why is rich better for power ??

[Robert Harris]

Check the FAQs,  http://www.landfield.com/faqs/autos/gasoline-faq/part2/

Check 4.13 for octane and autoignition temps.  In general, as the
weight of the molecule increase (i.e. heavier), the octane and 
Auto Ignition Temp (AIT) decreases, the exception being the 
aromatics - which are being phased out by law.

It isn't the burning speed that matters in antiknock/octane (see 6.3)
it is the autoignition temp so I presume you meant to say the slower
igniting molecules have the higher octane.

"When some one gets something for nothing -
             some one else gets nothing for something "

If the first ingredient ain't Habanero, then the rest don't matter.
Robert Harris <bob at bobthecomputerguy.com>


----------
> From: Johnny <johnny at johnny-enterprises.com>
> To: diy_efi at coulomb.eng.ohio-state.edu
> Subject: Re: why is rich better for power ??
> Date: Saturday, September 06, 1997 8:00 AM
> 
> Robert Harris wrote:
> > 
> > Try this thought pattern.  Gasoline is a blend of different chemicals -
> > ranging from methanol, butane to toluene etc.  Generally speaking
> > the lighter chemicals have higher latent heats of evaporation, octane,
> > and quicker burning. The heavier chemicals generally contain more
> > total energy but take longer to burn.  Sort of like kindling to logs.
> > 
> > By richening the mixture past stoich, more lights absorb more heat,
> > thus cooler denser mixture.  They are also higher octane - more
> > tolerance to detonation and they burn more uniformly faster. Kind of
> > like a fast bonfire  - more heat, more power, big chunks (heavys) left
> > unburnt. Over stoich means less efficiency - but higher power because
> > of faster wasteful combustion with more heat.  Also complete combustion
> > requires several stages which take time.  Rich mixtures generate more
> > heat from early stages and less from the slower burning later stages and
> > run out of oxygen and just throw away the slower heavys.
> > 
> > Now is every one confused????
> 
> No not at all. I got it... I just pull into the gas station and I say,
> "fill-er-up, and give me the stuff that has lots of logs in it, not that
> crap that's all kindling". ;)
> 
> BTW, the slower burning elements have the higher octane rating.
> 
> -j-