Experimental Propellants

Part 2

With data acquisition hardware now in place. I decided to move on with more tests. The tests for now will include KNO3/Sugar and various additives. There are two goals in this set of experiments.

• Create a stable, fast burning sugar propellant for use as an end burner.
• Create a slower burning sugar propellant without losing too much Isp.

I decided to do tests which were as standard as possible. To that end I am casting my test samples in 1" lengths of CPVC pipe. The CPVC will act as an inhibitor, allowing only burning on the grain end, and also make the grain of a standard weight. I cut the CPVC segments to 1.005" long. I will sand the surface down to an even 1". For now, I am using 1/2" and 3/4" CPVC diameter pipe.

Test X2-1: KNO3 65%/Sugar 30%/Sulfur 5%

C-star: 2,733.729

Temperature: 2,450

Isp: 138.8

Above is the Chem II output. Isp is the same as a basic 65/35 KNSU propellant, the c-star is slightly less and the temperature is slightly higher. All of the ingredients in the formula were finely powdered, and hand shaken in a plastic tub for about 5 minutes. The casting process was similar to standard sugar propellant casting at 325 degrees. The propellant turned a very viscous mustard yellow at the end of the heating process. Packing the propellant into the small CPVC pipe proved difficult. So I ended up pressing the pipe into a scoop full of propellant, 3 or 4 times to slightly overfill the pipe. Once the pipe was full it was pushed onto a piece of wax paper, and the top compressed with the bottom of the spoon.

Open air burning indicated a very fast burn rate, along with very acute burnt sulfur smell. After weighing each of the segments, it is apparent I did a pretty good job, or at least a consistent job, of getting the same density and length. Note, the sample weight does not includes the CPVC pipe the propellant is cast in, the 1/2" CPVC pipe weighs about 3.6 grams and the 3/4" pipe weighs about 5.7 grams per inch.

Clicking on the test will bring up an image of the pressure/time curve.

* These test grains were ball milled for a minimum of three hours before casting.

The first few tests were performed without using any external pressure. I now have a Nitrogen tank so I'll pretty much throw out the tests performed without the nitrogen.

Above is a plot of the burn rate tests. Points three and six are questionable. I'm not sure why they fall so far off the line, but may be due to density irregularities, igniter differences or trapped air in a test grain. Regardless, there are enough data points now to have a good idea of the propellants characteristics.

Analysis indicates, c=0.109; n=0.294.

With burn rates near .8" per second at 1,000 psi. it is a fast propellant. Not quite fast enough for a pure end burning motor yet, but it's close. The propellant also seems to burn cleaner than regular KNO3/Sugar propellant, very little residue and less smoke. When using the ball mill on the propellant it casts to a nice olive green color, even when heated very slowly. A nice plus, the sulfur appears to render the propellant non, or at least less hygroscopic. I have left a few slivers of propellant exposed to the air for several days, with none of the normal damp stickiness on the propellant.

Next, I'll cast some grains for a motor, and see how it performs.

Test X2-2: Ammonium Nitrate 60%/Magnesium 20%/R45M 20%

Ok, so this isn't a sugar propellant. I've been toying with the idea of doing an AN based propellant for some time. But the Mg powder can no longer be shipped, except by truck making it unreasonably expensive. Another EX'er I am in contact with, sort of talked me into trying it (it didn't take much), by making my own Mg powder from solid Mg. I tried several ways of turning the solid Mg into a powder, ball milling, drilling, grinding, and even a hand crank grain mill. In the end, the only way that even came close to working was using a cylindrical sander on my drill press. The particles from the sanding process range in size from flour to about half the size of sugar. That's still larger than would be desirable, but I'm going to do a few small test batches to see what happens.

This first test batch was only 20 grams total.

AN: 60%

Mg: 20%

R45M: 17.5%

Isonate 143L: 2.5%

I weighed the R45 into a small cup, then weighed in the 143L and mixed them together. Next was the Mg powder. The Mg powder was very light and fluffy, and it looked like a lot of Mg for the amount of R45 I was using. I worked the Mg into the R45 until it was coated completely, I then added the AN and worked it for about 10 minutes, trying to get the mix to a least resemble a paste. I never got it to a paste, it was more a damp sand type of consistency. If compressed it held its shape well, but if poked would break apart. I thought about adding more R45 at this point, but decided to go with what I had. It was a very small batch after all.

I loaded 2) of my 1" CPVC test holders, one each 1/2" and 3/4". I compressed the propellant as best I could without actually ramming the mix into the tube. After weighing the grains, the density was about .0422 lb. per cubic inch. That's about 73% of theoretical density and about 80% of what actual density should measure. So I know I have some work to do, I'm sure I'll have to increase the binder amount, and I think I'll try a lower Mg percentage in the next batch.

After filling the test grains, I had some extra so I tried burning an uncured small strand. To my surprise, it burned very well and very quickly.

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-2a	3.4grams(1.12")	.4421	1226.4	2.533	415.2	820.8	.5"	1.12365
X2-2b	7.6 grams	-	-	-		-	.75"	1.17211

Test X2-3: 60% AN/23% R45/17% Mg

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-3a	grams	-	-	-	-	.5"	-
X2-3b	grams	-	-	-	-	.75"	-

Test X2-4: 60% KNO3/35% Sugar/ 5% Mg

Now that I had some Mg, albeit not a very good powder. I just had to try some in a sugar propellant to so what would happen. I made a small batch of 40 grams. The KNO3 and sugar were premixed and melted in the conventional method. I then turned off the heat and added a very small amount of Mg to the still melted propellant. After stirring it in, I waited a moment for any adverse reaction. Then slowly added more Mg until the full 5% was added. The 5% was about as much as I think you could go, as the propellant was getting very thick at that point. Of course, the heat was still off, so the propellant may have started to cool and harden already at that point. I packed the propellant into four CPVC tubes listed below. As I packed in the propellant, it was apparent there was a sponginess to it. When forced into the tube it would expand back out some. The propellant with the Mg may need degassing, or a lower amount of Mg may be in order. The theoretical Isp of the propellant with the Mg is about 19 seconds greater than standard propellant.

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-4a	4.4 grams	.3316	140.02	3.016	70.01	.5"	-
X2-4b	4.3 grams	-	-	-	-	.5"	-
X2-4c	10.2 grams	.3488	432.69	2.867	216.35	.75"	-
X2-4d	10.2 grams	.4347	736.36	2.3	368.18	.75"	-

Test X2-5: 72%AN/23%Epoxy/3%Fe2O3/2%Carbon

Theoretical: Isp 164.2; C* 3626.4; Temp. 1811; Density 0.0565 lb./ci

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-5a	grams	-	-	-	-	.5"	-
X2-5b	grams	-	-	-	-	.5"	-
X2-5c	grams	-	-	-	-	.75"	-
X2-5d	grams	-	-	-	-	.75"	-

Open air burn rate was pathetic, it burned about like a candle. I tried igniting the propellant in the strand burner, and was unsuccessful. The epoxy based propellants also tended to leave a very heavy residue.

Test X2-6 64% KNO3/30% Sugar/4% Sulfur/1% Fe2O3/1% Charcoal

Theoretical: Isp136.2 ; C* 2687.3; Temp. 2293; Density 0.0698 lb./ci

This test propellant is a "throw in everything I can think of" attempt at a fast burning sugar propellant for an end burning motor.

Test	Sample Weight/Length	Burn Rate In/sec	Max PSI	Time	Start Pressure	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-6a	5.2 grams/1"	.625	873.93	1.60	328.3	601.1	.5"	-
X2-6b	5.1 grams/1"	.7496	1347.10	1.334	656.65	1001.8	.5"	-
X2-6c	5.0 grams/1"	.7143	1038.1	1.4	449.03	743.5	.5"	-
X2-6d	5.0 grams/1"	-	-	-	-	-	.5"	-
X2-6e	4.9 grams/1"	-	-	-	-	-	.5"	-
X2-6f	5.0 grams/1"	-	-	-	-	-	.5"	-

c=0.0713 n=0.343

Just another idea I had. Perhaps some R45 mixed with sugar propellant would slow the burn rate, render the propellant less hygroscopic and less brittle. The KNO3, sugar and Iron Oxide were ball milled together for 4 hours. They were then heated to 325 (F) and once melted I turned off the heat and added the 5% R45. It seemed to mix in well.

The iron oxide was added because I was concerned about the propellant burning too slowly. As you can see the propellant still burned faster than regular propellant. So for the next batch I will omit the iron oxide.

Test X2-8: 65%KNO3 /30% Sugar/ 5% R45M

X2-8a

5.1 grams

.6061

1062.2

1.650

502.1

782.15

.5"

This was interesting, the burn rate is about the same as regular sugar propellant, and only .04"/second slower than the prior test with the iron oxide. It was at a slightly higher pressure though. The next test I'll use more R45, I still think this could be a viable additive to slow the burn rate.

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-9a	-	-	-	-	-	-	-	-
X2-9b	-	-	-	-	-	-	-	-

This propellant batch would not even ignite in the open air. I guess 10% was too much. The first batch with 5% was a very smoky burn. I don't think I will pursue this combination. Grain strength was reduced yet was still very brittle.

Test X2-10: 65% KNO3/ 30% Sugar/ 5% Calcium Chloride

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-10a	-	-	-	-	-	-	-	-
X2-10b	-	-	-	-	-	-	-	-

Too much calcium chloride, this mix wouldn't even burn. I'll try a smaller amount in the next batch.

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-11a	5.2 grams	.504	1125.0	1.984	497.32	811.16	.5	-
X2-11b	-	-	-	-	-	-	-	-

Better, but this isn't much different than standard propellant.

Test X2-12 64% KNO3/ 34% Sugar/ 2% Calcium Chloride

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-12a	5.2 grams	.4723	1071.9	2.117	535.94	803.94	.5	-
X2-12b	5.1 grams	.7230	927.04	1.433	328.33	627.685	.5	-
X2-12c	5.1 grams	.4025	729.08	2.484	270.39	499.735	.5	-
X2-12d	5.0 grams	.4918	1158.8	2.033	564.91	861.855	.5	-

This batch looks more promising, burn rates are dropping.

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-13a	-	.4411	1057.4	2.267	487.66	772.53	.5	-
X2-13b	-	.3796	772.53	2.634	294.5	533.51	.5	-

Burn rates are still dropping but not fast enough. At 5% the propellant won't burn, I could try 4% but I'm afraid that will be about the limit.

Test X2-14 65% KNO3/ 30% Sugar/ 3% Calcium Chloride/ 2% Paraffin

This is another guess. If paraffin and KnO3 don't burn well together, let's try a small amount of paraffin with some Calcium Chloride. I used powdered KnO3, powdered sugar, powdered Calcium Chloride and I made paper thin shavings of paraffin. I mixed the ingredients in a small plastic tub with one lead disk to aid mixing. I heated the powders to melting using my standard method. Interestingly, the melted propellant had a whole new consistency to it. It sort of glossed over, and held together in a lump. The lack of sugar, only 30%, I'm sure had an effect on the mix, but the paraffin also had a definite effect. An open air burn of a strand resulted in a hard starting, slow burning strand.

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-14a	-	.3680	888.41	2.717	391.09	639.75	.5	-
X2-14b	-	.3703	777.36	2.7	299.36	538.36	.5	-
X2-14c	-	.3158	695.28	3.166	251.07	473.175	.5	-

I decided to try casting some grains, just to see what would happen. I cast 2) 1.5"x5.5" grains for my T-2 motor. The heating and casting of the propellant was uneventful, however, after the grains started cooling in the casting tubes the "error in my way" appeared. I hadn't even thought about this before. The wax melts at a very low temperature, much lower than the sugar. So when the propellant cools, the sugar solidifies and the wax remains liquid. So the wax being lighter than the KNO3/sugar rises to the top of the grain. This creates little tunnels and voids in the grains, not a good thing of course. So, wax wasn't a good choice as a burn rate inhibitor.

Test X2-15: 65% KNO3/32% Sugar/3% Magnesium Shavings

I prepared the mix using the non-powdered form of KNO3, adding all three ingredients together before heating. They were mixed by shaking the container by hand for several minutes. I doubt if the Mg shavings will help the impulse any, but it may make for a nice flame on a motor. Not that I really care about the flame, or smoke or sound they make. But, if the impulse remains the same, why not? The down side I can see already is the Mg makes the propellant less dense. My test samples are running about .5 gram lighter than standard propellant. That's a loss of about 8 or 9% in grain density. The same thing happened when I used the powdered Mg in an earlier test, although the 3% shavings are more dense than the powdered Mg.

With only 32% sugar in the mix, it was harder to melt and cast. I knew it would be, and the melted propellant looked about like thick oat meal. I heated for a long time, and never saw any bubbles like those that occur when casting standard sugar propellant. I'm not sure why, it may mean the Mg is bonding with the water, but I really don't know. I still wish I'd paid more attention in chemistry class!

I went ahead and did a large batch, 600 grams. And cast two grains for the T-2 motor and 5 test grains. I'll do a couple of tests in my strand burner before trying the propellant in the motor.

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-15a	4.5 grams	.6060	1443.7	1.65	733.91	1088.8	.5"	-
X2-15b	-	-	-	-	-	-	.5"	-
X2-15c	-	-	-	-	-	-	.5"	-

The propellant was tested in the T-2 motor with good results, see the information here.

Test X2-16 KNO3 65%/ Sugar 30%/ Ethylene Glycol 5%

This test arose in an odd manner. I was casting some grains, and I decided to use some food coloring in one of the grains, to color code different propellant formulas. I added a mere 11 drops to a 550 gram batch of standard sugar propellant and proceeded to mix it in. As I mixed the color into the melted propellant, I immediately noticed the propellant became much thinner. I wondered why such a small amount had such a noticeable affect on the viscosity. The label on the food color indicated propylene glycol as a main ingredient. Hmmm, glycol... So I did a little research on glycol. It seems it bonds or holds water, and is used in many everyday items. Ethylene glycol is used in most car antifreeze products, and is similar to propylene glycol although it is a bit toxic in large amounts. Not having a large source of propylene glycol, I decided to use some ethylene glycol in a test batch of propellant.

So a 100 gram batch was prepared using 65 grams of non powdered KNO3, and 30 grams of powdered sugar, once melted, 5 grams of ethylene glycol was added and stirred in. The propellant immediately became very liquid, enough so, that I really wondered how I was going to fill my 1" test strand containers. In the past, I had to push a lump into the pipe section, then pack it in with a dowel, or tamp the pipe into the hot propellant to fill it. Not with this batch, I just placed the pipe sections on some wax paper and poured them full with a spoon. This stuff was so liquid there was no way I could tamp it into the pipe.

Sounds good so far, but how will it affect the performance? If I had to guess, I would say it will slow the burn rate some, if the glycol indeed holds water. Perhaps some water could be added to the glycol before mixing in with the hot propellant to reduce burn rates further. That all remains to be seen. This opens up a whole new area of testing. I'm sure Isp will drop some, but if it's not much, this will make casting sugar propellant much easier.

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-16a	4.8 grams	1.11	1395.4	.9 sec.	695.28	1045.34	.5"	-
X2-16b	4.8 grams	.7692	1211.9	1.3	545.6	878.75	.5"	-

So much for my intuition. The ethylene glycol enhanced the burn rate, it didn't suppress it! Perhaps just a little less ethylene glycol would be in order.

Here I am using cherry extract, the primary ingredient of the extract is propylene glycol. So I thought I'd give it a whirl. Instead of adding a predetermined amount, I decided to add the extract from a known amount and keep adding it until the propellant was of the desired viscosity. I ended up adding 2.5 grams to a 100 gram mix of KNO3/Sugar. The result was again a pourable propellant, although not as thin as in the previous test. Best guess is the glycol may have been 50% to 60% of the actual extract, so I may have only added 1.25 to 1.5 grams of glycol.

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-17a	4.5 grams	.5455	1211.9	1.833	637.34	962.62	.5"	-
X2-17b	4.6 grams	.5040	1260.2	1.984	656.65	958.425	.5"	-

This is closer to what I was expecting from the first test. Slightly lower burn rates than standard propellant. I'll have to do more tests, but this seems to be a viable additive to make casting easier, and perhaps a burn rate suppressant as well.

Test X2-18: KNO3 63.45%/ Sugar 31.24%/ Mg 2.93%/ Extract 2.38%

My earlier test batch using Mg was encouraging. However, it was difficult to cast as it was very thick. So I thought, why not try some propylene glycol. I again didn't start with a predetermined amount of the cherry extract, I just added the extract after the KNO3/sugar/Mg were melted until the mix was fluid enough to pour. In this case I added 2.38% by weight of the extract. It should be noted, there is water in the extract and it boils off when added to the hot propellant. So the final amount of propylene glycol is a fair amount less than 2.38% in the final propellant. When researching propylene glycol, I found its' boiling point to be 700 degrees F., so I don't think any of the glycol is boiling off at casting temperature. New Note: I found another source of information now that indicates the glycol boils at 210 degrees F. So some of the glycol may be boiling off as well.

I cast 2 new grains for my T-2 motor, and a couple of test strands. The batch total weight was 563.4 grams.

357.5 grams KNO3

176 grams Sugar

16.5 grams Mg

13.4 grams Cherry Extract

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-18a	4.9 grams	.5405	1236.1	1.85	637.34	936.72	.5"	-
X2-18b	4.9 grams	.	-	-	-	-	.5"	-

The burn rate is about what would be expected, I don't think the propylene glycol had much of an effect on the burn rate. It may have slowed it slightly, but not significantly. The T-2 motor has been tested with these new grains. The test was successful, you can see it here. I appears the propylene glycol has little effect on burn time or Isp, and should make a nice tool to make casting sugar propellant easier.

Test X2-19

I said earlier I didn't have a supply of propylene glycol, well, after a little thought I decided I did. RV antifreeze had to be propylene glycol and not ethylene glycol because the RV antifreeze is potable. So I went out to my trailer and sure enough, there was a full gallon of it. It's probably only 50% glycol and the 50% water, but it is probably more pure than engine coolant antifreeze. A fellow EX'er did some research into the RV antifreeze, and it seems it is only 25% propylene glycol. That is, no doubt, why I have been having better luck with flavor extracts. I think they are a very high percent propylene glycol. Thanks for the info Bill. So I made another batch of propellant using the RV antifreeze. For this 600 gram batch I mixed a standard sugar mix of 65% non powdered KNO3 and 35% powdered sugar. After the mix had melted I added 24.9 grams of the RV antifreeze. I still don't know how much actual propylene glycol gets into the propellant, but it was enough to again thin the propellant to a pour able state. I cast 2 grains for the T-2 motor, and five 1" grains for my strand burner.

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-19a	5.0 grams	.5128	1197.9	1.95	690.74	944.32	.5"	-
X2-19b	4.9 grams	.3923	789.83	2.616	326.42	558.125	.5"	-
X2-19c	4.9 grams	.4167	988.02	2.4	469.24	728.63	.5"	-
X2-19d	4.9 grams	.4000	845.21	2.5	381.8	613.505	.5"	-

After the strand tests the results are: a= 0.015, n=0.512.

Test X2-20: 65 grams KNO3/ 35 grams sugar/ 10 grams RV antifreeze

I wanted to see how a larger percentage of the propylene glycol antifreeze would affect the propellant. Interestingly, it seemed to make the propellant more viscous again. It did thin it some, but not as much as in previous tests using less glycol. Another interesting aspect, it left the propellant soft. About like playdough only harder. If you broke a chunk off, you could reform it into any shape you wanted. An impromptu open air burn resulted in a good, but slower than normal burn, leaving some residue.

After leaving the propellant in the open air for a day, it is apparent the soft nature of this batch was water. After it dried it became brittle and chalky. This is the same result I have seen when trying to add water to the dry propellant ingredients before heating the mix.

Test X2-21: 65 grams KNO3/ 35 grams sugar/ 2 grams ethylene glycol

I thought I'd try the ethylene glycol again with a lower percentage. Again, it reduced the viscosity to the point you could pour the propellant. The propellant after cooling was hard, brittle and glossy.

Test	Sample Weight	Burn Rate In/sec	Max PSI	Time	Start PSI	Aver. Psi	CPVC Pipe Diameter	Density grams/cc
X2-21a	-	.5043	1113.3	1.983	550.84	832.07	.5"	-
X2-21b	-	-	-	-	-	-	-	-

This is a burn rate in line with other glycol tests. Test X2-16 had indicated a very high burn rate at 5% glycol. This test was just under 2%.

Test X2-22: Standard 65/35 Sugar Propellant Using Water

This isn't really a new propellant formula. But rather a different way of casting the propellant. I know there are a number of people who add water to the propellant before heat casting. Jimmy Yawn in particular has developed a form of hydrating the dry ingredients, then slowly drying them in an oven. When the propellant reaches a certain stage, he removes the propellant and forms balls from the soft propellant for later reheating and forming into grains.

I have used water to dissolve the dry mix several times. I simply add enough water to form a thick but runny paste. Then heat until mixture boils off most of the water and melts. I think what is happening is, and it's similar to making candy or fudge, some of the water bonds with the sugar, allowing some of the water to remain in the propellant even above waters normal boiling point. It leaves the propellant much like a thick putty, and re-heating under a 100 watt bulb is enough to soften it so you can work it into a new shape. Care must be taken however, if the propellant is allowed to dry out, it becomes very weak. I tested a couple of grains made in this manner in a small one inch motor, the dry propellant burned very quickly and nearly blew out the upper bulkhead in the motor. Care must also be taken not to make grains too soft, or the grains may slump on the G force of liftoff, causing throat blockage. On the positive side, I think this form of the propellant may be useful for a small, case bonded motor. The flexible nature should prevent grain fracturing as would sometimes occur in a case bonded sugar propellant.

The only real reason I want to pursue this is, what to do with all those left over scraps of propellant? They can be dissolved in water, and reformed into small grains. I don't think I'd use it for any a motor larger than a J class, or about 1.5" diameter. In fact, I've been thinking about working on a small motor, something to replace a commercial C or D class motor, and this may be a good place to use this process.

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