From: Doug Jones <random@eau.net>
Subject: Re: Launch the Shuttle Question
Date: 27 Aug 1997
Newsgroups: sci.space.tech

Eric Kouba wrote:

> >spray of sparks underneathe the main engines
>
> Uhh, it's like tossing a match into the stream of fuel/oxidizer to make
> a flame?
>
> Eric The Kouba

No, the combustion chamber is lit off by augmented spark injectors in
the chamber itself; those external pyrotechnics are there to burn off
the hydrogen that is dumped during the start sequence to precool parts
of the engines.  If that hydrogen weren't burned immediately, it could
accumulate, then deflagrate all at once with an overpressure that might
damage the shuttle in some way (tiles, ET, elevons, etc).

Only engines with low chamber pressure and modest nozzle
contraction/expansion ratios can be lit off by the "flaming mop"
technique. A *very* low flow start is required to make sure that flow
through the throat remains subsonic- else the flame cannot propagate
upstream.  If ignition does not occur on time, propellants can
accumulate in the chamber and then spontaneously ignite (LOX/kerosene is
infamous for this).  The combustion produces hot gases faster than they
can flow out the nozzle, the chamber bursts, and the pressurized
propellants in the feed lines and regen passages feed the fireball.
This tends to be ugly.

Very ugly.

--
Doug Jones  random@eau.net
The secret source of humor itself is not joy, but sorrow. -M. Twain
That explains why us comics are such screwed-up wierdos. -D. Jones

From: gherbert@crl3.crl.com (George Herbert)
Newsgroups: sci.space.policy
Subject: Re: Roton Reservations (was Re: Len's Bantam X: why not HTHL?)
Date: 29 May 1998 15:59:26 -0700

 <windski1@my-dejanews.com> wrote:
>Gary, we tried lighting our 450 lb thrust air/kerosene rocket last sunday with
>road flares. We are running a 240 gallon air tank from 125 psi to 80 psi. We
>are using a surplus fire extingiusher tank pressurized with air to run
>kerosene between approximately 80 psi to 30 psi. We think we are getting 8 lbm
>of air and .5 lbm of kerosene. We were shooting for a six second burn
>duration. We have 6 1/16 inch diameter holes in our pintle injector. We are
>using a 1 inch cross with air coming in unrestricted around the  the 3/8
>pintle tube. I think the air flow was too great and it was just blowing
>everything out. On the first run the flare was pointed at the injector and it
>was blown out by the air blast. On the second run we turned the flare around
>so it was pointed away from the injector and it did not blow out, but the fuel
>did not light. We switched to propane at .1 lbm/sec with no air and got a
>stack fire, but as soon as we cracked the 2 inch manual ball valve to the air
>tank the flame was blown out. I think we need to restrict the airflow further
>or get some pressure regulation valves. What do you think? Have you
>experimented with air and kerosene?

I built something like that, about a tenth
the size but same idea, in jr high school.
Ignition is just a pain.  I ended up blowing a lot of
unburned kero into the air.  The only successful
ignitions were either slow air pressure throttle up,
or an electric sparc ignitor (dad had a surplus coil from
a Model A ford, he said, which we wired up to a handmade
spark gap in the fuel/air stream and ran continuously.
We spent weeks trying to get pyro ignition to work with no success.


-george william herbert
Retro Aerospace
gherbert@crl.com

Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: S.S.M.E.
Date: Tue, 23 May 2000 03:52:38 GMT

In article <3929D7C9.DDEAB257@bellsouth.net>, Tom  <t2jr@bellsouth.net> wrote:
>Not 100% sure but I believe it involves some substance that is
>hypergolic with Oxygen. By hypergolic I mean burns automatically on
>contact...

While that approach is used in many rocket engines, the SSME uses torch
ignition -- little secondary combustion chambers with spark igniters,
firing into the main chambers -- for reusability and to avoid using toxic
fluids.  (Hypergolic igniters tend to use fairly obnoxious materials.)
--
Microsoft shouldn't be broken up.       |  Henry Spencer   henry@spsystems.net
It should be shut down.  -- Phil Agre   |      (aka henry@zoo.toronto.edu)

Date: Sun, 15 Oct 2000 10:55:44 -0700
From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.policy
Subject: Re: Alternatives to LH/LOX

Pat Kelley wrote:
>
> Pat Bahn wrote:
> >
> > Henry Spencer wrote:
> >
> > > IAbout the only major reasons why you wouldn't use common hydrocarbons --
> > > methane, propane, or kerosene -- would be an intense desire for absolute
> > > maximum Isp (which drives you to hydrogen) or an equally intense desire
> > > for hypergolic ignition (which drives you to hydrazine and its relatives).
> > > --
> >
> > Henry
> >
> > I believe you have made a minor oversight.
> >
> > Certain propellants will engage in active decomposition, which gives similar
> > results without using nasty toxic propellants.
> >
> > Peroxide decomposed, will generate a nice ignition, without
> > the nominal requirements of "Hypergolic" ignition.
>
> Good point, Pat, and "high-test" H2O2 will spontaneously decompose in
> the presence of hydrocarbon fuel, effecting a "hypergolic" ignition for
> easy restart.  If you're looking for ways to keep the propulsion system
> simple, reliable, and cheap to operate (which is what Beal is
> attempting), this is definitely one way to do it.

The ignition delay of H2O2/kerosene isn't short enough, Pat.  Many moons
ago I watched Jeff Greason do some simple cup tests with 90% peroxide
and various catalysts.  If it doesn't light off in milliseconds, you're
begging for a hard start with mixing before ignition.  Bad Juju.

Only if it is fail-safe reliable (if the igniter doesn't start the mains
don't open) is an igniter cheap to operate, since otherwise it will
eventually destroy your hardware.  Skimping on ignition is a false
economy.

--
Doug Jones, Rocket Plumber
XCOR Aerospace

Date: Sun, 15 Oct 2000 21:50:20 -0700
From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.policy
Subject: Re: Alternatives to LH/LOX

George William Herbert wrote:
>
> Doug Jones  <random@qnet.com> wrote:
> >The ignition delay of H2O2/kerosene isn't short enough, Pat.  Many moons
> >ago I watched Jeff Greason do some simple cup tests with 90% peroxide
> >and various catalysts.  If it doesn't light off in milliseconds, you're
> >begging for a hard start with mixing before ignition.  Bad Juju.
>
> Out of curiosity, is there anything you can put in kerosene which
> helps that?  Does permanganate dissolve in it?

No, kerosene is a classic nonpolar solvent and permanganate is a salt.
You might be able to pursuade an alcohol mixture with a few % water to
dissolve enough permanganate to be hypergolic with peroxide, but I'd
guess that the solubility would be poor and the salt would be in danger
of crystallizing out.

For kerosene, it might be possible to add a touch of diethyl zinc to
make it hypergolic with peroxide yet not make it pyrophoric with moist
air.  Having worked with DEZ in the distant past, that's not a game I'd
like to play myself.

I'm happy with a good simple augmented spark igniter since it works with
anything we've picked from column A and column B.  (And with six you get
eggroll.)

Oxidizers      Fuels
LOX            Alcohol
GOX            Propane
N2O            Ethane

We haven't tried it with kerosene, but that's just personal prejudice-
I'm confident that it too would light off nicely.

--
Doug Jones, Rocket Plumber
XCOR Aerospace

Date: Mon, 16 Oct 2000 21:02:08 -0700
From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.policy
Subject: Re: Alternatives to LH/LOX

George William Herbert wrote:
>
> Doug Jones  <random@qnet.com> wrote:
>
> >For kerosene, it might be possible to add a touch of diethyl zinc to
> >make it hypergolic with peroxide yet not make it pyrophoric with moist
> >air.  Having worked with DEZ in the distant past, that's not a game I'd
> >like to play myself.
>
> You're getting decidedly conservative in your old age, Doug.
> Not even once to blow up a test stand for the hell of it?

DEZ doesn't blow things up, it just makes pretty green flames with
orange edges and white smoke. If your propellant has any water in it
(such as 90% peroxide) it *will* light off.  It's a bit like TEA/TEB but
sensitive to water instead of oxygen.

> >We haven't tried it with kerosene, but that's just personal prejudice-
> >I'm confident that it too would light off nicely.
>
> You drank too much kerosene working for Gary and now you get
> queasy near airports?

Not so much drank as soaked it up through the skin, and the *sludge*
that builds up in a chamber- feh.  I never did like the smell of burning
kerosene or diesel, and that was a real trial.  LOX/Alcohol smells like
a day at the drag races, as Dan Delong put it today when the wind
shifted out at our test site.

--
Doug Jones
Rocket Plumber, XCOR Aerospace
http://www.xcor-aerospace.com

From: "Paul F. Dietz" <dietz@interaccess.com>
Newsgroups: sci.space.policy
Subject: Re: Alternatives to LH/LOX
Date: Mon, 16 Oct 2000 05:19:29 -0500

Doug Jones wrote:

> No, kerosene is a classic nonpolar solvent and permanganate is a salt.
> You might be able to pursuade an alcohol mixture with a few % water to
> dissolve enough permanganate to be hypergolic with peroxide, but I'd
> guess that the solubility would be poor and the salt would be in danger
> of crystallizing out.

Actually, potassium permanganate is fairly soluble in
alcohol.  However, it is also fairly *reactive* with
alcohol, oxidizing it to aldehydes and acids.

A better choice for a solvent would be acetone.
KMnO4 in boiling acetone is used as a oxidizing reagent
in some organic syntheses; the acetone doesn't
itself get oxidized.

	Paul