Re: I5 Power

[QSHIPQ@aol.com]

In a message dated 97-05-10 20:00:27 EDT, you write:

<< Nah.  The _only_ economy/performance tradeoff is the one under your right 
 boot.  You get maximum energy out of a fuel/air mixture at a quite specific 
 ratio - the stochiometric ratio.  You get maximum performance by using a
_lot_ 
 of both components at this same ratio - you get maximum economy by using
just 
 enough of both components - but again - at the same ratio.  The trick is to
get 
 the ratio right (with minor deviations for things like cold engine surfaces)

 across the entire load/rpm/temperature/pressure range.
 
 
 --
  Phil Payne
  phil@sievers.com
  Committee Member, UK Audi [ur-]quattro Owners Club >>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Not quite.  Lambda = 1.00 or (14.7:1 = Stoichiometric ratio) is when there is
just enough air to burn all the fuel in the chamber (lowest HC for the "most"
fuel in the chamber).  This ratio is "picked" by manufacturers (and
legislatures) for emissions (and gas mileage) not for power, it yeilds the
lowest byproducts of combustion (NOx, CO, and HC).  For power ("maximum
energy") , one would want Lambda .86 or 12.6:1 A/F ratio, for economy Lambda
1.05 or 15.4:1.  .86 unfortunately creates excess HC (unburnt fuel), the
byproduct of a rich motor, and can wreak havoc (as in fire or clogged) on
Catalytic converters, and reduces mileage. 1.05 ("maximum economy")
unfortunately creates excess CO.  Either extreme of Lambda, will make you
fail any emissions test.  One might think that 1.05 would yeild the best
emissions, but in fact, CO increases exponentially as Lambda passes 1.00 and
peaks before 1.03.    Lambda 1.00 (stoichiometric ratio) is an optimal
emissions (compromise of byproducts) choice only, NOT the optimum power
delivery.  Probst's book has the best description of this I've seen to date -
 "Choosing either maximum power or minimum fuel consumption means increased
exhaust emissions...  In general, this means slitght sacrifices of power and
fuel economy in exchange for optimum emissions control."

Just following this section is a very good technical presentation of
"pressure equalization" and "flow differential" vs motor demand.  A good read
for any confused on the earlier "ram air" discussion.

Scott
.86 lambda-ed whenever possible