Best beginner rocket fuels?

[dharak1]

I want to know what the best rocket fuels are for someone looking to make a basic rocket engine. I don't mean solid fuels. I want to know the best for liquid and hybrid. I was thinking and wondering if you could oxidize kerosene as it goes into the chamber and light it. I was working on making a roofing tar and GOX rocket but solid roofing tar is hard to find. LOX rockets are expensive and hard to make. I want something based on 3 things: 1. Attainability 2. Power 3. Ease of use. Everything is accepted! Thanks for the help.

[Ralathon]

Sadly there is no fuel that is all 3 of those things.

Anyway, the 3 main oxidizers used in liquid/hybrid rockets by amateurs are:

N2O (laughing gas). It is liquid at room temperature when you put it under a few bars of pressure. Sadly, since this stuff is classed as a anesthetic there are some restrictions to getting it. You can also make your own by heating dissolved ammoniumnitrate (fertilizer) but for the love of science be careful. If you do this wrong it'll blow up in your face, not to mention you need some equipment (specifically the compressor) to get this running reliably.

H2O2. You can use this as a monopropellant. But it is hard and expensive to get in its pure form. Also has a tendency to blow up in your face.

O2. As you said, rather hard to keep this stuff liquid. It is however relatively easy to get.

As for fuel, you can burn pretty much everything organic. It can be anything from alcohol to candle wax. I'd go with simple gasoline. It is relatively cheap, easy to get and burns easily.

[dharak1]

How would you recommend I push the gas out of the rocket? It's going to be very small maybe a meter tall at most. I was thinking GOX and Roofing tar. But gas is easy to get. Would diesel work too? It's cheaper than gas.

[Ralathon]

If the gas is pressurized (And it better be, else it isn't going anywhere ) it'll flow out on its own. All you need to do is give it a small opening. The size of that opening depends on how quickly you're pumping your fuel (so you get a proper mixture). You can all calculate it using fairly basic fluid dynamics. You should be able to find some guides after a bit of googling.

Diesel should work as a fuel. But for a gas rocket I don't know how well. The main problem would be getting the stuff to ignite. For LOX-Diesel that isn't much of a problem but GOX diesel is a lot less reactive.

[dharak1]

How would I open the opening before launch? With gas/solid hybrid you can open the valve then light it remotely but if you open the valve on the pressurized diesel it would flood out.

[K^2]

How would I open the opening before launch? With gas/solid hybrid you can open the valve then light it remotely but if you open the valve on the pressurized diesel it would flood out.

This is why people like hypergolic fuels. Failing that, you can look into catalyzed options. Propane + N2O might ignite without a heat source if you put a bit of platinum wire in the chamber. In terms of liquid fuel rocket, that's probably your best bet anyways. Finally, you can add a heat source in form of a starter coil from a model engine.

Hybrid might be a bit easier. Again, N2O is comparatively easily obtainable. For fuel you can even use paraffin wax. A hybrid is way easier to design than a liquid rocket engine, so it's much more likely that you'll build something that runs at all.

[dharak1]

Thanks! I can get paraffin very easily. Where would I get N2O? Do I have to order it or can I go somewhere that sells stuff for welding like oxygen tanks?

[lajoswinkler]

You'll never get your hands on high concentration peroxide and it's for the best. That thing is highly unstable.

Pure nitric acid (WFNA, RFNA) is also a very good oxidizer, but unless you're going to make your own, which is tedious and dangerous, you aren't going to see any of it.

N2O is pretty expensive. I think LOX is the best because of the price and availability.

[K^2]

If you can point me to a good public supplier of LOX that won't ask for any papers and provide it reasonably cheap, I'd appreciate it. I was unable to find any.

N2O is easy to obtain because it's common oxidizer for hobby hybrids and used for NOS boosters in cars. You can purchase it from many internet stores dealing in high power rocketry or car modifications. As lajoswinkler said, it isn't cheap, but building a custom rocket engine isn't the sort of thing that's going to be cheap anyways.

[Duxwing]

A Solution to Bi-propellant Ignition:

Control your fuel flow with (a) remotely-operated solenoid valve(s). Just before launch, with rocket fueled and solenoids shut, put a heat source (e.g., a small candle) under the nozzle. To launch, open the valve(s) with a remote control: the fuel-oxidizer mixture will spray into the nozzle, wherein the heat source will ignite it. The flame front thereby created will travel up into the combustion chamber, and your rocket will roar into the wild blue yonder.

-Duxwing

[Justy]

Dharak1, your profile says you're in Edmonton, I would strongly recommend you get in touch with the Canadian Association of Rocketry. They have people dedicated to home-made motors ("EX" or "Experimental") and safe testing of rocket motors (Motor Certification Committee). The Tripoli Rocketry Association is even more involved in experimental rocketry (in addition to the famous LDRS events, they organize BALLS, a three-day all-experimental launch in the States) but their website is down.

To start with, you might start with microhybrids using whipped cream dispenser N2O cartridges. They're roughly equivalent to D-class solid motors. Aerocon Systems' "S'Creamer" microhybrid is a ready-built unit with sections of acrylic pipe for fuel. You can find similar motors in kit form requiring some metalworking skill elsewhere, and if you want to scratchbuild one from Rene Caldera's original microhybrid design you can get the plans for $10 from Art Applewhite Rockets.

I have a G-class hybrid from a manufacturer I won't name. I've never fired it, because shortly after I bought it, one from the same batch exploded on the test stand, throwing pieces at least twice as far as the listed minimum safe distance (which is, itself, a couple times farther than pieces from a failed motor are supposed to fly; make sure the ENDS of the motor are weakest, so if it blows up on the pad, pieces go up and fall back down, not outward towards you!). I see that same manufacturer has a G-class available once again for just under twice what I paid; I assume he re-worked the design. This is why I suggest you start with known designs as a learning exercise before you strike out on your own, and for your first couple attempts, ask if the CAR Motor Certification Committee will let you park your motor on their test stand during their next testing day and push The Button from the safety of their blockhouse.

[dharak1]

I found these: http://www.amazon.ca/Mosa-Whipped-Cream-Charger-Pack/dp/B00281ONLG/ref=pd_cp_k_1

Would they work if I put them on a needle and put a tube in the needle to get the stuff out? Then I could run that to paraffin wax.

[K^2]

It should work, in principle, but the weight of the cartridge to amount of N2O it holds is going to be rather small. Still, it gives a pretty inexpensive way to test things out, so this might be good for a start.

The hard part will be working out flow rates and bore diameter for the wax.

[dharak1]

I saw a video a while ago that worked pretty good. It was a gas/solid hybrid using GOX and roofing tar. They took a pipe and put another smaller pipe inside it, something really small like 1/8th of an inch in a tube 1 inch inside. And filled the outside tube with molten roofing tar then froze the whole thing. When it was done they hammered out the smaller pipe leaving a hole in the tar. Then they ran a tube to the hole in the tar and since it was 1/8th of an inch they could use any hose or with that diameter. Here's the video:

The guy talking, Eric Stackpole apparently got hired by NASA. The rocket I'm talking about is at the end. It actually has mach diamonds.

[K^2]

Yeah, you really don't need much to make a hybrid engine. Mythbusters made one out of salami sausage once just to prove a point. The tricky part is building an efficient one. There are two challenging elements to it.

First, containing your oxidizer. GOX is good and all, but you need a pressure vessel for it, and that makes your rocket much heavier. This is why LOX is a better choice, but it's harder to work with. By far the best oxidizers for a hybrid are the nitric acid and dinitrogen tetroxide. Both are very corrosive and toxic, however. They are also not easy to obtain without raising some red flags.

Second is managing pressure in combustion chamber. Again, with GOX you know that pressure at which you feed oxygen into combustion chamber is your maximum continuous pressure. There can be blowback, which involves a pressure spike, but so long as your oxidizer is not volatile, it's not a big deal. So basically, your chamber just needs to withstand the pressure + a bit overhead to survive possible blowback. Of course, if you want some degree of efficiency, you also need to manage the flow rate to match the combustion rate, which depends on the pressure, and the pressure depends on the combustion rate and the outflow rate. So effectively, it's the same problem as managing the pressure in a solid fuel rocket, but you have that extra safety of both pressure and reaction rates are being oxidizer-limited, so instead of runaway reaction and explosion you just get drop in efficiency.

[dharak1]

I see. I looked at some solenoid valves, they look pretty pricey. I'm thinking about putting a parachute on this now. How would someone do that? It would have to be done electrically right?

[K^2]

You can have the engine burn through the casing intentionally when fuel is running out and eject the parachute this way, similar to how it's done on model rockets with solid motor, but it's probably more trouble than it is worth. Something on a timer is probably a better solution.

If you are going to have solenoid valves, you probably need to have a micro controller on that thing anyways. Might as well throw in some accelerometers and actuators to look after stable flight as well. This isn't the sort of thing you want crashing into the ground because thrust wasn't perfectly centered.

[dharak1]

I ca put together something with an arduino for that. How would I control the flight with it though? I was going to use fins but that's probably not going to be enough. Would I have to use something like Copenhagen suborbitals with the little servo controlled plates to divert thrust?

[K^2]

Yes. Alternatively, you can put a ring around the thrust plume. It does not give as much authority as plates in the flow, but it won't burn through as easily. As for coding it, just keep in mind that your z acceleration will baiscally just give you thrust. You should be looking at x and y accelerations to see if you went off course. Or you can use gyros if you can find some.

[dharak1]

How funny, I was looking at some accelerometers for arduino a few days ago. I found one with no Z axis that could be used for guidance then I could have another one with a Z to avoid mistakes in coding. http://arduino.cc/en/Tutorial/Memsic2125?from=Tutorial.AccelerometerMemsic2125 That's the accelerometer I was looking at. I want this rocket to be safe. If I use the plates for diverting thrust would tungsten be a good start? It has the highest melting point of any element I know. I don't think it's very expensive either.

EDIT: Tungsten can get as low as 35$ a kilo for industrial use. I might end up using around 500 grams but it's always good to have extra.

[K^2]

If you do this right, you are looking at exhaust velocities of over 3km/s. That's enough to heat the surface to ~10,000K. Any material you use will melt and evaporate from the surface. It's a lot like the problem of thermal shielding on a shuttle. You cannot get any material that will withstand these temperatures. You have to use something that will evaporate away. The reason you don't want to go with tungsten is high thermal conductivity, meaning it will melt and deform. You want something that will get super-hot at the surface, but stays put inside. For example, material that won't melt at all. Typical choice is graphite. It sublimates at 3,900K and it has no melting point.

This does mean that control plates will have limited life, but there is simply no way around that. If you go with the ring approach, the ring does get air-cooled, so it can be made from metal.

P.S. I'm sure you noticed that problems seem to keep on stacking. There is nothing impossible about any of this, but these problems are the reason why there are few amateur-built rockets of any significant power, and even fewer of these are successful.

Edited October 7, 2013 by K^2

[dharak1]

By ring do you mean something like an engine bell? I might take that route now. I could cool it with LOX before and during flight. I can also make it using liquid nitrogen. What would you recommend I make it out of? I was thinking steel or something.

[Kryten]

If I use the plates for diverting thrust would tungsten be a good start?

Tungsten is pretty heavy stuff. I'd try and see what kind of price graphite is; if it worked for the V2, it should work for yours.

[dharak1]

I checked graphite prices. Around 1.50$ a pound. I have no idea where to buy it by the pound though. How would i make the plates out of it? Do I just cut up blocks?

[Copenhagen_Suborbitals]

Thanks! I can get paraffin very easily. Where would I get N2O? Do I have to order it or can I go somewhere that sells stuff for welding like oxygen tanks?

I wont recommend using paraffin. We tried that and it does not stand up well to vibrations. As you can see the the 2 movies below, big chunks of paraffin was thrown out unburned and caused a lower ISP than anticipated.