This AI looks smart but a little ignorant too.
The BDC port is aways open and has no valve or flap.
It only let's out exhaust when the piston moves past it to BDC exposing the port. As soon as the piston moves moves up near an inch from BDC, it is "closed".
This AI is also confusing the intake stroke with the compression stroke. intake stroke is always downward.
Most interesting is that AI writes in good English that is easy to understand.