> >> >Rick Morrison wrote:
> >> >> The exhaust and intake are so tied. Simply put, what goes in,
> >> >must
> >> >> come out.
> >> >
> >> > That's just not true. What goes in comes out, along with a whole
> >> >lot more. Gasoline goes in as a vapour and comes out as various
> >> >gases which are much more voluminous.
> >> 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.
> >> > That is the central point.
> >
> >Actually, the correct statement is that ENERGY cannot be created or
> >destroyed, only altered in form (First law of thermodynamics).
> > Anyway, even though the matter DOES remain constant in your typical
> >non-nuclear-power MGB, volume is another concern entirely. As the
> >fuel/air mixture burns, it expands rapidly, so that the amount of
> >gas/vapor coming out of the head is much larger than the amount going
> >in. Whether this has any effect on carb/exhaust "matching" is left
> >to better engineers than I.
> >Scott
> >
>
> I believe you are both wrong. The typical statement in a chemical
> engineering class has to do with either mass or energy, and concerns all
> non-nuclear reactions. The statement goes - what goes in comes out, except
> what doesn't. That qualifier concerns recycling streams, and if you can get
> a grasp on all aspects of any reaction, the except what doesn't goes away.
> It is obvious that mass and volume are not the same, look at air, and look
> at gasoline, the same amount of volume weighs a lot different. When the two
> are combined, a lot of the heavy gasoline gets atomized, thus lowering its
> density, then it explodes in the combustion chamber and becomes different
> compounds, mostly carbon, carbon dioxide (a gas), some carbon monoxide (a
> gas) and water vapor (since it is vapor, aslo a gas). The gases take up a
> lot of volume, the carbon doesnt, but is minimal.
> Phil Bates
>
Phil,
Well, if you're going to ignore nuclear reactions, both mass AND
energy are going to be conserved in any reaction. My statement
of the First Law is simply the most general, and covers all
reactions, nuclear and otherwise. I was simply pointing out that the
destruction of matter is a pretty routine thing nowadays, so making a
general statement that matter "cannot" be destroyed isn't
technically correct. Anyway, on to the car problem.
Lets say we run one pound of air/fuel mixture through an engine, and
save up all of the exhaust products. The air/fuel mixture will weigh
EXACTLY the same as the exhaust mixture (one pound), and the chemical
energy in the fuel/air mixture is just mostly converted to heat and
work in the engine. True, the exhaust is a LOT less dense, which is
the point I was trying to make clear. When you keep mass the same,
but decrease the density (increasing the volume), it's clear that
more gases come out of a cylinder head than go in.
Scott
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