[Diy_efi] Re: Greenfire

[Bill Washington]

Mike, Adam,
    Perhaps this may help the understanding:
Looking at the situation from two perspectives...

1. First perspective:
At the end of the intake stroke we have a cylinder full of air/fuel 
mixture at approx 1 atmosphere,
assume an 8:1 compression ratio,
Imagine for a moment that there is no gas flow into the plug orifices 
during the compression stroke.
We would then have a plug with approx 1atm pressure inside, and 8 atm 
pressure outside with four orifices between - Instantaneous gas velocity 
through the orifices would be huge - I have neither the time nor the 
inclination to do the maths, however huge is a sufficient description 
for me....


2. second perspective:
At the end of the intake stroke we have a cylinder full of air/fuel 
mixture at approx 1 atmosphere,
assume again an 8:1 compression ratio,
during the compression stroke the culinder is a sealed (well close 
enough for the illustration) vessel including the volume inside the plug,
at the end of the compression stroke the volume has been reduced to one 
eighth of its starting volume, therefore, conserving PVT 
(Pressure-Volume-Temperature)
Pressure is now approx 8 atm (slightly more because the temperature has 
also increased), therefore the density (molecules per unit volume) of 
the gas has also increased by a factor of 8 -
Note that this means that the density of the gas inside the plug MUST 
have also increased by a factor of 8! IE there are now approx 8 times as 
many molecules inside the plug as there were at the start of the 
compression stroke - and these can only be a portion of the air/fuel 
mixture in the cylinder - they can't have come from anywhere 
else......this is more than enough to initiate the combustion event.

Another question now arises in my mind...... for a GDI engine - direct 
injection into the cylinder ..... when does the injection event occur 
.....would these Greenfire plugs work in this scenario?
I believe it would depend on the timing of the injection event..... 
early enough in the compression stroke and it would play out roughly as 
above, but late in the compression stroke and Adam's diffusion 
discussions start to become relevant - then the plugs may not work at 
all..........

Best Regards
Bill

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