Sciencemadness Discussion Board

Rocket propellant

rocketscience - 21-11-2004 at 14:32

I was wondering if any one knows if rocket propellant should have enough oxidizer to burn all the fuel or just most I am afraid if the oxidizer burns all the fuel if it will burn way to quick and possibly explode


Edit: bad spelling in title.

[Edited on 23-11-2004 by chemoleo]

Geomancer - 21-11-2004 at 15:15

The burn rate of propellant must be experimentally determined. I can see no reason why you shouldn't be able to burn lean (oxgen rich) propellants well. Nobody does it though, since rich mixtures provide better performance. There is a family of programs (ProPEP, etc.) that can predict the performance aspects of a given propellant, but they cannot determine such things as burn rate and pressure exponent.

For your sake, I recommend you do quite a bit more research before actually experimenting. Sutton's book Rocket Propulsion Elements is the standard, but there are others. Also check out Richard Nakka's site.

Rocket Candy

MadHatter - 21-11-2004 at 19:59

I've made rockets using the standard mix of potassium nitrate/sugar at a ratio of 65:35.
This is fuel rich but for whatever reason it gives the best performance. As for explosions, I
found that any type of airgap in the fuel is the culprit.

budullewraagh - 21-11-2004 at 20:29

i prefer potassium chlorate to nitrate when combined with sugar

JohnWW - 22-11-2004 at 00:49

Can Sutton's book Rocket Propulsion Elements be downloaded from any site?

Marvin - 22-11-2004 at 01:52

Potassium Chlorate fuels have safety problems. Its extremely unwise for someone just starting the hobby to use them.

To address the actual question, yes there must be enough oxidiser to burn all the fuel. Any unburned fuel or unused oxidiser constitutes dead weight.

The term 'burned' though gets very complicated. For example for carbon it usually better to consider carbon monoxide as 'burned' as this usually results in a fuel having a higher energy density. It is true however to say anything coming out of the exhaust in the same form as it was in the propelent is wasted.

neutrino - 22-11-2004 at 14:07

Why would you want to use chlorates? They have less oxygen than perchlorates, are much less stable, and generally more expensive. If you really want a good perchlorate, use ammonium perchlorate.

AngelEyes - 23-11-2004 at 04:23

Because Chlorates are easier to get hold of that perchlorates and cheaper. It's also a better oxidiser than a nitrate. Sure, there are incompatibility issues with Chlorates but if you're careful these can be dealt with. Just avoid sulphur (and sulphur compunds) at all times.

Not everyone lives in the US where you can simply mail order Perchlorates and fine Al powder form Skylighter - some of use have to look hard for our chems and we will gladly use a bit of chlorate if necessary. It all comes down to common sense - if you're careful then you'd be unlucky to get burned...but if you're a kewl chump then you deserve everything you get.

tokat - 24-11-2004 at 01:08

"I was wondering if any one knows if rocket propellant should have enough oxidizer to burn all the fuel or just most I am afraid if the oxidizer burns all the fuel if it will burn way to quick and possibly explode "

Make it so it in perfect balance, then add a binder,melted sugar, PVC,hell all most anything, then add a themite/redox Al-fe and use the amount of themite to goveing the speed.

Eg AN + Al + Fe2O3(one that is highly oxy) + Binder.
The themite makes heat to break down the AN, more themite per square inch more amount/quicker the reaction


[Edited on 24-11-2004 by tokat]

redneck - 24-11-2004 at 03:37

Hallo rocketscience

At high temperatures CO2 can't be formed under low pressure. CO ist formed instead. That's the reason why rocketfuels are balanced to produce CO.

Don't use chlorates as oxidiser because they are so sensitive that there is a great risk that the rocket will detonate instead of lift up. Nitrates are a better oxidiser for rocket fuels because they produce more gas and more energy. They burn slower thus they are saver.
Take 60% finely powdered potassium nitate and 40% powdered sugar (2% rust can be added to get a slightly higher burn rate). Give both substances in a cup and add enough lighter petrol to make a mush. Stir for 5 min and then insert the mush in your rocket. Let it dry for two days. This procedure gives a high density rocket fuel and so reduces the risk of an explosion.

To make a rocket with this medium fast burning fuel you need a small nozzle. For example if the internal diameter of your rocket is 16 mm then the diameter of your nozzle must be smaller than 3 mm if your rocket consists of a metall pipe. If its made out of a paper roll the nozzle must be wider because paper can't withstand as much pressure as metall.
The smaller the nozzle is the wider, higher and faster the rocket will fly. But if it's too small the rocket will explode. If it's too wide the rocket will just smoke instead of fly.
If you bild a rocket without fins you can inset it in a long pipe (round about 1.5 times as wide as your rocket) to start it.
Use a fuse that gives you enough time to get far away and behind cover when you try to start a selfmade rocket because it could explode. They are potentialy as lethal as pipeboms. Never stand next to it when it starts.

Harpoon - 24-11-2004 at 14:11

The only times I've seen rockets explode was when the propellant was compressed insufficiently, or the casing was too weak and the nozzle too small.

A weak casing will rupture, and loose propellant will burn faster as it has a greater surface area, leading to higher pressures and therefore ruptured casings.

As for chlorates, I've had good success (so far) in compressing a sodium chlorate/paper mix in a vice e.g. no unwanted ignitions.

The only time I could get this mixture to ignite was when I deliberately hammered a sample several times.

I like the idea of launching rockets from a pipe. Perhaps if one end of the pipe was sealed/restricted, the pipe buried, and the rocket dropped in like a (military) mortar shell...
Flick out fins could enhance the flight path of the rocket.

rocketscience - 24-11-2004 at 18:12

I personally don’t think that nitrates are worth a darn or at least kno3 because from some research I have done on it. It reluctantly release oxygen and know or potassium nitrite dose not decompose when heated and kno3 is pretty expensive butt also naoclo2 or sodium chlorate dose the same so for rocket propellants prechlorate would be the best and can easily be made from salt

Ramiel - 25-11-2004 at 05:39

RS: I've had some success with rich KNO<sub>3</sub> + Sugar mixes. Usually consistent and fine admixture is needed. Remember that reaction rates increase with pressure, so sometimes the ill-advised method of having the nozzle a tad too small is necessary to build up pressure (think of it as a paradoxical “semi-closed” system [I know! Its either closed or it fuggin aint, but tell that to any good professor] ).

This topic is very practical... I should hate to think what would happen if a mod were to see it.

And now to demonstrate my hypocrisy:
Harpoon, how would you create the flick out fins? Because I've tried for about 6 months without fining a solution - short of actual metal hinging (from the rear – which requires considerable machining prowess!) or spring coil (from the sides). I can recommend the tube method though, it's quite something!

tokat - 25-11-2004 at 06:29

"I personally don’t think that nitrates are worth a darn or at least kno3 because from some research I have done on it. It reluctantly release oxygen and know or potassium nitrite dose not decompose when heated and kno3 is pretty expensive butt also naoclo2 or sodium chlorate dose the same so for rocket propellants prechlorate would be the best and can easily be made from salt"'
i see were you coming from, i got my KNO3 from a farm sullpie, it was about $2 per KG, But allmost inposalbe to find.If you mix chacoal and sulpher it is hard to lit with a cig liter so use steel wool fumlments. Personly i don't like useing KNO3 becuase with sugar the limit between zero thrust and exploeding is small. I don't know weather you know about rockets but this is what i think.
Make the powder compressed so you can control suface area, i will check my notes and edit, but mild steel i think as 220psi per square inch, and was thinking but having a throat of say(9mmID,11OD,3mm throat for a lossly packet KNO3+sugar is about right(test),adding water to cake.

Melting

MadHatter - 25-11-2004 at 15:47

I mix my KNO3 and sucrose in water. Then I boil it down and carefully allow it to melt.
This way I can pour it molten into the rocket motor body. Mixing in water in advance makes
a more intimate mix before melting. It doesn't cool off to completely solid but more a rubbery
consistency.

Harpoon - 25-11-2004 at 16:59

Ramiel, I'd build the fins out of thin springy plastic, and roll them around the body of the rocket prior to loading them into the tube. You'll need to score the fins very lightly to provide a fold line where they attach to the rocket.

rocketscience - 25-11-2004 at 19:50

I don’t think I am going to put the rockets in a pipe I plan to do ones similar to the ones in October sky but with a recovery system and a lot smaller does any one have a suggestion for a ejection charge and a good binder (I need to know the chemical formula for the binder)

axehandle - 25-11-2004 at 20:47

Quote:

...suggestion for a ejection charge and a good binder (I need to know the chemical formula for the binder)

You don't want a binder in the ejection charge mix -- a binder would inhibit burning and the whole point of the ejection charge is that it should go "POF!" very very quickly, ejecting whatever it's designed to eject explosively. I'd suggest "Crimson Powder": http://www.nakka-rocketry.net/articles/Crimson_powder.pdf

It's a mix of ascorbic acid, KNO3 and Fe2O3 that is imtimately mixed by crystallization from an aqueous solution -- no grinding necessary. I've made it myself once for testing it, albeit sans the Fe2O3. It packs quite a whollop.

PS. The easiest to prepare and cast rocket fuel I've ever used was a 64/34/2 mixture of KNO3, sorbitol and Fe2O3. Lovely stuff, it can be intimately mixed by dissolving in water, then the water evaporated slowly and the sorbitol melted. Casts easily and doesn't caramellize if accidentally overheated. Only difficulty is finding sorbitol.

I've also used 64/34/2 KNO3/glucose/Fe2O3, all ingredients gently ball milled for 4 hours prior to melting. Doesn't caramellize as easy as sucrose based fuel but still worse than the sorbitol based fuel.

You'll want to build a dedicated melting pot from a deep-frier, BTW. Melting sugar/KNO3 based fuels on hotplate or flame is suicidal and a deep-frier already comes equipped with a thermostat ideally suited for the melting range of the sugar/sorbitol based fuels (100..120 degrees C or so-so). Continuous stirring is required though.

rocketscience - 25-11-2004 at 22:54

I think I am going to use ammonium prechlorate, aluminum, iron oxide, and carbon for the propellant. But I need a good binder that is cheap, simple, and I need to know is chemical formula.

Binder.

axehandle - 26-11-2004 at 07:53

This has degenerated into a practical discussion of pyrotechnics -- which is against the forum rules. I suspect the thread will be detritized very soon.

Still, I'll give you a couple of ideas for binders:

1) Parlon. Binder and fuel. Soluble in ethyl acetate.
2) PVC. Binder and fuel. Soluble in THF.
3) This is my own untested idea: PMMA (plexiglass). Binder and fuel. Soluble in acetone.
4) Asphalt + oil. Binder and fuel.

I'll bet you could find heaps more by a simple google search.

PS. IMHO, composite fuels using chlorates/perchlorates are unsuited for a beginner. I'd go with KNO3 based fuels. But it's your show.


[Edited on 2004-11-26 by axehandle]

vulture - 26-11-2004 at 09:10

CAUTION
Quote:

I personally don’t think that nitrates are worth a darn or at least kno3 because from some research I have done on it. It reluctantly release oxygen and know or potassium nitrite dose not decompose when heated and kno3 is pretty expensive butt also naoclo2 or sodium chlorate dose the same so for rocket propellants prechlorate would be the best and can easily be made from salt


Get your chemistry straight first! You obviously have no clue what you're talking about!

Because of your obvious lack of knowlegde and willingness to put effort into this, I not only see you as a potential hazard to yourself and others, but I will also close this thread.

[Edited on 26-11-2004 by vulture]