May 28, 2022
Coupled engine - a steam engine with multi-stage steam expansion. An engine in which the pressure in diesel cylinders is first reduced, and then the process is repeated in subsequent cylinders with lower and lower pressure. Systems with two, three and four levels of steam expansion have been encountered. Mostly, the steam between the cylinders is heated in secondary superheaters. Compound engines are more efficient than single-stage steam expansion engines, such as twin-cylinder engines, but are more complex. They dominated steamers and ships' propulsion, while they were rarely used in steam locomotives, where lower fuel consumption did not compensate for the complicated construction and operation as well as higher repair costs.