CDI + inductive ignition *combined*

[Circlotron]

Guys argue back and forth about which kind of ignition is better, CDI or inductive discharge. The fact is, they both have advantages and disadvantages. Capacitor discharge has super high voltage and current but very short duration. Inductive has more modest voltage and current but typically ten times the arc duration.

What I have done is make an add-on inductive box + coil that you attach to your existing MSD6 series or Digital 7-plus (not other 7 or 8 series). The idea is that the CDI punches through high boost pressure and wide plug gaps and establishes a conductive path in the form of a spark, then before the super short CDI spark goes out, the inductive fires and pours energy into that spark channel for a relatively long time. Each ignition type does what it does best with no downside. A marriage made in heaven.

First pic shows an MSD6 sparking across a HEI test plug and very slightly after the first spark begins, an inductive spark is shoved through the path that has just been established by the CDI. There is also a further five CDI sparks after the inductive has run out. You can easily see the difference. The MSD6 CDI sparks were measured at 38 mJ and the inductive at 150mJ.



Second pic shows the spark current and duration of the CDI and inductive combination. CDI spark by itself is 360mA for 0.15mS and inductive by itself is 150mA for 1.6mS. Look at the area under the curve for both sparks BTW. The MSD is making a "chirp" at low rpm, not running at high speed here.



Third pic shows millijoules energy output. Purple trace (50mJ / div) shows each CDI spark bumping the energy by 38mJ and the single inductive spark by 150mJ. The energy was measured putting the coil outputs to 1600 volts of zener diode in series with a 100 ohm resistor and measuring the integral of volts x milliamps over time. As you can see, the inductive really adds to the total energy.



If there is enough interest in this thing it will become a commercial product. Just want to get people's opinions. I have designed name-brand ignition systems in the past so this is not pie-in-the-sky.

[Chipped tooth]

Track test this with some more results

I'm sure there is a market as long as it's proven and reliable!

[user-23911]

It's called an HKS DLI....it's already been done.

They're not very good anyway.


It's all "trickery".
Looking at a spark tells you nothing because your eyes tell lies just like your ears do.
The commonly accepted way of measuring energy is all wrong because a spark , it's no different from a flourescent light or a welder, it's got a negative impedence.
Negative impedence means that once you establish the spark, the current starts flowing, the voltage across the gap decreases, current increases more, voltage across gap decreases more, current increases more until there's no longer enough stored energy to maintain the voltage....then the current decreases until the spark goes out.
Nor can you reliably measure anything on the secondary side of a coil without shunting the signal due to the added capacitance. You get errors of greater than 50% due to the added capacitance.

What you DON'T want is a brighter spark, you want it to last as long as possible.


It's relatively easy to measure stored energy either in a coil or in a capacitor.
As a general rule With a CDI, you'll lose 50% of the energy going from the capacitor to the coil, you'll lose another 50% of that going from the primary to secondary, you'll lose more still before it gets to the plug.
With an inductive ignition, you'll lose 50% again going from primary to secondary , lose more again before the plug.


So any quoted number as far as energy storage goes are really meaningless.


Like lots of other things to do with cars.......what you think is going on........ isn't.

[user-23911]

The easiest, cheapest, most effective ignition modification is to use wasted spark twin tower coils, daisy chain them up.

Using 2 of them roughly doubles the stored energy AND the max available voltage.
Using 3 of them triples it.
Using 4 of them........OK space will be a bit tight. It might kill you too.

It'll never catch on because it's pretty much free and as we all know.........you always get what you pay for?
There's no money in this for anyone except for the junk yards.

https://www.youtube.com/watch?v=2ig8wQ9uRvc

[Circlotron]

Looking at a spark tells you nothing because your eyes tell lies just like your ears do.

I'll post a video when I can of the sparks going on the test plug in the picture. At about 400Hz (6000rpm) with the 38mJ CDI sparks only, the sparks just buzz away merrily. Add the 150mJ inductive portion and after 20 seconds or so the centre insulator glows yellow hot. That means considerable extra energy is being put into the spark.

The commonly accepted way of measuring energy is all wrong because a spark , it's no different from a flourescent light or a welder, it's got a negative impedence. Negative impedence means that once you establish the spark, the current starts flowing, the voltage across the gap decreases, current increases more, voltage across gap decreases more, current increases more until there's no longer enough stored energy to maintain the voltage....then the current decreases until the spark goes out.

Current does not increase more with an inductive ignition feeding a spark gap because the secondary is a current source. Provided it can throw the voltage high enough it will give the same current if the load resistance increases, just for a correspondingly shorter duration. It will give the same current even into a short circuit. It will just take way longer to ramp down to zero.

Nor can you reliably measure anything on the secondary side of a coil without shunting the signal due to the added capacitance. You get errors of greater than 50% due to the added capacitance.

In what I have posted we are measuring the energy with the secondary voltage clamped at about 1600V, roughly what the voltage across a plug drops to after it strikes. Any energy absorbed by capacitance of a test setup would vary with the square of the voltage, as you know. Only letting the voltage rise to 1600V compared to say 30kV reduces the energy absorbed by the capacitance of the test setup by a factor of over 350:1. It can therefore reasonably be ignored.

What you DON'T want is a brighter spark, you want it to last as long as possible.

This is aiming for both.

As a general rule With a CDI, you'll lose 50% of the energy going from the capacitor to the coil, you'll lose another 50% of that going from the primary to secondary, you'll lose more still before it gets to the plug.
With an inductive ignition, you'll lose 50% again going from primary to secondary , lose more again before the plug.
So any quoted number as far as energy storage goes are really meaningless.

Fot the most part I agree with those figures
I wasn't talking about energy storage, I was talking about actual measured energy delivered to the load, the plug gap, regardless of how much might have been stored but lost somewhere along the way.
Thank you for your observations joe 90.

[Circlotron]

The easiest, cheapest, most effective ignition modification is to use wasted spark twin tower coils, daisy chain them up.

Using 2 of them roughly doubles the stored energy AND the max available voltage.
Using 3 of them triples it.
Using 4 of them........OK space will be a bit tight. It might kill you too.

It'll never catch on because it's pretty much free and as we all know.........you always get what you pay for?
There's no money in this for anyone except for the junk yards.

https://www.youtube.com/watch?v=2ig8wQ9uRvc

Have you ever tried using a wasted spark coil with the negative HV terminal going to the plug as usual and the positive HV terminal connected to a negative 500-1000V DC supply? Positive end of supply is grounded. As the DC voltage of the supply is raised the spark duration gets longer and longer. If you go too far (~1500VDC) the spark simply does not go out! Try it, you will like it.

[Circlotron]

Some time ago I summarised the benefit of long duration sparks like this: The mixture igniting is not just a black and white issue, as in, it ignited so there was enough spark and more will not improve things. The way I see it, things start as a tiny little bubble of flame, just like a baby in mummy's tummy. You want that bub(ble) to grow at a predictable rate so that by the time TDC is reached, the squish area pinches that now somewhat larger flame bubble into the remainder of the yet to be burnt mixture and things really get moving so that you reach peak pressure a little after TDC. Trouble is, it is a really rough environment and sometimes our little flame bubble pauses, staggers and stumbles on it growth to glory. Particularly when the bubble is very small and delicate and entirely between the faces of the plug electrodes, they can suck heat out of the bubble in the same way the combustion chamber quench area operates. A CDI just gives the bubble a short sharp shove and then it is all on it's lonesome in the wilderness. An inductive discharge spark keeps feeding heat into the flame bubble while it is growing and so probably contributes to it's orderly and predictable expansion. It does not make the good firings better so much as it makes the bad ones good. So it follows that under ideal conditions there would be no difference between CDI and inductive because IIRC gasoline vapour only needs about 2 millijoules to ignite it, but in the real world things can be far from ideal. Crazy turbulence, blobs of liquid fuel (especially if alcohol or with cold nitrous) exhaust gas dilution etc etc. That little flame bubble needs it's hand held along the way, not just booted in the bum and that's it.

[Circlotron]

It's called an HKS DLI....it's already been done.
They're not very good anyway.

HKS DLI looks exactly like MSD Stacker.
https://m.youtube.com/watch?v=n7-IaRRDlDQ
My one is different.

[les327]

I remember the Jacobs adaptive spark theory, does this method have merit? Has it been inproved or thrown in the dust bin of history? Just thinking, i recall reading his book on ignition and found it very interesting

[CharlieB53]

It would be interesting if someone could afford to dyno test the different ignitions to compare, to see what, or if, there is any measurable differences in HP and T curves. These tests maybe should be repeated on a few different engines from near stock to very much non-stock so we may see if the ignition differences make a worthwhile improvement at the various build levels.

If I win the powerball this weekend I would gladly volunteer.

[RevTheory]

If I win the powerball this weekend I would gladly volunteer.

Don't even THINK about it!

[Dan Timberlake]

Some of the fancy ignitions in previous eras claimed they would be able to light leaner mixtures than any other.

http://fireintheholedist.com/pulsePlugs.htm
http://www.boston.com/bostonglobe/obitu ... rn_engine/

Dr Ward's various patents get referenced from time to time.

7 times in this one alone.
http://www.google.com/patents/US20130104861

[Circlotron]

I remember the Jacobs adaptive spark theory, does this method have merit? Has it been inproved or thrown in the dust bin of history? Just thinking, i recall reading his book on ignition and found it very interesting

What is the name of his book? Their advertising blurb doesn't tell you anything useful.

[les327]

I remember the Jacobs adaptive spark theory, does this method have merit? Has it been inproved or thrown in the dust bin of history? Just thinking, i recall reading his book on ignition and found it very interesting

What is the name of his book? Their advertising blurb doesn't tell you anything useful.

,
The Doctors step by step guide guide to optimizing your igntion.

[Circlotron]

^^ Might try and find a copy and see if there is anything useful in it, although just because something is in print doesn't mean it is 100% fact, especially if money is involved. Almost completely hopeless trying to find anything useful on the interweb regards ignition stuff. Even many engineering papers turn out to be half assed tertiary student's school projects just regurgitating the same old assumptions. The only way is to spend several decades figuring it out yourself, and even then most people don't believe you. /rant over.