General > General Technical Chat
Ignition systems
HighVoltage:
--- Quote from: Circlotron on October 01, 2021, 01:39:37 pm ---
--- Quote from: HighVoltage on October 01, 2021, 01:13:50 pm ---I am just developing a new ignition coil for an OEM.
The difference these days is that we have 30A primary current after only 100us of charge time.
And the secondary peak voltage must be >50kV, besides a few other crazy requirements.
--- End quote ---
How much energy? Physically small coils don't give you much to work with. And why such high currents and short charge times? What's wrong with say 10A and 3mS? Less time for I2R dissipation in the primary?
--- End quote ---
Almost 150 mJ Energy in the sustained spark.
Short charge time to keep the windings cold
30A primary current to get about 300 mA peak current in the spark.
And ion measurement is built in as well.
There is not much room for error in the dwell time.
And you can not trigger these coils with a typical ON signal.
1us after the ON signal starts, a signature is transferred to the coil to really turn ON.
SeanB:
Going to guess that is for multipulse ignition, for ultra lean operation, so you will have enough spark to ignite the fuel mix, even if the plug area is transiently non combustible, you have enough high energy sparks that the lean mix will strike before TDC and complete combustion to a large degree.
I helped my father install high energy inductive ignition, that used a vane that blocked an optical sensor, that then triggered a low resistance (IIRC under 0,8R primary) coil, to provide the ignition pulse. Had to use inductive wound Bougicord leads, as the carbon ones basically melted, and spark plugs had to be special Lodge ones, as the other brands like NGK or Champion would only last a week before misfiring. But was able to run really lean, and provide extra power at the top end of the RPM, even if your 10 000km service was change 4 spark plugs, rotor and distributor cap, as they would all be badly eroded, and not likely to make another service.
Big difference, made it a stealth supercar, well capable of beating the common sports models, 3 series BMW, low end Porsche, VW 1st generation GTI. None of them thought an Alfasud 1.5l was capable of beating them stop to stop, or at top end. He kept the stock exhaust as well, so it did not sound any different. Just used to eat gearbox synchros, and brake disks.
paulca:
On coils.... related, sort of, but I read something suggesting that on motorcycles, the engine has a stator and a rotor for generation... like 99% of them do, that's our alternator, however they claimed that on some bikes at least, they use different sized coils and power different things from each coil.
So there was a larger, heavier coil for powering the ignition, a smaller coil for powering lights and another smaller one, gone through a rectifier for running electronics. Oh and a single neutral. It's like a 6 phase generator with the phases split and used in singles or pairs for different sub-systems. It makes sense to a degree, why pump all the current for the ignition at 17,000rpm through the rectifier and then use it t generate high voltage, reducing the size of the wiring and the rectifier.... and not broadcasting that ignition RF through out the bike, but keeping it close to the engine.
I'm just not sure how true this is or how common it is.
This video and section 1:33:
https://youtu.be/mdOJ717PKRc?t=93
langwadt:
--- Quote from: SeanB on October 01, 2021, 02:52:31 pm ---Going to guess that is for multipulse ignition, for ultra lean operation, so you will have enough spark to ignite the fuel mix, even if the plug area is transiently non combustible, you have enough high energy sparks that the lean mix will strike before TDC and complete combustion to a large degree.
I helped my father install high energy inductive ignition, that used a vane that blocked an optical sensor, that then triggered a low resistance (IIRC under 0,8R primary) coil, to provide the ignition pulse. Had to use inductive wound Bougicord leads, as the carbon ones basically melted, and spark plugs had to be special Lodge ones, as the other brands like NGK or Champion would only last a week before misfiring. But was able to run really lean, and provide extra power at the top end of the RPM, even if your 10 000km service was change 4 spark plugs, rotor and distributor cap, as they would all be badly eroded, and not likely to make another service.
Big difference, made it a stealth supercar, well capable of beating the common sports models, 3 series BMW, low end Porsche, VW 1st generation GTI. None of them thought an Alfasud 1.5l was capable of beating them stop to stop, or at top end. He kept the stock exhaust as well, so it did not sound any different. Just used to eat gearbox synchros, and brake disks.
--- End quote ---
sound like a story that gets better every time it is told, adding lots of spark energy isn't going to magically add sginificant power and running lean definitely isn't
HighVoltage:
--- Quote from: SeanB on October 01, 2021, 02:52:31 pm ---Going to guess that is for multipulse ignition, for ultra lean operation, so you will have enough spark to ignite the fuel mix, even if the plug area is transiently non combustible, you have enough high energy sparks that the lean mix will strike before TDC and complete combustion to a large degree.
--- End quote ---
Yes, Multi Pulse is another reason to have an ultra fast charge time.
To get the combustion more stabilized, the spark current must be increased.
Especially for lean burn mixtures, a higher spark current is required.
Spark duration has become secondary in modern systems and long spark duration are a relic in the past.
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