Optimizing A/F Mixture & Quality

[Seth Allen]

On Tue, 10 Jun 1997, Shane Moseley wrote:

> Date: Tue, 10 Jun 1997 21:56:18 -0500
> From: Shane Moseley <smoseley at ix.netcom.com>
> To: mml <mopar at mopar.tamu.edu>
> Cc: diyefi <diy_efi at coulomb.eng.ohio-state.edu>
> Subject: Optimizing A/F Mixture & Quality
> 
> Since there has been some recent talk about Air/Fuel ratios, Heat/Energy
> content of various fuels/additives, & other fuel delivery related
> topics, I would like to get some opinions on the following:
> 
> 1. Re: Optimum A/F ratios
> 
>   I understand that most O2 sensors have a fairly narrow band of
> operation and give primarily indications of 'too rich' or 'too lean'.  I
> assume that for this reason, they are used mostly (some say always) at
> either idle or cruise.  Most agree that they are useless at WOT & part
> throttle (agrees w/earlier assumption).  A recent post in one of these
> lists mentioned a new spin-off of Fel-Pro called FP Performance that has
> a computer-controlled FI setup with a wide-range O2 sensor (high dollar
> option?) that can sense a 12.5 (or whatever the optimum WOT A/F is).  If
> this is so - then wouldn't it be best to be in closed loop almost
> always? (after engine has reached operating temp of course)  Anyone with
> experience here?  I was thinking seriously about running down to
> Ashland, MS (home of FP Performance & about 40 min drive from Memphis
> 8-) and insisting they hire me on.


You are right  about the relative resolution of the two styles of o2 
sensors, but not exactly correct in the application.  A standard o2 
sensor goes from about 200mV at lambda of 1.005 to 800mV at lambda of 
.995. The output is only from 0-1V. The lean side of the curve (lamda 
above 1.1 or so is flat.  The rich side has a small slope and can be used 
to tune to a slightly rich condition with mediocre resolution. A 
"linear" oxygen sensor has uniformly mediocre resolution everywhere. It 
is much less sensitive than a regular o2 sensor at lambda=1, but is very 
good for controlling lean burn.  A combination of the two would be 
ideal. You could get a consistent lean burn at cruise and half throttle, 
then go to stoichiometric as the load ( and NOX levels rise) then go 
rich for maximum power and reduced NOX emissions. But the linear o2 
sensor cannot replace the conventional one for use when good emissions 
control is needed to use a three way catalyst. 



> 2. 
Re: Optimum conversion of fuels potential for energy (combustion) > 
> After being intrigued for many years about engine intake designs -
> nothing mixes up conversation better than Smokey Yunick (& other
> Otto-cycle designs) and his miracle engines that got 50-60 mpg with no
> performance loss (40% gains instead 8-) by HEATING the incoming A/F
> mixture to around 400 degrees.  Most say 'yeah right - then why are the
> factories all producing intercoolers?'  Well, I have read many of
> Smokey's articles and have the one with the design drawings of his Fiero
> experiment in Hot Rod June '84.  I understand that internal combustion
> engines probably average around 25% efficiency of converting fuels
> potential for energy (BTU's?) into actual usable energy (read flywheel
> horsepower).  And that current designs might be between 30-40 percent in
> optimum conditions (read hardly ever).  Seems to be alot of room for
> improvement here!  This is the basis for Smokey's design.  Further -
> according to several sources (nice one at
> http://www.autoshop-online.com/auto101/fuel1.html about all sorts of
> things including description of operation of Chrysler X-Ram intakes) the
> optimum condition of the incoming mixture are something like:
> 
> "Dry fuel vapor is an ideal form of fuel charge, but present-day fuel
> prevents this unless the mixture is subjected to high temperature."
> 
> Attempts to achieve a greater conversion rate (efficiency) are commonly
> known as supercharging & turbocharging that 'pump up' the incoming
> mixture causing a side effect (cant remember exact mixture
> condition/problem) thus the need for intercoolers (say what?
> contradiction?), additives, etc. for correction.
> 
> Seems kinda confusing I know - Why not skip the whole mechanical attempt
> at regulating all these variables and let a computer control all
> (especially temperature/condition of incoming mixture) for an optimum
> (under all conditions 8-) conversion/combustion/BURN!
> 
> Comments welcome!
> 
> 
> "We have the technology... We can build it..."
> 



Smokey Yunick can be a bit misleading at times, would you ever expect the 
straight truth from a guy who built a 7/8 scale stock car to reduce 
drag?  Clever, surely, but honest, no.

Heating the fuel to a dry gas can help at small throttle openings.  At 
large throttle openings, the gaseous fuel can displace air in the inlet 
tract, contribute to detonation, and in some two strokes, piston 
seizure.  If you have a 500 CID caddy that you never use full throttle, 
then try it, but the gains will mostly be in emissions, perhaps a bit 
with cruising fuel economy. 



> > -- > Shane Moseley    Home: 
http://www.netcom.com/~smoseley
> Systems Analyst  Work: http://www.healthsphere.com
> '96 Indy Ram     Play:
> http://www.geocities.com/MotorCity/3067/indyram.html
> '74 Challenger  <- 2 360 engines (magnum & non) 245hp each dying for
> flog time!
> 


REPLY AND OPINION 
courtesy of

Seth Allen