tigers
[Top] [All Lists]

RE: question for all you rocket scientists

To: " Ron Fraser" <rfraser@bluefrog.com>, "Lynn Wall"
Subject: RE: question for all you rocket scientists
From: "Smit, Theo" <Theo.Smit@dynastream.com>
Date: Wed, 13 Jun 2007 13:51:22 -0600
The ambient air pressure goes down with altitude; the average pressure
in Calgary (altitude 3500ft)  is about 90% of sea level pressure. The
oxygen content (by volume percentage) is still around 20-21%, but
engines up here don't make the same amount of power as they do at sea
level due to the reduced ambient pressure. You could compensate by
increasing the compression ratio - assuming you never take the car
anywhere lower in altitude. Turbochargers with the waste gate referenced
to absolute pressure are the way to go - constant performance regardless
of the ambient conditions.

As it relates to cooling: You're making less power at altitude so the
engine doesn't make as much heat. However, the air massflow through the
radiator is lower because the air density is lower, so the cooling
effectiveness is similarly reduced. The cooling system is limited to
(say) 13 PSI over whatever the ambient pressure is by the radiator cap,
but that's almost one full atmosphere (14.7 psi nominal) over ambient,
so the boiling point of the coolant is only fractionally reduced as a
result of the decrease in ambient pressure.
As an example, in Calgary, the boiling point of water is about 96.5
degrees C, where it would be 100 degrees at sea level. If you're running
your car within 3 degrees (that's about 5 or 6 degrees Fahrenheit) of
boiling over, then you're too close anyway.

Best regards all,
Theo




<Prev in Thread] Current Thread [Next in Thread>