Putting all of the theoretical aside, this is a short list of everything I have learned about these engines with the help of other forum members, especially Matt Brown, that I can only hope will encourage others to look at these engines differently than in the past. One would be served well to not just build another ST-05 clone.
-Thermal performance of materials is paramount. Every surface of the engine should serve to heat, cool, or insulate, and only at the right time. The displacer and chamber should have extremely low conductivity along the axis of displacer movement. Even very thin metal is too conductive for high overall efficiency. When thermal performance is optimized, there is no need for extreme temperatures like from an open flame.
-The problem with scaling engines is not that volume increases proportionally more than surface area. The problem is that it becomes increasingly difficult to keep the surface area of the heater and cooler far greater than the area of any surface that is not directly heated or cooled. In other words a large engine requires a large displacer, and that displacer had better maintain close to Tmax on one end and Tmin on the other. Otherwise it just serves to equalize the temperature of the gas that we are working so hard to maintain at extremes.
-The displacer must serve as a valve to regulate the flow of heat, not just a barrier. There's a reason internal combustion engine run poorly with leaking valves, and that logic should be applied to external combustion engines as well.
-Displacer timing and dwell must be adjustable, specifically a valvular type displacer, as its movement becomes more akin to an ignition event than a sinusoidal wave.
-Many small scale HTD engines operate at a much lower effective temperature differential than one would think, and still get away with a power piston volume nearly the size of the displacer volume. This means an engine that has an effective temperature differential of over 300k will allow a power piston far larger than what is traditionally recognized. Think double or more the size of the displacer.
-Hot connected power pistons allow a smaller displacer chamber. The hot expanding gas should not be made to double back through the cooler on its way to the power piston.
-The regenerator, if it can be made to have a gas flow path that makes sense when drawn on paper, should be much smaller than most are built. Just work out the heat capacity of the gas vs. your regen material and that will be apparent.
I will continue to update my youtube channel https://www.youtube.com/@The-Stirling-Power-Project as progress is made. My 150cc epoxy chamber engine is nearly complete and I hope to make record watts per cc, per rpm.
Thanks to all for the help here.
A review of key points
Re: A review of key points
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You are welcome. Good luck. Best wishes. Cary on.
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You are welcome. Good luck. Best wishes. Cary on.
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Re: A review of key points
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Some key points.
Many heat engines run with gas as a working fluid.
They work because the internal gas pressure is greater during expansion, and lower during compression.
During expansion and or compression, the internal gas pressure changes, it's non constant.
The higher the gas temperature during expansion the higher the pressure.
The lower the temperature during compression, the lower the pressure.
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Some key points.
Many heat engines run with gas as a working fluid.
They work because the internal gas pressure is greater during expansion, and lower during compression.
During expansion and or compression, the internal gas pressure changes, it's non constant.
The higher the gas temperature during expansion the higher the pressure.
The lower the temperature during compression, the lower the pressure.
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