Sciencemadness Discussion Board

Rocket Fuel

Jasonf - 30-9-2015 at 19:03

I am doing a school project that will last the entire year. My team is planning to make a solid fuel rocket/composite propellant that has a good thrust/weight ratio, is relatively clean burning, has a long lasting burst, and is very cost effective. Because of this we have chosen ammonium nitrate as our oxidizer, aluminum as our fuel, and sulfur to help the fuel ignite and burn. The present issue is in deciding what to use as a binder. Some ideas we have are GE silicone II (bathroom caulk), 2 part epoxy, contact cement, or some other urethane plastic. We decided not to use HTPB rubber because of it being difficult to obtain and it's cost. Any recommendations or advice is appreciated. Thanks:P

j_sum1 - 30-9-2015 at 19:08

Welcome to the board.
Standard procedure here is to post in Beginnings unless a reference is provided. (See FAQ.)
Sounds like a cool school project. Why don't you edit your post to include some research you have done thus far; including details of what you have decided for your ratios and your particle sizes. I am no expert in this area but I believe that with EM, these have a large effect on the outcome and the choice of binder will be related to this. The more specific you are, the better answers you will get when the experts arrive.

Jasonf - 30-9-2015 at 19:15

Good point. I am not able to access my research at the moment but I should be able to post some research and our starting point for the ratios in the morning. At the moment I can only think of these 3 links: (other than wiki pages about rockets and the different fuels)

http://www.nakka-rocketry.net/anexp.html

http://www.byui.edu/Documents/physics/Theses/Schyler_PorterW...

https://www.byui.edu/Documents/physics/Theses/David_NeweyF13...

[Edited on 1-10-2015 by Jasonf]

hyfalcon - 1-10-2015 at 06:02

Then this http://www.google.com/patents/US6372191 should be of interest.

[Edited on 1-10-2015 by hyfalcon]

Bert - 1-10-2015 at 07:18

Quote: Originally posted by Jasonf  
I am doing a school project that will last the entire year. My team is planning to make a solid fuel rocket/composite propellant that has a good thrust/weight ratio, is relatively clean burning, has a long lasting burst, and is very cost effective. Because of this we have chosen ammonium nitrate as our oxidizer, aluminum as our fuel, and sulfur to help the fuel ignite and burn. The present issue is in deciding what to use as a binder. Some ideas we have are GE silicone II (bathroom caulk), 2 part epoxy, contact cement, or some other urethane plastic. We decided not to use HTPB rubber because of it being difficult to obtain and it's cost. Any recommendations or advice is appreciated. Thanks:P


HTPB and PBAN are not that expensive or hard to acquire- can your class come up with $200.00 US?

http://www.firefox-fx.com/kits.htm

If not- 2 words: Sugar rocket

It's a question for a school project, and so this belongs in "beginnings".

See the FAQ: http://www.sciencemadness.org/madscifaq.html#2.1_Board_topic...

TheAlchemistPirate - 1-10-2015 at 12:23

I keep seeing these threads about school rocketry projects, and I'm just sitting here with my $200 tooling... Are these normal physics classes or just some more exotic ones?

Jasonf - 1-10-2015 at 13:37

Our group has bought about 55 pounds total of fuel. We got our fuel for a total of about $100. Our ratio for the fuel will start at 75% Ammonium Nitrate, 1% Sulfur, 20% Aluminum, and about 4% binder. Our plan originally was just to go ahead and buy the Silicone caulk so we have already bought and received our fuel. Doing some more research we are now not sure if we should buy the bathroom caulk, contact cement, 2 part epoxy, or something equally cheap but also able to fit our needs. Since our binder will make up only a small amount of our fuel we do not want to spend another $30-50. Also, in the project the goal is not to send a rocket into the air but to propell a given mass horizontally and hopefully eventually propell a bike. My group is competing against another group that is using a pulse jet engine.

Jasonf - 1-10-2015 at 14:47

In this article of Richard Nakka's research, neoprene contact cament "burned exceptionally good for some reason" and "is possibly a breakthrough"
http://www.nakka-rocketry.net/anexp.html

Silicone caulk seems to week fairly well in this experiment with ammonium perchlorate
https://m.youtube.com/watch?v=TllMf7DzYkA
And
https://m.youtube.com/watch?v=HgbF-Nr_64E
In another of Nakka's experiments it is stated "Epoxy plays a dual role, serving as fuel and binder. As a fuel, epoxy has good combustion characteristics, with a respectable energy content, and is a material that decomposes by pyrolysis (goes directly from solid to gas) upon heating. As a binder, epoxy has superb mechanical strength and toughness, good machineability (can be readily cut, drilled, milled, turned, etc.), is safe to use (with reasonable precautions), utilizes two-part curing (no evaporative solvents involved) and has low viscosity (allowing high solids loading). Epoxy's unique adhesive traits are also well suited to propellant usage. Epoxy bonds "like a bear" to most materials, making for superb bonding of grain inhibitor material, for example. Conversely, epoxy has zero adhesion to certain materials such as polyethylene. This is very convenient, allowing for easy removal from grain moulds lined with polyethylene sheet. Epoxy has only slight adhesion to PVC, making this a good candidate for mould material."
http://www.nakka-rocketry.net/rnx_int.html

[Edited on 1-10-2015 by Jasonf]

Bert - 2-10-2015 at 10:35

If you have Nakka as a resource, I have little to add- He's more experienced in this class of solid propellants than I am.

I am quite curious as to your project.

Could you post the full parameters of the "competition". Because the rules under which a competition is run and performance compared will have a great deal to do with choosing the best design strategy-

Could you please tell us (broadly, I do NOT want to know your school's name & address) which country, state/province and level of school has the balls to allow such a competition as this, these days? I might consider moving there-

Jasonf - 2-10-2015 at 19:51

In our competition we not actually launching our engines into the air. We will put our finalized design on a go-kart of sorts with a given mass. We will compare the engines' top speed, acceleration, distance traveled, weight to thrust ratio, and general safety. If everything goes according to plan we will team up and create a hybrid engine. This project takes place in a high school in Buda, Texas, USA. Thanks for responding and helping out with the project.

[Edited on 3-10-2015 by Jasonf]

The Volatile Chemist - 5-10-2015 at 13:18

Good luck! Pictures of the final products would be nice when you finish. be sure to post them!
Are you interested in amateur chemistry, or specifically rocketry?

Jasonf - 5-10-2015 at 17:11

The group went ahead and bought some silicone caulk. To make our fuel we ground our ammonium nitrate into a powder, measured out our proportions of AN, sulfur, and aluminum. We then added a little silicone at a time until we had the consistency we wanted. We let the fuel dry for two days and attempted to burn the fuel today with electric fuses. The fuel smoldered but did not burn. What could have gone wrong? Does anyone have any tips on making or igniting ANCP?

Bert - 5-10-2015 at 17:34

Did you do your test burn in a motor, or in open air? Many composite fuels will not burn quickly in the open, they have a "pressure exponent" that requires a fair degree of containment to reach their working pressure and sustain a rapid combustion.

Did you use any type of pyrogen, if so, WHAT and how much... A section of drinking straw filled with black Copper oxide/Aluminum thermite with an electric match placed in it and the whole shebang shoved up the nozzle is a popular choice of igniter...

(Edit)
Quote:

We then added a little silicone at a time until we had the consistency we wanted.


Please give an EXACT weight:weight description of all fuel components. You DID weigh your binder, RIGHT?!

[Edited on 6-10-2015 by Bert]

Jasonf - 5-10-2015 at 18:12

We used 22 grams AN, 6 grams Al, 1 gram Sulfur, and 15 grams Silicone Caulk. 15 grams was more than we planned, but anything less caused a crumbly fuel with lots of left over fuel. We put this fuel in a 3/4 inch diameter pvc pipe and compacted it with a dowel rod. We let the fuel cure for 48 hours and put a small hole in the center of the propellant. The burn was done in the pvs pipe outdoors. We then used Estes model rocket igniters to try and ignite the fuel. They smoked but never burned. There was no open flame. Do you think we should have compacted it better? I have read about people using a hydraulic pump to compact fuel. I have also read about drying out each component of the fuel before mixing it. Do you think these are valid options? Here is the link. This information is under "Preparation of Experimental Grains"
http://www.nakka-rocketry.net/anexp.html
Nakka also uses contact cement (neoprene). Do you think the silicone caulk is hindering the burn? Sorry for all the questions.
Thanks in advance,
Jason

[Edited on 6-10-2015 by Jasonf]

[Edited on 6-10-2015 by Jasonf]

Bert - 5-10-2015 at 19:20

Your mix has FAR too much binder. You do not mention a forward bulkhead or a nozzle- So, effectively, your grain was not contained.

Estes rocket igniters are intended to ignite a black powder fuel grain- A MUCH easier to ignite fuel than composite fuels. They are essentially useless (by themselves, at least) for the type of fuel you wish to compound. You will need an additional high temperature pyrogen.

Jasonf - 6-10-2015 at 03:50

Because there is so much binder, do you think we should try a less viscous binder? What would you recommend as a binder and an igniter?

Bert - 6-10-2015 at 06:28

Half the fun of learning this technology is doing the research- so I'm not going to give you any more links (except to whole books), just search strings for your own follow up.

You picked an oxidizer that is more difficult to use than some of the others. Money cheap, sweat expensive. It can be made to work...

Some have used the GE silicone II clear caulk effectively as a propellant binder, but they have usually done this with a different oxidizer such as ammonium perchlorate- Google "doc bar blue tailed rockets". There are many references to an apparent "crumblyness" of the uncured fuel, and notes that it is PRESSED into motor casings.

A propellant that chemically hardens is a much better choice than one which hardens by solvent evaporation. Excess solvent in a mix will likely produce voids on drying, or fuel grain may shrink away from case walls on drying and result in a too large surface area burning at once, exploding your engine. CATO! NOW IS NOT THE TIME!!! Also, drying fuel INSIDE a caseing or even a sleeve takes FOREVER.

Your choice of igniter for a solid propellant could be directed towards a composition that produces large quantities of hot gas/flame, which plays over the propellant surface and transfers heat- or one that produces a very hot molten "slag", which CLINGS to the propellant and transfers heat...

Vaporized Copper has pretty good heat capacity. Molten Silicon dioxide is pretty freaking HOT. A 2fer-

Look in the sciencemadness.org library

http://library.sciencemadness.org/library/index.html

for some texts on pyrotechnics and explosives.

Like these:

http://library.sciencemadness.org/library/books/the_chemistr...

http://library.sciencemadness.org/library/books/ignition.pdf

There is a dscussion of ifnition and priming compositions here as well-

http://www.scribd.com/mobile/doc/14654551/Fireworks-the-Art-...

Some high power rocket engine builders make "ignition grains" (small pieces of an easy to light rocket fuel), and place an ignition grain and an electrical igniter at the top of their rocket engine core when using a hard to light fuel-

That should be enough to run with for a bit. When does your school plan to do the competition burns?



[Edited on 8-10-2015 by Bert]

Jasonf - 6-10-2015 at 07:00

This is planned to be an all year project. This will give us hopefully plenty time to test, prototype, improve, and make a final product. If we finish by the end of the first semester, we will compete and switch gears and make a hybrid rocket with the other group and us working together. Thanks a lot for all your help. I will keep you guys posted.

MeshPL - 10-10-2015 at 10:27

I think you could do it binder-less. Just add acetone to the mix which dissolves ammonium nitrate and sulphur slightly. When it evaporates you'll be left with binded mix. It may require some testing though.

Jasonf - 12-10-2015 at 06:02

Cool. That is worth trying. Thanks!

The Volatile Chemist - 24-10-2015 at 12:10

As an autumn project, a friend and I are looking to build a rocket too. We haven't looked into details - we built one about a year ago, but didn't launch it because we didn't have any electronic fuzes (I think this is the proper place to use fuze, it was an electronic igniter) that weren't already used. Oh well. We cut a piece of PVC pipe to length, but a PVC cap on it, cut three wings out of copper sheet metal, and stuck three small engines in it in parallel. Perhaps it wasn't wise to hack a 'rocket' without planning it prior.