MARINE STEAM ENGINE
Introduction:
In all steam engines, steam is used as the working substance. These engines operate
on the principle of the first law of thermodynamics, i.e, heat and work are mutually convertible.
In reciprocating steam engines, the heat energy in the steam is converted into mechanical work
by the reciprocating (to and from) motion of the piston. It is also cálled reciprocating steam
engines.
Moreover, as the combustion of the fuel takes place outside the engine cylinder, it is
also called an external combustion engine.
Classifications of steam engines:
Various scientists on different basis have classified the steam engines. But the working
classifications are important from the subject point of view:
I) According to a number of working strokes:
a. The single-acting steam engine, and
b. Double-acting steam engine
2) According to the position of the cylinder
a. Horizontal steam engine
b. Vertical steam engine
3) According to the speed of the crankshaft:
a. Slow speed steam engine
b. Medium speed steam engine and
c. High-speed steam engine
4) According to the type of exhaust:
a. Condensing steam engine
b. Non-Condensing steam engine
5) According to.expansion of the steam in the engine cylinder:
a. Simple steam engine
b. Compound steam engine
6) According to the method of governing employed:
a. Throttling steam engine
b. Automatic cut off the steam engine
IMPORTANT PARTS OF A STEAM ENGINE:
All the parts of a steam engine may be broadly divided into two gróups i.e., stationary
parts and moving parts. Though a steam éngine consists of innumerable parts, both
stationary and moving yet the following are, important from the subject point of view.
1.Frame:
It is a heavy cast iron part, which supports all the stationary as well as moving past and
holds them in the proper position. It generally, résts on engine foundation.
2Cylinder:
It is also a cast-iron cylindrical hollow vessel, in which the piston to and fro under
the steam pressure. Both ends of the cylinder are closed and made stean tight. In small steam
engines, the cylinder is made an integral part of the frame.
3.Steam Chest:
It is the cast as an integral part of the cylinder it supplies to the cylinder with the
movement of D- slide valves.
4.D-Slide Valve:
It moves within the chamber with a Simple periodic motion. Its function is to exhaust
steam from the cylinder at proper moment.
5. Inlet And Exhaust Parts:
These are holes provided in the body of the cylinder for the movement of the steam. The
steam is admitted from the steam chest alternatively to either side of the cylinder through the
inlet ports, the steam after doing its add the cylinder is exhausted through the exhaust port.
6. Piston:
It is a cylindrical disc, moving to and fro, within the cylinder due to the steam pressure.
Its function is to convert heat énergy of the steam into mechanical work. Piston rings, made
from cast iron the leakage of steam.
7.PISTON ROD:
It is a circular rod, which is connected to the piston on one side and cross hçad to the
other. Its main function is to transfer motion from the piston. Their purpose is to prevent the
leakage of steam.
8.Cross Head:
It is a link between the rod and the connecting rod. Its function is to guide motion c
the connecting rod and to stop it from bending.
9.Connecting Rod:
It is made from forged steel, whose one end is connected to the crosshead and therefore the other
the crank. Its function is to convert the reciprocating motion of the piston (or crosshead) in
the rotary motion of the crank.
10. Crank Shaft:
It is the most shaft of the engine having a crank. The crank works on the lever principle
and produces rotary motion of the shaft. The crankshaft is supported on the main bearings
of the engine.
11. Eccentric:
It is generally madé of the. cast iron, and is fitted to the crankshaft. Its function is
próvide reciprocating motion to the slidė valve.
12. Eccentric Rod And Valve Rod:
The eccentric rod is made of forged steel, whose one end is fixed to the eccentric
other to the valve rod. Its function is to convert the rotary motion of the crankshaft into to and motion of the valve rod. The valve rod connects the eccentric rod and the D-slide valve. lts
Imation is to.provide simple harmonies notion lo the D-slide valve
13. Flywheel:
It is a heavy cast iron wheel, mounted in the crankshaft. Its function is to prevent the
fluctuation of the engine. It also prevents the jerk from the crankshaft.
14.Governer:
It is a device to keep the engine speed, moves or less, uniform at all load conditions. It is
done either by controlling the quantity of pressurè of the steam supplied to the engine
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