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Heat engineHeat engine
A heat engine is a device which transforms the
chemical energy of a fuel into thermal energy and
uses this energy to produce mechanical work.
It is classified into two types-
(a) External combustion engine
(b) Internal combustion engine
CLASSIFICATIONCLASSIFICATION
 External combustion engine:
– In this engine, the products of combustion of air and fuel
transfer heat to a second fluid which is the working fluid of the
cycle.
– Examples:
 In the steam engine or a steam turbine plant, the heat of
combustion is employed to generate steam which is used in
a piston engine (reciprocating type engine) or a turbine
(rotary type engine) for useful work.
 In a closed cycle gas turbine, the heat of combustion in an
external furnace is transferred to gas, usually air which the
working fluid of the cycle.
 Internal combustion engine:
– In this engine, the combustion of air and fuels take place
inside the engine cylinder and are used as the direct motive
force.
– It can be classified into the following types:
 1. According to the basic engine design-
– (a) Reciprocating engine (Use of cylinder piston
arrangement),
– (b) Rotary engine (Use of turbine)
 2. According to the type of fuel used-
– (a) Petrol engine, (b) diesel engine, (c) gas engine
(CNG, LPG),
– (d) Alcohol engine (ethanol, methanol etc)
CLASSIFICATIONCLASSIFICATION
 Internal combustion engine:
 3. According to the number of strokes per cycle-
(a) Four stroke and (b) Two stroke engine
 4. According to the method of igniting the fuel-
– (a) Spark ignition engine,
– (b) compression ignition engine and
– (c) hot spot ignition engine
 5. According to the working cycle-
– (a) Otto cycle (constant volume cycle) engine,
– (b) diesel cycle (constant pressure cycle) engine,
– (c) dual combustion cycle (semi diesel cycle) engine.
CLASSIFICATIONCLASSIFICATION
 6. According to the fuel supply and mixture preparation-
– (a) Carburetted type (fuel supplied through the carburettor),
– (b) Injection type (fuel injected into inlet ports or inlet
manifold, fuel injected into the cylinder just before ignition).
 7. According to the number of cylinder-
– (a) Single cylinder and (b) multi-cylinder engine
 8. Method of cooling-
– water cooled or air cooled
 9. Speed of the engine-
– Slow speed, medium speed and high speed engine
 10. Cylinder arrangement-Vertical, horizontal, radial, inline, V-
type, opposite cylinder piston engines etc.
CLASSIFICATIONCLASSIFICATION
 11. Valve mechanism-
– Overhead valve engines, and Side valve engines;
 12. Method of governing-
– Hit and miss governed engines, Quantitatively governed
engines and Qualitatively governed engine
Application
– Automotive engines for land transport,
– marine engines for propulsion of ships,
– aircraft engines for aircraft propulsion,
– industrial engines,
– prime movers for electrical generators etc
CLASSIFICATIONCLASSIFICATION
External combustion engine
 Combustion of air-fuel is outside
the engine cylinder (in a boiler)
 The engines are running smoothly
and silently due to outside
combustion
 Higher ratio of weight and bulk to
output due to presence of
auxiliary apparatus like boiler and
condenser. Hence it is heavy and
cumbersome.
 Working pressure and
temperature inside the engine
cylinder is low; hence ordinary
alloys are used for the
manufacture of engine cylinder
and its parts.
Internal combustion engine
 Combustion of air-fuel is inside
the engine cylinder (in a boiler)
 Very noisy operated engine
 It is light and compact due to
lower ratio of weight and bulk to
output.
 *Working pressure and
temperature inside the engine
cylinder is very much high; hence
special alloys are used
Comparison between external combustion engineComparison between external combustion engine
and internal combustion engine:and internal combustion engine:
Comparison between external combustion engineComparison between external combustion engine
and internal combustion engine:and internal combustion engine:
 It can use cheaper fuels
including solid fuels
 Lower efficiency about 15-
20%
 Lesser requirement of water
 High starting torque
 High grade fuels are used with
proper filtration
 Higher efficiency about 35-
40%
 Higher requirement of water
for dissipation of energy
through cooling system
 IC engines are not self-starting
External combustion engine Internal combustion engine
Main components ofMain components of
reciprocating IC engines:reciprocating IC engines:
 Cylinder: It is the main part of the engine inside which piston
reciprocates to and fro. It should have high strength to withstand high
pressure above 50 bar and temperature above 2000 Cᴼ . The ordinary
engine is made of cast iron and heavy duty engines are made of steel
alloys or aluminium alloys. In the multi-cylinder engine, the cylinders
are cast in one block known as cylinder block.
 Cylinder head: The top end of the cylinder is covered by cylinder
head over which inlet and exhaust valve, spark plug or injectors are
mounted. A copper or asbestos gasket is provided between the engine
cylinder and cylinder head to make an air tight joint.
 Piston: Transmit the force exerted by the burning of charge to the
connecting rod. Usually made of aluminium alloy which has good heat
conducting property and greater strength at higher temperature.
 Piston rings: These are housed in the circumferential grooves
provided on the outer surface of the piston and made of steel
alloys which retain elastic properties even at high temperature.
2 types of rings- compression and oil rings.
– Compression ring is upper ring of the piston which provides air
tight seal to prevent leakage of the burnt gases into the lower
portion.
– Oil ring is lower ring which provides effective seal to prevent
leakage of the oil into the engine cylinder.
 Connecting rod: It converts reciprocating motion of the piston
into circular motion of the crank shaft, in the working stroke.
The smaller end of the connecting rod is connected with the
piston by gudgeon pin and bigger end of the connecting rod is
connected with the crank with crank pin. The special steel
alloys or aluminium alloys are used for the manufacture of
connecting rod.
 Crankshaft: It converts the reciprocating motion of the piston
into the rotary motion with the help of connecting rod. The
special steel alloys are used for the manufacturing of the
crankshaft. It consists of eccentric portion called crank.
 Crank case: It houses cylinder and crankshaft of the IC engine
and also serves as sump for the lubricating oil.
 Flywheel: It is big wheel mounted on the crankshaft, whose
function is to maintain its speed constant. It is done by storing
excess energy during the power stroke, which is returned during
other stroke.
Terminology used in IC engine:Terminology used in IC engine:
Terminology used in IC engine:Terminology used in IC engine:
 1. Cylinder bore (D): The nominal inner diameter of the working
cylinder.
 2. Piston area (A): The area of circle of diameter equal to the cylinder
bore.
 3. Stroke (L): The nominal distance through which a working piston
moves between two successive reversals of its direction of motion.
 4. Dead centre: The position of the working piston and the moving
parts which are mechanically connected to it at the moment when the
direction of the piston motion is reversed (at either end point of the
stroke).
– (a) Bottom dead centre (BDC): Dead centre when the piston is
nearest to the crankshaft.
– (b) Top dead centre (TDC): Dead centre when the position is
farthest from the crankshaft.
 5. Displacement volume or swept volume (Vs): The nominal
volume generated by the working piston when travelling from the
one dead centre to next one and given as, Vs=A × L
 6. Clearance volume (Vc): the nominal volume of the space on
the combustion side of the piston at the top dead centre.
 7. Cylinder volume (V): Total volume of the cylinder. V= Vs +
Vc
 8. Compression ratio (r): r = Vs / Vc
Terminology used in IC engine:Terminology used in IC engine:
Sequence of Operations in aSequence of Operations in a
CycleCycle
In a continuously operating engine, we may
consider a cycle starting from any stroke.
When the engine returns back to the stroke
where it started, we say that the cycle has
been completed.
IDEAL OPERATING CYCLEIDEAL OPERATING CYCLE
TWO STROKE CYCLE ENGINE
EXPANSION &
EXHAUST PROCESSES
SUCTION/INTAKE &
COMPRESSION PROCESSES
INWARD
STROKE
( Piston
Movement)
OUTWARD
STROKE
( Piston
Movement)
4 Stroke Cycle Petrol4 Stroke Cycle Petrol
Engine/ SI EngineEngine/ SI Engine
Operation Cycle completed in
 4 strokes of the piston
 2 revolutions of the crankshaft
Also known as Otto Cycle (named after the German
Scientist who devised an engine working on this
cycle)
• Now we will be discussing about the actual
operating cycles
– Valves: Intake valve opens and exhaust valve is
closed
– Charge: Fresh air mixed with fuel vapour
(supplied in correct proportion) is drawn into
the cylinder due to the vacuum pressure created
by the movement of the piston
– Piston Displacement: TDC to BDC
(i) Intake/Suction stroke
(ii) Compression stroke
– Valves: Both valves closed
– Charge: Fresh charge is compressed into clearance
volume by the return stroke of the piston.
– The Pressure and Temperature of the charge
increases considerably (dependant upon the
compression ratio)
– Shortly before piston reaches TDC the charge is
ignited by the spark plug for combustion.
– Piston Displacement: BDC to TDC
Air/fuel mixture
is
– Valves: Both valves closed
– Charge: Due to combustion, there is a sudden
increase of pressure and temperature, but the
volume practically remains constant.
– High pressure of burnt gases force the piston down
with great force towards BDC. Hence, hot burnt
gases expand due to the speed of the piston. During
this expansion, some heat energy transforms into
(iii) Expansion stroke
(iv) Exhaust stroke
 Valves: exhaust valve opens,
intake valve is closed
 Charge: Burnt gases expel out
due to the movement of piston
 Pressure and temperature
decreases with exhausted gas
 Piston Displacement: BDC to
mechanical work and power is obtained at the crankshaft.
– Piston Displacement: TDC to BDC
ACTUAL INDICATOR DIAGRAMACTUAL INDICATOR DIAGRAM
-Suction stroke 1-2
remains below
Atmospheric Pressure line
i.e. there’s a pressure
difference.
-Inlet valve offers
resistance to fresh charge
-IVC beyond 2.
-IGN occurs shortly before
the end of compression
stroke. Sparking causessharp rise in pressure and temperature but volume practically remains constant
(3-4).
-EVO a little before 5.
-Exhaust stroke 5-1 lies above Atmospheric Pressure line, which pressure
difference causes burned gas to exhaust. Exhaust valve causes resistance to gas
flow so that it cannot escape suddenly.
VALVE TIMING DIAGRAM:VALVE TIMING DIAGRAM:
4 STROKE CYCLE ENGINE4 STROKE CYCLE ENGINE
 A valve timing diagram is a graphical representation of the
exact moments, in the sequence of operations, at which the
two valves (i.e. Inlet & exhaust valves) open and close as well
as firing of the fuel.
 It is expressed in terms of angular positions of the crankshaft.
 In 4 stroke cycle, the crank revolves through 2 revolutions.
• The actual valve timing diagram is different from the
theoretical one due to two factors –

Mechanical and
Dynamic factors.
Heat Engine
 Opening and closing of inlet valve
– Inlet valve opens 12 ~ 30 CA before TDCᵒ to facilitate silent
operation of the engine under high speed. It increases the
volumetric efficiency.
– Inlet valve closes 10 ~ 60 CA after BDCᵒ due to inertia
movement of fresh charge into cylinder i.e. ram effect.
 Opening and closing of exhaust valve
– Exhaust valve opens 25 ~ 55 CA before BDCᵒ to reduce the work
required to expel out the burnt gases from the cylinder. At the end
of expansion stroke, the pressure inside the chamber is high,
hence work to expel out the gases increases.
– Exhaust valve closes 10 ~ 30 CA after TDCᵒ to avoid the
compression of burnt gases in next cycle. Kinetic energy of the
burnt gas can assist maximum exhausting of the gas. It also
increases the volumetric efficiency.
 Valve overlap
– During this time both the intake and exhaust valves are open.
– The intake valve is opened before the exhaust gases have completely
left the cylinder, and their considerable velocity assists in drawing in
the fresh charge. Engine designers aim to close the exhaust valve
just as the fresh charge from the intake valve reaches it, to prevent
either loss of fresh charge or un-scavenged exhaust gas.
IgnitionIgnition
Advantages:
– Dedicated lubrication system makes to engine
more wear resistant
– Better efficiency that 2-stroke engine
– Less pollution
Drawbacks:
– Complicated construction
– Should work in horizontal position due to
lubrication
4 Stroke SI engine4 Stroke SI engine
4 Stroke Cycle GAS Engine/4 Stroke Cycle GAS Engine/
SI EngineSI Engine
 Similarities with Petrol engine
• Operation Cycle i.e. also uses Otto Cycle
• All mechanical features
• Ignition system
• Valve timing diagram and p-v diagram
 Only difference is that it uses natural gas or manufactured gas
as working fuel and the way it is supplied.
In most cases, the density and calorific value of gas is
considerbly less than that of fuel. Therefore for an equal power
engine, the cylinder of gas engine is made larger than that of
petrol engine
4 Stroke Cycle DIESEL Engine/4 Stroke Cycle DIESEL Engine/
CI EngineCI Engine
Operation Cycle completed in
 4 strokes of the piston
 2 revolutions of the crankshaft
Also known as Diesel Cycle.
• Now we will be discussing about the actual
operating cycles
– The same as the intake stroke in an SI engine with one major difference :
no fuel is added to the incoming air.
(i) Intake/Suction stroke
(ii) Compression stroke
• The same as in an SI engine except that only air is
compressed and compression is to higher pressures
and temperature.
• Late in the compression stroke fuel is injected
directly into the combustion chamber, where it
mixes with very hot air. This causes the fuel to
evaporate and self ignite, causing combustion to
start.
• Combustion is fully developed by TDC and continues at about constant pressure
until fuel injection is complete and the piston has started towards BDC.
• Self ignition of fuel occurs when the combustion chamber temperature reaches
flash point of the fuel.
• FLASH POINT: It is the minimum temperature at which the fuel will ignite
(flash) on application of an ignition source (here compression) under specified
conditions.
(iii) Expansion stroke
(iv) Exhaust stroke
(Same as an SI engine)
 Valves: exhaust valve opens,
intake valve is closed
 Charge: Burnt gases expel out due
to the movement of piston
 Pressure and temperature decreases
with exhausted gas
 Piston Displacement: BDC to
TDC.
The power stroke
continues as combustion
ends and the piston
travels towards BDC.
Heat Engine
ACTUAL INDICATOR DIAGRAMACTUAL INDICATOR DIAGRAM
-Suction stroke 1-2
remains below
Atmospheric Pressure line
i.e. there’s a pressure
difference.
-Inlet valve offers
resistance to fresh charge
-IVC beyond 2.
-FVO shortly before the
end of compression stroke
and fuel is injected to the
engine cylinder.Fuel is ignited by high temperature of the compressed air. This causes sharp rise
in volume and temperature but pressure practically remains constant (3-4).
-EVO a little before 5.
-Exhaust stroke 5-1 lies above Atmospheric Pressure line. This pressure
difference causes burned gas to exhaust. Exhaust valve causes resistance to gas
flow so that it cannot escape suddenly.
Heat Engine
Advantages:
– •self ignition (without electrical spark plug)
– •better efficiency
– •reliable
– •higher durability
– •supplied with worse fuels
Drawbacks:
– •more NOx production
– •more expensive production
– •more weight
– •louder
Two stroke engineTwo stroke engine
 -No piston stroke for suction and exhaust operations
 -Suction is accomplished by air compressed in crankcase or by a blower
 -Induction of compressed air removes the products of combustion through
exhaust ports
 -Transfer port is there to supply the fresh charge into combustion chamber
EXPANSION &
EXHAUST PROCESSES
SUCTION/INTAKE &
COMPRESSION PROCESSES
INWARD
STROKE
( Piston
Movement)
OUTWARD
STROKE
( Piston
Movement)
* Actual Indicator Diagram* Actual Indicator Diagram
- SI Engine- SI Engine
- CI Engine- CI Engine
** Valve Timing Diagram** Valve Timing Diagram
- SI Engine- SI Engine
- CI Engine- CI Engine
Two stroke engineTwo stroke engine
 Advantages:
– •lack of valves, which simplifies construction and lowers weight
– •fire once every revolution, which gives a significant power boost
– •can work in any orientation
– •good power to weight ratio
 Drawbacks:
– •lack of a dedicated lubrication system makes the engine to wear
faster.
– •necessity of oil addition into the fuel
– •low efficiency •produce a lot of pollution
COMPARISONCOMPARISON
FOUR STROKE ENGINE
&
TWO STROKE ENGINE
FOUR STROKE ENGINE TWO STROKE ENGINE
Four stroke of the piston and two
revolution of crankshaft
Two stroke of the piston and one revolution
of crankshaft
One power stroke in every two revolution
of crankshaft
One power stroke in each revolution of
crankshaft
Heavier flywheel due to non-uniform
turning movement
Lighter flywheel due to more uniform
turning movement
Power produce is less Theoretically power produce is twice than
the four stroke engine for same size
Heavy and bulky Light and compact
Lesser cooling and lubrication
requirements
Greater cooling and lubrication
FOUR STROKE ENGINE TWO STROKE ENGINE
Lesser rate of wear and tear Higher rate of wear and tear
Contains valve and valve mechanism Contains ports arrangement
Higher initial cost Cheaper initial cost
Volumetric efficiency is more due to
greater time of induction
Volumetric efficiency less due to lesser
time of induction
Thermal efficiency is high and also part
load efficiency is better
Thermal efficiency is low, part load
efficiency is lesser
It is used where efficiency is important. It is used where low cost, compactness and
light weight are important.
Ex-cars, buses, trucks, tractors, industrial
engines, aero planes, power generation etc.
Ex-lawn mowers, scooters, motor cycles,
mopeds, propulsion ship etc
COMPARISONCOMPARISON
SI ENGINE
&
CI ENGINE
SI engine CI engine
Working cycle is Otto cycle. Working cycle is diesel cycle.
Fuel and air are introduced as a
gaseous mixture in the suction stroke.
Fuel is injected directly into the
combustion chamber at high pressure
at the end of compression stroke.
Carburettor is used to provide the
mixture. Throttle controls the quantity
of mixture introduced.
Injector and high pressure pump are
used to supply fuel. Quantity of fuel is
regulated by pump.
High self-ignition temperature. Low self-ignition temperature.
Petrol or gasoline or high octane fuel
is used.
Diesel or high cetane fuel is used.
SI engine CI engine
Use of spark plug for ignition system Self-ignition by the compression of air
which increased the temperature
required for combustion
Compression ratio is 6 to 10.5 Compression ratio is 14 to 22
Higher maximum RPM due to lower
weight
Lower maximum RPM
Maximum efficiency lower due to
lower compression ratio
Higher maximum efficiency due to
higher compression ratio
Lighter Heavier due to higher pressures
SCAVENGINGSCAVENGING
 It is the process of clearing or sweeping out the exhaust
gases from the combustion chamber of the cylinder.
 It is necessary that cylinder should not have any burnt
gases because they mixed with the fresh incoming charge
and reduce its strength.
 Power will be lost if the fresh charge is diluted by the
exhaust gases.
 The scavenging is necessary only in two stroke engines
since piston does not help for clearing the burned gas from
the cylinder.
SCAVENGING: TYPESSCAVENGING: TYPES
1. Cross flow scavenging
2. Full loop or back flow scavenging
3. Uniform flow scavenging
Fuel RatingFuel Rating
Octane number, also called Antiknock Rating, measure of the
ability of a fuel to resist knocking when ignited in a mixture with
air in the cylinder of an internal-combustion engine.
The octane number is determined by comparing the knock
intensity of the fuel with that of blends of two reference fuels:
iso-octane, which resists knocking, and heptane, which knocks
readily.
Thus the octane number is the percentage by volume of
Iso-octane in the iso-octane–heptane mixture that matches the
Fuel being tested in a standard test engine.
46
Fuel RatingFuel Rating
cetane number. Measure of the ignition quality of
Diesel fuel; higher this number, the easier it is to start a
standard (direct-injection) diesel engine.
It denotes the percentage (by volume) of cetane
(chemical name Hexadecane) in a combustible
mixture (containing cetane and 1-methylnapthalene)
whose ignition characteristics match those of the
diesel fuel being tested.
47
PRE-IGNITIONPRE-IGNITION
 In SI engine the combustion during the normal working is
initiated by a electric spark.
 The spark is timed to occur at a definite point just before
the end of the compression stroke.
 The ignition of the charge should not occurs before the
spark is introduced in the cylinder, if the ignition start due
to any other reasons when the piston is still doing its
compression stroke is called as pre-ignition
PREIGNITION: CAUSESPREIGNITION: CAUSES
 High compression ratio
 Carbon deposit on cylinder wall.
 Overheated exhaust valve
 It may occur due to faulty timing of spark
initiation.
PREIGNITION: EFFECTSPREIGNITION: EFFECTS
Reduce useful work per cycle
Increase heat losses from engine
Reduction in the thermal efficiency
Subjects the engine components to excessive
pressure
IC Engine Systems
Transmission System
Cooling System
Lubricating System
Fuel System
Ignition System
Transmission SystemTransmission System
Transmission SystemTransmission System
Transmission SystemTransmission System
Transmission SystemTransmission System
Engine Flywheel Transmission
/ Gear Box
Differential
Rear
drive
axel/
half
shaft
Rear
Wheel
Universal
Joint
Clutch Propeller
Shaft
Universal
Joint
Block Diagram of a
Rear Wheel Drive (Manual Gear Transmission)
Cooling SystemCooling System
Cooling SystemCooling System
Four methods of Engine Cooling
– Air Cooling
– Water Cooling
– Steam Cooling
– Liquid Cooling
An automotive cooling system must perform
several functions
a. Remove excess heat from the engine
b. Maintain a consistent engine temperature
c. Help a cold engine warm-up quickly
d. Provide a means of warming the passenger
compartment
Cooling SystemCooling System
Cooling System- Water CoolingCooling System- Water Cooling
Cooling System- Water CoolingCooling System- Water Cooling
Upper Hose Bypass
Hose
Lower
Hose
Cooling System- Water CoolingCooling System- Water Cooling
1
2
3
4
5
6
7
8
Components used inComponents used in
Water Cooling systemWater Cooling system
1. Radiator
2. Radiator Cooling Fans
3. Pressure Cap & Reserve Tank
4. Water Pump
5. Thermostat
6. Bypass System
7. Water jacket/Coolant manifold
8. Hoses
Water Cooling SystemWater Cooling System
Radiator
Water
Pump
Water
Jacket
of
Cylinder
Block
Oil
Cooler
Water
Jacket of
Cylinder
Head
Thermostat
housing
Thermostat Bypass
Block Diagram
64
RadiatorsRadiators
 A radiator is a heat
exchanger.
 Tube and fin style
the most popular.
 Made of copper and
brass or aluminum
and plastic.
65
Radiator FansRadiator Fans
Keeps air moving
through the radiator
when the car is not
moving.
Several types:
 rigid,
 flex (not used much
anymore),
 Electric etc
66
Radiator CapRadiator Cap
 The cap allows access to
the cooling system for
filling and testing.
 The cap has two valves: a
pressure relief valve set at
around 15 PSI and a
vacuum valve which is
needed when the engine
cools down.
 Raises boiling point of
fluid
 Able to take on more heat
67
Water PumpWater Pump
 Usually driven by drive
belt from crankshaft.
 Simple impeller design
 Non-positive
displacement pump
which circulates coolant
around cooling system.
68
ThermostatThermostat
 Controls coolant
temperature.
 Uses a temperature
sensor and a valve.
 Usually opens around
195 degrees F.
69
Water JacketsWater Jackets
 Surrounds the
cylinders with water
passage.
 Absorbs heat from the
cylinder wall.
 Pump moves water to
radiator where heat is
exchanged to the air.
70
Coolant Recovery TankCoolant Recovery Tank
 Keeps the coolant level full
in the system at all times.
 Works in conjunction with
the radiator cap.
 When the engine heats up
the coolant expands and
flows to the recovery tank.
 When the engine cools the
coolant contracts and
creates a vacuum and
draws the fluid back into the
radiator.
• Advantages:
 Reduces air in system
 Reduces rust
 Less need to open radiator
71
Coolant Temperature Sensor (CTS)Coolant Temperature Sensor (CTS)
 Reports to computer
 Gauges
 Location
– Block
– Head
– Radiator tank
72
HeaterHeater
 The hot water in the
cooling system is used to
warm the passenger
compartment.
 A small radiator is called a
heater core is located in
the dash area.
 Heater hoses direct the hot
water to and from it.
Lubrication systemLubrication system
74
Lubrication systemLubrication system
 To reduce friction between moving parts
 To reduce wear of moving parts
 To act as cooling medium for removing heat
 To keep the engine parts clean, especially piston
rings and ring grooves, oil ways and filters
 To absorb shocks between bearings and other
engine parts thus reducing engine noises and
extending engine life
FunctionFunction
Function (cont)Function (cont)
 To form a good seal between piston rings and
cylinder walls
 To prevent deposition of carbon, soot and lacquer
 To absorb and carry away harmful substances
resulting from incomplete combustion
 To prevent metalic components from corrosive
attack by the acid from incomplete combustion
 To resist oxidation which causes sludge and
lacquers
Lubrication systemLubrication system
Lubricating SystemLubricating System
1
2
3
5
6
4
pressure
regulator
9
8
7
77
Lubricating SystemLubricating System
PartsParts
1. Oil pan/sump
2. Oil strainer
3. Pick-up screen
4. Oil pump
5. Pressure regulator
6. Oil filter
7. By-pass valve
8. Oil galleries
9. Pressure indicator
Lubricating SystemLubricating System
Block DiagramBlock Diagram
Sump
Oil
Pump
Filter Main oil
gallery
Pressure
Regulator
By Pass
Valve
Crank
shaft
Big end bearings,
connecting rod,
small end bearings,
Piston rings
Cam
shaft
Rocker arm ,
valve and
valve spring
Timing gear
mechanism
Strainer
79
Lubrication systemLubrication system
Main Functions of Lubricating Oil
To minimize friction and wear
To seal the pistons and thus preventing
escape of gases in the cylinders with
consequent loss of power
To cushion the parts against vibration and
impact
To clean the parts as it lubricates them,
carrying away impurities
To cool by carrying away heat
Fuel SystemFuel System
Fuel SystemFuel System
Fuel SystemFuel System
Block DiagramBlock Diagram
Fuel
tank
Primary
Filter
Fuel feed
pump/
low
pressure
pump
Secondary
Filter
Fuel
injection
pump/
high
pressure
pump
HP
line Injector
Cylinder
Residual
Fuel
Excess fuel
FUEL FEED SYSTEMFUEL FEED SYSTEM
CARBURETTORCARBURETTOR
 It is the most important device in the Fuel Feed System in
a SI engine.
 Connected between Fuel Filter and the Induction
Manifold.
 Function:
To atomize and vaporize the fuel and to mix it with
the air in varying proportions to suit the changing
condition of spark ignition engines.
The air-fuel mixture attained from carburettor is called
combustible mixture .
CARBURATIONCARBURATION
 The process of mixing the gasoline fuel with air to obtain
the combustible mixture is called carburetion.
 The carburettor must create an air fuel mixture that is
correct for different circumstances such as:
 Cold or hot starting
 Idling
 Part throttle
 Acceleration
 High speed operation
 Carburettors work on the principle of air pressure
differences.
Ignition SystemIgnition System
Ignition SystemIgnition System
Requirements
•To supply high voltage surges to current ( as high as 30000
volts) to the spark plug. These surges produce electric sparks
at the spark plug gap that ignite or set fire to the combustible
mixture in combustion chamber.
• The sparking must be properly times (at the end of
compression stroke)
• The system should function efficiently at the maximum
and minimum speeds of the engine
• It should be easy to maintain, light and compact
• It should not cause any interference
Ignition SystemIgnition System
• Types
1. Battery/ Coil Ignition system
 Used in passenger car, light trucks etc
 Battery supplies the current in the primary winding
2. Magneto Ignition System
 Magneto produces and supplies the current in the primary winding
Both systems are based on the principal of mutual electro- magnetic
nduction
Battery Ignition SystemBattery Ignition System
5
4
2
7
6
8
1
5
4
32
7
6
8
Components:
1. Battery
2.Switch
3.Ammeter
4.Ignition Coil
5.Condenser
6.Contact Breaker
7.Distributor
8.Spark Plug
Magneto Ignition SystemMagneto Ignition System
5
4
3
1
7
2
6
Components:
1. Magneto
2.Switch
3.Ignition Coil
4.Condenser
5.Contact Breaker
6.Distributor
7.Spark Plug
ComparisonComparison
S/N Battery Ignition System Magneto Ignition System
1 Current obtained from battery Current generated by magneto
2 Good sparking even at low speed Poor sparking at low speed
3 Engine starting is easier Difficult starting
4 Engine cannot be started if battery is
discharged
No such difficulty
5 Occupies more space Occupies less space
6 Complicated wiring Simple wiring
7 Less costly More costly
8 Spark intensity falls as the engine
speed rises
Spark intensity improves as the engine
speed rises
9 Used in cars, buses, trucks etc Used in motor cycles, scooters, racing
cars etc
Engine PerformanceEngine Performance
Compression Ratio
 Volume in the cylinder at the bottom of its travel as
compared to the top (r = Vs/Vc )
 Expressed as a ratio 10:1, 7:1, etc……..
 Higher compression ratios produce more power
 Compression ratio is limited by fuel octane and
engine strength
 However, higher compression ratio engines are
more apt to detonation or “knocking”
Compression RatioCompression Ratio
Super ChargerSuper Charger
TurbochargerTurbocharger
Engine PowerEngine Power
Power = work / time
P= w/t
Hp = 33,000 ft-lb (work) / 1 minute (time)
Hp = 550 ft-lb / 1 second
Kinds of Horse Powers
– Indicated Horsepower
– Brake Horsepower
– Frictional Horsepower
– Rated Horsepower
– Corrected Horsepower
95
Indicated Horsepower. The power developed within a cylinder
can be calculated by measuring the imep and the engine speed.
(The rpm of the engine is converted to the number of power
strokes per minute.) With the bore and stroke know (available in
engine manufacturers’ technical manuals), the horsepower
(hp) can be computed. This power is called indicated horsepower
(ihp) because it is obtained from the pressure measured with an
engine indicator. Power loss due to friction is not considered in
computing ihp.
ihp = P × L × A × N /33,000
P = Mean indicated pressure, in psi
L = length of stroke, in feet
A = Effective area of the piston, in square inches
N = Number of power strokes per minute
33,000 = Unit of power (one horsepower), or foot pounds
per minute.
96
Brake horsepower. Actual or useful horsepower of an
engine, usually determined from the force exerted on a
friction brake or Dynamometer connected to the drive
shaft.
Frictional horsepower. That part of the gross or indicated
horsepower developed in an engine cylinder which is
absorbed in frictional losses; It is the difference between
the indicated and the brake horsepower.
Rated horsepower. Power of an engine or prime mover,
The maximum horsepower that can be provided under
normal continuous operation.
Corrected horsepower. is the observed readings
"corrected" to standard temperature, humidity, and
barometer, conditions.
97
Efficiency of EngineEfficiency of Engine
 Brake thermal efficiency: brake power/rate of heat output for complete combustion
 Brake thermal efficiency=indicated thermal efficiency* mechanical efficiency
 the thermal efficiency () is a dimensionless performance measure of a device that
uses thermal energy, such as an internal combustion engine, a steam turbine or a
steam engine, a boiler, a furnace, or a refrigerator for example. In other words,
efficiency indicates how well an energy conversion or transfer process is
accomplished.
 Mechanical efficiency measures the effectiveness of a machine in transforming the
energy and power that is input to the device into an output force and movement.
Efficiency is measured as a ratio of the measured performance to the performance
of an ideal machine:
Factors Affecting Engine PerformanceFactors Affecting Engine Performance
 Detonation.
 Effect of Detonation:
DETONATIONDETONATION
 The explosion of the fuel/air mixture instead of a steady
burning. This explosion causes an abrupt rise in cylinder
temperatures and pressures that may cause engine damage;
 Also rapid combustion of fuel/Detonation results in loss of
power and a knocking sound (indication of abnormal
combustion )
Factors Affecting Engine PerformanceFactors Affecting Engine Performance
Detonation may be caused by several factors:
 Low octane fuel (SI Engine)
 High cylinder temperatures
 Lean/uneven mixture
 High compression ratios
 Shape of combustion chamber and position of
sparking plug
 Preignition of the fuel/air mixture before the
properly timed injection /spark occurs
Factors Affecting Engine PerformanceFactors Affecting Engine Performance
DETONATIONDETONATION
DETONATION: EFFECTSDETONATION: EFFECTS
 Noise
 Mechanical damage
 Increased heat transfer
 Pre-ignition
 Decrease in power output
• Exhaust BlowdownExhaust Blowdown : Late in the power stroke, the: Late in the power stroke, the
exhaust valve is opened and exhaust blowdownexhaust valve is opened and exhaust blowdown
occurs.occurs.
– This exhaust gas carries away a highThis exhaust gas carries away a high
amount of enthalpy, which lowers the cycleamount of enthalpy, which lowers the cycle
thermal efficiency.thermal efficiency.
– Opening the exhaust valve before BDCOpening the exhaust valve before BDC
reduces the work obtained but is requiredreduces the work obtained but is required
because of the finite time needed forbecause of the finite time needed for
exhaust blowdown.exhaust blowdown.
• Exhaust BlowdownExhaust Blowdown ::
– Pressure and temperature in the cylinderPressure and temperature in the cylinder
are still high relative to the surroundings atare still high relative to the surroundings at
this point, and a pressure differential isthis point, and a pressure differential is
created through the exhaust system whichcreated through the exhaust system which
is open to atmospheric pressure.is open to atmospheric pressure.
– This pressure differential causes much ofThis pressure differential causes much of
the hot exhaust gas to be pushed out of thethe hot exhaust gas to be pushed out of the
cylinder and through the exhaust systemcylinder and through the exhaust system
when the piston is near BDC.when the piston is near BDC.
• Exhaust stroke:Exhaust stroke: By the time piston reaches BDC,By the time piston reaches BDC,
exhaust blowdown is complete, but the cylinder is stillexhaust blowdown is complete, but the cylinder is still
full of exhaust gases at approximately atmosphericfull of exhaust gases at approximately atmospheric
pressure.pressure.
– With the exhaust valve remaining open, theWith the exhaust valve remaining open, the
piston travels from BDC to TDC in the exhaustpiston travels from BDC to TDC in the exhaust
stroke.stroke.
– This pushes most of the remaining exhaustThis pushes most of the remaining exhaust
gases out of the cylinder into the exhaust systemgases out of the cylinder into the exhaust system
at about atmospheric pressure, leaving only thatat about atmospheric pressure, leaving only that
trapped in the clearance volume when the pistontrapped in the clearance volume when the piston
reaches TDC.reaches TDC.
– Near the end of the exhaust stroke before TDC,Near the end of the exhaust stroke before TDC,
the intake valve starts to open, so that itthe intake valve starts to open, so that it is fullyis fully
open by TDCopen by TDC when the new intake stroke startswhen the new intake stroke starts
the next cycle.the next cycle.
– Near TDC the exhaust valve starts to close andNear TDC the exhaust valve starts to close and
finally is fully closedfinally is fully closed sometime after TDCsometime after TDC..
– This period when both the intake valve andThis period when both the intake valve and
exhaust valve are open is calledexhaust valve are open is called valve overlapvalve overlap,, itit
can be clearly seen in valve timing chart givencan be clearly seen in valve timing chart given
below.below.
Heat Engine
Heat Engine
Engine PartsEngine Parts
EnginesEngines
Engine Block
- Foundation of the engine
- It contains pistons, crank shaft, cylinders, timing
sprockets and sometimes the cam shaft.
EnginesEngines
Piston
A movable part fitted into a
cylinder, which can receive and
transmit power.
Through connecting rod, forces
the crank shaft to rotate.
EnginesEngines
Cylinder head
Part that covers and encloses the
Cylinder.
It contains cooling fins or water jackets
and the valves.
Some engines contains the cam shaft
in the cylinder head.
EnginesEngines
Connecting (conn.) Rod
Attaches piston (wrist-pin)
to the crank shaft (connecting
rod caps).
EnginesEngines
Crank Shaft
Converts up and down motion
into circular motion.
Transmits the power to
transmission.
DAMPNER PULLEY
Controls Vibration
EnginesEngines
•Exhaust Valve lets the exhaust gases escape the combustion
Chamber. (Diameter is smaller then Intake valve)
•Intake Valve lets the air or air fuel mixture to enter the
combustion chamber. (Diameter is larger than the exhaust valve)
Valves: Minimum two valves per cylinder
EnginesEngines
Valve Springs:
Keeps the valves closed.
EnginesEngines
Different arrangement of valve and camshaft.
EnginesEngines
Cam Shaft:
The shaft that has intake and
Exhaust cams for operating the
valves.
Cam Lobe:
Changes rotary motion into
reciprocating motion.
EnginesEngines
It provides the means of ignition when the gasoline
engine’s piston is at the end of compression stroke,
close to Top Dead Center(TDC)
Back
Spark Plug
Flywheel
-Attached to the crankshaft
-Reduces vibration
-Cools the engine (air cooled)
-Transfers power from engine
to the Drive train
-Helps glide through strokes
ENGINESENGINES
EnginesEngines
Configuration
• Inline Engines: The
cylinders are arranged in a
line, in a single bank.
• V Engines: The
cylinders are arranged in two
banks, set at an angle to one
another.
• Flat Engines:
The cylinders are
arranged in two
banks on opposite
sides of the engine.
•back
EnginesEngines
Piston Rings
Four stroke: Three rings
*Compression rings- Top two
(sealing the compression
pressure in the
cylinder)
*Oil ring- the third one
(scrapes excessive oil from
the cylinder walls)
Two Stroke: Two Rings
Both the rings are Compression
rings.

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Heat Engine

  • 1. Heat engineHeat engine A heat engine is a device which transforms the chemical energy of a fuel into thermal energy and uses this energy to produce mechanical work. It is classified into two types- (a) External combustion engine (b) Internal combustion engine
  • 2. CLASSIFICATIONCLASSIFICATION  External combustion engine: – In this engine, the products of combustion of air and fuel transfer heat to a second fluid which is the working fluid of the cycle. – Examples:  In the steam engine or a steam turbine plant, the heat of combustion is employed to generate steam which is used in a piston engine (reciprocating type engine) or a turbine (rotary type engine) for useful work.  In a closed cycle gas turbine, the heat of combustion in an external furnace is transferred to gas, usually air which the working fluid of the cycle.
  • 3.  Internal combustion engine: – In this engine, the combustion of air and fuels take place inside the engine cylinder and are used as the direct motive force. – It can be classified into the following types:  1. According to the basic engine design- – (a) Reciprocating engine (Use of cylinder piston arrangement), – (b) Rotary engine (Use of turbine)  2. According to the type of fuel used- – (a) Petrol engine, (b) diesel engine, (c) gas engine (CNG, LPG), – (d) Alcohol engine (ethanol, methanol etc) CLASSIFICATIONCLASSIFICATION
  • 4.  Internal combustion engine:  3. According to the number of strokes per cycle- (a) Four stroke and (b) Two stroke engine  4. According to the method of igniting the fuel- – (a) Spark ignition engine, – (b) compression ignition engine and – (c) hot spot ignition engine  5. According to the working cycle- – (a) Otto cycle (constant volume cycle) engine, – (b) diesel cycle (constant pressure cycle) engine, – (c) dual combustion cycle (semi diesel cycle) engine. CLASSIFICATIONCLASSIFICATION
  • 5.  6. According to the fuel supply and mixture preparation- – (a) Carburetted type (fuel supplied through the carburettor), – (b) Injection type (fuel injected into inlet ports or inlet manifold, fuel injected into the cylinder just before ignition).  7. According to the number of cylinder- – (a) Single cylinder and (b) multi-cylinder engine  8. Method of cooling- – water cooled or air cooled  9. Speed of the engine- – Slow speed, medium speed and high speed engine  10. Cylinder arrangement-Vertical, horizontal, radial, inline, V- type, opposite cylinder piston engines etc. CLASSIFICATIONCLASSIFICATION
  • 6.  11. Valve mechanism- – Overhead valve engines, and Side valve engines;  12. Method of governing- – Hit and miss governed engines, Quantitatively governed engines and Qualitatively governed engine Application – Automotive engines for land transport, – marine engines for propulsion of ships, – aircraft engines for aircraft propulsion, – industrial engines, – prime movers for electrical generators etc CLASSIFICATIONCLASSIFICATION
  • 7. External combustion engine  Combustion of air-fuel is outside the engine cylinder (in a boiler)  The engines are running smoothly and silently due to outside combustion  Higher ratio of weight and bulk to output due to presence of auxiliary apparatus like boiler and condenser. Hence it is heavy and cumbersome.  Working pressure and temperature inside the engine cylinder is low; hence ordinary alloys are used for the manufacture of engine cylinder and its parts. Internal combustion engine  Combustion of air-fuel is inside the engine cylinder (in a boiler)  Very noisy operated engine  It is light and compact due to lower ratio of weight and bulk to output.  *Working pressure and temperature inside the engine cylinder is very much high; hence special alloys are used Comparison between external combustion engineComparison between external combustion engine and internal combustion engine:and internal combustion engine:
  • 8. Comparison between external combustion engineComparison between external combustion engine and internal combustion engine:and internal combustion engine:  It can use cheaper fuels including solid fuels  Lower efficiency about 15- 20%  Lesser requirement of water  High starting torque  High grade fuels are used with proper filtration  Higher efficiency about 35- 40%  Higher requirement of water for dissipation of energy through cooling system  IC engines are not self-starting External combustion engine Internal combustion engine
  • 9. Main components ofMain components of reciprocating IC engines:reciprocating IC engines:
  • 10.  Cylinder: It is the main part of the engine inside which piston reciprocates to and fro. It should have high strength to withstand high pressure above 50 bar and temperature above 2000 Cᴼ . The ordinary engine is made of cast iron and heavy duty engines are made of steel alloys or aluminium alloys. In the multi-cylinder engine, the cylinders are cast in one block known as cylinder block.  Cylinder head: The top end of the cylinder is covered by cylinder head over which inlet and exhaust valve, spark plug or injectors are mounted. A copper or asbestos gasket is provided between the engine cylinder and cylinder head to make an air tight joint.  Piston: Transmit the force exerted by the burning of charge to the connecting rod. Usually made of aluminium alloy which has good heat conducting property and greater strength at higher temperature.
  • 11.  Piston rings: These are housed in the circumferential grooves provided on the outer surface of the piston and made of steel alloys which retain elastic properties even at high temperature. 2 types of rings- compression and oil rings. – Compression ring is upper ring of the piston which provides air tight seal to prevent leakage of the burnt gases into the lower portion. – Oil ring is lower ring which provides effective seal to prevent leakage of the oil into the engine cylinder.  Connecting rod: It converts reciprocating motion of the piston into circular motion of the crank shaft, in the working stroke. The smaller end of the connecting rod is connected with the piston by gudgeon pin and bigger end of the connecting rod is connected with the crank with crank pin. The special steel alloys or aluminium alloys are used for the manufacture of connecting rod.
  • 12.  Crankshaft: It converts the reciprocating motion of the piston into the rotary motion with the help of connecting rod. The special steel alloys are used for the manufacturing of the crankshaft. It consists of eccentric portion called crank.  Crank case: It houses cylinder and crankshaft of the IC engine and also serves as sump for the lubricating oil.  Flywheel: It is big wheel mounted on the crankshaft, whose function is to maintain its speed constant. It is done by storing excess energy during the power stroke, which is returned during other stroke.
  • 13. Terminology used in IC engine:Terminology used in IC engine:
  • 14. Terminology used in IC engine:Terminology used in IC engine:  1. Cylinder bore (D): The nominal inner diameter of the working cylinder.  2. Piston area (A): The area of circle of diameter equal to the cylinder bore.  3. Stroke (L): The nominal distance through which a working piston moves between two successive reversals of its direction of motion.  4. Dead centre: The position of the working piston and the moving parts which are mechanically connected to it at the moment when the direction of the piston motion is reversed (at either end point of the stroke). – (a) Bottom dead centre (BDC): Dead centre when the piston is nearest to the crankshaft. – (b) Top dead centre (TDC): Dead centre when the position is farthest from the crankshaft.
  • 15.  5. Displacement volume or swept volume (Vs): The nominal volume generated by the working piston when travelling from the one dead centre to next one and given as, Vs=A × L  6. Clearance volume (Vc): the nominal volume of the space on the combustion side of the piston at the top dead centre.  7. Cylinder volume (V): Total volume of the cylinder. V= Vs + Vc  8. Compression ratio (r): r = Vs / Vc Terminology used in IC engine:Terminology used in IC engine:
  • 16. Sequence of Operations in aSequence of Operations in a CycleCycle In a continuously operating engine, we may consider a cycle starting from any stroke. When the engine returns back to the stroke where it started, we say that the cycle has been completed.
  • 17. IDEAL OPERATING CYCLEIDEAL OPERATING CYCLE TWO STROKE CYCLE ENGINE EXPANSION & EXHAUST PROCESSES SUCTION/INTAKE & COMPRESSION PROCESSES INWARD STROKE ( Piston Movement) OUTWARD STROKE ( Piston Movement)
  • 18. 4 Stroke Cycle Petrol4 Stroke Cycle Petrol Engine/ SI EngineEngine/ SI Engine Operation Cycle completed in  4 strokes of the piston  2 revolutions of the crankshaft Also known as Otto Cycle (named after the German Scientist who devised an engine working on this cycle) • Now we will be discussing about the actual operating cycles
  • 19. – Valves: Intake valve opens and exhaust valve is closed – Charge: Fresh air mixed with fuel vapour (supplied in correct proportion) is drawn into the cylinder due to the vacuum pressure created by the movement of the piston – Piston Displacement: TDC to BDC (i) Intake/Suction stroke (ii) Compression stroke – Valves: Both valves closed – Charge: Fresh charge is compressed into clearance volume by the return stroke of the piston. – The Pressure and Temperature of the charge increases considerably (dependant upon the compression ratio) – Shortly before piston reaches TDC the charge is ignited by the spark plug for combustion. – Piston Displacement: BDC to TDC Air/fuel mixture is
  • 20. – Valves: Both valves closed – Charge: Due to combustion, there is a sudden increase of pressure and temperature, but the volume practically remains constant. – High pressure of burnt gases force the piston down with great force towards BDC. Hence, hot burnt gases expand due to the speed of the piston. During this expansion, some heat energy transforms into (iii) Expansion stroke (iv) Exhaust stroke  Valves: exhaust valve opens, intake valve is closed  Charge: Burnt gases expel out due to the movement of piston  Pressure and temperature decreases with exhausted gas  Piston Displacement: BDC to mechanical work and power is obtained at the crankshaft. – Piston Displacement: TDC to BDC
  • 21. ACTUAL INDICATOR DIAGRAMACTUAL INDICATOR DIAGRAM -Suction stroke 1-2 remains below Atmospheric Pressure line i.e. there’s a pressure difference. -Inlet valve offers resistance to fresh charge -IVC beyond 2. -IGN occurs shortly before the end of compression stroke. Sparking causessharp rise in pressure and temperature but volume practically remains constant (3-4). -EVO a little before 5. -Exhaust stroke 5-1 lies above Atmospheric Pressure line, which pressure difference causes burned gas to exhaust. Exhaust valve causes resistance to gas flow so that it cannot escape suddenly.
  • 22. VALVE TIMING DIAGRAM:VALVE TIMING DIAGRAM: 4 STROKE CYCLE ENGINE4 STROKE CYCLE ENGINE  A valve timing diagram is a graphical representation of the exact moments, in the sequence of operations, at which the two valves (i.e. Inlet & exhaust valves) open and close as well as firing of the fuel.  It is expressed in terms of angular positions of the crankshaft.  In 4 stroke cycle, the crank revolves through 2 revolutions. • The actual valve timing diagram is different from the theoretical one due to two factors –  Mechanical and Dynamic factors.
  • 24.  Opening and closing of inlet valve – Inlet valve opens 12 ~ 30 CA before TDCᵒ to facilitate silent operation of the engine under high speed. It increases the volumetric efficiency. – Inlet valve closes 10 ~ 60 CA after BDCᵒ due to inertia movement of fresh charge into cylinder i.e. ram effect.  Opening and closing of exhaust valve – Exhaust valve opens 25 ~ 55 CA before BDCᵒ to reduce the work required to expel out the burnt gases from the cylinder. At the end of expansion stroke, the pressure inside the chamber is high, hence work to expel out the gases increases. – Exhaust valve closes 10 ~ 30 CA after TDCᵒ to avoid the compression of burnt gases in next cycle. Kinetic energy of the burnt gas can assist maximum exhausting of the gas. It also increases the volumetric efficiency.
  • 25.  Valve overlap – During this time both the intake and exhaust valves are open. – The intake valve is opened before the exhaust gases have completely left the cylinder, and their considerable velocity assists in drawing in the fresh charge. Engine designers aim to close the exhaust valve just as the fresh charge from the intake valve reaches it, to prevent either loss of fresh charge or un-scavenged exhaust gas. IgnitionIgnition
  • 26. Advantages: – Dedicated lubrication system makes to engine more wear resistant – Better efficiency that 2-stroke engine – Less pollution Drawbacks: – Complicated construction – Should work in horizontal position due to lubrication 4 Stroke SI engine4 Stroke SI engine
  • 27. 4 Stroke Cycle GAS Engine/4 Stroke Cycle GAS Engine/ SI EngineSI Engine  Similarities with Petrol engine • Operation Cycle i.e. also uses Otto Cycle • All mechanical features • Ignition system • Valve timing diagram and p-v diagram  Only difference is that it uses natural gas or manufactured gas as working fuel and the way it is supplied. In most cases, the density and calorific value of gas is considerbly less than that of fuel. Therefore for an equal power engine, the cylinder of gas engine is made larger than that of petrol engine
  • 28. 4 Stroke Cycle DIESEL Engine/4 Stroke Cycle DIESEL Engine/ CI EngineCI Engine Operation Cycle completed in  4 strokes of the piston  2 revolutions of the crankshaft Also known as Diesel Cycle. • Now we will be discussing about the actual operating cycles
  • 29. – The same as the intake stroke in an SI engine with one major difference : no fuel is added to the incoming air. (i) Intake/Suction stroke (ii) Compression stroke • The same as in an SI engine except that only air is compressed and compression is to higher pressures and temperature. • Late in the compression stroke fuel is injected directly into the combustion chamber, where it mixes with very hot air. This causes the fuel to evaporate and self ignite, causing combustion to start. • Combustion is fully developed by TDC and continues at about constant pressure until fuel injection is complete and the piston has started towards BDC. • Self ignition of fuel occurs when the combustion chamber temperature reaches flash point of the fuel. • FLASH POINT: It is the minimum temperature at which the fuel will ignite (flash) on application of an ignition source (here compression) under specified conditions.
  • 30. (iii) Expansion stroke (iv) Exhaust stroke (Same as an SI engine)  Valves: exhaust valve opens, intake valve is closed  Charge: Burnt gases expel out due to the movement of piston  Pressure and temperature decreases with exhausted gas  Piston Displacement: BDC to TDC. The power stroke continues as combustion ends and the piston travels towards BDC.
  • 32. ACTUAL INDICATOR DIAGRAMACTUAL INDICATOR DIAGRAM -Suction stroke 1-2 remains below Atmospheric Pressure line i.e. there’s a pressure difference. -Inlet valve offers resistance to fresh charge -IVC beyond 2. -FVO shortly before the end of compression stroke and fuel is injected to the engine cylinder.Fuel is ignited by high temperature of the compressed air. This causes sharp rise in volume and temperature but pressure practically remains constant (3-4). -EVO a little before 5. -Exhaust stroke 5-1 lies above Atmospheric Pressure line. This pressure difference causes burned gas to exhaust. Exhaust valve causes resistance to gas flow so that it cannot escape suddenly.
  • 34. Advantages: – •self ignition (without electrical spark plug) – •better efficiency – •reliable – •higher durability – •supplied with worse fuels Drawbacks: – •more NOx production – •more expensive production – •more weight – •louder
  • 35. Two stroke engineTwo stroke engine  -No piston stroke for suction and exhaust operations  -Suction is accomplished by air compressed in crankcase or by a blower  -Induction of compressed air removes the products of combustion through exhaust ports  -Transfer port is there to supply the fresh charge into combustion chamber EXPANSION & EXHAUST PROCESSES SUCTION/INTAKE & COMPRESSION PROCESSES INWARD STROKE ( Piston Movement) OUTWARD STROKE ( Piston Movement)
  • 36. * Actual Indicator Diagram* Actual Indicator Diagram - SI Engine- SI Engine - CI Engine- CI Engine ** Valve Timing Diagram** Valve Timing Diagram - SI Engine- SI Engine - CI Engine- CI Engine Two stroke engineTwo stroke engine
  • 37.  Advantages: – •lack of valves, which simplifies construction and lowers weight – •fire once every revolution, which gives a significant power boost – •can work in any orientation – •good power to weight ratio  Drawbacks: – •lack of a dedicated lubrication system makes the engine to wear faster. – •necessity of oil addition into the fuel – •low efficiency •produce a lot of pollution
  • 39. FOUR STROKE ENGINE TWO STROKE ENGINE Four stroke of the piston and two revolution of crankshaft Two stroke of the piston and one revolution of crankshaft One power stroke in every two revolution of crankshaft One power stroke in each revolution of crankshaft Heavier flywheel due to non-uniform turning movement Lighter flywheel due to more uniform turning movement Power produce is less Theoretically power produce is twice than the four stroke engine for same size Heavy and bulky Light and compact Lesser cooling and lubrication requirements Greater cooling and lubrication
  • 40. FOUR STROKE ENGINE TWO STROKE ENGINE Lesser rate of wear and tear Higher rate of wear and tear Contains valve and valve mechanism Contains ports arrangement Higher initial cost Cheaper initial cost Volumetric efficiency is more due to greater time of induction Volumetric efficiency less due to lesser time of induction Thermal efficiency is high and also part load efficiency is better Thermal efficiency is low, part load efficiency is lesser It is used where efficiency is important. It is used where low cost, compactness and light weight are important. Ex-cars, buses, trucks, tractors, industrial engines, aero planes, power generation etc. Ex-lawn mowers, scooters, motor cycles, mopeds, propulsion ship etc
  • 42. SI engine CI engine Working cycle is Otto cycle. Working cycle is diesel cycle. Fuel and air are introduced as a gaseous mixture in the suction stroke. Fuel is injected directly into the combustion chamber at high pressure at the end of compression stroke. Carburettor is used to provide the mixture. Throttle controls the quantity of mixture introduced. Injector and high pressure pump are used to supply fuel. Quantity of fuel is regulated by pump. High self-ignition temperature. Low self-ignition temperature. Petrol or gasoline or high octane fuel is used. Diesel or high cetane fuel is used.
  • 43. SI engine CI engine Use of spark plug for ignition system Self-ignition by the compression of air which increased the temperature required for combustion Compression ratio is 6 to 10.5 Compression ratio is 14 to 22 Higher maximum RPM due to lower weight Lower maximum RPM Maximum efficiency lower due to lower compression ratio Higher maximum efficiency due to higher compression ratio Lighter Heavier due to higher pressures
  • 44. SCAVENGINGSCAVENGING  It is the process of clearing or sweeping out the exhaust gases from the combustion chamber of the cylinder.  It is necessary that cylinder should not have any burnt gases because they mixed with the fresh incoming charge and reduce its strength.  Power will be lost if the fresh charge is diluted by the exhaust gases.  The scavenging is necessary only in two stroke engines since piston does not help for clearing the burned gas from the cylinder.
  • 45. SCAVENGING: TYPESSCAVENGING: TYPES 1. Cross flow scavenging 2. Full loop or back flow scavenging 3. Uniform flow scavenging
  • 46. Fuel RatingFuel Rating Octane number, also called Antiknock Rating, measure of the ability of a fuel to resist knocking when ignited in a mixture with air in the cylinder of an internal-combustion engine. The octane number is determined by comparing the knock intensity of the fuel with that of blends of two reference fuels: iso-octane, which resists knocking, and heptane, which knocks readily. Thus the octane number is the percentage by volume of Iso-octane in the iso-octane–heptane mixture that matches the Fuel being tested in a standard test engine. 46
  • 47. Fuel RatingFuel Rating cetane number. Measure of the ignition quality of Diesel fuel; higher this number, the easier it is to start a standard (direct-injection) diesel engine. It denotes the percentage (by volume) of cetane (chemical name Hexadecane) in a combustible mixture (containing cetane and 1-methylnapthalene) whose ignition characteristics match those of the diesel fuel being tested. 47
  • 48. PRE-IGNITIONPRE-IGNITION  In SI engine the combustion during the normal working is initiated by a electric spark.  The spark is timed to occur at a definite point just before the end of the compression stroke.  The ignition of the charge should not occurs before the spark is introduced in the cylinder, if the ignition start due to any other reasons when the piston is still doing its compression stroke is called as pre-ignition
  • 49. PREIGNITION: CAUSESPREIGNITION: CAUSES  High compression ratio  Carbon deposit on cylinder wall.  Overheated exhaust valve  It may occur due to faulty timing of spark initiation.
  • 50. PREIGNITION: EFFECTSPREIGNITION: EFFECTS Reduce useful work per cycle Increase heat losses from engine Reduction in the thermal efficiency Subjects the engine components to excessive pressure
  • 51. IC Engine Systems Transmission System Cooling System Lubricating System Fuel System Ignition System
  • 55. Transmission SystemTransmission System Engine Flywheel Transmission / Gear Box Differential Rear drive axel/ half shaft Rear Wheel Universal Joint Clutch Propeller Shaft Universal Joint Block Diagram of a Rear Wheel Drive (Manual Gear Transmission)
  • 57. Cooling SystemCooling System Four methods of Engine Cooling – Air Cooling – Water Cooling – Steam Cooling – Liquid Cooling
  • 58. An automotive cooling system must perform several functions a. Remove excess heat from the engine b. Maintain a consistent engine temperature c. Help a cold engine warm-up quickly d. Provide a means of warming the passenger compartment Cooling SystemCooling System
  • 59. Cooling System- Water CoolingCooling System- Water Cooling
  • 60. Cooling System- Water CoolingCooling System- Water Cooling Upper Hose Bypass Hose Lower Hose
  • 61. Cooling System- Water CoolingCooling System- Water Cooling 1 2 3 4 5 6 7 8
  • 62. Components used inComponents used in Water Cooling systemWater Cooling system 1. Radiator 2. Radiator Cooling Fans 3. Pressure Cap & Reserve Tank 4. Water Pump 5. Thermostat 6. Bypass System 7. Water jacket/Coolant manifold 8. Hoses
  • 63. Water Cooling SystemWater Cooling System Radiator Water Pump Water Jacket of Cylinder Block Oil Cooler Water Jacket of Cylinder Head Thermostat housing Thermostat Bypass Block Diagram
  • 64. 64 RadiatorsRadiators  A radiator is a heat exchanger.  Tube and fin style the most popular.  Made of copper and brass or aluminum and plastic.
  • 65. 65 Radiator FansRadiator Fans Keeps air moving through the radiator when the car is not moving. Several types:  rigid,  flex (not used much anymore),  Electric etc
  • 66. 66 Radiator CapRadiator Cap  The cap allows access to the cooling system for filling and testing.  The cap has two valves: a pressure relief valve set at around 15 PSI and a vacuum valve which is needed when the engine cools down.  Raises boiling point of fluid  Able to take on more heat
  • 67. 67 Water PumpWater Pump  Usually driven by drive belt from crankshaft.  Simple impeller design  Non-positive displacement pump which circulates coolant around cooling system.
  • 68. 68 ThermostatThermostat  Controls coolant temperature.  Uses a temperature sensor and a valve.  Usually opens around 195 degrees F.
  • 69. 69 Water JacketsWater Jackets  Surrounds the cylinders with water passage.  Absorbs heat from the cylinder wall.  Pump moves water to radiator where heat is exchanged to the air.
  • 70. 70 Coolant Recovery TankCoolant Recovery Tank  Keeps the coolant level full in the system at all times.  Works in conjunction with the radiator cap.  When the engine heats up the coolant expands and flows to the recovery tank.  When the engine cools the coolant contracts and creates a vacuum and draws the fluid back into the radiator. • Advantages:  Reduces air in system  Reduces rust  Less need to open radiator
  • 71. 71 Coolant Temperature Sensor (CTS)Coolant Temperature Sensor (CTS)  Reports to computer  Gauges  Location – Block – Head – Radiator tank
  • 72. 72 HeaterHeater  The hot water in the cooling system is used to warm the passenger compartment.  A small radiator is called a heater core is located in the dash area.  Heater hoses direct the hot water to and from it.
  • 74. 74 Lubrication systemLubrication system  To reduce friction between moving parts  To reduce wear of moving parts  To act as cooling medium for removing heat  To keep the engine parts clean, especially piston rings and ring grooves, oil ways and filters  To absorb shocks between bearings and other engine parts thus reducing engine noises and extending engine life FunctionFunction
  • 75. Function (cont)Function (cont)  To form a good seal between piston rings and cylinder walls  To prevent deposition of carbon, soot and lacquer  To absorb and carry away harmful substances resulting from incomplete combustion  To prevent metalic components from corrosive attack by the acid from incomplete combustion  To resist oxidation which causes sludge and lacquers Lubrication systemLubrication system
  • 77. 77 Lubricating SystemLubricating System PartsParts 1. Oil pan/sump 2. Oil strainer 3. Pick-up screen 4. Oil pump 5. Pressure regulator 6. Oil filter 7. By-pass valve 8. Oil galleries 9. Pressure indicator
  • 78. Lubricating SystemLubricating System Block DiagramBlock Diagram Sump Oil Pump Filter Main oil gallery Pressure Regulator By Pass Valve Crank shaft Big end bearings, connecting rod, small end bearings, Piston rings Cam shaft Rocker arm , valve and valve spring Timing gear mechanism Strainer
  • 79. 79 Lubrication systemLubrication system Main Functions of Lubricating Oil To minimize friction and wear To seal the pistons and thus preventing escape of gases in the cylinders with consequent loss of power To cushion the parts against vibration and impact To clean the parts as it lubricates them, carrying away impurities To cool by carrying away heat
  • 82. Fuel SystemFuel System Block DiagramBlock Diagram Fuel tank Primary Filter Fuel feed pump/ low pressure pump Secondary Filter Fuel injection pump/ high pressure pump HP line Injector Cylinder Residual Fuel Excess fuel
  • 83. FUEL FEED SYSTEMFUEL FEED SYSTEM CARBURETTORCARBURETTOR  It is the most important device in the Fuel Feed System in a SI engine.  Connected between Fuel Filter and the Induction Manifold.  Function: To atomize and vaporize the fuel and to mix it with the air in varying proportions to suit the changing condition of spark ignition engines. The air-fuel mixture attained from carburettor is called combustible mixture .
  • 84. CARBURATIONCARBURATION  The process of mixing the gasoline fuel with air to obtain the combustible mixture is called carburetion.  The carburettor must create an air fuel mixture that is correct for different circumstances such as:  Cold or hot starting  Idling  Part throttle  Acceleration  High speed operation  Carburettors work on the principle of air pressure differences.
  • 86. Ignition SystemIgnition System Requirements •To supply high voltage surges to current ( as high as 30000 volts) to the spark plug. These surges produce electric sparks at the spark plug gap that ignite or set fire to the combustible mixture in combustion chamber. • The sparking must be properly times (at the end of compression stroke) • The system should function efficiently at the maximum and minimum speeds of the engine • It should be easy to maintain, light and compact • It should not cause any interference
  • 87. Ignition SystemIgnition System • Types 1. Battery/ Coil Ignition system  Used in passenger car, light trucks etc  Battery supplies the current in the primary winding 2. Magneto Ignition System  Magneto produces and supplies the current in the primary winding Both systems are based on the principal of mutual electro- magnetic nduction
  • 88. Battery Ignition SystemBattery Ignition System 5 4 2 7 6 8 1 5 4 32 7 6 8 Components: 1. Battery 2.Switch 3.Ammeter 4.Ignition Coil 5.Condenser 6.Contact Breaker 7.Distributor 8.Spark Plug
  • 89. Magneto Ignition SystemMagneto Ignition System 5 4 3 1 7 2 6 Components: 1. Magneto 2.Switch 3.Ignition Coil 4.Condenser 5.Contact Breaker 6.Distributor 7.Spark Plug
  • 90. ComparisonComparison S/N Battery Ignition System Magneto Ignition System 1 Current obtained from battery Current generated by magneto 2 Good sparking even at low speed Poor sparking at low speed 3 Engine starting is easier Difficult starting 4 Engine cannot be started if battery is discharged No such difficulty 5 Occupies more space Occupies less space 6 Complicated wiring Simple wiring 7 Less costly More costly 8 Spark intensity falls as the engine speed rises Spark intensity improves as the engine speed rises 9 Used in cars, buses, trucks etc Used in motor cycles, scooters, racing cars etc
  • 91. Engine PerformanceEngine Performance Compression Ratio  Volume in the cylinder at the bottom of its travel as compared to the top (r = Vs/Vc )  Expressed as a ratio 10:1, 7:1, etc……..  Higher compression ratios produce more power  Compression ratio is limited by fuel octane and engine strength  However, higher compression ratio engines are more apt to detonation or “knocking”
  • 95. Engine PowerEngine Power Power = work / time P= w/t Hp = 33,000 ft-lb (work) / 1 minute (time) Hp = 550 ft-lb / 1 second Kinds of Horse Powers – Indicated Horsepower – Brake Horsepower – Frictional Horsepower – Rated Horsepower – Corrected Horsepower 95
  • 96. Indicated Horsepower. The power developed within a cylinder can be calculated by measuring the imep and the engine speed. (The rpm of the engine is converted to the number of power strokes per minute.) With the bore and stroke know (available in engine manufacturers’ technical manuals), the horsepower (hp) can be computed. This power is called indicated horsepower (ihp) because it is obtained from the pressure measured with an engine indicator. Power loss due to friction is not considered in computing ihp. ihp = P × L × A × N /33,000 P = Mean indicated pressure, in psi L = length of stroke, in feet A = Effective area of the piston, in square inches N = Number of power strokes per minute 33,000 = Unit of power (one horsepower), or foot pounds per minute. 96
  • 97. Brake horsepower. Actual or useful horsepower of an engine, usually determined from the force exerted on a friction brake or Dynamometer connected to the drive shaft. Frictional horsepower. That part of the gross or indicated horsepower developed in an engine cylinder which is absorbed in frictional losses; It is the difference between the indicated and the brake horsepower. Rated horsepower. Power of an engine or prime mover, The maximum horsepower that can be provided under normal continuous operation. Corrected horsepower. is the observed readings "corrected" to standard temperature, humidity, and barometer, conditions. 97
  • 98. Efficiency of EngineEfficiency of Engine  Brake thermal efficiency: brake power/rate of heat output for complete combustion  Brake thermal efficiency=indicated thermal efficiency* mechanical efficiency  the thermal efficiency () is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a steam turbine or a steam engine, a boiler, a furnace, or a refrigerator for example. In other words, efficiency indicates how well an energy conversion or transfer process is accomplished.  Mechanical efficiency measures the effectiveness of a machine in transforming the energy and power that is input to the device into an output force and movement. Efficiency is measured as a ratio of the measured performance to the performance of an ideal machine:
  • 99. Factors Affecting Engine PerformanceFactors Affecting Engine Performance  Detonation.  Effect of Detonation:
  • 100. DETONATIONDETONATION  The explosion of the fuel/air mixture instead of a steady burning. This explosion causes an abrupt rise in cylinder temperatures and pressures that may cause engine damage;  Also rapid combustion of fuel/Detonation results in loss of power and a knocking sound (indication of abnormal combustion ) Factors Affecting Engine PerformanceFactors Affecting Engine Performance
  • 101. Detonation may be caused by several factors:  Low octane fuel (SI Engine)  High cylinder temperatures  Lean/uneven mixture  High compression ratios  Shape of combustion chamber and position of sparking plug  Preignition of the fuel/air mixture before the properly timed injection /spark occurs Factors Affecting Engine PerformanceFactors Affecting Engine Performance DETONATIONDETONATION
  • 102. DETONATION: EFFECTSDETONATION: EFFECTS  Noise  Mechanical damage  Increased heat transfer  Pre-ignition  Decrease in power output
  • 103. • Exhaust BlowdownExhaust Blowdown : Late in the power stroke, the: Late in the power stroke, the exhaust valve is opened and exhaust blowdownexhaust valve is opened and exhaust blowdown occurs.occurs. – This exhaust gas carries away a highThis exhaust gas carries away a high amount of enthalpy, which lowers the cycleamount of enthalpy, which lowers the cycle thermal efficiency.thermal efficiency. – Opening the exhaust valve before BDCOpening the exhaust valve before BDC reduces the work obtained but is requiredreduces the work obtained but is required because of the finite time needed forbecause of the finite time needed for exhaust blowdown.exhaust blowdown.
  • 104. • Exhaust BlowdownExhaust Blowdown :: – Pressure and temperature in the cylinderPressure and temperature in the cylinder are still high relative to the surroundings atare still high relative to the surroundings at this point, and a pressure differential isthis point, and a pressure differential is created through the exhaust system whichcreated through the exhaust system which is open to atmospheric pressure.is open to atmospheric pressure. – This pressure differential causes much ofThis pressure differential causes much of the hot exhaust gas to be pushed out of thethe hot exhaust gas to be pushed out of the cylinder and through the exhaust systemcylinder and through the exhaust system when the piston is near BDC.when the piston is near BDC.
  • 105. • Exhaust stroke:Exhaust stroke: By the time piston reaches BDC,By the time piston reaches BDC, exhaust blowdown is complete, but the cylinder is stillexhaust blowdown is complete, but the cylinder is still full of exhaust gases at approximately atmosphericfull of exhaust gases at approximately atmospheric pressure.pressure. – With the exhaust valve remaining open, theWith the exhaust valve remaining open, the piston travels from BDC to TDC in the exhaustpiston travels from BDC to TDC in the exhaust stroke.stroke. – This pushes most of the remaining exhaustThis pushes most of the remaining exhaust gases out of the cylinder into the exhaust systemgases out of the cylinder into the exhaust system at about atmospheric pressure, leaving only thatat about atmospheric pressure, leaving only that trapped in the clearance volume when the pistontrapped in the clearance volume when the piston reaches TDC.reaches TDC.
  • 106. – Near the end of the exhaust stroke before TDC,Near the end of the exhaust stroke before TDC, the intake valve starts to open, so that itthe intake valve starts to open, so that it is fullyis fully open by TDCopen by TDC when the new intake stroke startswhen the new intake stroke starts the next cycle.the next cycle. – Near TDC the exhaust valve starts to close andNear TDC the exhaust valve starts to close and finally is fully closedfinally is fully closed sometime after TDCsometime after TDC.. – This period when both the intake valve andThis period when both the intake valve and exhaust valve are open is calledexhaust valve are open is called valve overlapvalve overlap,, itit can be clearly seen in valve timing chart givencan be clearly seen in valve timing chart given below.below.
  • 110. EnginesEngines Engine Block - Foundation of the engine - It contains pistons, crank shaft, cylinders, timing sprockets and sometimes the cam shaft.
  • 111. EnginesEngines Piston A movable part fitted into a cylinder, which can receive and transmit power. Through connecting rod, forces the crank shaft to rotate.
  • 112. EnginesEngines Cylinder head Part that covers and encloses the Cylinder. It contains cooling fins or water jackets and the valves. Some engines contains the cam shaft in the cylinder head.
  • 113. EnginesEngines Connecting (conn.) Rod Attaches piston (wrist-pin) to the crank shaft (connecting rod caps).
  • 114. EnginesEngines Crank Shaft Converts up and down motion into circular motion. Transmits the power to transmission. DAMPNER PULLEY Controls Vibration
  • 115. EnginesEngines •Exhaust Valve lets the exhaust gases escape the combustion Chamber. (Diameter is smaller then Intake valve) •Intake Valve lets the air or air fuel mixture to enter the combustion chamber. (Diameter is larger than the exhaust valve) Valves: Minimum two valves per cylinder
  • 118. EnginesEngines Cam Shaft: The shaft that has intake and Exhaust cams for operating the valves. Cam Lobe: Changes rotary motion into reciprocating motion.
  • 119. EnginesEngines It provides the means of ignition when the gasoline engine’s piston is at the end of compression stroke, close to Top Dead Center(TDC) Back Spark Plug
  • 120. Flywheel -Attached to the crankshaft -Reduces vibration -Cools the engine (air cooled) -Transfers power from engine to the Drive train -Helps glide through strokes ENGINESENGINES
  • 121. EnginesEngines Configuration • Inline Engines: The cylinders are arranged in a line, in a single bank. • V Engines: The cylinders are arranged in two banks, set at an angle to one another. • Flat Engines: The cylinders are arranged in two banks on opposite sides of the engine. •back
  • 122. EnginesEngines Piston Rings Four stroke: Three rings *Compression rings- Top two (sealing the compression pressure in the cylinder) *Oil ring- the third one (scrapes excessive oil from the cylinder walls) Two Stroke: Two Rings Both the rings are Compression rings.