[Diy_efi] Link for greenfire spark plugs...

[Mike]

At 02:58 PM 9/06/05, you wrote:
>--- Mike <niche at iinet.net.au> wrote:
>
>> Although you may interpret the small flow through
>> the holes as "diffusion" it isnt technically correct
>> at all to call it that - the pressure in that region
>> of the plug is not static, therefore there is flow.
>
>Except the vast majority of the volume of "empty
>space" in the tip of the plug is between combustion
>chamber and sparking electrode.  The suggestion was
>made that the mixture would be "pushed through" the
>"empty space", which of course it cannot be;

heh ? Why cant the mixture be pushed through/into this space
since 'dynamic pressure effectively equals flow',  is there
some other implication you are not articulating ?

There are many situations where plug electrodes dont
extend that much into the chamber and are very close
to the chamber edge or below with negligible effect,  read on...

> and
>despite the compression of the end gases inside the
>"empty space", I doubt very much that by the time
>combustion occurs, especially at higher engine speeds,
>the now-compacted "plug" of end gases surrounding the
>sparking electrodes will support combustion by itself.

Surely most people who have been on this list for more than
a few years and/or who have an engine background would have
likely seen some of those high speed flow videos at school,
shows just how turbulent the inside of a chamber actually is
or had occasion to understand flow in the chamber is not simple,
your implication there isnt enough time is sheer speculation
and borders on a ludicrous over-simplification to save thinking,
there is more than enough time as the gases have really low
inertia in comparison with the forces moving them around, the
instantaneous accelerations during compression alone,
depending on chamber squish design can initiate combustion.
If your logic was even partly true then the IC engines in F1
would have great trouble managing 18,000 rpm especially at
AFR's of just over 4:1 they seem to do this readily and beyond.

In any case the end gases wont stay compacted for long,
most of them disperse during a large part of the exhaust stroke
and not only due to flow from the exhaust valve, turbulence
generated by asymmetrical combustion effects also occur
from mixture in state of motion and not homogenous.

You seem to be fixated on the paradigm that the compressed
end gases from the last combustion cycle wont be able to exit
through the 5 or so peripheral holes of the spark plug cap, with
the huge pressure fluctuations they will be exhausted pretty damn
quickly and I might add not necessarily symmetrically by any means.

It could be you believe the apparent symmetry of the plug means
they wont get in because the previous cycle didnt get them out etc.

Is that your view ?

Well in anticipation this is your conception, I can state its extremely
unlikely there is any sort of dispersion flow symmetry across that region
(or any other region for that matter) that might form a type of static
gas containment scenario. As the piston ascends there are huge
asymmetrical pressure gradients across the plug region and not just
in one direction, in essence all over the place and this means
flow - there is no need to only consider the paradigm of diffusion.

> Since it's a "blind" hole, there is no real mechanism
>for the mixing of the end gases and the intake charge
>except for...
>
>...diffusion.  Like I said.

Adam,
I think you are grasping at straws here, the mixing of the end
gases and charge occurs already before most reaches the plug.

Um, the top of the combustion chamber is effectively the same,
if we followed your interpretation and logic the region at the top
or near the top or in fact anywhere not too distant from a wall 
of the chamber might also be interpreted as a "blind" hole
and would not get any mixture - other than the boundary layer
the new gases already mixed do get there, read on re escort...

It is appropriate however to speculate that the mixture will not
be homogenous and the various patterns of mixture and flow in and
around the spark plug may not be optimum as in not stochiometric
but this is the case all throughout the chamber, there are huge
multifarious dynamics in progress which wont allow much of any
static containment as you imply and further propose can only be
circumvented by the notion of "diffusion" as the mechanism.

I'm inferring from your grammar above that you may believe the
gases need to mix in that little virtual pre-chamber in the plug
(and that they arent mixed at all before they get there..)
and you are calling this only route "diffusion"  <hrrrrm>

Of course the opposite is much more likely to be true, long
before the fresh gases get anywhere near -  there is already a huge
amount of mixing achieved by entry into the chamber where diffusion
has already likely achieved its highest probabilistic outcome
and in any case as the piston rises there is a heap of turbulence
to mix the atomised fuel, some of that fuel will of course become
gaseous vapour due to latent heat of vapourisation as this also
provides wonderful mixing opportunities before this mixture is
pushed into the virtual pre chamber by pressure alone...

I am referring here to an ICE with conventional manifold EFI.

>> Its quite easy to see how you dont understand how it
>> functions if you are attached to the notion of the
>> only path being "diffusion" - clearly its not...
>
>Perhaps you can explain how it is "easy to see".  Once
>again, you've left a bit of a put-down without posting
>anything factual to back it up; if I'm "wrong", great,
>but at least explain yourself if you're going to throw
>around 'accusations'.  Certainly there must have been
>a less smug-sounding way of claiming that the device works.

Um yeah sorry about that, I was having a bit of a sarcastic dig,
because it would be obvious to me diffusion has occurred some
time before the mixed gases are pushed into the end regions
and its more than obvious to me pressure does the job adequately.

I'm actually surprised you are attached to the notion of a static
gas containment scenario hence my purile attempt to get you
to snap out of it as its easy to see how your logic has import
for you as you seem attached to it as a huge over simplification.

I guess I have the benefit of experience of a 4cyl ford escort flathead
motor (bowl in piston conventional layout) where I was faced with
occasional plug fouling so (what the heck) got 4 spacer
washers and put them under the plugs, the net effect was the
plug electrodes were significantly recessed into the head - did this
make a difference (?), none readily discernable - which I thought
a bit strange at the time. If your logic were actualised in that
scenario the effect would have been noticeable with somewhat
poorer performance. Other than the possible placebo effect of
a sensation of actual improvement in performance there wasnt any
real perception of any degradation at all. The plug fouling was
slightly less - or so it seemed - until I discovered I had the
wrong heat range afterall and reverted to the better plugs as I
didnt like the idea of not much thread holding them in...

I any case, I'm not claiming the greenfire device works (fully) in respect
of the possible exaggerated claims of the inventor, what I am doing
is offering a scenario that allows it to operate at least in terms of
firing the mixture reliably and countering your notion that it shouldnt
operate and why you see its difficult to think how it can even work
at all.

Rgds

Mike
PS: On further reflection, there might be types of chamber layouts where the
greenfire might actually work better.  ie. By having the sparking electrode
in some degree protected by the cap, the spark might well not be
so likely to be snuffed out or 'fluffed' by the dynamics during the last part of
compression - especially where the mixture is lean and/or where the
sparking voltage has degraded etc I'm not saying this is the case for
all situations but its understandable how it might well be an advantage
and this aspect might well assist in improving overall combustion.

One wonders if this lucky situation is that which explains the independent
test results and why the major engine manufacturers havent progressed
with it - other than the commercial/political resistance any large manufacturer
has against adopting a key technology they havent already developed.

MM



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Regards from


Mike Massen
Perth, Western Australia
VL Commodore Fuse Rail that wont warp or melt !
http://niche.iinet.net.au