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Opposed-piston engine

An opposed-piston engine is a piston engine in which each cylinder has a piston at both ends, and no cylinder head. Petrol and diesel opposed-piston engines have been used mostly in large-scale applications such as ships, military tanks, and factories. Current manufacturers of opposed-piston engines include Cummins, Achates Power and Fairbanks-Morse Defense (FMDefense). Compared to contemporary two-stroke engines, which used a conventional design of one piston per cylinder, the advantages of the opposed-piston engine have been recognized as: Eliminating the cylinder head and valve-train, which reduces weight, complexity, cost, heat loss, and friction loss of the engine. Creating a uniflow-scavenged movement of gas through the combustion chamber, which avoided the drawbacks associated with the contemporary crossflow-scavenged designs (however later advancements have provided methods for achieving uniflow scavenging in conventional piston engine designs). A reduced height of the engine The main drawback was that the power from the two opposing pistons have to be geared together. This added weight and complexity when compared to conventional piston engines, which use a single crankshaft as the power output. The most common layout was two crankshafts, with the crankshafts geared together (in either the same direction or opposing directions). The Koreyvo, Jumo, and Napier Deltic engines used one piston per cylinder to expose an intake port, and the other to expose an exhaust port. Each piston is referred to as either an intake piston or an exhaust piston, depending on its function in this regard. This layout gives superior scavenging, as gas flow through the cylinder is axial rather than radial, and simplifies design of the piston crowns. In the Jumo 205 and its variants, the upper crankshaft serves the exhaust pistons, and the lower crankshaft the intake pistons. In designs using multiple cylinder banks, each big end bearing serves one inlet and one exhaust piston, using a forked connecting rod for the exhaust piston.

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