[Diy_efi] RE: Throttling intake air

[Brian Michalk]

> >Er yes - sort of but thats mostly a static interpretation, in controlling
> >boost (where the turbo is sized for it), you are controlling the source
> >of combustion not the much larger energy in the end product.
>
> What I should have said here is,...' you are controlling the
> source of combustion which takes less energy than the hotter
> consumed end product which is wasted when wastegate opens.
>
> <cough> even thats not quite kosher, theres a better way to
> explain it - though I think Greg did very well <:-)

I think Greg was referring to the second law of thermodynamics:

Introduction to the Second Law of Thermodynamics
The second law is concerned with entropy (S), which is a measure of
disorder. The second law says that the entropy of the universe increases. An
increase in disorder (overall) is therefore spontaneous. If the volume and
energy of a system are constant, then EVERY CHANGE TO THE SYSTEM INCREASES
THE ENTROPY (emphasis mine--BKM). If volume or energy
change, then the entropy of the system can actually decrease. However, the
entropy of the universe does not decrease. The molecules in one's body exist
in great order; this only happens because the entropy of the rest of the
universe is increased to a greater amount than the entropy of the body is
decreased.

So, every time you suck or squeeze a gas in an engine, you increase it's
entropy, therefore lowering the efficiency of the engine.

Side note:  intercoolers decrease the entropy by ejecting heat to the
universe, because even though volume is contant (pressure), heat is
decreased.


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