What is Steam Engine?
A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder.
This pushing force can be transformed, by a connecting rod and flywheel, into rotational force for work. The term “steam engine” is generally applied only to reciprocating engines as just described, not to the steam turbine.
Steam engines are external combustion engines, where the working fluid is separated from the combustion products. The ideal thermodynamic cycle used to analyze this process is called the Rankine cycle.
In general usage, the term steam engine can refer to either complete steam plants (including boilers, etc.), such as railway steam locomotives and portable engines, or may refer to the piston or turbine machinery alone, as in the beam engine and stationary steam engine.
Although steam-driven devices were known as early as the aeolipile in the first century AD, with a few other uses recorded in the 16th and 17th centuries, Thomas Savery is considered the inventor of the first commercially used steam-powered device, a steam pump that used steam pressure operating directly on the water.
Who Invented the Steam Engine?
The first commercially successful engine that could transmit continuous power to a machine was developed in 1712 by Thomas Newcomen. James Watt made a critical improvement by removing spent steam to a separate vessel for condensation, greatly improving the amount of work obtained per unit of fuel consumed.
By the 19th century, stationary steam engines powered the factories of the Industrial Revolution. Steam engines replaced sails for ships on paddle steamers, and steam locomotives operated on the railways.
Reciprocating piston-type steam engines were the dominant source of power until the early 20th century when advances in the design of electric motors and internal combustion engines resulted in the gradual replacement of steam engines in commercial usage. Steam turbines replaced reciprocating engines in power generation, due to lower cost, higher operating speed, and higher efficiency.
How Does a Steam Engine Work?
In a steam engine, hot steam, usually supplied by a boiler, expands under pressure, and part of the heat energy is converted into work. The remainder of the heat may be allowed to escape, or, for maximum engine efficiency, the steam may be condensed in a separate apparatus, a condenser, at comparatively low temperature and pressure.
For high efficiency, the steam must fall through a wide temperature range as a consequence of its expansion within the engine. The most efficient performance that is, the greatest output of work in relation to the heat supplied is secured by using a low condenser temperature and a high boiler pressure.
The steam may be further heated by passing it through a superheater on its way from the boiler to the engine. A common superheater is a group of parallel pipes with their surfaces exposed to the hot gases in the boiler furnace.
By means of superheaters, the steam may be heated beyond the temperature at which it is produced by boiling water.
In a reciprocating engine, the piston and cylinder type of steam engine, steam under pressure is admitted into the cylinder by a valve mechanism. As the steam expands, it pushes the piston, which is usually connected to a crank on a flywheel to produce rotary motion. In the double-acting engine, steam from the boiler is admitted alternately to each side of the piston.
In a simple steam engine, expansion of the steam takes place in only one cylinder, whereas in the compound engine there are two or more cylinders of increasing size for greater expansion of the steam and higher efficiency; the first and smallest piston is operated by the initial high-pressure steam and the second by the lower-pressure steam exhausted from the first.
In the steam turbine, steam is discharged at high velocity through nozzles and then flows through a series of stationary and moving blades, causing a rotor to move at high speeds. Steam turbines are more compact and usually permit higher temperatures and greater expansion ratios than reciprocating steam engines. The turbine is the universal means used to generate large quantities of electric power with steam.
Parts of Steam Engine
- Firebox: This is where the fuel is burned to create heat.
- Boiler: Lindy uses a fire tube boiler. Hot gases produced in the firebox are pulled through a rack of tubes in the boiler. The tubes heat the water that surrounds them to produce steam. The steam collects in the steam dome on the top of the boiler.
- Steam Dome: Inside the steam dome are the regulator valve, safety valve, and whistle. The regulator valve is attached to the throttle in the cab. The engineer uses the throttle to control the quantity of steam delivered to the cylinders. The whistle is a four-chime, 1925 Baldwin whistle which blows by the steam pressure. The safety valve opens to release steam when the pressure becomes too high.
- Valves, Cylinders, and Pistons: The steam is converted to mechanical energy in the cylinders. Steam under pressure is passed through cylinder valves into a chamber and drives the piston. Lindy, like most locomotives, uses double-action cylinders. This achieves twice the power by alternately introducing steam on either side of the piston so the piston rod is both pushed and pulled, generating power on both strokes.
- Rods: The piston is aligned in the cylinder by a crosshead running on a guide. The crosshead carries the small end of the connecting rod. The other end, the big end, transmits the power to the wheels with the crank pin. Lindy, like most locomotives, has more than one set of driving wheels to share the power generated by the double-action cylinders. Cranks on either side of the locomotive are offset by 90° to spread the power over a complete revolution of the wheels.
- Smokebox: Spent steam is released from the cylinders through the blast pipe below the stack. This arrangement produces a reduction in pressure in the smokebox which draws the firebox gases through the boiler tubes. The harder the locomotive works, the more gas is drawn through the tubes, generating more steam.
- The Stack: The spent steam from the blast pipe mixes with the gases from the boiler tubes and exits through the stack. The harder the locomotive works, the more gases and steam comes out the stack.
- Cab: The train crew operates the engine from the cab. The fireman’s job is to make the steam by controlling the fire in the firebox and the water supply to the boiler. The engineer uses the steam by operating the throttle and monitors the steam pressure, fuel, and water.
- Sand Dome: Dome contains sand to be utilized by the engineer by spraying in front or behind driving wheels for traction between the wheels and rail.
Application of steam Engine
Steam engines were used in all sorts of applications including