the basic designs have become standardized around the UNI-flow scavenging system. This system started life with opposed piston engines where the exhaust piston was arranged to uncover the exhaust ports. Approximately on third of the engine’s power was transmitted through the exhaust piston and eccentrics arranged on the crankshaft on either side of the unit’s main journal. Figure 2.44 shows the arrangement of the latest Wartsila engine showing the cooling channels and the position of one of the three injectors.