethane has been fired with H2O2 - JPL tried it, along with a
bunch of
other fuels, in the mid-1940's [Clark, p.68] - the combination has the
odd
characteristic that the O/F is very low (i.e., the combination is
mostly fuel)...
I once many years ago ran some performance calculations which seemed
to indicate
that the Isp was rather insensitive to the mixture ratio over a fairly
broad range:
so the combination would have the disadvantage of low density (since
most of the
reaction mass isn't peroxide) and the advantage that one could use a
"propellant
utilization" control that adjusted the mixture ratio to deplete both
tanks at the
same instant, with little detriment to the operating Isp.

-dave w






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