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In all steam engines, the steam is used as a working substance. These engines operate on the principle of first law of thermodynamics, i.e. heat and work are mutually convertible. In a steam engine, as the heat energy of steam is converted into mechanical work by the reciprocating (to and fro) motion of the piston, it is called reciprocating steam engine. Moreover, as the combustion of the fuel takes place outside the engine cylinder, then it is called external combustion engine.

Classification of steam engines:

The steam engines are classified in different different ways which are discussed below-

1.) ACCORDING TO NUMBER OF WORKING STROKES

a. Single acting steam engine

b. Double acting steam engine

When steam is admitted on one side of the piston and one working stroke is produced during each revolution of crankshaft, then it is said to be a single acting steam engine. But when the steam is admitted on both sides of the piston and two working strokes are produced during each revolution of the crankshaft, then it is said to be a double acting steam engine. A double acting steam engine produces double the power than that produced by a single acting steam engine.

2.) ACCORDING TO POSITION OF THE CYLINDER

a. Horizontal steam engine

b. Vertical steam engine

When the axis of the cylinder is horizontal, it is said to be a horizontal steam engine. But when the axis of the cylinder is vertical then it is said to be a vertical steam engine. A vertical steam engine requires less floor area then the horizontal steam engine.

3.) ACCORDING TO THE SPEED OF THE CRANKSHAFT

a. Slow speed steam engine

b. Medium speed steam engine

c. High speed steam engine

When the speed of the crankshaft is less than 100 revolution per minute, it is called a slow speed steam engine. When the speed of the crankshaft is between 100 r.p.m. to 250 r.p.m. then it is called a medium speed steam engine. Similarly when the speed of the crankshaft is above 250 r.p.m. then it is known as a high speed steam engine.

4.) ACCORDING TO THE TYPE OF EXHAUST

a. Condensing steam engine

b. Non – condensing steam engine

When steam after doing work in the cylinder passes into a condenser, which condenses the steam into water at a pressure less than the atmospheric pressure, it is said to be a condensing steam engine. But when the steam after doing work in the cylinder is exhausted into atmosphere, it is said to be a non condensing steam engine. The steam pressure in the cylinder is, therefore, not allowed to fall below the atmospheric pressure.

5.) ACCORDING TO EXPANSION OF THE STEAM IN THE ENGINE CYLINDER

a. Simple steam engine

b. Compound steam engine

When expansion of the steam is carried out in a single cylinder and then exhausted into the atmosphere or a condenser, it is said to be a simple steam engine. But when the expansion of the steam is completed in two or more cylinders, the engine is called a compound steam engine. The compound steam engines are generally condensing engines. But some of them may be non condensing also.

6.) ACCORDING TO THE METHOD OF GOVERNING EMPLOYED

a. Throttling steam engine

b. Automatic cut off steam engine.

When the engine speed is controlled by means of a throttle valve in the steam pipe, which regulates the pressure of the steam to the engine, then it is called a throttling steam engine. But when the speed is controlled by controlling the steam pressure with an automatic cut off governor, it is called an automatic cut off steam engine.

In all steam engines, the steam is used as a working substance. These engines operate on the principle of first law of thermodynamics, i.e. heat and work are mutually convertible. In a steam engine, as the heat energy of steam is converted into mechanical work by the reciprocating (to and fro) motion of the piston, it is called reciprocating steam engine. Moreover, as the combustion of the fuel takes place outside the engine cylinder, then it is called external combustion engine.

Classification of steam engines:

The steam engines are classified in different different ways which are discussed below-

1.) ACCORDING TO NUMBER OF WORKING STROKES

a. Single acting steam engine

b. Double acting steam engine

When steam is admitted on one side of the piston and one working stroke is produced during each revolution of crankshaft, then it is said to be a single acting steam engine. But when the steam is admitted on both sides of the piston and two working strokes are produced during each revolution of the crankshaft, then it is said to be a double acting steam engine. A double acting steam engine produces double the power than that produced by a single acting steam engine.

2.) ACCORDING TO POSITION OF THE CYLINDER

a. Horizontal steam engine

b. Vertical steam engine

When the axis of the cylinder is horizontal, it is said to be a horizontal steam engine. But when the axis of the cylinder is vertical then it is said to be a vertical steam engine. A vertical steam engine requires less floor area then the horizontal steam engine.

3.) ACCORDING TO THE SPEED OF THE CRANKSHAFT

a. Slow speed steam engine

b. Medium speed steam engine

c. High speed steam engine

When the speed of the crankshaft is less than 100 revolution per minute, it is called a slow speed steam engine. When the speed of the crankshaft is between 100 r.p.m. to 250 r.p.m. then it is called a medium speed steam engine. Similarly when the speed of the crankshaft is above 250 r.p.m. then it is known as a high speed steam engine.

4.) ACCORDING TO THE TYPE OF EXHAUST

a. Condensing steam engine

b. Non – condensing steam engine

When steam after doing work in the cylinder passes into a condenser, which condenses the steam into water at a pressure less than the atmospheric pressure, it is said to be a condensing steam engine. But when the steam after doing work in the cylinder is exhausted into atmosphere, it is said to be a non condensing steam engine. The steam pressure in the cylinder is, therefore, not allowed to fall below the atmospheric pressure.

5.) ACCORDING TO EXPANSION OF THE STEAM IN THE ENGINE CYLINDER

a. Simple steam engine

b. Compound steam engine

When expansion of the steam is carried out in a single cylinder and then exhausted into the atmosphere or a condenser, it is said to be a simple steam engine. But when the expansion of the steam is completed in two or more cylinders, the engine is called a compound steam engine. The compound steam engines are generally condensing engines. But some of them may be non condensing also.

6.) ACCORDING TO THE METHOD OF GOVERNING EMPLOYED

a. Throttling steam engine

b. Automatic cut off steam engine.

When the engine speed is controlled by means of a throttle valve in the steam pipe, which regulates the pressure of the steam to the engine, then it is called a throttling steam engine. But when the speed is controlled by controlling the steam pressure with an automatic cut off governor, it is called an automatic cut off steam engine.