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1. The displacer piston (2) has moved most of the gas to the hot heat exchanger, as a result the gas is heated up and expanding. The power piston (1) is being pushed away, this is the power stroke. |
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2. The heated gas increases its pressure and pushes the power piston along the cylinder towards its top dead centre (TDC). Meanwhile, the displacer piston is moving the heated gas to the cold zone. |
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3. The heated gas is cooling down, decreasing its volume. The displacer piston has moved most of the gas to the cold zone of the cylinder. The power piston is compressing the gas by the flywheel momentum. This takes less energy because the gas pressure is decreasing. |
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4. The cooled gas has decreased its volume and pressure, the power piston is at its bottom dead centre (BDC). Meanwhile, the displacer piston is moving the cooled gas to the heated zone, so the gas can heat up and expand again, pushing the power piston away. |
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Animated version. In this example, the power piston lags the displacer piston by 90°. In this design the displacer piston shaft passes through the power piston in a gas proof sleeve. |
