Short question topic

[jrrdw]

So did some testing at 10x with my burst disk hybrid and the new ignition circuit. The spark was jumping the spark plug (different one to the tests from above) as evident by visible sparks between the chamber and wire. However, no ignition. One click of the piezo sparker, boom.

Is it possible that the spark has enough juice to jump the gap at 10x mixes but not enough juice to ignite the fuel mixture?

That's why you open the spark plug gap to .060, it simulates operating conditions with the pats you will be using. What exact make and model spark plug you're trying to use? Stay away from resistor spark plugs they will only hinder your progress.

[MrCrowley]

I haven't actually changed the spark gap spacing on the new spark plug, it came sufficiently small (I had options to choose from). Can't recall the spacing for the spark plug used in testing today (on the burst disk hybrid) but it'd be smaller than 0.06". I'll come back tomorrow with model numbers for both spark plugs. I have a feeling that the issues today aren't unrelated to the suspected issues from the previous day with the other spark plug.

Maybe tomorrow I'll remove the spark plug from the equation and use some homemade electrodes that I have used previously in hybrids.

[MrCrowley]

OK more updates and testing.

Got the burst disk hybrid to ignite at 5X and 7X with the new ignition circuit. I'll try 10X once more to make sure that problem wasn't a one-off. However, there's a catch. The ignition would only ignite the fuel mixture when I held the chamber wire slightly off the chamber, it wouldn't work when the wire was directly connected to the chamber. Again, I think this is related to the earlier issues I identified.

Maybe the spark gap has to be larger for this circuit to ignite mixes, will have to try this tomorrow. Is it possible that the output generated by the sparker is partially dependent on the spark gap? A small spark gap might result in a smaller output voltage while a large spark gap may result in a larger output voltage. Is this possible or likely? If so, it's an easy fix. Just means I have to have one wire fixed a couple of millimetres away the top of the sparkplug electrode. That may explain why the sparks jumping the sparkplug gap are very small and almost inaudible.

In the mean time, here are the model numbers of the spark plugs I have used for testing:
NGK 6097 BKR7E (new piston hybrid spark plug)
Champion J8C (burst disk hybrid spark plug, used for recent testing)

[jrrdw]

Maybe the spark gap has to be larger for this circuit to ignite mixes, will have to try this tomorrow. Is it possible that the output generated by the sparker is partially dependent on the spark gap? A small spark gap might result in a smaller output voltage while a large spark gap may result in a larger output voltage. Is this possible or likely? If so, it's an easy fix. Just means I have to have one wire fixed a couple of millimetres away the top of the sparkplug electrode. That may explain why the sparks jumping the sparkplug gap are very small and almost inaudible.

In the mean time, here are the model numbers of the spark plugs I have used for testing:
NGK 6097 BKR7E (new piston hybrid spark plug)
Champion J8C (burst disk hybrid spark plug, used for recent testing)

Spark gap has nothen to do with out put voltage of the sparker / ignightor. Changing the gap changes the tempature of the spark. Seems to me from what you're discribing the spark plug isn't grounded enough for it to work as it should. If you attach the sparker ground to the base of the plug, the electricity will have a better path to least resistance.

Remember electricity is like water...lazy...takes the easy way out...of the sparker.

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[wyz2285]

I accidentally bought a 300mm long 32mm OD 2.5mm walled seamless precision cold-drown steel tube. I would use it as a 3000 psi PCP chamber if I figure out a way to keep it from rusting! I could try to blue it, but I only know slow rust bluing and it requires me to sand of the rust several times which is difficult to do to the inside... What should I do??

[jrrdw]

Depends on if you're wanting a certain look. If you want it to look like the metal it's made of, clear coat it, or paint it. You could have it powder coated as well. A few ways to clean rust out, 1. stripping gel (Navel Jelly), 2. steel wool, 3. sand paper on a stick locked in a drill.

[wyz2285]

Look doesn't matter much, I need something durable. The inside will have to deal with o-ring seals so I think paint is out of the question... Powder coating can't be done in my workshop, can't get the powder nor the huge furnace...

[jimmy101]

Spark gap has nothen to do with out put voltage of the sparker / ignightor. Changing the gap changes the tempature of the spark. Seems to me from what you're discribing the spark plug isn't grounded enough for it to work as it should. If you attach the sparker ground to the base of the plug, the electricity will have a better path to least resistance.

Remember electricity is like water...lazy...takes the easy way out...of the sparker.

You don't have that right. the spark gap has everything to do with the voltage of the ignitor. The output voltage of the ignitor rises until it reaches the breakdown voltage of the gap. The breakdown voltage is a function of the width of the gap, the sharpness of the electrodes and the gas. Once the breakdown voltage is reached the output voltage of the ignitor drops to a very low value basically instantly. The remaining energy in the ignition circuit is dumped at low voltage but high (for a high voltage circuit) current through the gap. The temperature of the spark is probably always basically the same (roughly surface of the sun type temperature), what changes from setup to setup, and what is much more important for igniting things, is the energy in the spark and the volume of gas that that energy is dumped into. To get ignition you need to exceed a minimum energy density in some volume of gas. It is the energy density that matters, not the total energy or the temperature. Smacking a combustion gun with your hand probably introduces more energy into it than does the ignition system. The difference is that the energy of a hand slap is spread out through the entire volume of the chamber and the energy density is low and can't ignite the fuel. The ignition system puts out less energy but that energy is put into a very small volume.

[jrrdw]

You don't have that right. the spark gap has everything to do with the voltage of the ignitor

I didn't qoute you fully here, just enough to ask my question. Where are you getting your information? :bounce:

[MrCrowley]

Spark gap has nothen to do with out put voltage of the sparker / ignightor. Changing the gap changes the tempature of the spark. Seems to me from what you're discribing the spark plug isn't grounded enough for it to work as it should. If you attach the sparker ground to the base of the plug, the electricity will have a better path to least resistance.

Remember electricity is like water...lazy...takes the easy way out...of the sparker.

You don't have that right. the spark gap has everything to do with the voltage of the ignitor. The output voltage of the ignitor rises until it reaches the breakdown voltage of the gap. The breakdown voltage is a function of the width of the gap, the sharpness of the electrodes and the gas. Once the breakdown voltage is reached the output voltage of the ignitor drops to a very low value basically instantly. The remaining energy in the ignition circuit is dumped at low voltage but high (for a high voltage circuit) current through the gap. The temperature of the spark is probably always basically the same (roughly surface of the sun type temperature), what changes from setup to setup, and what is much more important for igniting things, is the energy in the spark and the volume of gas that that energy is dumped into. To get ignition you need to exceed a minimum energy density in some volume of gas. It is the energy density that matters, not the total energy or the temperature. Smacking a combustion gun with your hand probably introduces more energy into it than does the ignition system. The difference is that the energy of a hand slap is spread out through the entire volume of the chamber and the energy density is low and can't ignite the fuel. The ignition system puts out less energy but that energy is put into a very small volume.

Very useful, thanks Jimmy!

So if I have a small spark gap, the volume of gas is relatively small but the voltage of the spark is also relatively low. If the spark gap is wider, the volume of gas increases but so does the voltage (to a point). Do I just need to find a goldilocks zone to get it to work? I've done more testing and can definitely conclude these things: the ignition circuit is sparking across the spark plug; the ignition circuit does not ignite mixes at 10x even though it is sparking correctly; and, using the piezo sparker immediately after trying the ignition circuit ignites the fuel mixture without problem (so its not a fuel mixing issue).

[jrrdw]

So if I have a small spark gap, the volume of gas is relatively small but the voltage of the spark is also relatively low. If the spark gap is wider, the volume of gas increases but so does the voltage (to a point).

Wait...what? You're really really going to have to convince / explain to me how changing the width of the electrode gap changes the "volume of gas" in the chamber. Unless you fill the chamber then remove the spark plug and some mix sneeks out while you're changing the gap, then you have a change of volume with a changed gap. If you could change the gap with a sealed chamber the mix and volume of it stays the same no matter what the gap is changed to.

Do I just need to find a goldilocks zone to get it to work?

There will all ways be a "goldilocks zone" in any combustion chamber with what ever ignition system you are using to a paticular combustion chamber. But that wont keep it from working.

I've done more testing and can definitely conclude these things: the ignition circuit is sparking across the spark plug; the ignition circuit does not ignite mixes at 10x even though it is sparking correctly; and, using the piezo sparker immediately after trying the ignition circuit ignites the fuel mixture without problem (so its not a fuel mixing issue).

How long does it take you to swap the ignition systems untill it's able to fire the cannon? Another thing, how consistent is the mixing once the fuel/air is in the chamber? Cleaning the electrodes and chamber in between every attempt? Seems overboard I know but all these things are contributing factors to what's causing your ignition issues.

[MrCrowley]

You're really really going to have to convince / explain to me how changing the width of the electrode gap changes the "volume of gas" in the chamber

I assume jimmy was talking about the volume of gas between the spark gap. If the distance is 3mm, then say there would be a 3mmx1mmx1mm cylinder of gas between the two electrodes. Widen that gap to 6mm and suddenly the volume of that cylinder is double. In other words, the amount of gas the spark has to jump increases with the gap width.

There will all ways be a "goldilocks zone" in any combustion chamber with what ever ignition system you are using to a paticular combustion chamber. But that wont keep it from working.

If there is a goldilocks zone with this ignition system, where a wide gap increases the energy of the spark but also the volume of gas the spark has to pass through and a a small gap decreases the energy of the spark and also the volume of gas it passes through, then it could prevent the ignition system from igniting the fuel. There may be a specific width where the spark energy:gas volume ratio is perfect.

How long does it take you to swap the ignition systems untill it's able to fire the cannon? Another thing, how consistent is the mixing once the fuel/air is in the chamber? Cleaning the electrodes and chamber in between every attempt? Seems overboard I know but all these things are contributing factors to what's causing your ignition issues

Instantaneous, the piezo is already wired to the cannon (electrodes disconnected for ignition circuit testing, though). The fuel mixture is not an issue, I've ruled it out. I've tried the sparker at various points over 5 minutes and nothing. One click from the piezo, boom. Done this multiple times. Electrodes are clean as well.

At first, I didn't adequately control for some variables but in later testing I did. Everything held constant, the new ignition system will spark but not ignite the fuel above 7X (well, worked at 7X and didn't at 10X) and the piezo will ignite the mixture instantaneously.

[MrCrowley]

Need to be prompt here, can add details later.

Been trying to "fix" my remote ignition system (can't ignite mixes above 9X). Possible causes:
1 - Using 9V battery with AAAs
2 - Step-down converter limiting current to 700mA

I fixed these today by wiring 8 AAAs in series and buying this:
http://www.surplustronics.co.nz/product ... adjustable

In+:Input positive
In-:Input negative
Out+:Output positive
Out-:Output negative
Weight:33g
Dimensions:56 *38 *23mm(length*width*height)
Input voltage:5-30V(maximum input voltage 32V)
Output voltage:1.25-26V (step-down mode, Inputs must be greater than the output above 2 v)
Output current:0.15-2A Adjustable output(maximum output current 2.6A
Ripple frequency:About 52 KHz
Ripple peak to peak value :50mv (typical value)

Function:

Voltage Indicator(CV): The module is in the constant voltage mode.
Current Indicator(CC) : The module is in the constant current mode.
Voltage potentiometer: The multimeter adjusted to voltage is connected the module output. Adjust potentiometer clockwise, the output voltage increases. Adjust potentiometer counter-clockwise, the output voltage drops. The multimeter will display voltage. (In constant voltage working state)
Current potentiometer: The multimeter adjusted to current is connected the module output. Adjust potentiometer clockwise, the output current increases. Adjust potentiometer counter-clockwise, the output current drops. The multimeter will display current.(In constant current working state).

Problem is, when I switch the circuit on, the LED driver is in "Constant Current" mode when I want it in "Constant Voltage" so I can fix it at 3V and let it draw whatever current it needs. Anyone got any ideas on why I can't use "Constant Voltage" mode (which works when only connected to a multimeter)?

[jrrdw]

Problem is, when I switch the circuit on, the LED driver is in "Constant Current" mode when I want it in "Constant Voltage" so I can fix it at 3V and let it draw whatever current it needs. Anyone got any ideas on why I can't use "Constant Voltage" mode (which works when only connected to a multimeter)?

Is the output from the LED Driver steady?

[MrCrowley]

I wouldn't have thought so, the output is a high voltage sparker. Seeing as it's supposed to run off 2 AAs/AAAs, I would've thought it'd regulate the current and not the voltage.