What are Opposed Piston Engines and their Advantages?

Posted on September 28, 2021 linda strong jet engines

Piston engine technology has a long history for automobiles and aircraft engine assemblies, ensuring the generation of thrust and propulsion through the combustion of fuel-and-air mixtures. Since their inception, various piston engine types have come about for aircraft and automobiles, examples being in-line, rotary, V-type, radial, and horizontally opposed engines. The opposed piston engine in particular is a more specialized type, featuring cylinders that have a piston on both ends and a lack of a cylinder head.

Often used in large-scale applications, opposed piston engines have historically found implementation on naval vessels, military tanks, and within factories. When compared to more traditional two-stroke engines, opposed piston engines do not feature one piston per cylinder. With their differing construction and design, opposed piston engines reduce weight, complexity, cost, friction loss, and heat loss through the removal of the cylinder head and valvetrain. They are also well capable of achieving a uniflow-scavenged movement of gas as it moves through the combustion chamber of the engine, ensuring that various drawbacks of crossflow-scavenged designs are eliminated. Nevertheless, two opposing piston engines must have their power geared together, meaning that such assemblies would add weight and complexity that is not seen in some contemporary designs.

While opposing piston engines often vary in their construction, the most common configuration is to have two crankshafts that are geared together. When gearing, the crankshafts could be placed in the same direction or in opposing directions. To achieve the most optimal scavenging, many layouts utilized one piston per cylinder to expose intake and exhaust ports. This would allow for gas to flow axially through the cylinder instead of radially, simplifying various processes. In some variants, the upper crankshaft of the assembly would operate the exhaust pistons while a lower crankshaft would control the intake pistons.

Opposing piston engines have had a long history, the first variation coming about in 1882 as the Atkinson differential engine. Failing to meet success, other various opposed engines were invented over the years, many of which found recognition for their capabilities and for their use in automotives. By the 1900s, opposed engines began being implemented in marine applications, many models being released after World War I.

Leading into the present, opposed engines continued to find refinement as more implementation was made for locomotives and boats. In 1954, the Napier Deltic engine was released for use in military boats. With three crankshafts that were situated in each corner of the assembly, three banks of double-ended cylinders could be achieved for an equilateral triangle. Despite being a long-standing technology, opposed engines still find use in various applications to this day. For example, Cummins Inc. was recently awarded a contract by the U.S. Army in 2021 for the development of the Advanced Combat Engine (ACE), that of which is a modular and scalable diesel engine based on opposed piston technology.

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