DIY_EFI Digest V5 #34

[Hunt David]

>Ok.... so the inlet manifold temp goes up but the mixture is diluted by the

>exhaust gas from the erg. I would have thought that this would have leaned 
>the AFR if anything causing detonation or isn't there enough O2 left in the

>exhaust?

Having worked with oxygen sensors in other applications, it is the excess
oxygen that is measured, so lean is less oxygen not excess fuel.  The
exhaust is just an inert that has little to do with the combustion process
except that it has to be heated by the oxidation process.  The result is
less fuel, less oxygen and cooler PEAK temperatures, thus improved
emissions. I believe, but ain't sure, that the exhaust temperature is
reduced with an increase in the engine's efficiency. The free oxygen
remaining (and sensed) is relatively unchanged.

Now I have a question, when a piston is burned, is the excess oxygen
reacting with the Aluminum?  Or is it something else?

>How does the hot exhaust gas cool the fresh charge....  is a good
>question. Unfortunately it's not the right one.

>If you want to get/or seemingly pissy, fine, I'll withdraw my efforts to 
>answer your questions. 
>              Grumpy 

Grumpy,
I find your answers quite enlightening and enjoyable, but you too can come
off as pissy.  Don't take this to heart, but in this format anyone can be
misunderstood.  Review your first response.  In my opinion, we should be
expecially accomodating and understanding in a forum such as this.  Or are
you just upholding your good name, Grumpy.  Don't get upset, we all love
you.

>This doesn't make sense to me.  Static CR would remain the same.
>The dynamic/effective CR should still be the same since nothing none
>compressable was added to the mix.  The VE should drop (less O2 to react),
>hence lower fuel amount needed, leaner mixture takes longer to burn hence
>more timing needed.
>Grumpy

Since the spend gas is added after the throttle plate the total gas in the
combustion chamber is increased as compared to no recirculation. Thus the
"dynamic" pressure (effective compression ratio) is increased.  At part
throttle the chamber certainly doesn't fill due to the restriction of the
throttle and the dynamic compression ratio is quite small, so even a small
amount of recirculated gas increases the dynamic compression ratio.  It also
increases the preignition temperature (promoting better vaporization
(mixing)), and provides a (relatively) cooling effect for pockets of
"leanness" reducing the possiblity of detonation.  REDUCING.

That "leanness" might be caused by fuel dropout which means that the oxygen
rich, low fuel (lean) areas will also have a lot of recirculation gasses.
Win - Win - Win - Win situation, quite ingenous actually.

Bama
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