Rick Morrison wrote:
> Please explain how a whole lot more goes out than comes in. Maybe I
> missed something, but I was under the impression that matter can neither
> be created nor destroyed - only changed.
As Scott already mentioned, it's because fuel goes into
the carb as liquid droplets and comes out as a gas. The gas has
a LOT more volume, which is what powers the engine after
all. The rapid expansion is what gives the car power, the cylinder
is driven down with a lot more energy than required to
drive it up.
If the gas didn't expand, there would be no power gained,
since compression would take as much power as the power stroke
would yield.
If it wasn't for this gas expansion, a car would be a
very towable air compressor that eats it's 12V battery
every couple of minutes. ;>
> Assume a cylinder has a maximum volume of say 500cc,and further that the
> volumetric effeciency of the engine is 80% (a good VE for LBC engines),
> then on the intake cycle the cylinder will ingest compress and fire 400
> cc of fuel/air mix. On the exhaust cycle, that 400cc of burnt gases will
> have to be removed by the exhaust system.
That's the point you are missing, it's a hell of a lot MORE than
400cc. This expansion is what drives the engine.
> exhaust which is only capable of handling 400cc in the alloted time
> period.
This type of statement is just unscientific. Real world systems
are not fixed volume. More volume is always possible, just requires
more pressure and there is the law of diminishing returns. However
if the exhaust pressure coming out of the valve is higher, you
will flow more air than the previous example, not simply flow the
same air and leave the rest stuck in the chamber.
--
Trevor Boicey
Ottawa, Canada
tboicey@brit.ca
http://www.brit.ca/~tboicey/
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