Condensers

I tried to stay away from the mathematics. I understand LC circuits and delta i/delta t, Kirchoff's Law etc. But the trick to me is in being able to express something intangible with tangible analogies but without the math. Not everyone even understands basic equality statements, it depends on what you spend/spent your time or life doing. So the more different ways you can come up with to illustrate the intangible, without voiding the basics laws, the better. Saying it with math or cut and pasting facts is easy and but kinda like speaking a foreign language to some.

I made alot of money, translating engineerese into English (from power supplies to the 5E digital telecom switch) to make it understandable for Com Techs and such. And no it wasn't fun. You engineers can make a soul feel stupid in 30ms or <! And I do that pretty well on my own! lol

It is correct that the inverse EMF in the primary is 200-300volts. I had completely forgotten about how much it was. The pattern and number of oscillations was the important part back in the battery/point days.

By the way, if anyone ever sees 20-30K across the spark plug with a battery point ignition system it would be a one off. Most automotive B/P ign. systems had coils "rated" as 20Kv but the voltage drop across the spark plug is only 5Kv or so, depending on plug gap, fuel-mix density and compression, wire resistance etc. I've never measured a Norton's but I would be surprised if it was more that 3Kv. Even the GM HEI 40KV coils didn't get much higher than 7-10Kv, if my memory serves me right. A 20-30KVdrop across the plug would probably produce an ultraviolet spark that you wouldn't be able to see! By the way, the spark plug acts like a capacitor too! (that should stir up somebody!) But I digress. :shock:

Mike

Sometimes talking about technical things in technical terms is the best way to convey them. Too much truth tends to get lost in the translation into layman's terms. And yes, I'm a geek...

Further to that...

The voltage required to bridge a spark gap is generally given by Paschen's Law. I won't bore folks with any more math, but the rule of thumb is that 12KV is the worst case requirement for a typical passenger vehicle with .030 gap plugs.

You won't see the 20-30 KV at a spark plug, because the plug fires long before that. Once the spark starts the gas between the electrodes ionizes and the voltage drops to a sustaining level until the energy in the coil is depleted. If you hold the plug wire and become the spark plug, however...

Modern HEI ignitions with .080 plug gaps can reach 50KV I'm told. Ouch.

Dave, you are right about the challenge of accuracy with layman explanation, but that's the fun of it to me. I don't think you'll ever see that much voltage even in the DEI systems and I KNOW FOR CERTAIN that you won't see that much on an o'scope in a B/P or HEI. Too many years of looking to get that one wrong!

The voltage Potential is that high but not the Actual Voltage that it takes to bridge the plug gap. Like I stated earlier it takes a 40KV coil to produce a 7-10Kv spark at the plug of an HEI w/wires of 1-3Kohms resistance per foot and a .060 plug gap. That's measured with an Allen O'scope on hundreds of cars. If I've got that one wrong, I gonna go shoot myself because I have lost it!

Mike

By the way, the spark plug acts like a capacitor too! (that should stir up somebody!) But I digress.

Click to expand...

Plug gap capacitance can alter the spark timing a bit too, bigger gap delays spark till builds enough v's to jump then flow in ionized air. Electronic knock detection works this way, ionization of fuel in gap is measured, too much =
Bang instead of kaPow.

If an ignition spark did reach over 10 kv potential we could see inside the head via the soft x-rays produced which can pass through some amount of Al which is a poor shield to x-rays.

Laser firing is here but don't know if it''ll adapt to our old things.

Dang hobot, now that made ME go hmmm....I thought knock sensors were a broadly tuned self resonant device that included a piezoelectric element mounted on a central mounting stud, with an element including a generally annular vibratable portion having a variable radial dimension so as to exhibit resonant vibrations at a plurality of relatively closely spaced resonant frequencies essentially spanning an engine determined knock frequency band. (I stated it that way to try and alieviate any potential misunderstanding!...lol)

In what system(s) are they using air ionization as an indicator of detonation? I've been away from automotive electronics for 10 years, so tell me more, my friend!!

Mike

Mike we both need to ride more and think less. Your description only covers the sonic-vibration knock detection 'microphones' - which do come in a range of resonance freq, usually 4-7000 hz, which about covers all sizes of chambers near TDC which is when detonation happens. I plan to use a knock sensor in head steady center bolt on my supercharged hi CR low octane Ms Peel. But now you mention it maybe can use the fancier method below.

Ionization detection has nothing to do with sonic vibrations but the break down of resistance to current flow as fuel breaks down into more reactive radicals when heated up too fast via photon radiation and compression heating across most the combustion volume - just before the BANG>
Basically a trickle current sensor of plug gap that if flows too much, ignition is retarded and/or fuel enriched before the next ignition spark voltage spike.

http://www.google.com/search?client=fir ... gle+Search

Mike we both need to ride more and think less.

Click to expand...

Steve, I wish I could. I have been pretty much immobilized for nearly 4 years (unable to drive but very little). I still have a PEG feeding tube. If it weren't for the love of math and science and an insane curiosity, I would be stark raving mad :evil: To find a group of guys to have this type of dialog is a Godsend for me and I have enjoyed and appreciated the input and demeanor from everyone. It's as good as a head shrink for this ole Nam Vet Gearhead!

Regarding the knock sensor, how do you plan on developing a calibration map/matrix for the sensor? That's gotta be tedious at best. I've written basic assembly language routines for microcontrollers using simple sensors and actuators and that almost fried my little lump of gray matter. I can only imagine just building the data base! I haven't looked into what the sensors are made of, but in the early days it was obvious that to get closer to real time, the information had to come from the combustion chamber. Of course at that time, clock speeds, propagation delay, etc. was as much a problem as making something live in the combustion chamber (which is no small feat). It kinda made real-time vs feedback a mute point.

This is probably not the place but I'm very interested in hearing/learning how you make that sucker work!

Mike

Aw man Mike your body/mind situation and detonation busting insights leave me tingling. I just came in after finishing mowing after dark while tornadoes and hail blast the surrounds counties, but missed me so far na na na na....
[had to 4wd PU pull mower out of muddy creek bed 3x's and jumper it once...

I don't know if or how to pull off Ms Peel's deal yet or if she can really exist in the combustion and heat states I seek out of her. I need a restless educated curious techno brain to bounce off of then mind meld with, so give me a ping and I'll give ya fodder to feed that processing unit and then go out and spank some 'puterized Might even have some insights on your personal plight. We were meant to thrive at all ages and bounce back if data channels working and fuel and oxygen and correct fluid levels and pressures.

A place to be, something to do and things to look forward too...
hobot @ madison county. net. [separated to keep online 'bots' recognizing it, just take the spaces out and lets get rolling. I'm not ridden since goats got me last summer ok. Now I'm scared as I've about got Trixie going...