A four stroke diesel engine has

🔑 Key Points
Explanation of Engine Cycles:
→ There are two types of valves in an engine cylinder: Inlet Valve and Exhaust Valve.

Suction Stroke:
→ The piston moves from TDC to BDC. A vacuum is created inside the cylinder. The inlet valve opens while the exhaust valve remains closed. The charge (air/air-fuel mixture) enters the cylinder.

Compression Stroke:
→ The inlet valve closes. The exhaust valve remains closed. The piston moves from BDC to TDC. The charge (air/air-fuel mixture) is compressed, increasing the pressure and temperature.

Power Stroke:
→ S.I. Engine: The charge is ignited, and pressure develops inside the cylinder. The gas expands, forcing the piston down from TDC to BDC. Both the valves remain closed.
→ C.I. Engine: At the end of the compression stroke, diesel fuel is injected into the hot compressed air in the combustion chamber, causing instantaneous combustion. The gas expands, and the piston is forced down from TDC to BDC. Both the valves remain closed. Power is supplied to the flywheel.

Exhaust Stroke:
→ The inlet valve remains closed. The exhaust valve opens, and the piston moves from BDC to TDC due to the energy stored in the flywheel. The burnt gases inside the cylinder are expelled through the exhaust valve. At the end of the stroke, the exhaust valve closes.

📌 Important Points
→ The cycle of suction, compression, power/expansion, and exhaust are repeated. In this type of engine, one power stroke is obtained in two revolutions of the crankshaft. Power is supplied to the flywheel.