A two-stroke diesel fills and compresses the cylinder in one piston movement, then combines the power and exhaust events rather than assigning each a separate stroke. Because intake and exhaust ports can be open together near bottom dead center, a pump or blower must force in fresh air and clear the combustion gases through scavenging. Roots-type superchargers served this role in many ship engines before turbochargers became standard from the mid-1950s. The design promises high efficiency, but it depends on carefully coordinated air handling around the cylinder.
Notable Point · 32:53-35:49
Two-stroke diesels and scavenging
The technical explanation shows how two-stroke marine diesels combine strokes, need scavenging air, and later move from blowers to turbochargers.