What's the Compound Engine?

A compound steam engine unit is a type of steam engine in which the working fluid is expanded successively in two distinct phases so as to minimize losses (as from cylinder condensation) and so allow a high ratio of expansion to be used, the working fluid (as steam) after expanding in the high-pressure cylinder being exhausted into a low-pressure cylinder and then exhausted usually into a condenser.

How Does the Compound Engine Work?

What's the Reciprocating Engine?

A reciprocating engine is an engine that where steam acts upon a piston under pressure and the action of the steam forces the piston to move. They use the reciprocating (up-and-down) motion of the pistons to translate this energy. There are many different types, including the internal combustion engine which is used in most motor vehicles, the steam engine which is a type of external combustion engine, and the Stirling engine. 

How Does the Reciprocating Engine Work?

The power created by reciprocating engines comes from pressurizing fuel using a piston or pistons to create combustion and, in turn, produce a circular, rotating motion. This process is called the four-stroke cycle as, like a rotary engine, reciprocating engines rely on a repeating pattern of intake, compression, combustion, and exhaust to function. The first step is the intake, in which fuel is injected into the cylinder, pushing the piston to the bottom. Next, during compression, the piston is pushed to the top of the cylinder. This puts pressure on the fuel, and the spark plug ignites it, creating the next step: combustion. This ignition pushes the piston back down, creating energy. Waste is released in the last step, exhaust, and the cycle begins again.

The crankshaft (red) converts reciprocating motion from the pistons (grey) which is often combined with a flywheel (black)