Re: S4 Summa cum Lambda

[QSHIPQ@aol.com]

Randall M writes:
>I just got done reading an article out of a Euroean Audi club magazine
>on the S4 and its amazing engine.  One thing that I found interesting
>about it was a little tidbit on EGT's.  Earlier this year(or late last
>year) Some on the list stated that EGT's were unimportant in
>turbocharged applications, but interestingly enough  the new S4 has
>*two* sensors! 
Two EGT sensors?  Or 2 O2 sensors, or 2 of both.  

 >Their rationale?  This way they can keep turbine and EM
>temps below the limit wihtout dumping gross quantities of fuel into the
>system to keep temps down.  An Audi Engine Designer said, "Even at full
>load we can now run at stoichiometric air/fuel mixtures which reduces
>emissions and improve fuel economy."  Maybe EGT's are relavant to engine
>management discussions!

Er, ah, not sure this changes things much.  We are talking of WOT-free (maybe
not soon) in terms of potential EPA regulations here.  Right now, on WOT,
emissions are free, that is to say, most lambda circuits are bypassed in
favour of a fixed lambda value or duty cycle.  A couple of reasons for that.
First is that O2 sensors aren't the fastest animals in the world, and that
gets worse as they age (in fact, many Ford 5.0 mustangs with freeflow exhausts
actually run in limp mode cuz the O2 can't react to the flow).  So another
measure could be used.  EGT.  For the moment, maybe a necessity, or a temp
solution.  However, given the reaction of EGT vs time vs O2, I'm not sure that
the EGT is the long term solution.  But for now, might get us closer to what
the boys across the pond enjoy for HP.

Too much fuel (HC) in the exhaust creates more than emission problems.
Burning O2 sensors (especially with turbo cars) and melting cats are
byproducts of too much fuel.  A major concern for the 100k emissions
warrantees.  EGT measures may be the temp fix between fixed lambda WOT and a
better O2 sensor.  What we really need is a better O2 sensor.  EGT is not
really relevent to lambda, it is relevent only to WOT bypassed/fixed lambda
values.  Stoichmetric is still a lambda equation, .86 lambda gives maximum
power, 1.05 lambda maximum economy.  1.00 still is the best compromise of
exhaust byproducts, the key is to address WOT and lambda.  EGT can do this.
So could a better mousetrap (02 sensor).  

Regardless, nice to see some 'cool' toys on the S4.  However, given the delays
in the launch of said EGT equipped missile, I would venture that EGT is hardly
a bragging right for the boys at Ingolstat right now.  Get the friggin bugs
out of it, and get it over here....  Randall's ready!!!

I'd advise you to just get a bug, but maybe better to just wait till spring...
or later. :)

EGT skeptic

Scott Justusson