GIANT SPARKPLUG!!!

[leo]

Or small Chinese?.

[DanielS]

Whoah, how much did the giant sparkplug cost? :D.

[Mark]

I kind of toyed with that idea, using one of my "Eclipse" and "Auburn" spark plugs. The thread is 3/4 inch NPT which in reality makes them one inch in diameter if you mic the threads. I also toyed with a 1/2 inch NPT plug, (national pipe thread), which fit some half inch bell.
Mark
PS For perspective, this Loganish design, which never ran but might have if I had tried acetylene, the combustion chamber of the Logan is the same diameter as the jumbo spark plugs, and at the top of the Logan is a little CM-6 spark plug.

[steve]

Oh, no... not this again....

[Mark]

Oh yes, the Steve size spark plug topic. I'm boring myself, but thought the new members might like to see the variety. From now on, I promise I will only post "new" stuff.
The V-3 plug pictured on this link is 1/4 inch shorter than my 1/4 32 rimfire plugs. I kind of think it looks better not so tall and Steve-ish. ha
Mark
http://www.modelflight.com/larrydavidson.html

[leo]

Here’s a other picture off the sparkplug/Chinese.

Oh, no... not this again....

That’s two times for Steve (the Steve size sparkplug and maybe again the beating off your pocket Lockwood)
I get a video next week from a fellow employee at my work (I started it at my workplace because I don’t have acetylene at home).

[alex]

Nice work Leo!! Now, plans:)

[Mark]

Nice work Leo, yet another curiosity from you. I always liked your little spherical astro blaster pulsejet too. It would have been cute if you had typed a little band to wrap around the spark plug with the word STEVE on it.
Steve might have used the "jumbo" spark plug to mount the engine or to weight it down to keep it from flying off philosophy. Or perhaps reading Gulliver's Travels several times, he found the Lilliput/Brobdingnab paridigm fascinating. ha
Mark

[DanielS]

Where'd you buy the NPT plugs from, never seen those before. A quick search doesn't turn up much of anything. Thanks!

[Mark]

The half inch pipe thread spark plug is a pretty common find at most auto parts stores. It is an Autolite 3095 spark plug. It's really a neat plug because most of the barrel is hollow with just a narrow piece of ceramic and electrode in the center, it is tempting to see it as a mini combustion chamber even.
The 3/4 inch pipe thread plug I found on eBay. One brand is Auburn and the other is Eclipse. Those have a really long electrode as you saw. Here is another kind on eBay now where both side electrode and center electrode gap far down from the plug. I'm not sure what size thread these pictured are for sure, but mine thread into 3/4 inch plumbing pipe fittings nicely, same thread.
Mark
http://tinyurl.com/on9d4
http://tinyurl.com/mfe3j
Here's some enviable Steve size plugs for cheap. Remember they have the neat hollow interior unlike normal plugs.
http://tinyurl.com/kaa2v
Another source for the bomber sizes.
http://tinyurl.com/qzrfj
And who can forget the all important use for an Autolite 3095, fusion experimentation! ha If you scroll down the fusion page you can get a good look at the 3095 hollow quality of the cavity where the center electrode is.
http://tinyurl.com/kwdpf

[leo]

Here are the measurements, in a few days I probably have the video.

[milisavljevic]

Thanks, Leo!

May I assume that the "front" of the combustor is located 17,5-mm inside the motor, i.e., after the threaded section?
If not, how far does the combustor (open space) extend into the threaded section? (Where does the sparkplug end?)

M.

[leo]

M.
Yes the front of the combustion chamber is 17,5 mm inside the motor, the treaded section of the sparkplug is exactly that long, of course the electrodes stick in the combustion chamber.
Not a nice smooth front combustor chamber wall.

[leo]

Bad news and good news, I got the video today, its more than 40MB and it’s a QuickTime movie.
I don’t have the software to edit it, I will search for it.
The good news is, its running over 1000 HZ!!

[Mark]

Don't shoot me but everyone keeps making these very small pulsejets running on acetylene. It might be a lot of fun to see what frequency you could get a mini jam jar to run or just a length of pipe perhaps can be coaxed to build feedback and run somewhere inbetween a jam jar and a pulsejet with the perky acetylene which is so forgiving and easy to do these kinds of small engines with.
Don't make me have to try it first! ha
Acetylene is a race horse.
Mark