10 replies to this topic

[Magoo]

Here's an amusing humbug: a V8 engine in which all eight spark plugs fire at the same time. 

 

Story link:

 

The 1965 Kaehni Ignition Mystery

 

 

 

 

 

 

[PJGD]

This reminds me that there was a flat twin 2-stroke engine back in the 1920's(?) that had a single magneto that fired both plugs in the conventional manner at the same time.  The secret is that the magneto was sitting on a block of wood so that it was insulated from the engine, thus the HT lead went from the magneto to one of the plugs as normal but the circuit was made through the engine structure to the other plug where it jumped the gap backwards to the center electrode and then from that spark plug to the magneto body.  One assumes that the magneto-generated voltage had to be perhaps twice as high as normal to jump two typical gaps at once?

[gruntguru]

This reminds me that there was a flat twin 2-stroke engine back in the 1920's(?) that had a single magneto that fired both plugs in the conventional manner at the same time.  The secret is that the magneto was sitting on a block of wood so that it was insulated from the engine, thus the HT lead went from the magneto to one of the plugs as normal but the circuit was made through the engine structure to the other plug where it jumped the gap backwards to the center electrode and then from that spark plug to the magneto body.  One assumes that the magneto-generated voltage had to be perhaps twice as high as normal to jump two typical gaps at once?

 

Isn't that the principle of all waste-spark ignition systems? Two plugs in series (BTW Magoo the Kaehni system is parallel not series), one on compression the other on exhaust?

For the simultaneous-firing two stroke both cylinders are on compression of course.

Yes that would require double the coil voltage.  4 stroke waste-spark not so because the lower pressure during the exhaust stroke requires a much lower voltage.

[gruntguru]

Amazing ignition system. Rudimentary control over ignition timing the big drawback.

High compression, low octane, early ignition . . what could possibly go wrong.

[GregThomas]

This reminds me that there was a flat twin 2-stroke engine back in the 1920's(?) that had a single magneto that fired both plugs in the conventional manner at the same time.  The secret is that the magneto was sitting on a block of wood so that it was insulated from the engine, thus the HT lead went from the magneto to one of the plugs as normal but the circuit was made through the engine structure to the other plug where it jumped the gap backwards to the center electrode and then from that spark plug to the magneto body.  One assumes that the magneto-generated voltage had to be perhaps twice as high as normal to jump two typical gaps at once?

 

A normal mag in good condition will jump two gaps. Insulating the mag body as above is one way to do it.There are i believe twin-spark mags - simultaneous firing.

 

What is common now are twin lead coils. The spark path is - center electrode to one plug body, Another plug body to center electrode. 

Some twostroke twins with 180 degree cranks fire both cylinders at both TDC and BDC via a twin lead coil. Obviously only the TDC spark fires anything.

[gruntguru]

 . . Some twostroke twins with 180 degree cranks fire both cylinders at both TDC and BDC via a twin lead coil. Obviously only the TDC spark fires anything.

 

You would want to fire the waste spark before the transfer port starts flowing!

[BRG]

This reminds me that there was a flat twin 2-stroke engine back in the 1920's(?) that had a single magneto that fired both plugs in the conventional manner at the same time.  The secret is that the magneto was sitting on a block of wood so that it was insulated from the engine, thus the HT lead went from the magneto to one of the plugs as normal but the circuit was made through the engine structure to the other plug where it jumped the gap backwards to the center electrode and then from that spark plug to the magneto body.  One assumes that the magneto-generated voltage had to be perhaps twice as high as normal to jump two typical gaps at once?

I think the flat two aircooled Citroen 2CV engine fires both plugs every stroke.  One of the tricks of maintaining them in good starting order was to replace the plugs regularly (back in the days when plugs burnt out at 10,000 miles or so)

[10kDA]

In principle, at least at the plugs, similar to a shower-of-sparks ignition system which can be found on numerous aircraft. It's used during starting but does not run continuously as this setup does.

 

 

 

Amazing ignition system. Rudimentary control over ignition timing the big drawback.

High compression, low octane, early ignition . . what could possibly go wrong.

I'm thinking anybody running a nailhead with the pictured induction & exhaust has probably also bumped the compression enough to know premium gas is required. Back in the day high octane gas was ubiquitous in the US.

[10kDA]

I think the flat two aircooled Citroen 2CV engine fires both plugs every stroke.  One of the tricks of maintaining them in good starting order was to replace the plugs regularly (back in the days when plugs burnt out at 10,000 miles or so)

Do BMW flat twin motorcycle engines fire both at once also?

[GregThomas]

Do BMW flat twin motorcycle engines fire both at once also?

 

Last one i worked on had the ignition driven off the end of the cam. So the pushrod ones,no.

 

The late cam in head motors have crank triggered ignition so it depends what was the cheapest ignition they could source....

[Magoo]

(BTW Magoo the Kaehni system is parallel not series), 

 

Quite right, correction made. I don't even know what that was about.