technical 'pyro free' hybrid ignition

Discussions on hybrid rocketry including rockets, motors and technologies.

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cody1382
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Postby cody1382 » Fri Sep 19, 2008 10:13 am

i emailed doug pratt an
he sggested using a 1\4 inch slab
cut of a 18mm D size white lightning or black jack
reload so if he thinks its legit i cant see why
it wouldnt be
i guess its really up to the club your flying with
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PatchleAD
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Postby PatchleAD » Sat Sep 20, 2008 7:19 am

I am an electrican, and love electronics....

It is very easy to draw a big spark... I made a few devices at would draw a 2 inch spark almost constantly (about 300 sparks per second) ... grab a new generation car coil could make a bigger one...

Is this something loke you are looking for? Or are you looking for more of a constant DC High Voltage? With the right insulation 10Kv or 100Kv would give a great spark

:twisted:

now where's that coil ..

PatchleAD
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Postby PatchleAD » Sat Sep 20, 2008 7:24 am

just reading a few more posts on these\...

How hot do we need to make the fuel before the spark? 100^C or 500^C??

How big is the entry point we have to play with?

i'm sure we could design a non pyro design to light these babys

cody1382
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Postby cody1382 » Sat Sep 20, 2008 7:46 am

yeah you can but im just being cheap an trying to get away from using oxygen
http://www.nowhybrids.com/pyro-free.htm
but im not sure if we could do it with the 29mm or 38's
TRA#11807

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Non pyro ignition.

Postby PK » Sat Sep 20, 2008 8:20 am

PatchleAD wrote:
i'm sure we could design a non pyro design to light these babys


I put a lot of work into this a while back. Mostly trying to find a way to light UC valve hybrids without any pyrotechnics. To start with you rig a combustion chamber vent. That way you have a steady flow of NOX you can use. It has to be a bigger vent than you would normally see on a little hybrid too. I found that 0.4-0.5mm was the go. A normal vent on a small motor is about 0.35mm, or No 80.

Forget spark ignition. To get nitrous to burn anything you have to heat a fair bit of it to 500 ish degrees. Whist an ignition coil spark is an energetic thing, it's only there for a short period and just can't break down enough NOX to get the thing going.
Instead, pack a fair bit of 0000 steel wool into the top of the motor and just poke two wires into it. 12V @ a few amps gets it glowing and it will burn fairly violently in the venting nitrous.
You'll need some prety good shielding of the fill tube as this process isn't as energetic as GOX or pyro ignition and there's an increased risk of a low burnthrough, but its dead simple to rig..

PK

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Postby b-h » Sat Sep 20, 2008 10:13 am

A cattle prod has a fair bit of spark to it. I know you can light a smoke with one. They also get those big "Drought Masters" going like rockets :)

cody1382
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Postby cody1382 » Sat Sep 20, 2008 10:45 am

ive been hit before
they suck
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PatchleAD
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Postby PatchleAD » Sat Sep 20, 2008 10:50 am

I can see where your comming from with the spark... You can up the current and form an arc more like a welding arc... but this could melt through more that you want....

Is there any chance of the Al of the filler etc catching alight? i've done a few experiments with lighting Al with powered Fe... hard to do but very energetic when it goes....

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Postby PK » Sat Sep 20, 2008 11:02 am

Thing is, the nitrous oxide comming out of that vent has just boiled off from liquid in the tank. So its anything up(down) to -70deg C. The spark has to heat enough of it to 500degC and ignite enough propellant (solid plastic) to give off enough heat to get the next bit of NOX to 500deg.
It works if you introduce a gaseous or volatile liquid fuel. but then you're back to GOX injection.
The end result of my experiments was a single fill spike up the nozzle held into the motor with cable tie. A bit like a mini hypertek sans gox.
I 'd pack the top of the motor with steel wool and stick an ordinary igniter up there..
Image

I was doing this at the time when Marcus Leech (propulsion polymers) was experimenting independantly with steel wool in UC valve motors.
After a short debate on who held the prior art, We ended up calling my setup the KLK (click) valve. Kline, Leech, Kelly
If you put a decent sized grain in a KLK valve motor you can do 3 or 4 flights without stripping the motor..

Re aluminium. Thermite works very well lighting UC motors. But it's hardly non pyro so using a spark isn't much of an advantage..

PatchleAD
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Postby PatchleAD » Sat Sep 20, 2008 11:13 am

Cool...

<-- is not knowledgeable in this field .. but always up for ideas 8-)

I was not thinking of using Thermite directly.. just woundering if it could form indirectly ... and suff things up 8-)

But seeing you have a motor named .. i think you have the floor in this field 8-)

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Postby Avachovy » Sat Sep 20, 2008 11:18 am

i have thought of using a thermite brick up top to get things moving. I only worry that my injector is aluminium and i could damage it a tad
Will fly beer for rockets

PatchleAD
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Postby PatchleAD » Sat Sep 20, 2008 11:20 am

I know I know... how about we put the whole lot into a kiln, and heat everything till it goes boom....

ok ok now i'm being distructive.... :twisted:

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Heat

Postby PK » Sat Sep 20, 2008 11:24 am

Avachovy wrote:i have thought of using a thermite brick up top to get things moving. I only worry that my injector is aluminium and i could damage it a tad

Most small motor casings are Al which melts at 600 deg. Most propellant burns (under pressure) at more than 2000 deg. If you've got your insulation strategy sorted such that the motor survives the burn then a little bit if thermite at the beginning won't be a problem.

PK

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Postby Avachovy » Sat Sep 20, 2008 11:26 am

hmm... i spose so. Just dont use too much!
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Postby PatchleAD » Sat Sep 20, 2008 11:36 am

Yea i guess it is a matter of energy ... you need enough to get the suff burning but not so much that the temp of the filler gets to melting point...

humm....

does the GOX system use a gass exchange to preheat the nos?

Could we use an electric heater to perheat the core before we interduce the liquid nos? Maybe a fine plug to stop the nos entering the chamber until needed.... Or even an extra heater ste to a different temp for the nos...

and yes i'm speaking ideas.. with out any real work experence... but it all sounds like fun and i'm sure lots of great ideas started from a stupid one... :D


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