Two-Stroke Engine

The two-stroke diesel engine completes its thermodynamic cycle — induction, compression, combustion, and exhaust — in just two strokes of the piston, one up and one down, firing on every revolution. This inherently high power density makes the two-stroke engine the preferred choice for large slow-speed marine main engines, where the crosshead design allows the crankcase to be isolated from the combustion space by a stuffing box, permitting the use of system oil for the crankcase without contamination from combustion products. Power outputs on the largest engines exceed 80 MW, making them among the most powerful internal combustion engines in existence. Scavenge air for two-stroke engines is supplied by turbochargers and, at low loads, by auxiliary blowers to ensure effective cylinder scavenging. SOLAS II-1/40.2 requires crankcase oil mist detectors on engines above a certain crankcase volume to provide early warning of bearing overheating before a crankcase explosion can occur. Engineers monitor exhaust valve timing, injection pressure, and fuel quality closely because the two-stroke engine's higher combustion temperatures and pressures make it more sensitive to poor-quality fuel and valve timing errors than a four-stroke unit.