Solid State Ignition Coil Operation? 2

[triage]

I had to replace an ignition coil on my vehicle and realized for a six cylinder engine, only three ignition coils are uses, wherein the connection diagram has each end of the secondary going to a separate spark plug.

To me this implies that both plugs will fire at the same time, using the engine block as ground.

Is this correct?
Do two cylinders cycle in pairs, or is one cylinder spark wasted?

 

[TurboXS]

This is a "waste spark" setup and is used on a number of cars.

Yes both spark plugs do fire at once.

http://www.procarcare.com/icarumba/...icar_resourcecenter_encyclopedia_ignition.asp

 

[Fabrico]

Operation:
The ignition coil fires two spark plugs simultaneously, one on the compression stroke and one on the exhaust stroke.

Effective Spark:
When a piston is on compression stroke, most of the ignition coil's available current jumps the gap of the spark plug firing from the center electrode to side electrode, because the resistance is low.

Wasted Spark:
When the companion piston is on exhaust stroke, the spark is wasted. Very little coil energy is wasted. The companion plug fires from the side electrode to the center electrode.

 

[triage]

Thanks for the interesting info.

To fully understand the configuration, I suppose that
the primary is energized at a time which will produce in the secondary, a good spark (center electrode to case) for spark plug A (which is in compression) and a waste spark for plug B (which is in exhaust), then time the primary
cutout, to give a secondary reversed polarity good spark to plug B and a waste spark to plug A.

Have I got it???

 

[Fabrico]

Perhaps someone more into electronic design can answer that.

Below is a link to a pretty good blurb on lots of things ignition, combustion, and avoiding B/S. There is some info on DIS ignition systems right about in the middle of it all. Enjoy and don't forget to bring a cup of cofee.

http://toyotaperformance.com/ign_combust.htm

 

[PLeon]

Firing a plug is easier when cruising than under full throttle. Is the spark on the wasted side stronger than the effective side?

 

[pmrobert]

The wasted spark propagates through the air gap through exhaust gas, a hot, low pressure gas full of combustion products including water, partially ionized, reactive chemical species, etc.. It typically is much easier for the spark to jump the wasted gap due to relatively low resistance as compared to the working side. I'm pretty sure more energy would be emitted from the non-wasted spark due to the potential required to jump that gap being quite larger. So I don't know if "stronger" is a description for this or not.

 

[Warpspeed]

When the primary is energized is not when the plug fires. It fires when the current to the primary is abruptly cut off.

The magnetic flux that has built up in the core suddenly collapses, producing a very high voltage in both primary and secondary windings. With waste spark systems the secondary winding has two ends, and the centre of the winding is connected to the primary, (as in a "normal" ignition coil).

When a waste spark coil fires, one plug receives a positive high voltage, and the other a negative high voltage. So half the spark plugs in the engine must always fire with reverse polarity. That is a disadvantage, but only a slight disadvantage. In practice it works fine.

The electronic modules that drive these coils are highly sophisticated. They automatically adjust dwell time, automatically correct for battery voltage, and protect the coil from perhaps burning out if the ignition is inadvertently left on without the engine running.

 

[dgallup]

Warpspeed is right, half the plugs have reverse polarity. OE Ford plugs have platinum on the center electrode on one bank and on the side electrode for the other bank. You would think the extra cost of having different parts and having to install them correctly would wipe out any savings. Especially since the service plugs have a third part number with platinum on BOTH electrodes.

 

[GregLocock]

Weird thing about the economies of scale - at a certain point they stop. For instance, there is a necessary minimum cost per injection moulded part since, no matter what the production volume, a given mould only has a certain life.

So it may be as cheap to have three designs of spark plug as just one. Or they may have screwed up.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[carnage1]

After the week I have had at work I can tell you why there are three part numbers for fords plugs. They save enough money by coating just one of the sides in platnum to justify it at the factroy, and someone is smart enough to realise that no mater how hard you try someone will figure out a way to put the plugs on the wrong sides after it leaves the assembly plant. hence the coating on both sides.
(I wont bore you good people with the details about my week but let me assure you my belief that peoples stupidity can be limitless was reafirmed. [frown])

 

[Warpspeed]

How about fitting round plugs on one side, and square plugs on the other ?

 

[waross]

Round plug in a square hole? I like it.

 

[GregLocock]

Then we'd need a tool to remove the square plugs from the round holes, and vice versa.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

An oxy torch works wonders at removing difficult to remove metal parts, however the installation of the replacement parts then becomes problematic.

It needs to be considered if these problems would outweigh the problem of ensuring a few poorly trained individuals in the parts replacement process can outperform well trained monkeys.

Regards

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