Need help igniting liquid fuel for rocket propulsion?

[Aki]

Okay, so I'm building a liquid propulsion rocket, about 4m tall, with a 2000lb trust. The propellants used are liquid oxygen and kerosene. Now the trouble is to find a way to ignite the fuels to start the combustion. Do you guys have any ideas? Thanks!

 

[Cyrus]

Is that even legal...

A 12 foot rocket without permits, I don't think so.

 

[Danger]

Once you have the fuel flowing, I'm partial to using a flashbulb with the glass cut off. Nothing like a bit of magnesium wool to get things rocking.

 

[FredGarvin]

2000 Lbf? Damn. You're using LOX and kerosene? Damn. How are you storing the LOX?

 

[Mech_Engineer]

Sounds pretty scary, I hope you stand way the heck back when you launch this thing... and I hope it doesn't land on anyone on the way back down. You DO realize you'll need some pretty heavy duty permits for this kind of stuff right?

That being said, I think the space shuttle uses large "sparkers" that throw hot sparks directly below the nozzle. I'm not really sure how they work, just trying to remember from videos I have seen. Once the fuel starts, it is ignited by the sparks. You could also try electrical ignition such as a hot wire, or something like a barbeque sparker.

BTW, igniting the fuel is the easy part, how did you even make this 4m rocket in the first place?

 

[LURCH]

That being said, I think the space shuttle uses large "sparkers" that throw hot sparks directly below the nozzle. I'm not really sure how they work, just trying to remember from videos I have seen. Once the fuel starts, it is ignited by the sparks. You could also try electrical ignition such as a hot wire, or something like a barbeque sparker.

I was thinking of the same thing; possibly with road flares? That might be a bit pf overkill, but you could be dang sure that puppy's going to light!

 

[Aki]

Well to address everyone's concerns, this is an university student project team, and our goal is to build a reusable rocket capable of carrying a payload. We have obtained a permit from the Canadian rocketry association for launches. There are approximately 30 people working on this, and this project started about 3 years ago.

So far, I've looked at the idea of an "augmented spark plug". It's a spark plug withing a tiny chamber mounted above the combustion chamber. So a tiny bit of lox and kerosene will be injected into the tiny chamber and the spark plug will ignite it. Afterwards, this flame will spread into the main combustion chamber where more lox and kerosene will be injected.

I'm open to comments :)

 

[3trQN]

How about a glow plug like device. A metal conductor you can heat initially at the launch pad using a current, then which remains hot (by the ignited rocket) throughout the burn. I guess the main filament would burn out, so it would be a one off thing.

Or some blue touch paper...hehe...why complicate things.

 

[Danger]

Just got a different sort of idea here. If you can incorporate a small spring-loaded piston in a cylinder (think 'pellet gun' here), an orifice from it could be installed in the combustion chamber. Remotely triggering the piston to release would force the air through into the fuel mixture. The heat of compression with the proper orifice size should be in the area of 1,000 degrees F.. That temperature is only for a fraction of a second, but should be enough to get things cooking. It was the ignition system for the caseless ammo in the old Daisy VL .22 rifle.

 

[Ki Man]

for a low tech solution, you could use magnesium-water reaction. just put a magnesium cap at the nozzle and have something squirt water at it out of the launch pad :/ although it might not be the safest idea...

 

[Danger]

I'm no chemistry wizard by any means, but I've never seen an adverse reaction involving magnesium and water. Are you thinking of sodium? If so, not a bad idea.

 

[Mech_Engineer]

for a low tech solution, you could use magnesium-water reaction. just put a magnesium cap at the nozzle and have something squirt water at it out of the launch pad :/ although it might not be the safest idea...

I think you mean potassium and water. Doesn't sound like a very effective solution to me.

 

[FredGarvin]

Let's get the preliminarys out of the way. Are you incorporating small pumps to move the liquid propellants? How are they stored and mixed in the vehicle? Do you have a premix/ignition chamber incorporated in the design? Are you atomizing the fuel? Since you are going with a liquid based system, this brings up the question as to whether or not you need more spark energy.

From what I have seen of the big rocketry guys, they use solid propellants. They also use a heaftier version of the old Estes igniter which is basically two wires whose exposed ends are inclose proximity to create a spark. Since you are going with a liquid based system, this brings up the question as to whether or not you need more spark energy.

 

[3trQN]

Magnesium & Water = Hydrogen gas, you still have the ignition problem

A quick google brings this up http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1512585

Which describes one system, it also mentions a problem with the type of ignition system i suggested which I've heard mentioned before.

From the tests, it was observed that this injector provides well-atomized and well-mixed mixtures of fuel and oxidizer. Type of the ignition system is very critical in such systems. If a pyrotechnic igniter is used, timing becomes the most important factor. If fuel and oxidizer are injected just a few milliseconds before the igniter is activated, the igniter performance can degrade and ignites very late. Such a scenario ends with a detonative explosion and causes catastrophic damages. If the opposite happens, the nozzle exit cover opens before the fuel and oxidizer reach to the motor. In this case longer ignition delay may occur. Therefore usage of traditional igniters is quite dangerous and difficult in liquid fuelled rocket motors.

Best watch your eyebrows...

 

[Flyboy]

May I suggest a solution that was used by the Germans on the V-2? They used a pinwheel firework placed in the rocket engine throat to ignite the fuel/oxidizer mixture. Or you could use a sparkling, wand-like firework that is very popular with children in America on July 4th celebrations. lots of sparks from that!
Another idea is a piezoelectric sparker, like what is used for pushbutton starters on barbeques.

 

[carp]

I would use a simple wire ignition system. Take two insulated wires separated by 1/8th inch with a cotton ball soaked in gasoline or kerosene attached to it. Create your spark with an automotive or small engine ignition coil.

-carp
PropulsionAccess.com

 

[B. Elliott]

You could pick up a $25 stun gun at a local flea market. Solder positive and negative leads to it.

 

[Danger]

Not in Canada, he can't. Stun guns are classed as Prohibited Weapons up here, in the same category as switchblades, machine guns, grenades, etc.. Go figger...

 

[carp]

Can you tell me what the pressure will be in you combustion chamber?

carp
PropulsionAccess.com

 

[Aki]

Can you tell me what the pressure will be in you combustion chamber?

carp
PropulsionAccess.com

It will be 100psi

 

[Aki]

I decided I am going to use a spark plug, and I have the Go-Ped Kicker spark plug in mind. Has anyone else used it before?

http://www.msdpowersports.com/go-ped.html"

 

[carp]

I was going to suggest a spark plug. However, I wouldn't try to tap a hole in your combustion chamber and screw the spark plug in it. I would go for an offboard ignition system.

carp
http://www.propulsionaccess.com/

 

[KleptoPanda]

This may not be a "good" method, but it should work and is easy to do with basic chemistry knowledge. The gist of the equation would be
Manganese(VII) oxide + meth/ethanol (Any oxidize-able organic molecule) = Ignition source; and really be something along the lines of; C₂H₄O₂ from Mn₂O₇ and C₂H₆O

Forgive the incompleteness of this post; I'm writing in a hurry.

 

[turbo]

Have you thought about designing a mechanical ignition system using a series of type 209 shotgun primers? You could set them off with a series of spring-loaded triggers to bracket the time of propellant release. These primers are really cheap and readily available so you could experiment with little cost.

 

[H_man]

If its only a "one shot" device you need then perhaps a bank of capacitors and a thyristor... you could potentially get a spike of order kV & kAmps. Which I would guess (having no background in rocket ignition ) would be enough to set off a chemical reaction!

Alternatively an inductor, thyristor would do a similar job... there are alternatives to thyristors, it all depends on the exact specifications which ideally need to be carefully understood.