Are the intake and exhaust valves open During the stage of internal combustion engine operation in which the piston rises and compresses the fuel in the combustion chamber?

Answer 1

No, both valves are closed so as to create a seal around the combustion chamber so the fuel/air mixture can be compressed.

It goes like this:

Stroke 1 - the piston is drawn down in the combustion chamber with the intake valve open, allowing air to enter the chamber. At the same time, fuel is injected into the chamber as well.

Stroke 2 - the piston is pushed up towards the head with both the intake and exhaust valves closed, compressing the fuel air mixture and lowering the mixture's flash point (kind of like how a pressure cooker works). This also makes the subsequent explosion more powerful

Stroke 3 - the spark plug fires and the mixture ignites, forcing the piston back down the combustion chamber. Both valves are still closed here.

Stroke 4 - the piston returns to the top of the combustion chamber and forces the exhaust and any remaining fuel vapors out of the chamber through the open exhaustvalve.

The valves open and close in perfect succession thanks to the cam shaft which is linked to the crank shaft by a timing belt (which is actually a chain, like on a bicycle). Some models use two to three gears in lieu of a chain, which prevents a loss of timing which could be catastrophic to your engine.

Any other questions, feel free to ask!

If anyone finds any discrepancies, please inform me!