[Vwdiesel] Hydraulics...

Val Christian val at swamps.roc.ny.us
Sun Jul 18 22:39:42 EDT 2004

Let's talk gases for a moment.  Skipping details I've long since 
forgotten, the ideal gas law is 


n=amount of gas (moles)
R=gas constant

So if you decrease temperature, and nothing else changes, the pressure
of a cylinder will go down.  

The ideal gas law is emphirically derived, and is merely an approximation.
You'll recall that liquids (fuel oil) will expand with an increase in 
temperature.  The big difference between fuel oil and a gas is the 
degree of springiness.  A gas is much more compressable, therefore 
more energy can be stored in a unit volume.

I don't know the compressibility of fuel oil.  Water will reduce volume
5% when compressed to 16000 PSI.  Hydrostatic testing of gas cylinders 
is done, because if there was a rupture, there is little energy stored
in the relatively "unspringy" water.  Gas would be a very different 
situation. (Remember "Jaws" when the shark eats the scuba tank?  Right.)

Remember that energy is PV (like V*A in an electrical setting).  So high
pressure alone does not mean higher energy.  You still need a flow (current).
So even though there are high pressures, significant work (heat, energy)
requires a flow.  Does the injector pump have that flow.


With regard to "sloshing".  I used that term loosely to describe the agitation
or stiring of the fuel in the pump, both by vanes (centrifugal pump) and 
be flyweights.  If you don't believe that spinning things in a liquid takes
energy, take a battery operated drill, with a paint stirring attachment,
and spin it in a can of paint (or fuel oil).  The current will be higher
for the same speed in the liquid.  A good way to run the battery down fast.
The energy taken from the battery heats the drill motor, and the paint 
(or fuel oil).  You can measure the increase in temperature.

Unfortunately, most of the heat goes to the drill motor.


Oh well, enough babbling.  If we can't come up with an answer, perhaps I
can task one of the Mechanical Engineering seniors with an analysis.
He'll need more details on the injector pump.


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