1. Intake Stroke:
- The poppet valve opens, allowing fresh air to enter the cylinder.
- This air mixes with fuel, forming a combustible mixture.
2. Compression Stroke:
- The poppet valve closes, trapping the fuel-air mixture in the cylinder.
- The piston compresses the mixture, increasing pressure and temperature.
3. Power Stroke:
- The compressed mixture ignites, creating a powerful explosion.
- The expanding gases push the piston down, generating power.
- The poppet valve remains closed during this stroke.
4. Exhaust Stroke:
- The poppet valve opens again, allowing the burnt exhaust gases to escape the cylinder.
- The piston pushes these gases out through the exhaust port.
Key Features of Poppet Valves:
- Shape: They are typically disc-shaped with a conical head.
- Valve Stem: They are connected to a stem that runs through the valve guide.
- Valve Spring: A spring holds the valve closed, ensuring a tight seal.
- Valve Seat: The valve sits on a machined seat in the cylinder head, creating a tight seal when closed.
- Camshaft and Lifters: A camshaft, through a system of lifters, opens and closes the valves at precise intervals during the four-stroke cycle.
In essence, poppet valves are the critical components that regulate the flow of gases into and out of the engine's cylinders, enabling the combustion process and the creation of power.
