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Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
i started making a simple small hydrogen gun. The hydrogen is made in a small medicine bottle, the electrodes being 2x carbon rods (?) from D-batteries. affter running it a few times, at 12v 400 ma, i opened it up and found the water a gray-black color, with little black things floating. is that the rods being broken/destroyed? or any impurities on the rod,water,or bottle? im using cold water with some baking powder.
Even though that happened, i was able to get some hydrogen and oxygen and was able to light it. my triggering used a piezo from a butane lighter (a couple months old) connected to 2 tacks angled to each other to make a spark.
When the tank was fallied and i tried,nothing happened until after around 20 sparks, which finally combusted. When looked in the dark, i was getting a small spark almost everytime. is the spark not hot enough?
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
I have had that happen and it is usually fixed by proper cleaning of the rods. Try to scrape them clean or use a stiff brush to make sure you get them cleaned completely.
If you don't have a lot of air in themicture then you only need something like 0.02mJ of energy for ignition. A glow wire is often more reliable than a spark in such experiments.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Yeah, I wonder about that too...
butane/air mix also didn't mind to ignite at all using the piezo.
In lighter the gas passes through a small spring which could be acting as some sort of miniature bunsen burner... and spark hits it *right* at tip in order to ignite... if wire is deformed and spark hits just a little under, lighter hardly fires anymore.
I wonder what's with it? Spark looks more than hot enough, how can it be that hard to ignite the mixture?
Bjorn, why do you mention *energy as ignition requirement?
If I wanted simple and reliable ignition I would use car ignition coil... even better would be a high-energy capacitor discharge.
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
would the tacks being wet inside effect it in anyway?
about the glow wire, the adapter im using is a universal adapter, 1.5V - 12V constant 300ma max. do i just run the electricity through a thin wire? if so, then would getting the filamant from a regular stranded copper wire work? dont wanna risk shorting out or ruining anythng.
to clean the rods, would boiling them in water or burning them directly be a smart/good way to clean?
im thinking the gas was pure hydrogen-oxygen mixture, as i used a tube connected to a bottle submerged in water, so i knew when it was full (any other way of knowing home-made?).
i dont wanna get any new stuff to make it as it is a very small project for fun. As a capacitor discharge, i have 3x 250v 100(u)f caps, alot of very small ones (5-20v) different uf's, and a 330v cap from a disposable camera.
im sure that the 250v caps will work, but how to spark INSIDE the chamber? only way i can think of is directly moving the elctrode to touch the other, which i cant make air tight ;(.
just speculation, would discharging a cap into a thin wire be brief glow wire enough for ignition?
its hard to tell, but there may be a loose connectin at the tack, i gotta check, but globs of hot glue stand in my way =p
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Bjorn, why do you mention *energy as ignition requirement?
All combustible gasses has a minimum energy requirement before ignition, hydrogen mixture has a very low required energy for ignition. The ignition energy is fairly constant with sparks ranging from nanoseconds to milliseconds. It is not significantly affected by humidity either so it can be considered a constant in reasonable cases.
It is important to remember because things that are safe with butane might easily ignite hydrogen. Since the ignition energy is so low and the range of explosive mixture is so wide it is not safe to collect hydogen in any quantity without understanding the details.
There is also a required minimum temperature, which is not relevant for sparks.
to clean the rods, would boiling them in water or burning them directly be a smart/good way to clean?
I think I used a brush to get rid of a soft outer layer.
do i just run the electricity through a thin wire?
Yes, but you need to use Ohm's law to get the right resistance. Unless you have a better PSU you need to use special wire with high resistance to avoid shorting out the PSU.
A capacitor should be able to deliver enough current. The ones you have are able to explode thin wires and that will always ignite a gas mixture if it is combustible. The problem is constantly replacign the thin wire and there is also a chance of forgetting to disconnect the capacitor and shocking yourself so charging the capacitor to just enough voltage to glow the wire is probably the simples method.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
All combustible gasses has a minimum energy requirement before ignition, hydrogen mixture has a very low required energy for ignition. The ignition energy is fairly constant with sparks ranging from nanoseconds to milliseconds. It is not significantly affected by humidity either so it can be considered a constant in reasonable cases.
Now I admit that is confusing - intuitively I would expect energy density, and not energy to be important.
Why can't too-low energy spark ignite gas even if very hot? And why is it easier in some cases (in lighter it needs to hit the tip of the spring).. I guess it's about proper mixture ratio?
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
i think ive got the sparking working 100%,now i gotta clean rods and test.
are there any home items that have/are high resistance good for glow wire?
as for collecting, im collecting 1 Hotel shampoo bottle (my combustion chamber) at a time :)
i just tested using the water method to see when tank was full. i used the piezo in the dark, and saw the spark inside the tank, but nothing else. i tried a couple times, but still nothing. is there any chance im getting something that isnt flamable?
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Why can't too-low energy spark ignite gas even if very hot?
My first guess is that you must reach a certain critical level before the reaction generates enough power that it is sustainable. So a very low energy spark will just set off a limited number of reactions and the energy gets radiated away without being able to start new reactions fast enough.
are there any home items that have/are high resistance good for glow wire?
Just about anything electric that involves heat contains high quality resistive wire. Hairdryers, coffee makers... You could also use graphite from a pencil but you should be careful to heat it up slowly until it stops smkoking and don't heat it up close to your face because it can explode if it contains humidity or is not pure.
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electrolysis hydrogen gun
