Classification of Internal Combustion Engines and Engine Components (automobile engineering)
Diesel Engine
ContentsObjective 1 : Classification of Internal Combustion Engines
Objective 2 : Internal Combustion Engine Components
Objective 3 : The Fuel Injector
Objective 4 : Supercharging
Objective 5 : Cooling System
Objective 6 : Engine Cooling
Objective 7 : Lubricating Oil Systems
Objective 8 : Crankcase Ventilation
Objective 9 : Induction and Exhaust Systems
Objective 10 : Starting Methods
Objective 11 : Engine Monitoring and Protection
Objective 12 : Basic Engine Tune-up
Objective 13 : Preventive Maintenance Programs
Learning Outcome
When you complete this learning material, you will be able to:
Explain the operating principles, designs, support systems, and operation of
industrial internal
combustion engines (ICE).
Learning Objectives
You will specifically be able to complete the following tasks:
1. Explain the principles of compression ignition; describe the operating cycles
for twostroke
and four-stroke designs.
2. Identify and state the purpose of the major mechanical components of an
internal
combustion engine.
3. Describe individual pump, distributor, and common rail fuel injection systems
for a
diesel engine.
4. Explain the purpose and describe the operation of superchargers and
turbochargers.
5. Describe and explain the operation of a typical cooling system for an
industrial ICE.
6. Describe and explain the operation of a typical lubrication system for an
industrial
ICE.
7. Describe engine-starting devices/systems for diesel and gas engines.
8. Explain the monitoring, protection and control devices on a large industrial
diesel or
gas engine, including shutdowns and governing.
9. Explain a typical start-up procedure for a large industrial diesel engine,
plus the
routine monitoring requirements of a running engine.
Objective 1
Explain the principles of spark ignition and compression ignition; describe the
operating
cycles for two-stroke and four-stroke designs.
CLASSIFICATION OF INTERNAL COMBUSTION ENGINES
Internal combustion engines may be divided into general groups according to: the
type of fuel
used the method of ignition, and the number of strokes that constitute a working
cycle. The
three major types of fuels used are gasoline, gaseous fuels, and fuel oils.
The fuel, gasoline, is in liquid form and is vaporized by being drawn through
fine jets by the
powerful suction of the engine during the intake stroke. At the same time, air
is drawn in to
mix with the vaporized fuel.
Gaseous fuels include natural gas, blast furnace gas, sewage gas, and producer
gas. Natural
gas is the most commonly used of these and engines burning natural gas are used
in locations
where this fuel is plentiful and particularly as the drive units for gas
compression machinery.
Similarly, engines burning the other types of gaseous fuels have become common
in sewage
treatment plants and steel plants where gaseous fuels are readily available.
Fuel oils include light oils such as kerosene and heavier oils such as diesel
fuel. The heavy oil
engine, commonly called the diesel engine, has many applications such as a prime
mover for
electrical generation in capacities up to 15 000 kW.
SPARK IGNITION
Internal combustion engines, which have spark ignition, may be either two cycle
or fourcycle
engines. The compressed gas is ignited by a spark near the end of the power
stroke in
both two stroke and four stroke designs. A high voltage current jumping across
the gap of a
spark plug creates the spark. Most gasoline and gaseous fuel engines are of the
spark ignition
type. The two types of spark ignition internal combustion engines are: the
four-stroke and the
two-stroke.
Four-Stroke Cycle Spark Ignition Engine
The diagrams in Fig. 1 show the operating principle of the four-stroke cycle
gasoline engine.
It will be seen that the four-cycle engine requires four strokes or two complete
crankshaft
revolutions to produce one power stroke. Taking each diagram in turn, A to D,
they can be
designated as:
Intake or Suction Stroke (A): The inlet valve is open while the piston
moves down, drawing
in a mixture of gasoline and air from the carburetor into the cylinder.
Compression Stroke (B): The inlet valve is closed and the piston moves
upward
compressing the mixture in the combustion chamber. Near the upper end of this
stroke the
spark plug is timed to ignite the mixture.
Power Stroke (C): The mixture burns, generating a high pressure, which
forces the piston
downward and produces useful power. Near the end of this stroke the exhaust
valve opens to
begin the removal of burned gases from the cylinder.
Exhaust Stroke (D): The exhaust valve remains open while the piston moves
upward and
pushes out most of the remaining burned gases in preparation for the next intake
stroke.
The four-cycle engine is usually lubricated by a definite quantity of oil in its
crankcase,
which is either pumped under pressure to the bearing surfaces or is splashed
onto them by
rotation of the crank webs. The piston rings limit the amount of oil entering
the combustion
chamber and keep the carbon deposits to a minimum.
Two-Stroke Spark Ignition Cycle
As can be seen in Fig. 2, A and B, this engine functions by utilizing three
openings or “ports”
in its cylinder wall which are covered or uncovered by the piston. Thus there
are no valves of
the ordinary type, no camshaft and no gearing.
Since the intake and exhaust functions are performed simultaneously during
only a part of
one stroke, the two-cycle engine has a power stroke every crankshaft revolution.
Referring to Fig. 2A: The upward stroke of piston F compresses a mixture of
gasoline vapor
and air in the combustion chamber D. The same piston stroke also creates a
partial vacuum in
crankcase B that draws in the next mixture charge through the carburetor and
port A. Near
the upper end of the stroke, spark plug G is timed to ignite the compressed
mixture.
Referring to Fig. 2B: The pressure in the cylinder resulting from fuel
combustion, forces
piston F downward on its power stroke, closes intake port A, and compresses the
new
mixture charge in the crankcase B. Near the lower end of this stroke the piston
uncovers
exhaust port E which releases cylinder pressure and discharges most of the
burned gases.
Further piston movement then uncovers the transfer port C that allows the
compressed new
mixture in the crankcase to flow upward into the combustion chamber where it
assists in
pushing the exhaust gases through the exhaust port E. The head of the piston is
usually
shaped to direct the flow of new mixture upward so as to get maximum
displacement of
exhaust gas with minimum loss of new mixture out of the exhaust port.
The two-cycle engine is lubricated by thoroughly mixing a measured quantity of
special
lubricating oil with the gasoline in the tank. When this gasoline-oil mixture
passes through
the carburetor the gasoline is vaporized, the oil is carried through as an oil
fog and lubricates
all parts of the engine in its passage through.
COMPRESSION IGNITION
In the compression ignition system, only air is drawn into the cylinder during
the suction or
intake stroke of the engine. This air charge is then compressed by the engine
piston and near
the end of the compression stroke liquid fuel in an atomized form, or in some
cases a gaseous
fuel, is injected. The fuel ignites due to the high temperature developed by the
compression
of the air. Compression ignition is the method of ignition used in the diesel
engine.
The diagrams in Fig. 1 and Fig. 2 illustrated the operation of gasoline engines
working on the
two-stroke and four-stroke cycle. Almost identical diagrams could be drawn to
illustrate the
operation of diesel engines; both two-stroke and four-stroke cycles can be used.
The major differences of the diesel engine compared to the gasoline engine are:
1. The charge drawn into the cylinder is air only.
2. The fuel is injected at high pressure at the end of the compression stroke
directly into
the engine cylinder in liquid form, though finely atomized.
3. Ignition is due to the high temperature resulting from the compression of the
air and
takes place without the aid of a spark. Thus diesel engines are known as
compression
ignition engines.
FOUR-STROKE COMPRESSION IGNITION CYCLE
Referring to Fig. 3, the four strokes in sequence are Suction, Compression,
Power and
Exhaust.
Suction Stroke: the inlet valve is opened just before the piston reaches
the top dead-center
position, and the exhaust valve closes just after the piston reaches top dead
center. This
allows a charge of air to be drawn into the cylinder through the inlet valve as
the piston descends.
Compression Stroke: after the piston has passed the bottom dead-center
position the air inlet
valve is closed and compression is begun as the piston rises. Shortly before top
dead-center,
fuel injection begins. Meanwhile compression of the air will have raised its
temperature to
the range of 540°C to 650°C, and its pressure in the range of 2750 kPa to 4100
kPa. Under
these temperature and pressure conditions the fuel will ignite almost as soon as
it enters the
cylinder and mixes with the hot air. There will be a momentary increase of
temperature and
pressure as the fuel burns and the power stroke commences.
Power Stroke: the hot gases of combustion expand and force the piston downwards.
Before
it reaches bottom dead-center, the burning gases have expended their energy and
the exhaust
valve is opened to allow them to escape from the cylinder.
Exhaust Stroke: as the piston again ascends in the cylinder; the remaining
exhaust gases are
forced out through the open exhaust valve. Just before the piston reaches the
top dead-center
position, the inlet valve is opened and the whole cycle of events is repeated.
TWO-STROKE CYCLE COMPRESSION IGNITION ENGINE
Figs. 4A and 4B show two types of two-stroke cycle diesel engines. One
difficulty
experienced in the two-stroke engines is in achieving a complete clearing of the
exhaust gases
from the cylinder after the completion of one working stroke and the beginning
of the next.
This operation of removal of exhaust gases is called “scavenging.” In order
to get a more
complete clearance of the cylinder, it is common in larger engine sizes, to
provide inlet air at
a slightly increased pressure. This becomes known as “scavenging air” and is
supplied by a
scavenge pump.
Fig. 4A shows cylinder scavenging being carried out across the cylinder much as
was done in
Fig. 2, the two-stroke gasoline engine.
Fig. 4B shows an alternative method with the air inlet in the same position
but the exhaust
being carried through exhaust valves in the cylinder head, giving a “Uniflow”
type of action.
Note that with this latter arrangement we have a two-stroke engine with
valves.
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Objective 2
Identify and state the purpose of the major mechanical components of an internal
combustion engine.
INTERNAL COMBUSTION ENGINE COMPONENTS
There are many internal combustion engine types. This learning objective
discusses a typical
engine with construction features that are common to all internal combustion
engines. It is a
size common for stationary service, used to drive pumps or generators.
Fig. 5 shows a diesel engine made by the W. H. Allen Co. It is a
twelve-cylinder, vee-form
four-stroke cycle and is used to drive a 600 kW generator.
Bedplate
The engine frame is mounted on a deep-section bedplate as shown in Fig. 6. It is
made ofr>
high-grade cast iron. The main bearings are steel-backed with white metal
linings. It is
provided with numerous internal joint bolts and studs to secure a rigid union of
frame and
bedplate. The last two flywheel end main bearings have white metal thrust faces
for the axial
location of the crankshaft. The bedplate forms a wet sump and contains all the
engine
lulubrication oil. Provision for a dry sump system of lubrication is possible.
Crankshaft
The pistons of the engine are connected to the crankshaft by connecting rods.
The crankshaft
converts the linear, or back and forth movement, of the pistons to rotary
movement. All the
power of the engine is transferred through the crankshaft. The crankshaft is
forged from steel,
with balance weights as required. Oil feeds to the connecting rod bearings are
taken through
passages in the crankshaft from the adjacent main bearings.
Frame and Crankcase
The frame is fitted over the bedplate and crankshaft. The frame has numerous,
thick internal
ribs to form a rigid framework for the cylinder bank. All working parts inside
the crankcase
are easily accessible through doors provided on both sides of the engine.
Cylinders
Separate cast-iron cylinder banks, each housing a chain driven camshaft, are
mounted onr>
either side of the engine frame. The cylinder liners fit in the cylinder, and
provide a machined
surface for the pistons and piston rings to fit into. Cylinder liners are of the
“wet” type. “Wet”
type liners refers to the fact that cooling water circulates next to the liner.
“Dry” type liners fit
inside the cylinder bank or cylinder head. There is no direct contact of liner
and cooling
wawater. The water cools the head, which in turn cools the liner.
Cylinder Liners
Cylinder liner or sleeve is a replaceable insert that protects the block
from wear. The piston rings wear the liner instead of the block. The wet
liners are made of special close-grained cast iron. Each liner is
inspected and hydraulically tested for safety reasons.
Connecting Rods
The connecting rods connect the pistons to the crankshaft. Each cylinder has one
piston and
one connecting rod. The wrist pins connect the piston to the rod. The connecting
rods are of
fully machined forged steel, and are hollow bored to convey lubricating oil to
the bushings
and gudgeon pins (wrist pins) of the small end. The large end bearing connects
the rod to the
crankshaft. It has a detachable bottom half with the top half forming a part of
the forged
connecting rod.
The piston rings fit in the grooves in the piston. The four rings at the top
of Fig. 12 fit into the
four top grooves in the piston in Fig. 13. These are the compression rings. They
seal the space
between the piston and the cylinder. They also conduct heat away from the piston
to the
cylinder wall. The bottom ring in Fig. 12 and Fig. 13 is an oil control ring.
Its purpose is to
distribute oil in a uniform film over the cylinder wall. It also prevents oil
from leaking into
the combustion chamber. Oil is scraped form the cylinder wall on the piston down
stroke. It
drains through the holes in the piston ring groove. These holes are visible in
the bottom
piston groove in Fig. 13.
Pistons
The piston is designed with large bearing areas, and is fitted with four
pressure rings and a
scraper ring below the gudgeon pin. The case-hardened steel gudgeon pin is fully
floating and
retained by circlips. The piston is of cast iron or aluminum alloy, depending on
the rated
speed chosen for a particular application. The piston in Fig. 13 is the type
fitted to engines
running at speeds, of approximately 750 r/min.
Cylinder Heads and Valves
The cylinder heads are individually detachable, and made of a special
heat-resisting cast iron.
Ample waterways are provided with the water coming from the cylinder jackets
through
external connections. This cylinder head has an open type combustion chamber.
The piston
crowns are concave and the fuel is injected into the center of the combustion
space.
The interchangeable inlet and exhaust valves are actuated by push rods and
rocking levers.
Each valve has two concentric springs and a renewable seat of heat-treated
nickel-iron alloy.
Each head has a relief valve and provision for taking pressure measurements. The
heads and
valve gear have removable covers.
Camshaft
The camshaft is the link between the crankshaft and the valve train. It is
driven through gears
or a chain by the crankshaft. The lobes on the camshaft move the pushrods up and
down. The
pushrods through a rocker arm assembly move the intake and exhaust valves up and
down.
There are two camshafts, one on the outward side of each of the two cylinder
banks. Each is
in a separate compartment with its own oil bath. Some engines have overhead
camshafts,
which are mounted above the valves, on top of the heads. They move the valves
directly, with
no pushrods or rocker arms. Overhead camshafts are usually belt or chain driven
from the crankshaft.
This arrangement allows easy access and short push rods. An oil-way, bored
the full length of
each shaft, delivers lubricating oil to the bearings. The camshaft is driven
from the crankshaft
by a triplex roller chain at the driving end of the engine. A geared extension
from the
camshaft operates the governor and tachometer through a flexible coupling. A set
of cam
blocks (for fuel pump, inlet valve, exhausts valve and starting air valve) is
provided for each
cylinder. The cam followers are of the guided roller type. Each push rod has an
individual
return spring.
Flywheel
The flywheel is cast iron with timing marks on the periphery. The main coupling
bolts pass
through both the flywheel and crankshaft half-coupling flange. Two additional
bolts retain
the flywheel on the crankshaft when the driven machine is disconnected.
Governor
A hydraulic governor controls the fuel pump rack rods through a short
interconnecting
linkage to each bank. The governor has centrifugal speed-sensing devices, such
as weights or
fly balls.
The governor must be sensitive enough to hold the engine speed inside the safe
operating
limits. The governor can be adjusted with a hand-wheel, which changes the spring
tension.
The governor for the diesel engine in Fig. 16 is a hydraulic governor and has
a set of weights
operating a very small pilot valve. The governor is driven from the camshaft at
camshaft
speed or at a lower speed through a reduction gear. The pilot valve controls
hydraulic
pressure to the fuel pump to control the speed of the engine.
in the next lesson we will learn about:
Describe individual pump, distributor, and common rail fuel injection systems
for a diesel engine.
Section 2 :Internal Combustion Engines Components 2 (Course)
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