yes
They are closed during the power stage.
Both the intake and the exhaust valve are closed.
Closed
Closed.
Closed
Closed
If im not mistaken, during the power stage the intake and exhaust valves are both closed. the intake valve opens pulling air into the cylinder (cycle one) and the exhaust valve opens (cycle 4) to relase the air fuel mix that was ignited.
During the power or combustion stage of a piston cycle, both valves are necessarily closed, because the expansion of gases is driving the piston down.
intake stroke, compression stroke, power stroke, exhaust stroke in that order
closedUpdated answer,Firstly the four stages of an "Otto Cycle Engine" are, Induction the intake valve is opening, to let fuel and air mixture into piston chamber. Compression the intake valve and exhaust are shut to compress fuel air mixture. Powerfuel air mixture ignited, both the intake and the exhaust valves are closed. And finally Exhaust when the exhaust valve is open to release spent gasses. At idle speed approximately 800 rpm it should be appreciated timing is important.
The power stroke * intake / compression / power / exhaust
intake compression power exhaust