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capacitive vs. inductive ignition
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jim beam
May 5, 2012, 10:38:18 AM5/5/12
to
being somewhat surprised to find so many people apparently not
understanding the distinction between the two different types* of
electronic ignition used on cars, i dug up this which i should think
explains it well:
<http://www.auroraelectronics.com/ignition_systems_-_basics_to_high%20performance.htm>
i particularly like the burning paper analogy to explain spark energy
requirement. anyone with access to a dual plug ignition system [like
you'll find in planes] will be familiar with the fact that if you shut
one plug bank off, power output of the engine will decrease
significantly, which is about as dramatic a demonstration of spark
energy requirements as i think you can find.
i find the whole obsession with cdi to be fascinating. it came to fame
in the 1970's when consumer electronics was reliable enough and
affordable enough to tinker in this way, and it was indeed an
improvement over kettering ignition**, but there's almost no technical
overlap between combustion physics and electronics, so i guess what
might seem like a great electronics project would continue to seem like
a great ignition idea if the spark energy vs. spark voltage concept is
not understood.
inductive ignition on the other hand, particularly coil on plug, is
absolutely the way to go simply because it provides not just sparking
voltage, but significant total energy in a sustained event whose
duration outlasts the whole combustion nucleation phase. kettering may
not have had access to clean reliable switching [or dwell management]
technology, but he absolutely knew what he was doing when it came to
lighting off air/fuel mixtures.
* strictly speaking, it's debatable whether cdi /is/ actually "used" on
cars - not a single oem that i know of uses it. it's the exclusive
territory of aftermarket ignition - and a great example of inferior
product getting mind-share over superior product simply because of
better marketing. seriously, who in their right mind wants an ignition
system whose only debatable benefit [multiple spark events - which are
irrelevant if the thing could produce a sustained spark in the first
place] cuts off at only 3,000 rpm and that fails to address the whole
spark energy concept???
** kettering has a major problem:
mechanical [points] switching is noisy. noisy in make, noisy in break.
if you look at a fast oscilloscope trace of contact voltages at
switch, there are great fuzzy regions where multiple rapid on/off
contacts are made at each main event. that noise disrupts the coil
input current in undesirable ways each time, thus translating to
similarly "dirty" coil output. electronic switching is much cleaner on
make and break, thus dramatically improving spark output. compared to
kettering, even cdi output looks great!
<http://www.8052.com/users/klaas/bounce1.gif>
--
nomina rutrum rutrum
understanding the distinction between the two different types* of
electronic ignition used on cars, i dug up this which i should think
explains it well:
<http://www.auroraelectronics.com/ignition_systems_-_basics_to_high%20performance.htm>
i particularly like the burning paper analogy to explain spark energy
requirement. anyone with access to a dual plug ignition system [like
you'll find in planes] will be familiar with the fact that if you shut
one plug bank off, power output of the engine will decrease
significantly, which is about as dramatic a demonstration of spark
energy requirements as i think you can find.
i find the whole obsession with cdi to be fascinating. it came to fame
in the 1970's when consumer electronics was reliable enough and
affordable enough to tinker in this way, and it was indeed an
improvement over kettering ignition**, but there's almost no technical
overlap between combustion physics and electronics, so i guess what
might seem like a great electronics project would continue to seem like
a great ignition idea if the spark energy vs. spark voltage concept is
not understood.
inductive ignition on the other hand, particularly coil on plug, is
absolutely the way to go simply because it provides not just sparking
voltage, but significant total energy in a sustained event whose
duration outlasts the whole combustion nucleation phase. kettering may
not have had access to clean reliable switching [or dwell management]
technology, but he absolutely knew what he was doing when it came to
lighting off air/fuel mixtures.
* strictly speaking, it's debatable whether cdi /is/ actually "used" on
cars - not a single oem that i know of uses it. it's the exclusive
territory of aftermarket ignition - and a great example of inferior
product getting mind-share over superior product simply because of
better marketing. seriously, who in their right mind wants an ignition
system whose only debatable benefit [multiple spark events - which are
irrelevant if the thing could produce a sustained spark in the first
place] cuts off at only 3,000 rpm and that fails to address the whole
spark energy concept???
** kettering has a major problem:
mechanical [points] switching is noisy. noisy in make, noisy in break.
if you look at a fast oscilloscope trace of contact voltages at
switch, there are great fuzzy regions where multiple rapid on/off
contacts are made at each main event. that noise disrupts the coil
input current in undesirable ways each time, thus translating to
similarly "dirty" coil output. electronic switching is much cleaner on
make and break, thus dramatically improving spark output. compared to
kettering, even cdi output looks great!
<http://www.8052.com/users/klaas/bounce1.gif>
--
nomina rutrum rutrum
Scott Dorsey
May 7, 2012, 10:59:37 AM5/7/12
to
In article <jo3e0o$g95$1...@speranza.aioe.org>, jim beam <m...@privacy.net> wrote:
>
>i find the whole obsession with cdi to be fascinating. it came to fame
>in the 1970's when consumer electronics was reliable enough and
>affordable enough to tinker in this way, and it was indeed an
>improvement over kettering ignition**, but there's almost no technical
>overlap between combustion physics and electronics, so i guess what
>might seem like a great electronics project would continue to seem like
>a great ignition idea if the spark energy vs. spark voltage concept is
>not understood.
It's nice because it's cheap, it's easy to build, there are plenty of
>
>i find the whole obsession with cdi to be fascinating. it came to fame
>in the 1970's when consumer electronics was reliable enough and
>affordable enough to tinker in this way, and it was indeed an
>improvement over kettering ignition**, but there's almost no technical
>overlap between combustion physics and electronics, so i guess what
>might seem like a great electronics project would continue to seem like
>a great ignition idea if the spark energy vs. spark voltage concept is
>not understood.
aftermarket systems out there, and you get a nice fat hot spark with a
cheap junkyard ignition coil. The Mark Ten is a nice retrofit, or you
could make your own if you want, and it costs less than a single one of
those coil-on-plug coils. It's a nice step up from a Kettering system
with minimal expense.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
hls
May 7, 2012, 12:37:41 PM5/7/12
to
"Scott Dorsey" <klu...@panix.com> wrote in message
news:jo8o0p$6ct$1...@panix2.panix.com...
It's a nice step up from a Kettering system
> with minimal expense.
> --scott
>
CD systems were definitely a step up from the Kettering systems, in
> with minimal expense.
> --scott
>
general. A properly
functioning and well maintained Kettering system did a good job most of the
time but,
especially as engines began to age and as spark plugs lost their "edge",
there was a
definite loss of performance.
The CD had such a high firing voltage and such a sharp waveform that it
would fire
many fouled and deteriorated plugs.
IMO, it is adequate, even today, to most ignition applications, is
relatively simple,
and is cheap and easy to implement.
jim beam
May 7, 2012, 10:27:17 PM5/7/12
to
On 05/07/2012 07:59 AM, Scott Dorsey wrote:
> In article<jo3e0o$g95$1...@speranza.aioe.org>, jim beam<m...@privacy.net> wrote:
>>
>> i find the whole obsession with cdi to be fascinating. it came to fame
>> in the 1970's when consumer electronics was reliable enough and
>> affordable enough to tinker in this way, and it was indeed an
>> improvement over kettering ignition**, but there's almost no technical
>> overlap between combustion physics and electronics, so i guess what
>> might seem like a great electronics project would continue to seem like
>> a great ignition idea if the spark energy vs. spark voltage concept is
>> not understood.
>
> It's nice because it's cheap,
it's actually more expensive than inductive.
> In article<jo3e0o$g95$1...@speranza.aioe.org>, jim beam<m...@privacy.net> wrote:
>>
>> i find the whole obsession with cdi to be fascinating. it came to fame
>> in the 1970's when consumer electronics was reliable enough and
>> affordable enough to tinker in this way, and it was indeed an
>> improvement over kettering ignition**, but there's almost no technical
>> overlap between combustion physics and electronics, so i guess what
>> might seem like a great electronics project would continue to seem like
>> a great ignition idea if the spark energy vs. spark voltage concept is
>> not understood.
>
> It's nice because it's cheap,
> it's easy to build, there are plenty of
> aftermarket systems out there, and you get a nice fat hot spark with a
> cheap junkyard ignition coil.
sub-optimal results. technically, the "coil" used on cdi is a step up
transformer, not an inductive discharge reservoir.
> The Mark Ten is a nice retrofit, or you
> could make your own if you want, and it costs less than a single one of
> those coil-on-plug coils.
down in price a LOT.
> It's a nice step up from a Kettering system
> with minimal expense.
spark duration, inferior spark energy delivery and can't effectively
fire past 3krpm??? seriously, i simply do not understand why cdi is so
deeply rooted in the popular psyche that cold hard facts get completely
ignored. utterly bizarre.
> --scott
>
--
nomina rutrum rutrum
jim beam
May 7, 2012, 10:28:00 PM5/7/12
to
people like you just can't figure that out or pay attention when the
explanation is right under their nose.
--
nomina rutrum rutrum
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