Renewable Energy Sources for the mCCHP-SE-RES Systems - Design for Micro-Combined Cooling, Heating and Power Systems - page 113

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Fig. 13 Alpha Stirling engine, 1 regenerator, 2 expansion piston, 3 hot piston, 4 source of heat, 5
fuel, 6,12 cylinder jacket, 7, 11 connecting rod, 8 flywheel, 9 crankshaft, 10 hinge, 13 radiator, 14
compression piston, 15 gas cooler

As the process gas is compressed at lower temperatures and expands after being
heated, it pushes the pistons back and forth between both cylinders. One cylinder is
therefore termed the expansion cylinder, while the other is the compression cylinder.
The working gas is located between the upper ends of the two pistons in the
actual Stirling process, in the heater, regenerator, and gas cooler. This is where the
circulation process, with constant changes of pressure and temperature, takes place.
As the process gas remains in the engine, it can be put under higher pressure which
offers improved and/or variable performance by varying the pressure. One of the
supply tank with working gas is the bottle. Here, (in bottle) the pressure level is
always higher than the average cycle pressure. Helium may

flow into the engine or

be pumped back.
The heater is located inside a cylindrical combustion chamber in which com-
bustion is constantly taking place. The process gas cooler comprises a bundle of
small pipes through which cooling water

flows and the regenerator that forms a
thermal accumulator between the two temperature levels. The regenerator greatly
improves the thermodynamic circulation process and therefore the ef ciency.

A crankshaft with friction bearing and forced feed lubrication drives the pistons.
The con rods are connected to the cross heads which support the lateral forces in
their cylinders. The pistons are connected to the cross heads by a rod. Both pistons
run inside the cylinders without lubrication as this would carbonize.
The SE drives an electrical generator (asynchronous) via a direct coupling at
speed of around 1,500 rpm at 50 Hz.
The Stirling engines are 15 - 30 % efficient in converting moving energy to
electricity, and the total ef ciency of a micro-CHP with SE is of 80 - 90 %. Stirling

engines are more ef cient on account of their thermal balance, as the difference