edmechanic > wrote in message
oups.com...
> Well I have a rather unorthodox view of combustion

Yes you do and not a correct one I'm afraid to say.

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.
> Now a lean mixture will not burn fast enough to produce maximum
> push and produces pressure when piston is further down and volume is
> too great for maximum power.
> So heat and pressure of rich mixture is converted more into
> kinetic energy of piston, which lowers the temperature of the burning
> mixture as the piston goes down. The heat of the lean mixture is not
> converted to kinetic energy of piston so it retains more heat as piston
> goes down and that is why exhaust is hotter and metal is hotter.
> So with a lean mixture you have more waste heat.

The change in burn time over the range of mixtures used in a modern SI
engine (14.7:1 at cruise to about 13:1 at full power) is not significant. In
any case the ignition advance can be mapped to take account of this if
needed. The mixture that gives maximum power does so because the most fuel
molecules are burned in a given time. It's that simple.

What does alter burn time very considerably is the amount of cylinder
filling which is why engines need more ignition advance at part throttle.


> Why does a diesel engine have more torque, because it pushes on
> piston longer as long as injector is open while with a gas engine it
> just pushes alittle while after top dead center.

Diesel engines don't have 'more torque' as the most cursory look at the
torque per litre figures from normally aspirated diesel and petrol engines
will tell you. Even if they did it would have nothing to do with how long
something pushed on the piston.


> So a rich mixture produces more instant heat and pressure energy
> right where it is needed for maximum power while a lean mixture extends
> the burning time and therefore pushes weaker and at past best time.

Poppycock.
--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)