LTD Stirling Engine Development-Regenerator

[VincentG]

In the past I have questioned the role of a regenerator in a Stirling engine. I understand the potential efficiency gain, but I don't think it belongs inside the engine. In a system where the ideal operation is a light switch response between full hot and full cold, an internal regenerator forces an extra volume of dead space to be essentially at an average operational temperature. In an atmospheric engine we are already limited by low max pressure swings, so this space only serves to dampen the pressure blows the piston should be utilizing.

Instead, we can move the regeneration outside of the engine to both maximize power and efficiency. This will also apply to medium and high temperature engines. This flow chart should be pretty self explanatory. The cold medium(in this case engine coolant or similar) starts at the PCSE(1) where it is then pumped to the cold sink of the engine. From there it picks up the rejected heat from the engine. Now slightly warmer, it moves to the pre heater/regenerator(2) where it picks up more heat from the discharge of the hot sink. This will reduce the energy needed by the PHSE(3) to warm the coolant to the source Tmax. After the coolant passes through the hot sink of the engine, it loses heat to the regenerator(2) before moving to an optional DHE(4) where the remaining heat can be used for domestic hot water or space heating. Then the cycle is closed when the coolant returns to position (1) and its temperature is reduced to ambient Tmin(via water to air or water to water) before restarting the cycle.

LTD External Regenerator flow diagram.jpg (163.52 KiB) Viewed 12937 times

All of the exchangers are of course intended to be insulated tanks, and residential water heaters would make good candidates for conversion.