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Compressed air spark gaps
Posted: Sat Jan 03, 2009 5:23 pm
by Moonbogg
In a 3xi chamber, would the spark gaps have to be closer than at atmosphere? Is there additional resistance due to the thicker air? Can it be figured out without trial and error?
Posted: Sat Jan 03, 2009 5:30 pm
by Sticky_Tape
the sparkgaps do need to be smaller I discovered that in my mini it was hard to get 4x to ignite.
From the spudwiki hybrid cannon page:The ignition of a hybrid gun is more difficult than a normal combustion, as the length of a spark is roughly inversely proportional to the density of the gas. This necessitates the use of high-powered ignition source such as a stungun, flyback circuit, or other high-voltage source; grill igniters frequently won't jump a spark gap in pressurized fuel/air environments.
You can use piezo sparkers for hybrids I did. But you have to keep the spark gap small and use low x mixes.
EDIT: Yeah sparks are fun but you can also use steel wool and a 9volt batterie it was done before by daccel I think.
Posted: Sat Jan 03, 2009 5:38 pm
by Moonbogg
OK thanks. I might get a more powerful stungun and also shorten the spark gaps. I will be using 3 gaps, I think this ought to work.
Posted: Sat Jan 03, 2009 7:00 pm
by Hotwired
Double the pressure halve the distance of the spark gap.
...and so on.
When you get to the pressures where you really can't be bothered trying to measure a spark gap in fractions of a millimetre you can go from high voltage low current arcs to low voltage high current glow wires.
Posted: Sat Jan 03, 2009 7:26 pm
by Moonbogg
Hotwired wrote:Double the pressure halve the distance of the spark gap.
...and so on.
When you get to the pressures where you really can't be bothered trying to measure a spark gap in fractions of a millimetre you can go from high voltage low current arcs to low voltage high current glow wires.
Awesome. Thanks for that tip. First time i've heard that.
Edit...will the sparks still be as effective if they are super tiny? As long as there are 3 of them, I would think it would be good still.
Posted: Mon Jan 05, 2009 12:13 am
by daccel
Don't quote me, but I'm sure as long as the sparks are there they will still work, just marginally slower ignition rate.
Yes, I used steel wool and 9v to ignite 8.5x mix. The downside is it has to be replaced each time.
How high a mix can you go before a stungun or similar circuit becomes ineffective?
Posted: Mon Jan 05, 2009 5:41 pm
by jimmy101
Moonbogg wrote:t...will the sparks still be as effective if they are super tiny? As long as there are 3 of them, I would think it would be good still.
A spark is a spark. Big-ass spark, tiny little spark, doesn't make much difference. You need less than 1mJ to ignite propane in air. The propane either ignites or it doesn't. Adding the extra 100mJ of a big ass spark doesn't make a bit of difference considering the combustion process is going to be generating thousands of joules.