Compression stroke The piston moves from BDC to TDC (up). Both valves are closed. The piston compresses the air and fuel mixture. Exhaust valve Intake valve closed closed Top dead centre (TDC) Stroke Bottom dead centre (BDC) stroke Figure 20—Compression Power stroke The piston moves from TDC to BDC (down). Both valves are closed. The spark plug fires. The fuel mixture burns rapidly. This expanding heated mixture forces the piston down. Intake valve valve closed closed Top dead centre (TDC) Stroke Bottom dead centre (BDC) Figure stroke
Compression stroke The piston moves from BDC to TDC (up). Both valves are closed. The piston compresses the air and fuel mixture. Intake valve closed Exhaust valve closed Top dead centre (TDC) Stroke Bottom dead centre (BDC) Figure 20—Compression stroke Power stroke The piston moves from TDC to BDC (down). Both valves are closed. The spark plug fires. The fuel mixture burns rapidly. This expanding heated mixture forces the piston down. Intake valve closed valve closed Top dead centre (TDC) Stroke Bottom dead centre (BDC) Figure stroke
Basics4StrokeEngines.docx