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Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: ralphd » Sat Sep 27, 2008 7:53 am

Don't forget that automotive sparkplugs have resistance. Different plugs have different resistances. Ask a (good) mechanic or autoparts store which are hotter.
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Unread postAuthor: jimmy101 » Sun Sep 28, 2008 2:05 pm

ralphd wrote:Don't forget that automotive sparkplugs have resistance. Different plugs have different resistances. Ask a (good) mechanic or autoparts store which are hotter.

That is not correct. The electrical resistance of the plug is dominated by the spark gap itself which has a huge resistance. The rest of the plug has minimal resistance (a couple ohms or so at most). If there is a small difference in the spark energy (not it's temperature which is basically irrelevant in a spudgun), it won't make any difference.

The "heat" of a spark plug refers to what temperature it is designed to operate best at. A "hot" spark plug is designed to be operated at a higher temperature, it conducts heat poorly and is sometimes inserted farther into the cylinder. A "cold" spark plug conducts heat better (so it stays cooler) and is sometimes not inserted as far into the cylinder.

In a spudgun, the temperature range of a spark plug would be irrelevant. The plug is operating at ambient temperature, not the very high temperature that exist in a running ICE. The gases in a spudgun chamber will get to several thousand degrees during firing but by then the sparkplug has already done its job.

Bottom line, any spark plug will work in a spudgun and the type of spark plug will not significantly affect performance..
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Unread postAuthor: ralphd » Sun Sep 28, 2008 7:49 pm

Center electrode
The center electrode is connected to the terminal through an internal wire and commonly a ceramic series resistance to reduce emission of radio noise from the sparking. The tip can be made of a combination of copper, nickel-iron, chromium, or precious metals. In the late seventies, the development of engines reached a stage where the ‘heat range’ of conventional spark plugs with solid nickel alloy centre electrodes was unable to cope with their demands. A plug that was ‘cold’ enough to cope with the demands of high speed driving would not be able to burn off the carbon deposits caused by stop-start urban conditions, and would foul in these conditions, making the engine misfire. Similarly, a plug that was ‘hot’ enough to run smoothly in town, could actually melt when called upon to cope with extended high speed running on motorways, causing serious damage to the engine.[3] The answer to this problem, devised by the spark plug manufacturers, was a centre electrode that carried the heat of combustion away from the tip more effectively than was possible with a solid nickel alloy. Copper was the material chosen for the task and a method for manufacturing the Copper cored center electrode was created by Floform.
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Unread postAuthor: jimmy101 » Mon Sep 29, 2008 1:46 pm

Ralphd
So? (And, you shouldn't be posting things you've cut and pasted from another site without a link.)

None of that stuff has much to do with using a spark plug in a spudgun. The internal resistance is minimal compared to the resistance of the air gap.

The low resistance wire (i.e., generic copper wire) used in a spud gun is much lower resistance than automotive ignition wire. The difference in the wire is enough to make up for the small internal resistance of the splug.

The "temperature" of a plug is irrelevant to a spudgun.

The "heat" (as in how much energy is produced in the spark) is irrelevant to a spudgun.
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Unread postAuthor: ralphd » Mon Sep 29, 2008 2:30 pm

Whatever. Get over it.
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Unread postAuthor: jimmy101 » Mon Sep 29, 2008 4:24 pm

ralphd wrote:Whatever. Get over it.

I'll try.

We wouldn't want to insist on anything so silly as actually posting correct information.
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Unread postAuthor: Ragnarok » Mon Sep 29, 2008 4:44 pm

ralphd wrote:Whatever. Get over it.

You know, it pays to be polite to people like Jimmy, he knows a heck of a lot.

Normally if you're proven wrong, it's much better to stop digging and admit the mistake - and not resort to being rude.
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