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Enhancing ID ignition, thoughts

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tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
I was contemplating the shortcomings of the standard ID ignition and wondering how one could combine the higher energy and quick recovery of a CD with a longer glow stage. Something like a DC supply of only 500 V or so, diode isolated from the primary CD system, so the CD does the ionization and arc stages, where the DC supply maintains glow stage. What I have not figured out is how to stop the DC, if one needs to. Anyone heard of such a system?

I then ran across something called a resonant converter ignition. Crane used to make one, but seems no one else ever did. Anyone have any experience with them? Too complicated/expensive, or just did not work? Newer head and fuel delivery designs just don't need such things?

Has a CD ever been used in wasted spark config? Saab and Porshe used CD in production CNP I think.

As a CD uses the coil as a simple pulse transformer, how could one vary (lengthen) the arc or glow stage? Vary the time constant of the primary side? What could be done in the coil design? What if the coil was super high inductance? 20mH or so?

Just thoughts. Likely the best way to improve the ignition is to have the head reworked by a pro to improve the gas mixture and reducing the burden. Kind of like modern engines.



Cogito ergo sum periculoso

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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
Supercharge it. That will improve your mixture homogenization and give a lot bigger horsepower gain than any fancy ignition.

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

ozieagle Avatar
ozieagle Gold Member Herb Adler
Geelong Victoria, Australia   AUS
1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"
Hi Scott,

I haven't thought it through in detail, but would increasing the value of the storage capacitor do it?

Herb



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tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
I don't think so Herb, as it is transformer coupled. It might work if direct coupled, but I don't think I want to build a 30kV cap. I need to put a CD design into Spice to see. Not easy as transformers are not easy to model and my efforts to model a spark plug have not been terribly successful. I was thinking about increasing the TC of the discharge circuit, but extending it by 10 times and how that works with the frequency response of the transformer may be a problem in rise time for ionization making the timing variable. If it were that easy, MSD would not be the SOP. I can get 30kV diodes for about $25 each, so my piggy back DC idea may be at least build-able. Pretty expensive though as one still needs a 500 or 600 volt power supply.

This is just some off the wall thinking while recovering from too much yard work.



Cogito ergo sum periculoso

ozieagle Avatar
ozieagle Gold Member Herb Adler
Geelong Victoria, Australia   AUS
1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"
Scott,

Wouldn't the TC of the discharge be determined by the impedance of the coil and the value of the storage capacitor? Increasing C may increase discharge time.

Of course increasing C would require a much beefier pump circuit, to charge it in the time available.

I think I understand what you are thinking, with using 5 - 600 volts DC supply, but I can't see how that could make any difference. The volts are too low for the HT and on the primary of the coil you are still faced with a transformer, which doesn't pass DC.

Herb



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tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
The DC would be applied right at the plug boot to overcome unknown differences in HT leads. It is too low of a voltage to do anything until the ID or CD system provides the 9 to 12K necessary for ionization and flashover.

The catch-22 of the CD circuit is you want the fast rise time for ionization ( in that case, almost instant) , and flashover, which is all you get. CD does not have the long slow decay for the glow stage preferable to get through all the various stages of chemical reactions that have to happen before it is self-sustaining. I have noticed, most coils recommended for CD are very low inductance as they are only functioning as transformers, not storage banks. Not passing DC is the issue for sure.

Oh well, just food for thought. Probably an idea with no actual problem to apply it to.



Cogito ergo sum periculoso

ls1ac Avatar
ls1ac scott sommer
bristol, WI, USA   USA
You could go BIG and use an electronic distributer for a crank position sensor and feed a control box ala Honda/Toyota to individual coils per cylinder.

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Fred Winterburn Avatar
Ripley, ON, Canada   CAN
Scott,
- I think you could do it all from the coil primary side if you wanted to and run both types of ignition in parallel with the CD pulse happening first to breakdown the gap with the inductive spark as a chaser. The opposite of the Pertronix 2nd Strike that puts the inductive discharge first. That method makes no sense at all. The CD spark should be of the same polarity as the inductive spark and the inductive spark should occur just as the CD voltage is falling off but not so low that the inductive spark has to breakdown the gap again. I don't think it would be that hard to do, but I haven't given it a whole lot of thought. I'm reasonably certain that it could be done with a standard inductive coil. Maybe I'll run an experiment sometime to prove whether it is at least feasible.
- I think there are a couple of reasons most CDI manufacturers want low inductance coils. The first being that there are fewer losses which makes sense on something like a motorcycle that doesn't have a battery supply, but it also makes sense for multiple spark discharge. A high inductance coil can interfere with the next spark in the series if the next spark for instance happens to be of the wrong polarity (destructive interference). If you are going multiple spark with CDI you also want a very efficient coil so that the power supply can keep up, Problem is most multiple spark discharge ignitions have the separate sparks separated by too much time. Maybe good for emissions if the first strike didn't get the mixture going, but not so good for power.
- In the case of the CDI I'm building, the inductance helps by storing energy that didn't go into the first strike and then charging the capacitor for another powerful, albeit less energetic discharge than the first, with a 3rd and then more strikes if secondary side resistance is low enough. The extra inductance and some resistance in the primary also has the effect of protecting ignition components including the CDI. Both by slowing the voltage rise on the secondary to reduce corona and cross-fire, and to protect the CDI itself. The discharge of a shorted capacitor is a violent event and taming it somewhat is a good thing.
- I really doubt that the glow phase gives much benefit and there is very little power left in the spark with most inductive ignitions after 200µS. Just more spark plug erosion. Better to hit it with a few more shock waves. Fred

In reply to # 3715605 by tvrgeek The DC would be applied right at the plug boot to overcome unknown differences in HT leads. It is too low of a voltage to do anything until the ID or CD system provides the 9 to 12K necessary for ionization and flashover.

The catch-22 of the CD circuit is you want the fast rise time for ionization ( in that case, almost instant) , and flashover, which is all you get. CD does not have the long slow decay for the glow stage preferable to get through all the various stages of chemical reactions that have to happen before it is self-sustaining. I have noticed, most coils recommended for CD are very low inductance as they are only functioning as transformers, not storage banks. Not passing DC is the issue for sure.

Oh well, just food for thought. Probably an idea with no actual problem to apply it to.



'Anyone who likes liver, can't taste it'
'If you want to repair car electrical systems successfully, learn Ohm's Law'.

GMB3 Avatar
GMB3 Silver Member George Badger
Soquel, CA, USA   USA
1965 Jaguar E-Type Coupe "1QUICK E"
1968 MG MGB "1QUICK B"
Interesting thoughts. BI bikes can use aftermarket CD systems that operate in the wasted spark phase.

MSD and Pertronix champion a multi-spark system though the former goes to a single spark at higher RPM.

The late model Saabs use a interesting way of dealing with optimal combustion. The plugs have an individual coil mounted on them through a "cassette". The plugs "sense" the ionization feeding it back to the CPU which adjust the burn time on each plug as needed. My 2L AERO develops 320HP.



---
GEO

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tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
Yes, the Saab feedback was a big deal and one of the reasons GM bought them. They derived their knock detection that way.

Fred, thinking right as you are, the short strike from the typical unit, designed for nitro race cars not being what we need with just poor old gas. The issue is how to keep enough energy going into the kernel for the reaction to become self sustaining, This is after one strips the Hydroges off and splits the Oxygens. Time as well as energy. Time does seem to be variable and the shock wave from compression seems to effect it as RPM increases. It seems it becomes exothermic quicker as RPM increases. Good thing otherwise we would never rev past 5K or so.

Sounds like you are onto something with the rise time issue. When I put a 6AL on my Spit, I had cross-fire if my gaps were more than .035. TIny cap, no vents. So a slightly softer CD strike which would do well for dirty plugs, then a longer ID. But we get back to the problem of how to get the energy into the coil fast enough so it does not drop off so fast. My crazy thought was to replace it with a stiff DC supply post coil so the supply does not have to be that big.

Yes of course, a Microsquirt driven COP ID system is on my list. We all know they work as every car on the road uses this configuration. This exercise is just thinking outside the box, be it black, silver, red or errr yellow grinning smiley

Oh well, fun to think. What I really need to do is get my dash back in and get it through NC inspection.



Cogito ergo sum periculoso

GMB3 Avatar
GMB3 Silver Member George Badger
Soquel, CA, USA   USA
1965 Jaguar E-Type Coupe "1QUICK E"
1968 MG MGB "1QUICK B"
The lower resistance coils attempt to have a faster rise time.

A healthy battery is a pretty stiff power supply. They can produce kJ's. The MSD 6AL can produce up to 150 mJ and the Pertronix new Digital HP can produce up to 187 mL.



---
GEO

Fred Winterburn Avatar
Ripley, ON, Canada   CAN
Those mJ numbers are the energy stored in the capacitor before each strike and have little to do with the spark energy. The losses are huge. Even when given those numbers, the amount that is wrung out of the capacitor varies considerably with CDI designs. I don't quote numbers because they mean almost nothing and aren't a good comparison of ignition systems. Fred

In reply to # 3715732 by GMB3 The lower resistance coils attempt to have a faster rise time.

A healthy battery is a pretty stiff power supply. They can produce kJ's. The MSD 6AL can produce up to 150 mJ and the Pertronix new Digital HP can produce up to 187 mL.



'Anyone who likes liver, can't taste it'
'If you want to repair car electrical systems successfully, learn Ohm's Law'.

ohlord Avatar
ohlord Gold Member Rob C
North of Seattle, N.W., USA   USA
1957 Land Rover Series I "EYEYIYI"
1971 MG MGB
1971 MG MGB "Bedouin 2"
More techno babble from someone that doesn't race, desires an automatic, professes not going over 65mph. Where is the shortcoming of any ignition under those lame parameters? You could light matches quick enough eye popping smiley
Or is this another circle jerk like struggling with tuning a DDweber?
Inquiring minds like you know...

Popcorn at the ready



"I'm a long way gone down this wild road I'm on
It's gonna take me where I'm bound
It's a long way around"



"These are the days that must happen to you"

RD2 Radar/ Electronic Warfare Technician
Vietnam 1969-1972



Edited 2 time(s). Last edit at 2018-04-13 05:11 AM by ohlord.

tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
But they do make impressive counter displays! Almost as good as magic spark plug adds. Got to love Madison Avenue Engineering*

George,
Yes, lower inductance coil means faster rise time, but it means less energy stored. Lower resistance means higher current, so more energy stored. In an ID system, these are balanced against each other to optimize for the engine need. Some do better than others. For instance Lucas did one coil for all cars, where Bosch did just about a unique one for every customer. Hair splitting design, but typical cultural differences. The end result is the Bosch Blue coil is better suited to a 4 cylinder 3 Ohm car needing all the help it can get at idle. The Lucas is more of a middle if the road coil. Their "sport" coil is biased to higher RPM use ( sport, when it meant something as in race). Now the balance all changes with CD as it is no longer a storage device, just a pulse transformer. I do not know how that balance works with different CD designs. You can play with these parameters on http://www.bgsoflex.com/igncoil.html

Can coils being I-core design, are very inefficient in energy transfer. Below 75% depending on some subtle details like the exact metal of the can, internal sleeve etc. E+I core, commonly just called E-core are more like 85% efficient, but much more expensive to wind. Industry went to the E-core in the 80's when emission and mileage requires more reliable ignition. ( the short comings for all street cars some trolls on the forum do not understand) Now with the vastly better coupling efficiency of COP, they are back to I-core. No room to stuff an E-core down the valve cover hole. The CNP design lets them use the larger E-core and a short HT lead. Compromise. Everything is a compromise. Both give the engineer a better control over the system, where in aftermarket, one has to design for all possible configurations.


* For those not in the USA, Madison Av. is the center of advertising in New York. Claims made by advertising execs, not real engineers.



Cogito ergo sum periculoso

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
Here is the coil I'm running. Is it all hype or is it a decent coil?

http://www.cbperformance.com/product-p/2009.htm

Turns Ratio: 72:1
Inductance: 8 mh
Primary Resistance: 1.1 OHMs
Secondary Resistance: 13.5K OHMs
Maximum Voltage: 30,000 Volts
Peak Current: 45 mA
Spark Duration: 2.5 mS

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.


Attachments:
CB coil.JPG    27.3 KB
CB coil.JPG

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