stacked pistons=hi compression

[fullofhotair]

A smaller piston is recessed in larger piston. When larger piston reaches top ,smaller piston continuous up in smaller cylinder .Looks like stepped pyramid from side, when extended.

[fullofhotair]

This doesn't increase pressure because the piston is smaller but because it decreases dead space between the piston and top of the cylinder. It couldn't be used on an engine with an open cylinder. The pistons would need a head to compress against.

[fullofhotair]

I realized that once the larger piston tops out, this forms another temporary closed system for the smaller piston . This smaller piston doesn't have to equalize pressure with the displacer cylinder. If a cavity has been left around the smaller piston and the smaller piston extends out of the cavity ,and into an open cylinder ,then pressure and heat have built up, in the cavity ,to do more work. The push from below the second piston would be extra work you wouldn't realize if the larger piston was solid and just reached the top of its stroke. The con rod is connected to the top of the smaller piston. Remember in a conventional gamma configuration, all the work being done is force underneath the power piston. This is extra pressure taking place above the power piston.

[fullofhotair]

If this doesn't make sense to you ,picture it this way. You have a gamma engine with a heavy power piston. Its cylinder is twice as long as usual. As you run it up to max rpms, it is still using half the cylinder. You magically, I don't how else to put it, disconnect the piston from the con rod, but keep the same resistance on the piston as did the con rod and flywheel. What do think will happen? Do think the piston will reach 1/2 the length of the cylinder as usual and stop or do you think it will continue up the full length? I don't believe stirling engines have a strong vacuum stroke, so the piston will continue up . If you agree with this analysis ,then there is an extra force not being used. I believe the stirling engine mechanically stops the piston and then shuttles it back down by means of the revolution of the flywheel. Like you slugging a brick wall. Your fist had more energy to expend but is mechanically stopped by the wall. This second piston captures this extra force without compromising the conditions in the displacer cylinder. If you used the collapsible displacer /regenerator you could gain the extra length needed for the second piston to travel up. Just a displacer that contracts to half its length. That is the same length stroke you give your second piston.