Model of Vertical Marine Steam Engines

Description:

This is a model illustrating the details of three marine steam engine designs. At the left of the image of the model is a single cylinder steam engine. The middle engine model is a triple expansion, compound design. The left engine model is a double expansion, compound engine. Each model engine is highly detailed and shows the workings of the valves, crankshafts and other key elements.

A compound steam engine consists of a high pressure cylinder and one or more lower pressure cylinders. The steam exhausted from the high pressure cylinder is used as inlet steam for the next lower pressure cylinder. Each cylinder is sized in proportion to its inlet steam pressure so that each produces the same amount of work. Compounding was introduced in the early 19th century and widely used in many applications from steamship propulsion to powering large electrical generators.

The benefit gained from the increased complexity of compounding was efficiency. A single cylinder engine (other than those using uniflow valves) suffers from repetitive cooling and heating of the cylinder walls and piston at each stroke. These temperature differences create no work and consume fuel. A compound engine reduces this effect by having the same amount of steam expansion and cooling spread over multiple cylinders.