Components of an Engine;
Even though reciprocating internal combustion engines look
quite simple, they are highly complex machines. There are hundreds of
components that have to perform their functions satisfactorily to produce
output power. There are two types of engines, viz., spark ignition (S1) and
compression-ignition (CI) engine. Let us now go through the important engine
components and the nomenclature associated with an engine.
Terms connected with i.c.
engines;
·
Bore: The inside diameter of the
cylinder is called bore
·
Stroke: The linear distance along
the cylinder axis between two limiting position s is called stroke.
·
Top Dead Center ( T.D.C.) : the top
most position of the piston towards cover end side of the cylinder is
called T.D.C.
·
Bottom dead Center ( B.D.C.) : The
lowest position of the piston towards the crank end side of the cylinder
is called B.D.C.
·
Clearance Volume : The
volume contained in the cylinder above the top of the piston , when the
piston is at top dead center , is called the clearance volume.
·
Swept Volume: The
volume swept through by the piston in moving between T.D.C. and B.D.C,
is called swept volume or piston displacement.
·
Compression Ratio: It is the
ratio of Total cylinder volume to clearance volume
Definition of
‘Engine’
An
engine is a device, which transforms one form of energy into another form.
Normally, most of the engines convert thermal energy into
mechanical work and therefore they are called ‘heat
engines’.
Engine
Components
The
major components of the engine and their functions are briefly described below.
Cylinder Block:
The cylinder block is the main supporting structure for the
various components. The cylinder of a multicylinder engine is cast as a single
unit, called cylinder block. The cylinder head is mounted on the cylinder
block.
The cylinder head and cylinder block are provided with water
jackets in the case of water-cooling with cooling fins in the case of
air-cooling. Cylinder head gasket is incorporated between the cylinder block
and cylinder head. The cylinder head is held tight to the cylinder block by
number of bolts or studs. The bottom portion of the cylinder block is called
crankcase. A cover called crankcase, which becomes a sump for lubricating oil
is fastened to the bottom of the crankcase. The inner surface of the cylinder
block, which is machined and finished accurately to cylindrical shape, is
called bore or face.
Cylinder
As the name implies it is a cylindrical vessel or space in
which the piston makes a reciprocating motion. The varying volume created in
the cylinder during the operation of the engine is filled with the working
fluid and subjected to different thermodynamic processes. The cylinder is
supported in the cylinder block.
Piston
It is a cylindrical component fitted into the cylinder forming
the moving boundary of the combustion system. It fits perfectly (snugly) into
the cylinder providing a gas-tight space with the piston rings and the
lubricant. It forms the first link in transmitting the gas forces to the output
shaft.
Combustion Chamber
The space enclosed in the upper part of the cylinder, by the
cylinder head and the piston top during the combustion process, is called the
combustion chamber. The combustion of fuel and the consequent release of
thermal energy results in the building up of pressure in this part of the
cylinder.
Inlet Manifold
The pipe which connects the intake system to the inlet valve
of the engine and through which air or air-fuel mixture is drawn into the
cylinder is called the inlet manifold.
Gudgeon Pin
It forms the link between the small end of the connecting rod
and the piston.
Exhaust Manifold
The pipe that connects the exhaust system to the exhaust valve
of the engine and through which the products of combustion escape into the
atmosphere is called the exhaust manifold.
Inlet and Exhaust Valves
Valves are commonly mushroom shaped poppet type. They are
provided either on the cylinder head or on the side of the cylinder for
regulating the charge coming into the cylinder (inlet valve) and for
discharging the products of combustion (exhaust valve) from the cylinder.
Connecting Rod
It interconnects the piston and the crankshaft and transmits
the gas forces from the piston to the crankshaft. The two ends of the
connecting rod are called as small end and the big end. Small end is connected
to the piston by gudgeon pin and the big end is connected to the crankshaft by
crankpin.
Crankshaft
It converts the reciprocating motion of the piston into useful
rotary motion of the output shaft. In the crankshaft of a single cylinder
engine there is pair of crank arms and balance weights. The balance weights are
provided for static and dynamic balancing of the rotating system. The
crankshaft is enclosed in a crankcase.
Piston Rings
Piston rings, fitted into the slots around the piston, provide
a tight seal between the piston and the cylinder wall thus preventing leakage
of combustion gases
Camshaft
The camshaft and its associated parts control the opening and
closing of the two valves. The associated parts are push rods, rocker arms,
valve springs and tappets. This shaft also provides the drive to the ignition
system. The camshaft is driven by the crankshaft through timing gears.
Cams
These are made as integral parts of the camshaft and
are designed in such a way to open the valves at the correct timing and to keep
them open for the necessary duration.
Fly Wheel
The net torque imparted to the crankshaft during one complete
cycle of operation of the engine fluctuates causing a change in the angular
velocity of the shaft. In order to achieve a uniform torque an inertia mass
in the form of a wheel is attached to the output shaft and this wheel is called
the flywheel.
Basic Parts of the Gasoline
Engine:
Basic
Parts of the Gasoline Engine are listed below;
·
Cylinder block
·
Piston
·
Piston rings
·
Piston pin
·
Connecting rod
·
Crankshaft
·
Cylinder head
·
Intake valve
·
Exhaust valve
·
Camshaft
·
Timing gears
·
Spark plug
Cylinder Block:
Cylinder
Block Basic frame of gasoline engine. Contains the cylinder.
Piston:
Piston
A sliding plug that harnesses the force of the burning gases in the cylinder.
Piston Rings:
Piston
rings seal the compression gases above the piston keep the oil below the piston
rings.
Piston Pins:
Piston Pins Also known as the wrist pin, it connects the
piston to the small end of the connecting rod. It transfers the force and allows
the rod to swing back and forth.
Connecting Rod:
Connecting
Rod Connects the piston and piston pin to the crankshaft.
Crankshaft:
Crankshaft Along the the piston pin and connecting rod it
converts the up and down motion (reciprocating) of the engine to spinning
(rotary) motion.
Flywheel:
Flywheel
Carries the inertia when there is no power stroke.
Cylinder Head:
Cylinder Head Forms the top of the combustion chamber.
Contains the valves, the passageways for the fuel mixture to move in and out of
the engine.
Intake and Exhaust Valves:
Intake
and Exhaust Valves Doorway that lets the gases in and out of the engine.
Camshaft:
Camshaft Through the use of an eccentric the cam lobes push
the valves open. The valve springs close them.
Timing Gears:
Timing Gears These gears drive the camshaft from the
crankshaft.
Why not diesel engines are not
preferred in commercial ?:
1.
Diesel engines, because they have much higher
compression ratios (20:1 for a typical diesel vs. 8:1 for a typical gasoline
engine), tend to be heavier than an equivalent gasoline engine.
2.
Diesel engines also tend to be more expensive.
3.
Diesel engines, because of the weight and
compression ratio, tend to have lower maximum RPM ranges than gasoline engines
.This makes diesel engines high torque rather than high horsepower, and that
tends to make diesel cars slow in terms of acceleration.
4.
Diesel engines must be fuel injected, and in the
past fuel injection was expensive and less reliable
5.
Diesel engines tend to produce more smoke.
6.
Diesel engines are harder to start in cold
weather, and if they contain glow plugs, diesel engines can require you to wait
before starting the engine so the glow plugs can heat up.
7.
Diesel engines are much noisier and tend to
vibrate.
8.
Diesel fuel is less readily available than
gasoline
Advantages diesel engines:
The two things working in favor of diesel engines are better
fuel economy and longer engine life. Both of these advantages mean that, over
the life of the engine, you will tend to save money with a diesel.
However, you also have to take the initial high cost of the
engine into account. You have to own and operate a diesel engine for a fairly
long time before the fuel economy overcomes the increased purchase price of the
engine.
The equation works great in a big diesel tractor-trailer rig
that is running 400 miles every day, but it is not nearly so beneficial in a
passenger car.
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