Power piston port size

Cartech · Post by **Cartech** » Thu Nov 02, 2006 2:00 pm

I am building a LTD Stirling (second one) and would like to know how important the port size from the power piston to the displacer is? I will be using a 7/8ths piston with a 1 inch stroke with a displacer area of about 10 times that volume. Thanks.

SScandizzo · Post by **SScandizzo** » Thu Nov 02, 2006 6:42 pm

I'm guessing that as long as the port doesn't impose a restriction to air movement (along the lines of a pin hole sized opening), it probably doesn't have much of an effect. It might be a cool experiment if you installed a spot for a restrictor plate in order to test different port sizes, but that may be a project within itself...

-Stefan

Cartech · Post by **Cartech** » Thu Nov 02, 2006 8:13 pm

It would seem that having the compression end of the power cylinder completely open to the displacement chamber would be best but I have seen plans that state otherwise. Not sure what an off-center hole half the size of the bore would help? Anyone heard of this?

SScandizzo · Post by **SScandizzo** » Fri Nov 03, 2006 12:39 am

My understanding is that a turbulent air flow is desirable; that being the case I would suspect that off-center and less than full bore ports may actually be beneficial. Just speculating, though.

-Stefan

stanhbaker · Post by **stanhbaker** » Fri Dec 01, 2006 10:50 am

As usual "it depends."

For an LTD pancake displacer Stephan is right, offset from center, but not too far.

For other configurations make the passageway as short as possible and large enough but not too large. Say about 25% of piston diameter.
The passageway is "dead space" that contributes nothing to efficiency but must be adequate for operation.