What is steam engine? It’s a very common question for all of us. In this article, we will learn, the basics, definition, parts, working principle, advantages, disadvantages of steam engines.
Steam engines at earlier stages are not practical power producers. During the industrial revolution, with more advanced designs they became a major source of mechanical power.
As combustion takes place outside the engine cylinder, many steam engines are ‘External Combustion Engines’.
The heat cycle used in the steam engines is the Rankine cycle. It is also called ‘Reciprocating Steam Engine’ as the piston inside the cylinder performs reciprocating motion (To and Fro).
It is a heat engine that uses steam as a working fluid to do mechanical work. The steam engines use the force generated by the steam pressure to make the piston move back and forth in the cylinder.
This motion is transformed into rotational motion by Connecting rod and flywheel. In this way, steam engines do useful work.
In 1781, James Watt applied for a patent for the steam engine, which provided power for various manufacturing equipment. Stationary steam engines are an indispensable part of the industrial revolution.
The steam engines can also run traction engines and railway locomotives.
Let’s see a simple diagram of steam engines, to get simple basic idea of steam engine parts,
Now, we will see all the parts of the steam engine, in brief, let’s explore!
Following are important parts of a single-cylinder reciprocating steam engine,
Let’s try to understand all the parts in brief to have a basic idea of steam engine’s parts.
The frame is made up of heavy cast iron that supports all the stationary and moving parts. It rests on engine foundations and holds all engine parts in a proper position.
It is a hollow cylindrical container made of cast iron. The piston moves back and forth in the hollow container under steam pressure. Both ends of the cylinder are closed and made steam tight.
The piston is a cylindrical disc that moves back and forth in the cylinder under the action of steam pressure. Its function is to convert the thermal energy of steam into mechanical work.
The steam chest is moulded as an integral part of the cylinder. The superheated steam coming from the boiler at high pressure (above 20 Atm.) is fed into the steam chest. This steam is then supplied to the cylinder using a D-slide valve.
This valve moves with a simple harmonic motion in the steam chest. It is used to exhaust steam from the cylinder.
Inlet and Exhaust Ports
These ports are used for steam movement in the cylinder body. The steam from the steam chest enters the cylinder through inlet ports. Steam is exhausted through the exhaust port after doing work in the cylinder.
The piston rod is a round rod, its one side is connected with the piston, and the other side is connected with the cross-head. It transfers motion from the piston to the cross-head.
This is the connection between the piston rod and the connecting rod. It is used to guide the movement of the piston and prevent the piston from bending.
Connecting rod is made of forged steel. Its one end is connected to the crosshead and the other the crank. It converts the reciprocating motion of the piston into the rotary motion of the crank.
This is the main shaft of the engine with a crank. The crank works according to the lever principle and generates the rotational movement of the shaft.
Its function is to provide back and forth to the slide valve. It is made of cast iron and is mounted on the crankshaft.
The flywheel is a heavy cast iron wheel mounted on the crankshaft. It prevents fluctuation of the engine and jerks of the crankshaft.
Governor has the function to keep the speed uniform at varying loads. This is achieved by controlling the amount, or pressure of steam supplied to the steam engines.
Eccentric Rod and Valve Rod
An eccentric rod made of forged steel converts the rotary motion of the crankshaft into the reciprocating motion of the valve rod. The valve rod has the function to provide a simple harmonic motion to the D-slide valve. It connects the eccentric rod and D-slide valve.
Let’s try to understand how does steam engine works,
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The steam engines are classified on the following basis:
Let’s see all types of steam engines in brief,
On basis of the number of working strokes, there are two types of steam engines;
Single Acting Steam Engines
Here steam is allowed to enter from one side of the piston, and only one working stroke is produced during each revolution of the crankshaft.
Double Acting Steam Engines
If steam is admitted from both sides of the piston, two working strokes are produced during each revolution of the crankshaft. It is said to be a double-acting steam engine. This engine produces double power in comparison to the first engine.
Two types of steam engines according to the position of the cylinder are;
Horizontal Steam Engines
Here the axis of the cylinder is horizontal.
Vertical Steam Engines
It has a vertical axis of the cylinder. This engine requires less floor area.
On basis of the speed of the crankshaft, steam engines are classified into three types:
Low-Speed Steam Engines
Here the speed of the crankshaft is less than 100 rpm (revolutions per minute).
Medium Speed Steam Engines
It has the speed of crankshaft lies between 100 rpm and 250 rpm.
High-Speed Steam Engines
This engine has a speed of a crankshaft of more than 250 rpm.
There are two types of steam engines according to the type of exhaust.
Condensing Steam Engines
A steam engine in which the steam condenses to water at a pressure less than the atmospheric pressure is called condensing steam engines.
Non-condensing Steam Engines
A steam engine in which the steam doesn’t condense to water and is exhausted into the atmosphere is called a non-condensing steam engine.
On basis of this criteria, two types of steam engines are;
Simple Steam Engine
When the steam expansion occurs in a single cylinder and the steam then escapes into the atmosphere or reaches the condenser, this type of engine is called the simple steam engine.
Compound Steam Engine
When the steam expansion occurs in two or more cylinders, this type of engine is known as a compound steam engine.
Governing is applied to control the speed of the engine. There are two types of steam engines on the basis of the method of governing.
Throttling Steam Engine
If a throttle valve is used in the steam pipe to control the engine speed as it regulates the pressure of steam to the engine, an engine with this setup is called a Throttling steam engine.
Automatic Cut Off the Steam Engine
When we control engine speed by controlling the steam pressure using an automatic cut-off governor, it is called an Automatic cut-off steam engine.
Let’s see the main uses or applications of steam engines,
We can get the efficiency of the steam engines by dividing the energy output in the form of mechanical work on input to the engine by burning fuel.
Efficiency of Steam Engines = Energy output in form of mechanical work/ energy input by burning fuel
To achieve the greatest efficiency, the steam temperature should be the highest possible (superheated steam), and the exhaust of waste heat should be at the lowest temperature possible. Higher efficiency is also possible if the steam expands to lower pressure and temperature in the steam engines.
For a power station with steam reheat and economizer, the thermal efficiency can be increased up to 40 percent. If we use waste heat for heating by utilizing cogeneration, we can make input energy useful by as much as 85 to 90 percent.
Steam engines consist of some critical parts like boilers and pressure vessels. They contain a huge amount of potential energy. The explosion of these components can cause damage to human life and property.
In the past, a lot of accidents were caused due to the explosion of the boiler. Failure modes include over-pressurization of the boiler, faulty design, poor material, insufficient water in the boiler, and pressure vessels may fail due to inadequate construction or maintenance.
This is a brief introduction to the steam engines. If you have any queries regarding any part of this topic, feel free to contact us. We will love to answer.
To keep learning, click here to completely understand boiler mountings, it’s working, function, and construction.
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