<VV> Straight talk on octane and alky (no Corvair)

[burkhard at rochester.rr.com]

Hey, I have been quietly following this thread and biting my tongue, 
not wanting to pollute the list further with off-topic stuff. Well, 
enough quarter-thruths have flown by that I've got to pipe up.  At 
least I'll tag the subject as "No Corvair".... Don't people do that 
anymore? 

Most of the stuff you have been discussing (namely Flexible Fuel 
vehicles and Electronic Throttle Control) has been in VOLUME production 
at GM and most other OEMs for many (over 10!!) years.  It's nothing 
new!   ANYBODY could have bought these things for years and years.  
REPEAT: It's nothing new!   The fact that Saab is finally coming to the 
party with an E-85 <--> E0 (straight Gasoline) flex fuel vehicle is 
probably not something worth them heralding.  Keep in mind that very 
very few of these flex fuel vehicles ever run on anything other than 
straight gasoline (E0) or "gasohol" (E10).  They only exist because the 
manufacturers get credits for making them and sometimes the buyers get 
some nice tax incentives for buying them.  In the free market, they 
would not exist at all (ask Brazil about what happned to their very 
popular Ethanol program when they turned off teh subsidies).  
Realistically, people in the industry all know that Ethanol is not a 
serious means to reduce the nation's dependence on foreign oil. That's 
delusional at best.  Ethanol "encouragement" only exists as a political 
payoff to corn farmers and agribusiness giants like Archer Daniels 
Midland.  Few serious engine researchers work on it anymore.  The 
economics aren't there and the science isn't either -- growing 
corn/beets/whatever (even biomass) only to process it and reduce it to 
fuel and bring it to market is a net energy CONSUMER in a big way.

The description of electronic throttle control is also a bit confused.  
Firstly, by no means is ETC a requirement for a flex fuel vehicle!  All 
these need to do is measure/estimate airflow (via the conventional 
means of an airmeter or speed density (MAP & manifold temp & rpm) 
calculation like any other car) and then divide by the air/fuel ratio 
desired to figure out the required pulse width of the injectors. The 
only difference with "normal" engines is that there is an inline fuel 
sensor that figures out what % gasoline/ethanol blend is present and 
then from this the proper A/F ratio is figured.  You don't need 
electronic throttle control at all ... the throttle can be directly 
coupled to the pedal in the old fashioned way. As the driver steps on 
the pedal, the throttle opens and from there the airflow gets measured 
in the manner I stated. It's an "air lead" system in which the 
fuel "follows". No need for ETC. 

Point #3: Saying that adjusting the throttle changes "the effective 
compression ratio" is a stretch.  You can do this via some variable 
valvetrain systems, but an ETC ain't it.

Point #4: Super/Turbocharging belongs everywhere, not just at 
altitude!  Of course it is especially needed at altitude, but there is 
nothing magic about 20,000 feet or any other altitude. Why allow one's 
engine's volumetric efficiency to be limited because of the silly and 
arbitrary contraints of atmospheric pressure?

Point #5:  It seems you are saying that OEMs control spark knock by 
closing the ETC (throttle).  This is not true *unless* perhaps the 
engine is having so many faults, it is doing so as a last result to 
keep from destroying something. It certainly is not the first approach 
taken. Closing the throttle reduces airflow into the engine and that 
reduces torque pretty much linearly.  ETC opening is reduced to provide 
torque management during upshifts, traction control, limp home 
modes, "valet modes" (limited throttle authority), and several other 
things. A primary means of knock control they are not.  Knock control 
is done via spark retard; smarter systems do this on a individual 
cylinder basis.  But whether applied to the whole engine or per-
cylinder, the torque loss with retard is FAR less than closing the 
throttle.  

So what is ETC useful for?   Well, besides the things I mentioned 
earlier, it does provide enabling technology for direct injection 
gasoline engines, vacuum control for high-authority variable valvetrain 
engines, engine air control for hybrid vehicle engines, supply vacuum 
when needed on low vacuum engines, air control for homogeneous charge 
compression ignition engines (not yet in production), and a bunch of 
other things.  Basically, anytime the airflow needs to be modulated 
without driver input, an ETC is the way to do it.  In these cases, the 
accelerator pedal acts on a pedal position sensor, which supplies 
information to the engine's ECM about how much torque the driver 
wants.  The ECM software figures out the best way to deliver it and 
adjusts the throttle, valvetrain, spark timing, etc. to provide that 
torque in the best (usually least fuel consumption and least emissions) 
way.  As long as the driver gets the torque he wants, it doesn't matter 
to him how it happens.

Point #6: It also seems like you are saying that the ECM 
somehow "knows" combustion chamber pressure.  There are probably engine 
management systems that attempt to model (and thius estimate) this, but 
nobody has an engine with combustion chamber sensors in *production* 
(everybody does it in the lab, though, via expensive equipment).  
Actually sensing chamber pressure is a bit of a "Holy Grail" in engine 
research.  Everybody would love to have it as it would enable a slew of 
technology, but the systems proposed and tested to date are either very 
expensive, fragile, or don't work under all conditions.

I'll try to be quiet now. If anybody wants to talk more about any of 
this, write me off-list.

Jim Burkhard