"Rodan" <Rodan@[EMAIL PROTECTED]
> wrote in message
news:UYPPj.8039$NK1.5551@[EMAIL PROTECTED]
> "Kevin" wrote:
>
> ok explanation is, inert gas can not burn so adding it to the cyl
> mixture dilutes the burnable ****tion of the cyl mixture, less burnable
> less heat produced. the computer will compensate for any richening
> effect and lean it out again, as egr is pretty much continous no
> richening effect will occur. so the cooling effect is strictly from less
> burnable mixture. also as a side effect it slows the burn rate so
> timing can be increased some to gain back some lost power. KB
>
> ================================================
>
> Thanks for providing a reasonable alternate explanation for EGR
> function, particularly for pointing out that the EGR pretty much
> continuously operates in its feedback mode to compensate for
> transient variations in combustion temperature.
>
> My explanation for EGR function assumed a ****t-injected fuel
> system (no fuel in the intake manifold, only air and recirculated
> inert EGR gases). For throttle-body injectors or carburetors,
> the manifold mixture includes fuel so calculation of the resultant
> enrichment is more complex.
>
> I have only two small disagreements with your approach:
>
> 1.) My understanding is that excessive combustion temperature
> is much more strongly related to the leanness of the burn mixture
> than to the amount of the burn mixture, so reducing the quantity
> of a lean mixture to be burned, without enrichment, is of little help.
>
> 2.) Increasing injector fuel flow for enrichment would make an
> EGR valve unnecessary, but adding fuel would cause an unwanted
> power surge along with the desired combustion cooling. This is
> avoided by using EGR feedback to enrich the burn mixture by
> decreasing the oxygen content without increasing the fuel flow,
> thereby maintaining smooth power.
>
> In any case, I appreciate your point of view.
>
Both of you are incorrect about how EGR actually works.
Yes, the inert gas lowers combustion temps
However, it ALSO increases engine efficiency and extracted energy-per
gallon of gas.
The idea that a richer mixture would cool the cylinders is false. A
leaner mix runs slightly hotter but a richer mixture produces even
more NoX than a leaner mix. EGR cools much more than a richer
mixture.
For an explanation of the chemistry, see the following:
http://en.wikipedia.org/wiki/Egr
Ted
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