Tests of CDI Ignition Modules

[dsage]

Don:
The neighbours must love you with that Spark gap transmitter with large antenna wires.
A couple of questions:
I can understand the 12k resistor in order to get reasonable attenuation etc for your scope but is that a typical value for say a resistor sparkplug wire or a resistor plug? I don't know. Resistor wire is so many ohms per foot so it can vary. I don't know what a resistor plug itself is.
Not that it really matters the effect is what counts.
On page three I'm perplex why "arc initiation - No R", is just ringing about the zero voltage point. Doesn't that indicate that the arc did not initiate?
If the arc was initiated I would have thought the voltage would be regulated at some positive value by arc current flow though the load. If you look at the waveform with the resistor, it holds a voltage about 5000 meaning that there is some current flow .

Good work. I'm glad you are performing these experiments. It's something I've always wanted to do but never got down to all the work.

 

[dsage]

Also. What are the blue devices (and values) you have stacked up in the tube?
It wasn't until I zoomed the picture that I realized the very professional setup you have there with proper mounting with test points and coax cable etc.
Very nice.

 

[DKGrimm]

On page three I'm perplex why "arc initiation - No R", is just ringing about the zero voltage point. Doesn't that indicate that the arc did not initiate?
If the arc was initiated I would have thought the voltage would be regulated at some positive value by arc current flow though the load. If you look at the waveform with the resistor, it holds a voltage about 5000 meaning that there is some current flow .

The secret is in the scale. Because the burst is such a high voltage the scale of this waveform is 50kv per division. It looks like a small little offset in the picture but the initial voltage for the arc is really about the same -- about a tenth of a division, 5000 volts. As to the ringout part, the time scale shows only a tiny part of the total. I see that in the picture it appears to be ringing about a zero (actually a negative) voltage at the end, but that is only the beginning of a much longer ringout during the arc, followed by a completely separate and larger ringout at a much lower frequency when the arc quenches.

 

[DKGrimm]

Also. What are the blue devices (and values) you have stacked up in the tube?

It's a frequency compensated divider. Those little blue things are capacitors paralleled across the resistors. All high voltage parts rated 10kv.

 

[DKGrimm]

I can understand the 12k resistor in order to get reasonable attenuation etc for your scope but is that a typical value for say a resistor sparkplug wire or a resistor plug?

I don't know. Just a guess that I chose for testing the effect. I chose resistance that was big enough to have a good damping effect but small enough to waste only about 20% of the total discharge energy. You are right to observe that using a resistor for damping to facilitate measurements does not mean it is necessary or even beneficial to use one in practice. I notice that Roy Sholl supplied a 1000-ohm resistor in his S/S kit that I bought several years ago, but I have seen so far that CDI discharges are much higher spark plug current for a shorter time. Most likely would need a lower resistance than a coil system.

 

[dsage]

Ok. I'll check out the waveforms again.
Wow, that's a pretty nice arrangement you've made there. Not sure I know what a frequency compensated divider is. Except maybe an elegant name for a voltage divider with a filter capacitor?
In any case, very nice work.

Edit:
I think we were typing at the same time. The resistor in car ignitions was usually for RF suppression for radio interference. Since Roy's more recent ignitions included a microprocessor maybe he added the resistor to suppress some interference he was getting with the processor? He was pretty successful I'd say because from my experience running a microprocessor even on the same bench as an ignition causes great havoc. I notice my fluke meter acts up now and then when too close to my ignition test setup.

 

[DKGrimm]

Ok. I'll check out the waveforms again.
Wow, that's a pretty nice arrangement you've made there. Not sure I know what a frequency compensated divider is. Except maybe an elegant name for a voltage divider with a filter capacitor?
In any case, very nice work.

Edit:
I think we were typing at the same time. The resistor in car ignitions was usually for RF suppression for radio interference. Since Roy's more recent ignitions included a microprocessor maybe he added the resistor to suppress some interference he was getting with the processor? He was pretty successful I'd say because from my experience running a microprocessor even on the same bench as an ignition causes great havoc. I notice my fluke meter acts up now and then when too close to my ignition test setup.

If you string a bunch of resistors together to make a high voltage resistance divider, stray capacitance will turn it into a low pass filter. Small bypass capacitors around each resistor can compensate for that.

 

[peterl95124]

Yes I have. The waveforms are pretty much textbook. You can look it up anywhere. See below. They can vary a lot. But the basics are always there.
The primary side is a reflection of the what's going on in the secondary. On the primary a 12v signal level followed by a ground dwell time where the coil in energized, a release of the ground followed by a large positive spike before ionization. There is a negative spike right after the positive one but that is before ionization in the spark plug gap where the actual energy causes an arc. That is the voltage level I mentioned before where either the transistor or IGBT suppresses the coil. If you suppress that at too low a level you are taking energy away from the spark to follow. Which is why an IGBT is superior to a regular bipolar transistor (higher breakdown voltage)
Once the plasm arc is formed (burn time) the mixture acts like a resistance with a pretty steady discharge of the coil (all above ground) Following that is ringing and decay when the burn extinguishes. The ring is caused by left over energy in the coil insufficient to maintain the burn time and looking for somewhere to go.
If that's where you are seeing a large spike then I would suspect that perhaps your spark plug gap is too large the mixture is too lean and won't fire or any number of things causing the burn to extinguish early leaving a lot of un-used energy in the coil.
There should be just minimal oscillations at the end and they should decay quickly because the coil should be pretty much out of energy if it was used up properly during the burn time.
The whole burn time and ringing etc. is very much dependant on what's going on in the cylinder. For instance the steady state height of the burn time above ground is indicative of how hard it is to start and maintain the arc. A higher line might be a lean mixture or the sparkplug gap is too wide or other factors.
The rise at the end of the burn time (shown below) indicates that the mixture is becoming lean (voltage rises - harder to burn) as the mixture is burned. The roughness in the burn time is due to turbulance in the cylinder affecting the smooth burning of the mixture.
I have never seen really large oscillations after the burn time as shown below. I just grabbed that picture quickly from the internet. They may have been illustrating a fault.
I suggest you research the waveforms. There is a lot to be learned about the workings / health of your engine "system".

Dave, both your waveform and DKGrimm's show a huge negative spike before the "burn time", that's the one I'm thinking about.
-Pete.

 

[DKGrimm]

Dave, both your waveform and DKGrimm's show a huge negative spike before the "burn time", that's the one I'm thinking about.
-Pete.

Don't mean to jump in on your question to Dave, but as I have it figured out the negative spike is actually a verrrry short burst of ringing driven by the avalanche breakdown of the spark itself. The top waveforms on the attachment on page 3 (post #79) show this burst expanded in time 20,000:1. A resistor at the spark plug reduces it but does not eliminate it. As to how much this feeds back and stresses the switch in the primary, that's kind of beyond my pay grade, but I'd guess that it could very well damage an unprotected semiconductor switch.

 

[HMEL]

Don't mean to jump in on your question to Dave, but as I have it figured out the negative spike is actually a verrrry short burst of ringing driven by the avalanche breakdown of the spark itself. The top waveforms on the attachment on page 3 (post #79) show this burst expanded in time 20,000:1. A resistor at the spark plug reduces it but does not eliminate it. As to how much this feeds back and stresses the switch in the primary, that's kind of beyond my pay grade, but I'd guess that it could very well damage an unprotected semiconductor switch.

I have been following this thread with great interest because I have a Bantam engine from about 1930 equipped with a set of points and the ability to retard or advance the ignition. I have an idea what it would take to get it to work but because of its age I have no confidence I could get it to work. For reference it had a 8 inch diameter prop on it.

So the first question is I know under pressure the energy to cross the gap is dependent on the gap size and the cylinder pressure. Aircraft has lots of research on this topic. So what should I expect to have at spark plug as a firing voltage?

Would it be possible to mimic the advance and retard of some of the systems you are testing? Looking for a way to fire the spark plug with original condition. Might not be doable. Could I use the original points to trigger such a circuit.?

If the rpm of the engine is high as you find in small aircraft engines how is the timing of the firing circuit done? It would seem to me that a few electrical tricks would need to be employed. Is there an rpm limit to some of these systems? I ask this because every capacitor has a charge time.

And do you have a recommendation of what type of system I should look at.

Thanks

No hurry on this as I have been looking at that thing for a few years. But felt this was an opportunity to gain insight, from an expert.

By the way I suspect the discharge in some of your systems does act like a lighting bolt first opening the gap and then current coming back due to the intense polarity formed. It would seem to me that grounding is extremely important in these ignition systems. Sort of like a spark gap transmitter which resonates with right settings.

HMEL

 

[DKGrimm]

So the first question is I know under pressure the energy to cross the gap is dependent on the gap size and the cylinder pressure. Aircraft has lots of research on this topic. So what should I expect to have at spark plug as a firing voltage?

Firing voltage will naturally go up with pressure. I will eventually run some tests to see how much, but I have no data now.

Would it be possible to mimic the advance and retard of some of the systems you are testing? Looking for a way to fire the spark plug with original condition. Might not be doable. Could I use the original points to trigger such a circuit.?

If the rpm of the engine is high as you find in small aircraft engines how is the timing of the firing circuit done? It would seem to me that a few electrical tricks would need to be employed. Is there an rpm limit to some of these systems? I ask this because every capacitor has a charge time.

There are a bunch of people on threads like "Model Engine Ignition" who are pursuing things like auto-advance and timing with microprocessors. There is a lot of flexibility approaching it this way. Never looked at this aspect of it myself.

And do you have a recommendation of what type of system I should look at.

Not yet. I got into this because I was having a problem with my scratch-designed four-cylinder engine. I hope eventually to find an ignition driver that could give more spark energy than the typical CDI module does now, but something that is affordable, available, small, light, and can run on a small battery. Just getting started answering those questions.

By the way I suspect the discharge in some of your systems does act like a lighting bolt first opening the gap and then current coming back due to the intense polarity formed. It would seem to me that grounding is extremely important in these ignition systems. Sort of like a spark gap transmitter which resonates with right settings.

Part of my career was to design and test lightning protection for aircraft. I'm finding that a spark in a spark plug is pretty much the same animal as a lightning strike.

 

[petertha]

Sorry if this is detracting the main theme of this post. If so, just ignore. But I'm wondering with all the electrical testing equipment wizardry & knowledge, is there any way to qualify that the ignition wires & plug elbow/boot has to be as big as they always seem to be. I suspect the answer is yes for electrical reasons & aesthetics comes second. Its just that we can obtain nice, small, scale looking spark plugs in 1/4-32 format (about same size as an RC glow plug) but then seems like we must install the obligatory firehose cable. Not too bad on a larger displacement engine but rather unflattering & busy plumbing on a smaller multi-cylinder engine.

Is the (I assume) braided shielding to protect for RC noise interference & could be eliminated to reveal a smaller actual wire for a non-RC (stationary bench) engine for example?

I should know this but do the elbow caps do anything electrically other than secure the wire to the terminal & keep the wire assembly orientated in position? (ie. there is no ground/return contact to the hex part of plug, its just a locking mechanism?)

 

[HMEL]

Firing voltage will naturally go up with pressure. I will eventually run some tests to see how much, but I have no data now.


There are a bunch of people on threads like "Model Engine Ignition" who are pursuing things like auto-advance and timing with microprocessors. There is a lot of flexibility approaching it this way. Never looked at this aspect of it myself.

Not yet. I got into this because I was having a problem with my scratch-designed four-cylinder engine. I hope eventually to find an ignition driver that could give more spark energy than the typical CDI module does now, but something that is affordable, available, small, light, and can run on a small battery. Just getting started answering those questions.

Part of my career was to design and test lightning protection for aircraft. I'm finding that a spark in a spark plug is pretty much the same animal as a lightning strik

Thanks for the reply,, Keep up the interesting research
HMEL

 

[dsage]

Sorry if this is detracting the main theme of this post. If so, just ignore. But I'm wondering with all the electrical testing equipment wizardry & knowledge, is there any way to qualify that the ignition wires & plug elbow/boot has to be as big as they always seem to be. I suspect the answer is yes for electrical reasons & aesthetics comes second. Its just that we can obtain nice, small, scale looking spark plugs in 1/4-32 format (about same size as an RC glow plug) but then seems like we must install the obligatory firehose cable. Not too bad on a larger displacement engine but rather unflattering & busy plumbing on a smaller multi-cylinder engine.

Is the (I assume) braided shielding to protect for RC noise interference & could be eliminated to reveal a smaller actual wire for a non-RC (stationary bench) engine for example?

I should know this but do the elbow caps do anything electrically other than secure the wire to the terminal & keep the wire assembly orientated in position? (ie. there is no ground/return contact to the hex part of plug, its just a locking mechanism?)

Roy Scholl sells some silicon wire 0.118" diameter rated for 20Kv. It's made by Wiremax. It's what I use. I think he also has some lower KV stuff of a lesser diameter. But I always go for the 20Kv version.
It's about as scale as it gets. Electricity is one of those things that does not scale unfortunately.
As far as the boots are concerned Ive never had a problem with sparking through the boot. And you shouldn't if your spark plug is working properly. The wire should be making positive contact to the top of the plug.
I've forgotten the part number but there are vacuum boots made by Dorman that look just like 90deg spark plug boots.

 

[DKGrimm]

Sorry if this is detracting the main theme of this post. If so, just ignore. But I'm wondering with all the electrical testing equipment wizardry & knowledge, is there any way to qualify that the ignition wires & plug elbow/boot has to be as big as they always seem to be. I suspect the answer is yes for electrical reasons & aesthetics comes second. Its just that we can obtain nice, small, scale looking spark plugs in 1/4-32 format (about same size as an RC glow plug) but then seems like we must install the obligatory firehose cable. Not too bad on a larger displacement engine but rather unflattering & busy plumbing on a smaller multi-cylinder engine.

Is the (I assume) braided shielding to protect for RC noise interference & could be eliminated to reveal a smaller actual wire for a non-RC (stationary bench) engine for example?

I should know this but do the elbow caps do anything electrically other than secure the wire to the terminal & keep the wire assembly orientated in position? (ie. there is no ground/return contact to the hex part of plug, its just a locking mechanism?)

You raise important points, Peter (I assume from you ID). I think you got it right. I am planning to try cutting off the shields on some CDI modules that have them, and replace the shields with a ground wire, but I haven't actually done that yet. Of course, you need high voltage wire for the plug lead. RCEXL seems to have the shielded leads on all their CDI products, although S/S CDI modules and many others have unshielded spark leads, including some of the Chinese modules such as Cison and NFStrike.

You are right that the shielded wire potentially hides most of the spark plug noise from the rest of the world. Full-sized piston aircraft have had shielded ignition at least since the middle of last century. As you say, shielding is done to suppress noise effecting radio control of models, but that is not necessarily the only goal. Those noise spikes have busted a lot of Hall sensors over the years if the wiring is not done carefully. Wiring effects are pretty difficult to predict, but I definitely would have a good ground (shields or direct wire) from the engine to the ignition module. The tight-fitting hex ends on those elbows is definitely an intentional ground connection for the module. I would not run other ground wires back to the battery, for example, because that could couple noise pulses back into the whole circuit.

Don

 

[Stefan-K]

Sorry if this is detracting the main theme of this post. If so, just ignore. But I'm wondering with all the electrical testing equipment wizardry & knowledge, is there any way to qualify that the ignition wires & plug elbow/boot has to be as big as they always seem to be. I suspect the answer is yes for electrical reasons & aesthetics comes second. Its just that we can obtain nice, small, scale looking spark plugs in 1/4-32 format (about same size as an RC glow plug) but then seems like we must install the obligatory firehose cable. Not too bad on a larger displacement engine but rather unflattering & busy plumbing on a smaller multi-cylinder engine.

Is the (I assume) braided shielding to protect for RC noise interference & could be eliminated to reveal a smaller actual wire for a non-RC (stationary bench) engine for example?

I should know this but do the elbow caps do anything electrically other than secure the wire to the terminal & keep the wire assembly orientated in position? (ie. there is no ground/return contact to the hex part of plug, its just a locking mechanism?)

The Metal parts of the elbow cap as Well as the Metal "shielding" around the sparkplug wire is the only ground connection of the whole CDI ignition. RCexl and most of the other manufacturers build it this way. If you remove all that and fire the ignition you will most probably kill it, because the HV will jump anywhere in the electronics but not where its supposed to. I saw many CDI Systems die that way. High Voltage has its own laws.

 

[74Sprint]

Ray,
my questions were for the people doing the evaluations and comparisons between CDI and LDI,

the energy in a capacitor is 1/2 C V^2, the energy in an inductor is 1/2 L I^2, these are computable,
measurable, and knowable, but no one seems to be doing it.

the resonant frequency of an LC circuit is 1 / 2 PI sqrt(L C), again this is computable, measurable,
and knowable, and while this is sometimes being observed with a scope it isn't being compared
across designs.

so the questions still are, 1) why do CDI seem to generate short sparks, and 2) why do CDI seem
to deliver only a fraction of their energy to the actual spark (where does all the rest of the energy go)

we need to have a handle on the absolute minimum basic question like how much energy are we
starting with when comparing CDI to LDI, and how do the ring down frequencies compare, and think
about what else could be making a difference. I see circuit diagrams for CDI using SCR, and LDI
using IGBT, but they are both 4-layer devices and the difference seems to be in the gate rather than
in the power diode, so I'd like to better understand the difference in power handling rather than
what sort of trigger they require. One thing that puzzles me is that neither design seems to have
a "free wheeling diode", so how does the primary ring down without an AC circuit.

another thing on my mind is from back in an earlier life when I toyed with tesla coils, there were
lots of people working on models for the resistance of a spark based on instantaneous and
average measurements of coil power, a complicated subject due to the non-linear, and even
negative, resistance of the spark. the question being is a spark plug arc similarly complicated.

Peter.

Short form:
CDI Short Spark;
Yes CDI's have a short spark and the main reason is they Don't use dwell time. They only have the time constants for the capacitor and the time constants of the primary coil. On top of this one needs to also include the ESR (internal resistance) of the capacitor and the resistance of the coil. Those resistances will slow down the charging of the coil. Once the size of the capacitor is chosen (based on RPM) one needs to match up the time constants of the cap to that of the coil, or at least try to come close. As far as energy (joules) is concerned on a CDI, one needs to remember that P = I x E. So you can have high current with low voltage or high voltage with low current and the power will still be the same. It will just look different. Also remember with a CDI once ionization has takes place any left over energy gets converted to current because the secondary gets shorted out. And don't forget because of resistance and impedance heat is created taking up some energy.

With an LDI we try to match the dwell (current charge time) with what the coil can handle without over heating it.

Ok, first, according to the laws of thermal dynamics "energy can neither be created or destroyed, it can only be converted from one form to another". So going by that and in a perfect world, if both the CDI & LDI started out with the same energy then they both must put out the same energy. In simple terms we basically have only voltage and current to work with. But the world isn't perfect, so where does the energy go and why does the CDI put out such a short spark. The equation for the energy stored in a capacitor that you mentioned is the key to a short spark. A capacitor stores a charge and when it is charged is only voltage! You can not step up voltage by itself but, you can step it up using current through a transformer aka ignition coil. CDI coils are not built the same as LDI coils. CDI coils have less resistance and less inductance than LDI coils. The reason being is that capacitors store a charge that leans towards voltage and inductors store current which can also be considered a charge. Yes I'm well aware that inductors work with magnetic fields (flux). But it is current that creates those fields. So with a capacitor we need to convert the voltage to current, capacitors are not known as current monsters, unless we get into huge caps. We need a low resistance, low inductive primary so we can create a magnetic field fast. We don't want to slow down the conversion with either higher resistance or higher inductance. We don't have a dwell time with a CDI ignition to build up a magnetic field. The faster we can create a magnetic field and collapse it the better the transfer of energy to the secondary and the better the spark. No matter what we do the CDI system will never create as much magnetic flux as a LDI system. LDI coils because of the higher resistance and higher inductance will also convert some of that energy into heat, more than the CDI coil. It's the current that creates that heat along with the field. And that is why CDI's have a shorter spark, no dwell time just the time constants. CDI's also generally have a higher step up ratio and a spark of higher voltage. And yes large companies that make ignition systems do calculate all this stuff and can afford to have custom coils and parts made.

LDI coils are siblings from the magneto days. Lets take this further. If you short out a battery, the battery will still produce a voltage based on it's internal resistance. This internal battery resistance is much higher than the internal resistance of a generator or magneto (same thing). If you short out an unregulated (voltage wise) generator or a magneto you will have almost no voltage, they produce current and not voltage. If you measure a magneto ignition coil you'll find that the primary coil is of high resistance and inductance to produce a voltage across the coil, this is what drives the current. The inductance may or may not be higher than an LDI coil but generally they are. The mag ignition coils that I have worked with tend to produce a spark where the current is of higher energy value than the voltage. These mags became a problem in WWII when superchargers started being used more and more with higher boosts. The mags were redesigned to put out higher voltages to overcome the higher cylinder pressures. So there are low voltage mags and high voltage mags but, they still don't produce a spark of high voltage like a CDI does. Take for example my friends racecar, it has 16.5:1 compression and he uses an MSD 7AL CDI ignition with a MSD Pro Tower coil to light it. A standard GM HEI (LDI) won't light the air/fuel mixture above idle rpm, it needs higher spark voltage.

Resonance; As far as resonance is concerned you must know that when a circuit whether it is a L, C, LC, RC, LR, or LRC is at resonance, that resistance/impedance is lowest and current flow through the circuit is at it's highest. Why doesn't anyone take this into account and build such an ignition? 2 things, it's either the cost is to high or they just don't know about resonance. I built an ignition like a buzz coil ignition that used the resonant frequency of a given ignition coil. It is basically a buzz coil circuit, actually it's a resonant tank circuit (oscillator) that is allowed to ring for a certain amount of time based on the trigger pulse width. It, the system, has more pluses than minuses. Current draw is very high reaching as high as 48 amps, because the current was not regulated, each succussive spark grew in voltage and current draw went up. If you know how coils work, and that a 12 volt system is actually +6 and -6 volts, and that that negative going wave/pulse can be put to good use, then you'll know how this circuit works. When you disconnect the primary from the voltage source the voltage across the coil gets inverted which, is where that big -100 to -200 volt negative pulse is coming from. So if one turns the power back on when that negative pulse is at max you now have +6 and say -150 across the primary of the coil, your going to draw a lot of current and build a really big magnetic field. Do this at resonance and your going to keep building up that magnetic field each time it fires. You have to stop or limit the resonating or the circuit will run away and burn up. Been there, done that. So what did I learn? If you get the timing right and try to build a magnetic field while the other field you previously built is collapsed you can raise the voltage across the coil from 13.5 volts to 1,200 volts and makes a neat light show. If you try to build the field while the other is collapsing you get a lot of heat in the coil. When I used it on my racecar I found that ignition coils didn't last long but, with 11:1 compression I could run 0.065" gap on the plugs and the engine ran like it was balanced. I also had to drill holes in the distributor cap to let out the ionized gases or I got cross-firing.

The spark used on IC engines can be way more complicated than a Tesla coil. In fact there are circuit designs for ignitions that can analyze the spark and convert that info into figuring out the air/fuel mixture ratio for that cylinder firing. There is a lot more I could talk about but, there would need to be an interest and spare time for me.

Cheers
Ray

 

[74Sprint]

With R/C engines we use the braided ignition wire mostly to cut down on RF interference on the radio receiver. Some like me use standard RG-59 TV cable and smaller silicone plug caps. Just need to break out the grounding braid a bit, hide it, and make sure it's grounded. The RG-59 cable actually looks like sparkplug wire. Also you can get smaller or larger cable if need be.

 

[peterl95124]

Don't mean to jump in on your question to Dave, but as I have it figured out the negative spike is actually a verrrry short burst of ringing driven by the avalanche breakdown of the spark itself. The top waveforms on the attachment on page 3 (post #79) show this burst expanded in time 20,000:1. A resistor at the spark plug reduces it but does not eliminate it. As to how much this feeds back and stresses the switch in the primary, that's kind of beyond my pay grade, but I'd guess that it could very well damage an unprotected semiconductor switch.

DK, didn't mean to sound exclusive!, I was seeing a large reverse voltage on the low voltage side of the circuit, which I'm suspecting has the effect of killing off Hall Effect sensors, I guess I'll have to get my scope out and see if I can take photo of its trace and share

 

[peterl95124]

Short form:
CDI Short Spark;
Yes CDI's have a short spark and the main reason is they Don't use dwell time. They only have the time constants for the capacitor and the time constants of the primary coil. On top of this one needs to also include the ESR (internal resistance) of the capacitor and the resistance of the coil. Those resistances will slow down the charging of the coil. Once the size of the capacitor is chosen (based on RPM) one needs to match up the time constants of the cap to that of the coil, or at least try to come close. As far as energy (joules) is concerned on a CDI, one needs to remember that P = I x E. So you can have high current with low voltage or high voltage with low current and the power will still be the same. It will just look different. Also remember with a CDI once ionization has takes place any left over energy gets converted to current because the secondary gets shorted out. And don't forget because of resistance and impedance heat is created taking up some energy.

With an LDI we try to match the dwell (current charge time) with what the coil can handle without over heating it.

Ok, first, according to the laws of thermal dynamics "energy can neither be created or destroyed, it can only be converted from one form to another". So going by that and in a perfect world, if both the CDI & LDI started out with the same energy then they both must put out the same energy. In simple terms we basically have only voltage and current to work with. But the world isn't perfect, so where does the energy go and why does the CDI put out such a short spark. The equation for the energy stored in a capacitor that you mentioned is the key to a short spark. A capacitor stores voltage! You can not step up voltage but, you can step up current using a transformer aka ignition coil. CDI coils are not built the same as LDI coils. CDI coils have less resistance and less inductance than LDI coils. The reason being is that capacitors store voltage and inductors store current. Yes I'm well aware that inductors work with magnetic fields (flux). But it is current that creates those fields. So with a capacitor we need to convert the voltage to current, capacitors are not known as current monsters, unless we get into huge caps. We need a low resistance, low inductive primary so we can create a magnetic field fast. We don't want to slow down the conversion with either higher resistance or higher inductance. We don't have a dwell time with a CDI ignition to build up a magnetic field. The faster we can create a magnetic field and collapse it the better the transfer of energy to the secondary and the better the spark. No matter what we do the CDI system will never create as much magnetic flux as a LDI system. LDI coils because of the higher resistance and higher inductance will also convert some of that energy into heat, more than the CDI coil. It's the current that creates that heat along with the field. And that is why CDI's have a shorter spark, no dwell time just the time constants. CDI's also generally have a higher step up ratio and a spark of higher voltage. And yes large companies that make ignition systems do calculate all this stuff and can afford to have custom coils and parts made.

[...]

The spark used on IC engines can be way more complicated than a Tesla coil. In fact there are circuit designs for ignitions that can analyze the spark and convert that info into figuring out the air/fuel mixture ratio for that cylinder firing. There is a lot more I could talk about but, there would need to be an interest and spare time for me.

Cheers
Ray

Ray, you are confused, you said:
"A capacitor stores voltage! You can not step up voltage but, you can step up current using a transformer aka ignition coil."
no, a capacitor stores charge, and no, an ignition coil does not step up current it steps up voltage (and steps down current). and from there things just get worse...
Peter.