Hi Paul,
The amount of oxygen in the air (i.e. the mass of oxygen in a cubic
foot, or any fixed volume) determines the amount of power that the
engine can make and therefore the amount of waste heat generated. If the
"air" has a higher or lower percentage than normal of oxygen, then the
potential power output of the engine goes up and down accordingly, even
though the air density hasn't changed. On the other hand, if the air
itself is being compressed or expanded, thereby giving either a greater
or lesser total mass per unit volume, then the power output of the
engine will also go up and down in a corresponding fashion, even though
the percentage oxygen as a function of the total weight of the volume of
air hasn't changed.
So if you cram more oxygen into a given volume of air, whether that is
by increasing the total air mass or just by increasing the oxygen part,
you will make more power and more heat, and if you reduce the oxygen
content, you will make less power and less heat. The oxygen content by
itself has little to do with the radiator cap function.
The radiator cap is a pressure difference limiting valve, between the
coolant on one side and the ambient air on the other. The radiator cap
allows the coolant pressure to be up to XX PSI higher than the outside
air pressure, and then it opens. So if the ambient air pressure
(referenced to outer space) is 14.7 PSI and the cap is rated to 13 PSI,
then it will limit the cooling system to 27.7 PSI absolute pressure. If
the ambient air pressure is 12.5 PSI, then the cap will limit the
cooling system to 25.5 PSI absolute pressure, and the boiling
temperature of the coolant will be correspondingly reduced. The coolant
boiling temperature depends on the absolute pressure, not the pressure
relative to the ambient air.
Best regards,
Theo
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