Sugar Syrup Propellant | Improved version
Click Here for description |
An alternative method of making KN/Sucrose propellant
Please Note: The propellant DOES NOT EVER go in
the microwave oven!
Only the sugar syrup is made there.
If the propellant is reheated, it must be done in a conventional oven
such as a toaster-oven.
Overview:
Sugar and corn syrup are mixed in a heavy glass vessel, and heated
to boiling in a microwave oven.
The vessel is removed from the oven, taken to a safe spot, and pre-heated
KNO3 is stirred-in.
Advantages:
- It is a quick and simple way to make KN/SU propellant.
- Seems reasonably safe if appropriate precautions are taken.
- Sugar syrup can be made on a camp stove, so this method could be
used in the field.
- The propellant works OK in test motors, most likely it will work
in flight tests as well.
Disadvantages:
- The experimenter is exposed to hot propellant for a brief period
while the KNO3 is stirred-in.
- Requires grinding or milling of the KNO3, not necessary with recrystallization
- There is more waste with this method (but scraps can be recycled
as recrystallized propellant or fertilizer)
- The resulting propellant is inferior in quality to the recrystallized
version.
It is more brittle, does
not burn as cleanly, and seems to offer lower delivered ISP
When re-heated, it does
not easily attain the fine texture and pliability of recrystallized propellant.
- It is easy to overcook the syrup, turning it brown. The resulting
propellant will ignite with difficulty and burn very slowly. This
might be OK for larger motors with adequate pyrogen ignition.
Here is the initial recipe:
(note that this has been refined, see below)
Sugar and corn syrup are placed in a 1-quart Pyrex measuring pitcher, mixed together, and heated in a microwave oven on "high" until the liquid is perfectly clear.
Heavy shirt, face mask, and gloves are used to make the body more attractive and flame-resistant, just in case.
Sugar syrup is stirred to eliminate any "hot spots." Then the KNO3 added, and everything is stirred vigorously with a wooden spoon. Whilst stirring, mouth of glass container is pointed away from face and other things of importance, just in case.
Upon cooling, this propellant tends to be somewhat crumbly and more brittle than recrystallized propellant. Heating to 200 degrees F does not soften it like recrystallized. But heating to 250 to 270 degrees brings it to a near-liquid state, at which point it can be stirred and then kneaded as it cools a bit. The result is a propellant with a texture and molding characteristics similar to recrystallized KN/SU. I believe it is somewhat less brittle after the heating/kneading procedure - this will be tested soon.
Static Tests
Here are a couple of uninhibited grains burned in a test-motor.
The motor is 1-1/4 inch PVC, using the steel nozzle Foy gave me 2 years
ago. The nozzle has been used a hundred or so times, and is still
in good shape. Throat diameter is 5/16 inch.
General idea of the test motor, PVC case with steel nozzle | Crude but effective test stand. Well... crude, anyway. |
Light propellant, sugar syrup cooked until clear
Click Here to see how this grain burns Hint: Pretty darned well! (800k download, 5 seconds of video) |
Dark propellant, sugar syrup cooked until brown.
Click Here to see how this grain burns Hint: Not well at all (3.5 meg download, 12 seconds of video) |
How's this for a finale: see what happens when you rush things and don't give the PVC cement enough time to dry!
Click Here for a movie of this burst.
(1.6 meg file for 6 seconds of exciting video)
Summary: Cap at the head-end came off - the case was otherwise intact. Prime suspect: bad glue job.
Comparison of sugar syrup propellant and recrystallized propellant
Two motors were assembled to be as near identical as my little hands
can make them, and fired on the test stand to compare their performance.
Sugar Syrup propellant - 10/6/03A | Recrystallized propellant - 10/6/03B | |||||
Click Here to see this baby burn!
(950k file, 4 seconds of video) Or Here for an Excel spreadsheet analyzing this test |
Click Here for a video of this grain in
static test
(975k file, 4 seconds of video) Or Here for an Excel spreadsheet analyzing this test |
|||||
Results: As expected, the recrystallized propellant performed better, a 120 gram uninhibited grain providing 133 N-seconds of thrust as compared to the sugar syrup propellant offering 112 N-secs. ISPs are 112 and 95, respectively. Thus the recrystallized propellant appears roughly 18% more effective. Then again, a single pair of tests is hardly definitive. And there
were other differences that could account for the discrepancy, not the
least of which were limited resolution of the videos leading to some guessing
as to where the pointer pointed on some frames. And "bouncing" of
the test stand, which was overwhelmed by the thrust of these motors.
Oh, it occurs to me that this propellant is rather fuel-rich, as evidenced
by the recipe, which would be nearly balanced except for the addition of
corn syrup, which contains many sugars. The carbon-rich residue is
verification that the sugar syrup propellant contains an excess of fuel.
10/11/03B: Revised recipe, better oxidizer/fuel ratio:
Since there was less syrup, the propellant hardened more quickly and
a lot of it stuck to the mixing container. So
10/12/03B Replication of 10/11/03B but with larger grain Same as above, but 120.2 gram grain used. Burned well, but ISP
registers 89. Should be higher. Maybe I will try the fuel-rich
version again!
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Next... Improvements made over the Winter Holiday. Click Here for that page.
Jimmy Yawn
jyawn@sfcc.net
10/6/03
rev. 10/13/03