Engine Energy Conservation

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amaurer
Posts: 2
Joined: Fri Jan 17, 2003 4:30 pm
First Name: Andrew
Last Name: Maurer

Engine Energy Conservation

Post by amaurer »

I'm having trouble concerning the energy conservation in the
Stirling cycle:

It appears that some quantity of energy is added to the 'hot side'
of the engine, and some quantity is removed from the 'cold side'.

Because the volume changes in a displacement type engine are
essentially equal, I would expect that these two quantities are
equivalent. Where does the net energy come from to accelerate the
disk?

Is the fact that the power piston is on one side of the displacement
piston? In the coffee cup engine's case, the power piston is on the
cold side, does this mean the engine is most efficient when energy
is being added to the hot side (i.e. coffee cup) rather than removed
from the cold side? (ice on top)

Am I missing something? I'll admit I've really only glanced at
principles and diagrams of the principle, perhaps I should do so.
Comments?
stan.hornbaker
Posts: 532
Joined: Thu Jun 20, 2002 6:01 pm
First Name: William S.
Last Name: Hornbaker

Response to Engine Energy Conservation

Post by stan.hornbaker »

The Coffee Cup Engine, like any heat engine takes a form of energy in, extracts a second form to perform some useful task, and rejects the remainder.

Q1 = W1 + Q2 or the (work) W1 = Q1 (energy in) - Q2 (energy out)

Heat on the bottom plate heats the air causing it to expand and push the piston outward to rotate the propeller (flywheel would do as well) and push the displacer downward, (2nd crankthrow) forcing the air into contact with the top (cold) plate. A regenerator is made in one of similar design by cutting out circles in the displacer and inserting a differnt foam which passes some of the air through thus alternately heating and cooling it.

There is only ONE volume of air in the engine, it is just in several places and moves from place to place. Even in the convential alpha engine with two cylinders, a piston in one and a displacer in the other, the gas volumes must be connected as one else it is trapped and there is no action other than continuous heating of the air 'trapped' in the displacer cylinder.

The power piston in the MM-5 is a diaphragm and could be located anywhere it connected to the area above the displacer.

The MM-5 runs equally well on ice or coffee. Set it on a saucer full of ice cubes, then take it out in the noonday sun and see the increse in speed. Alternately set a plastic baggie of ice cubes or crushed ice on the top with coffee on the bottom.

Note: The Stirling Store has a Smart Stirling lab engine for classroom use to explore the theory and operation, for physics and engineering lab courses. A bit expensive for casual use. The manual may be downloaded in .pdf by anyone having an interest in more information.
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