5Vdc from 48Vdc - Options?

Yes, (I did see the smiley) but a 4 cycle engine take 720deg per full circle so a spark every 360 degrees is necessary for each pair of cylinders in a convetional inline 2 or 4 cylinder layout.

Yes, I figured that out about 5 minutes after I posted, and realized that it wasn't a typo.

snipped-for-privacy@NOT.AT.Arargh.com escribió:

In other words, a 4 cycle engine has spin 1/2. (Sorry, I couldn't resist it)

Let me draw you a picture so we both understand what the other is talking about...

Do you understand the mechanism that causes the breakdown voltage to increase when the gases are compressed? I suppose that in the presence of the electric field each molecule forms a dipole reducing the field locally. With more molecules in the path of the electric field, it might be that each molecule sees a smaller electric field, but I can't say that for certain since I expect the applied field to be much larger than the local fields. But I guess it is reasonable that the molecules are close enough together that the local fields nearly cancel the applied field.

Sounds good, but is that how it works?

Rick

t -

I like the gudgeon (wrist) pin.

Apparently this can cause major problems a high altitude. Some equipment is rated for maximum altitude operation based on potential of arcing taking place with the consequential damage to electrodes as well as issues with depostion of metal vapour on circuitry.

My wild-ass guess would be that since the mean free path decreases, it would take more energy to blast an electron through.

Thanks for the link. But that didn't really explain much. It gave a formula and sort of waved hands over the term "secondary emission".

Rick

at

Ok, I won't say that isn't on target, but what exactly is mean free path? Is that the average distance an electron travels without hitting something? I would expect that *not* to be important in this case. Mean free path would affect the speed of electron motion, but how would it affect the breakdown voltage?

I suppose it might determine the average energy of a collision and therefor the likelihood of a secondary electron emission? That might make some sense.

Rick

You didn't run a speel chick on that diagrim, didja? It's "dissipated", not "dissapated".

;)

Sorry, couldn't resist. I'm a grumpy old geek too.

I *love* this newsgroup ;). Despite farting around with ignition systems (mechanical vs. electronic) on British bikes (BSA, AJS, Triumph, mostly singles and twins) [1] far too many years ago to admit to, I'm finding this diversion utterly fascinating ;). And finding I know nuffink, which is not unusual ;).

Steve

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If your statement about impedance vs pressure is accurate, that has to be the mechanism. I don't know. If the relationship is opposite, the plugs have to be wired in parallel, and again only the appropriate one will go off.

... snip ...

I've graduated through several Austins, Hillmans, Volvos, VWs, Mitsubishis, Subarus, Hondas to a Ford (Escort). I don't count the GM machines, which were disasters. I no longer ride, but all my bikes had magneto ignition (including a Douglas and a BMW). My wife got a Honda with electric starter and a coil. (Look up the Douglas - great bike except the Lucas electrics).

Even if the compressed air-fuel mixture has a lower breakdown voltage, they plugs do not have to be wired in parallel. I just can't see putting plugs in parallel because of potential problems causing two plugs to misfire rather than just one. In that situation I expect they would add a center tap to the coil and in essence treat the coil as two coils that fire from the same control.

Rick

I belong to a model engine builders club...

And we have had builders try to run 2 plugs in parallel. It doesn't work, the exhaust plug breaks down and fires first, hogging all the current.

OTOH, my Subaru works just fine wired as I illustrated.

Two weekends ago a member showed us his ignition test stand. He had a small chamber for a spark plug that he could pressurize with air to simulate the required breakdown conditions inside an engine.

Here is some meat...

ns

on

ave

That is an interesting curve. Is the curve truly only dependent on the product of pressure and gap distance? I would expect the point of the curve to be sensitive to the pressure, but less so to the gap distance. The knee being at a certain pressure, gap product value says to me that the knee is produced by a certain number of molecules being in the gap regardless of the distance.

Of course, I don't really understand the mechanism, so I guess I shouldn't expect much...

Rick

Allright. I'm convinced.

I was going to mention the curve as well, but its old and very incomplete and I'm honestly out of my depth on fuller aspects of this subject and figured I'd better let someone else discuss it.

I do know, because I've had email exchanges a few years ago with one of the few experts around on the subject, that plasma descriptions require at least two spatial and one time dimension of PDEs, coupled to at least 6-dim ODEs in order to apprehend with modern accuracy. Plus radiation transport and atomic interactions, which complicate things further. I'm told you can do a fair amount with global rate equations which assume spatially averaged densities for the charged particles and neutral atoms and molecules, excited and metastable states. He added that there is an intermediate text by Lieberman and Lichtenberg, called "Principles of Plasma Discharges and Materials Processing," out of John Wiley and Sons, which does a good treatment of the fundamentals of discharges, collisions, DC and RF discharges.

Jon