Spark plug tech question?

[MikDee]

Ok, lets see if anyone can give me a logical answer to this one?

Basically, most all vehicles, auto, marine, & off road, today have a negative ground system, I am led to believe then that when a spark plug fires, the spark travels from the side electrode (negative/ground), to the center electrode (positive/power), on a negative ground system. This appears to be the case, but doesn't seem logical to me, as I always pictured in my mind, it firing from the center electrode to the side? and figuring this way it would work better!

 

[ThumbPkr]

Re: Spark plug tech question?

Electrons flow from negative to positive,basic DC theory using the righthand rule you can predict the north and south poles of a coil conducting DC current to prove the theory.By making a fist with the electrons flowing into the tips of your fingers your thumb will be pointing to the north (positive) pole of the coil.
I would think that the negative ground was intentional to inhibit transfer of electrode material during the life of the plug but that is a function of other circuit factors such as resonance which is also designed into the circuit.Ron G

 

[Dunaruna]

Re: Spark plug tech question?

Me thinks you are referring to a waste spark ignition system. One coil fires 2 cylinders simultaneously, one of the cylinders is on the compression stroke and it receives a conventional positive to negative induced current flow, the other cylinder (it's partner) is on the exhaust stroke and it receives a negative to positive induced current flow, but it is wasted, it does nothing.

On a conventional single coil motor, the secondary induced circuit flows positive to negative.

Mother nature sets the rules for electron flow, negative to positive, the difference here is that it is not induced.

 

[MikDee]

Re: Spark plug tech question?

That's the point, current always flows from the negative to the positive pole, meaning, the spark plug wire delivers a positive spark, and the spark plug itself is grounded negative. So the way I figure it, it fires from the side electrode to the center electrode, No?
It seems to me, that it would work better if all vehicles were a positive ground.

 

[JustJason]

Re: Spark plug tech question?

2 Different theorys Mikdee.

Conventional theory says positive runs to negative.

Electron theory says negative runs to positive.

It is still theory, and not law. And technically both theorys are interchangable 99% of the time.
None of that really matters though, as all electricity runs in loops.

Spark plugs fire from the center electrode, to the grounding tip. The only way I guess I can "prove" that statement is with this. If you take and old worn plug, It is the center electrode that wears down, and if there are deposits on the plug, it is always on the grounding tip.

Another way to look at it is like this. It takes 20+ thousand volts (DC) to fire the plug (20KVDC). The voltage comes from the coil, shoots down the wire, jumps the gap to the tip, and goes back to the batterys ground.
If it was the other way around, the coil would have to induce 20+KVDC to the block itself, and something else would have to switch that voltage on/off to each plug.

 

[MikDee]

Re: Spark plug tech question?

DC current runs from negative to positive.

jason, with all due respect, I'm still not convinced that a spark plug fires from the center tip, it seems to make sense it's the other way around, because the sparking towards it from the side electrode, would appear to wear away the center electrode.

 

[JustJason]

Re: Spark plug tech question?

DC current runs from negative to positive.

Does it?

In order to fire from the side electrode.... all the voltage potential would have to be on the block itself.

 

[ThumbPkr]

Re: Spark plug tech question?

The block is just as much a part of the circuit as the center electrode is,it is the difference in potential that causes the arc.The current still flows from negative to positive.Actually,when the coil creates the spark the field is collapsing,not building in the secondary.I am led to believe that the reason it was designed that way is to control the transfer of material between the contact points.That may have changed with the introduction of solid state devices but I think that the circuit reactance could be better controlled with the collapsing field just as before because that is what controls the pitting and erosion of the spark surfaces.Ron G

 

[v1_0]

Re: Spark plug tech question?

Ok, lets see if anyone can give me a logical answer to this one?

Basically, most all vehicles, auto, marine, & off road, today have a negative ground system, I am led to believe then that when a spark plug fires, the spark travels from the side electrode (negative/ground), to the center electrode (positive/power), on a negative ground system. This appears to be the case, but doesn't seem logical to me, as I always pictured in my mind, it firing from the center electrode to the side? and figuring this way it would work better!

Why should it work better one way or the other? The spark will occur at the 'best' point either way. The fuel/air mixture doesn't care. The sparkplug doesn't care.

I've heard that some cars were wired with positive grounding, even as late as the 50's. So, it's been done - but seems to me that there wasn't any, or enough, advantage to doing it that way so it just died out.

As for current vehicles - all of your stuff is now wired for a negative ground. That is, the stuff that cares: tachometer, alternator, etc. Now if you went with a positive ground then you couldn't use off the shelf components, or at least you'd have to wire things to take this into consideration.

 

[v1_0]

Re: Spark plug tech question?

Does it?

In order to fire from the side electrode.... all the voltage potential would have to be on the block itself.

Well... a *path* needs to exist. The block is part of that path. (Either way, in fact - positive ground, or negative ground). From an electrical perspective, the block is equivilent to a wire.

 

[puddle jumper]

Re: Spark plug tech question?

JustJason is right the spark does jump from the center electrode to the ground side of the spark plug. Think of it as lightning. The charged sky (your ignition system) becomes loaded with a positive charge, it needs a path to ground ( your engine block). The volt of lightning finds the easiest path to ground(your spark plug). You have to have the positive charge in a modern ignition system to have spark. The colapsing of the coil creats the positive charge or push of electrons. The engine block can not on its own, with out some kind of something create the charge.

did i make any sence :redface:

 

[MikDee]

Re: Spark plug tech question?

JustJason is right the spark does jump from the center electrode to the ground side of the spark plug. Think of it as lightning. The charged sky (your ignition system) becomes loaded with a positive charge, it needs a path to ground ( your engine block). The volt of lightning finds the easiest path to ground(your spark plug). You have to have the positive charge in a modern ignition system to have spark. The colapsing of the coil creats the positive charge or push of electrons. The engine block can not on its own, with out some kind of something create the charge.

did i make any sence :redface:

No,,,

v1-o

Fords were positive ground in the 50's, and I think into the 60's too?
You've each gone off on a tangent going over my head giving me electrical theory
But nobody has proved, or can prove that the spark jumps from the center electrode to the side electrode, in a negative ground system. A spark plug with it's copper, or exotic metal core would appear to fire better, stronger, more consistantly, if it were to fire this way, rather then through it's ordinary steel (negative) body, to the exotic (positive) metal core.

 

[sportsmanphil]

Re: Spark plug tech question?

I dig discussions like this.

The way it was described to me that made the most sense:


The current has to go through a path (between pos and neg)

The 'path' is found from neg to positive first, once that is established the current travels through that path from positive to negative.

 

[MikDee]

Re: Spark plug tech question?

I dig discussions like this.

The way it was described to me that made the most sense:


The current has to go through a path (between pos and neg)

The 'path' is found from neg to positive first, once that is established the current travels through that path from positive to negative.

Isn't that the theory of AC current? Alternating continually from plus, to minus, not DC (direct current)?

 

[Fun Times]

Re: Spark plug tech question?

DC current runs from negative to positive.

jason, with all due respect, I'm still not convinced that a spark plug fires from the center tip, it seems to make sense it's the other way around, because the sparking towards it from the side electrode, would appear to wear away the center electrode.

Have you ever watched a spark plug fire before

 

[bruceb58]

Re: Spark plug tech question?

Electron flow is the opposite of what we call electrical current.

 

[JustJason]

Re: Spark plug tech question?

I guess this is the easiest way to "prove" it.

Take any old engine and run it without changing the plugs until the motor just won't run anymore.

Pull the plugs out and look at them. It's the center electrode that is worn down, it is missing material. It's missing material because every time that plug fires, on a microscopic scale, it takes a little bit of the electrode with it.
Now have a look at the ground tang. It's usually covered with deposits. Sometimes they can have alot of deposits on them. Those deposits are/were what was the center electrode.

Now if the plug fired the other way around. Then it would be the ground tang that would be worn down and missing material, and the center electrode would be covered with deposits.

Does that make it any easier Mikdee?

 

[MikDee]

Re: Spark plug tech question?

I guess this is the easiest way to "prove" it.

Take any old engine and run it without changing the plugs until the motor just won't run anymore.

Pull the plugs out and look at them. It's the center electrode that is worn down, it is missing material. It's missing material because every time that plug fires, on a microscopic scale, it takes a little bit of the electrode with it.
Now have a look at the ground tang. It's usually covered with deposits. Sometimes they can have alot of deposits on them. Those deposits are/were what was the center electrode.

Now if the plug fired the other way around. Then it would be the ground tang that would be worn down and missing material, and the center electrode would be covered with deposits.

Does that make it any easier Mikdee?

So, basically you're saying the laws of electricity don't apply here?

Sure I've noticed a worn down center electrode, but never a buildup on the side electrode? Usually the build up's are on the ceramic part.

So, then in contrast I can say the center electrode is worn away, because of the constant spark firing towards it from the side (ground) electrode

 

[bruceb58]

Re: Spark plug tech question?

Now I am getting confused!

 

[dolluper]

Re: Spark plug tech question?

Your voltage goes down the center electrode and jumps the gap...reason for timming , proper gap,and a rotor....if the plug is not grounded to the block voltage does not jump the gap