TRIPLE EXPANSION ENGINE
Triple expansion engine, a further development of the marine reciprocating engine. It was introduced in ships between 1870 and 1880 by adding a third cylinder to the two-cylinder compound engine. The third cylinder was introduced between the compound engine's high- and low-pressure cylinders, and its effect was to use the available steam three times instead of twice as in the compound engine. The steam was first led to a high-pressure cylinder, the exhaust steam from that cylinder being led into an intermediate pressure cylinder, and then into a low-pressure cylinder before being converted by a condenser back into the boiler feed water. It drove three pistons connected to the same crankshaft to add to the power transmitted to the propeller shaft, and was made possible by improved boiler design which produced higher steam pressures. In the 1890s quadruple expansion engines were introduced by adding a fourth stage in the expansion of the steam, and were fitted in some ships, notably the four big German ocean liners built between 1897 and 1902. And even after the introduction of the steam turbine some ships had engines on the quadruple expansion principle, using three cylinders for the first three stages and a low-pressure steam turbine for the fourth.
Multiple expansion engines
High-pressure steam enters from the boiler and passes through the engine, exhausting as low-pressure steam to the condenser.
It is a logical extension of the compound engine to split the expansion into yet more stages to increase efficiency. The result is the multiple expansion engine. Such engines use either three or four expansion stages and are known as triple and quadruple expansion engines respectively. These engines use a series of double-acting cylinders of progressively increasing diameter and/or stroke and hence volume. These cylinders are designed to divide the work into three or four, as appropriate, equal portions for each expansion stage. As with the double expansion engine, where space is at a premium, two smaller cylinders of a large sum volume may be used for the low pressure stage. Multiple expansion engines typically had the cylinders arranged inline, but various other formations were used. In the late 19th century, the Yarrow-Schlick-Tweedy balancing 'system' was used on some marine triple expansion engines. Y-S-T engines divided the low pressure expansion stages between two cylinders, one at each end of the engine. This allowed the crankshaft to be better balanced, resulting in a smoother, faster-responding engine which ran with less vibration. This made the 4-cylinder triple-expansion engine popular with large passenger liners (such as the Olympic class), but was ultimately replaced by the virtually vibration-free turbine.
The development of this type of engine was important for its use in steamships as by exhausting to a condenser the water can be reclaimed to feed the boiler, which is unable to use seawater. Land-based steam engines could exhaust much of their steam, as feed water was usually readily available. Prior to and during World War I, the expansion engine dominated marine applications where high vessel speed was not essential. It was however superseded by the British invention steam turbine where speed was required, for instance in warships, such as the dreadnought battleships, and ocean liners. HMS Dreadnought of 1905 was the first major warship to replace the proven technology of the reciprocating engine with the then-novel steam turbine.
Return to Gallery / Regresar a Galería
