Knock

[Robert W. Hughes]

> > Actually, the exhaust gases dilute the mixture and make the combustion
> > temperatures lower. 
> 
> How do you add hot and get cold?
> I'm confused....
> 
> > From: "Scott Croughwell" <scott at outwest.net>
>  
> > > How does the hot exhaust gas cool the fresh charge.... Or have I got this
> > > wrong and you mean that the exhaust gas isn't heating the cool intake charge
> > > and the cold intake charge is causing the detonation????
> > 
> > Believe it or not... the gasses coming from the EGR have had enough time to cool
> > enough so that the portion of exhaust temp re-entering the intake port is cooler
> > than the intake manifold.

and from another note

> With EGR operational, as
> soon as the valve opened under the same conditions the intake manifold temp
> jumped to 210F on a 75F day.  I think that it is less a temperature issue
> than a charge dilution issue.  But with some fine tuning of the spark map,
> you can easily eliminate any detonation you may experience.

This is what I was saying. The exhaust gases dilute the mixture and and
result in cooler combustion chamber temperatures which reduces nitrogen
oxide formation. The mixture also burns slower and so requires more
ignition advance. The exhaust gases are not cooler than the intake, on
my car they are hot enough to melt and burn out 60-40 solder in copper
piping.

> 
> Wow so the exhaust gas is cooler than the intake I never would have thought 
> so.... hell I'm not even running emmissions gear, don't have to here in NZ. It 
> is even legal to remove cats.... 
How about dogs? sorry
-- 
Robert W. Hughes (Bob)
BackYard Engineering
29:40.237N, 95:28.726W
Houston, Texas
rwhughe at ev1.net