Loaded parraffin hybrid rocket fuel

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dbohara@mindspring.com - 13 Sep 2005 21:06 GMT

My initial experiments in making parraffin fuel with bubbles of another
hydrocarbon were not too successful.
I had simply mixed melted parraffin with various hydrocarbons including
various oils and hexane and butyl alcohol. The idea being that if the
hydrocarbon was imiscible that it would make bubbles. I could not tell
if there were bubbles even under a microscope although I may see some.
Experiment today involved melting paraffin and blowing air into it
through an aquarium bubbler. It was fairly easy to make paraffin foam
of various densities. I can imagine doing the same with H2 instead of
air so that I get a solid paraffin fuel block with bubbles of H2.
I really want to get something better than H2 in it, something that
will be better fuel. So, i tried pumping the Butyl alchohol throught
he aquarium bubbler into the melted paraffin. Didnt work. At first I
couldt figure out why but then the aquarium bubbler that I thought was
a ceramic dissolved int he Butyl alchohol, oops. next attempt will use
a sintered metal bubbler..........

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Damon Hill - 14 Sep 2005 01:18 GMT

> My initial experiments in making parraffin fuel with bubbles of
> another hydrocarbon were not too successful.
[quoted text clipped - 12 lines]
> that I thought was a ceramic dissolved int he Butyl alchohol, oops.
> next attempt will use a sintered metal bubbler..........

About all you've accomplished is to greatly reduce the density of the
fuel grain and thus the energy. Paraffin is roughly similar
to kerosene and thus has a good energy density already,
though the physical properties as a solid fuel leave something
to be desired. You appear to trying to add solvents to the
paraffin, which will be counterproductive.

Finely powdered aluminum comes to mind as a high-temperature
additive.

I assume you're already familiar with recent experiments with
paraffin hybrids, and the things done to modify the paraffin
to make it mechanically stronger and provide good melting
and burn rates. Getting good burn rates for a given surface
area with hybrid motors is a difficult and tricky business
for highly knowledgeable scientists and engineers, let alone an
amateur.

What are you using for an oxidizer? Be careful.

--Damon

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dbohara@mindspring.com - 16 Sep 2005 02:03 GMT

I am a total amateur that happens to have access to good equipment. My
concept is to increase the burn rate of the paraffin by use of bubbles
that will rapidly expand and burst thus throwing tiny droplets into the
burn area where their high ratio of surface area to volume will cause
rapid burn. Of course, we really want the bubbles to be filled with
fuel.

I do not really plan to do any experiments for now other than mixing
the paraffin.

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kpmorton@bellsouth.net - 25 Sep 2005 00:30 GMT

Seems to me you won't have as much trouble getting the wax to
volatilize as you will keeping the grain intact. If you have an
opportunity, try making a composite of some sort of fibrous material
(paper slurry, flax, etc) with wax. I don't know if this would apply
to your engine, but I recalling hearing that waves formed in the liquid
wax layer on some wax grains, and the wave tops broke off forming
droplets of wax, like you are trying to acheive. Another thing you
might try is melted, cast grains of sulfur. It has some interesting
properties around it's melting point which might make it a good
candidate for hyrbid grains.

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Anvil* - 14 Sep 2005 01:44 GMT

dbohara:

> My initial experiments in making parraffin fuel with bubbles of another
> hydrocarbon were not too successful.
> I had simply mixed melted parraffin with various hydrocarbons including
> various oils and hexane and butyl alcohol.

*snip*

>something that will be better fuel.

*snip*
-----
You may want to describe a bit more of the total system.

Paraffin is a decent hydrocarbon fuel but the usual problem in
a hybrid is making a mix that does not melt uncontrollably due
to heat. Mixing in oils is possible but a solid hydrocarbon seems
more practical (actually a number of solid fuels are being looked
at in combination with paraffin).

Questions:
What oxidizer and what size engine are we talking about?

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Space Forum / Space Flight / September 2005

Loaded parraffin hybrid rocket fuel