Don Stauffer > wrote in message
...
> edmechanic wrote:
> > Well I have a rather unorthodox view of combustion developed as a
> > smog tech. One of my smog instructors said that the difference between
> > a rich mixture and a lean mixture is that the rich mixture burns faster
> > because fuel molecules closer together and a lean mixture burns slower.
> > So the way I look at it is a rich mixture will burn when the piston is
> > near Top dead center producing alot of pressure and heat where you can
> > do the best work for pushing down the piston.
>
> Any difference in distance (mfp) between molecules is insignificant.
> Further, the speed of the molecules is very high compared to their mean
> free path.
>
> The flame front speed doesn't vary that much with mixture ratio, at
> least over the ratios we are talking about. Also, the burning time is
> insignificant in SI engines in terms of degrees of crankcase revolution
> angle except at VERY high rpms.

Perhaps you mean the change in burn time (i.e with different mixture ratios)
but if not then certainly the burn time occupies a significant portion of an
engine revolution or we wouldn't need ignition advance in the first place.

I'm also unaware of any engines in which the crankcase revolves
--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)