Internal combustion engines

INTERNAL COMBUSTION ENGINES
The automobile engine will come, and then I will consider my life's work complete.
- Rudolf Diesel
Dr. Rohit Singh Lather

IC ENGINES ARE CYCLIC DEVICES TO SATISFY HUMAN NEEDS
Comfort!
Power to do more work efficiently!
2Introduction to IC Engines - Dr. Rohit Singh Lather

COMMON APPLICATIONS OF IC ENGINES

PAST TO PRESENT
4
Simple Gas Engine 1800’s
Present Day
Complex Electronically Controlled Engines
(Cocktail of Technologies)
Over 100 years of
Continuous
Development
Introduction to IC Engines - Dr. Rohit Singh Lather

HEAT ENGINE
• An engine which derives heat energy from the combustion of the fuel and converts part of this energy in to
mechanical work is known as heat engine
5
HEAT ENGINES
Internal Combustion External Combustion
SI Engine CI Engine
Otto Cycle Diesel Cycle
Advantages of I.C.E over E.C.E
• Mechanically simple and lower weight/power ratio
• Don’t need auxiliary equipment, such as boiler & condenser
• Can be started and stopped in a short time
• Higher Thermal efficiency
• Low initial cost

INTRODUCTION
• The purpose of internal combustion engines is the production of mechanical power from the chemical
energy contained in the fuel
• Fuelled by oil/gas and air mixture
6
• The internal combustion engine is an machine which converts LOW grade energy (Heat) to HIGH
grade energy (Work)
• Internal combustion engines convert reciprocatory motion to rotary motion

WHAT IS / IS NOT AN I.C. ENGINE
IS
• Gasoline-fueled reciprocating pistonengine
• Diesel-fueled reciprocating pistonengine
• Gas turbine
• Rocket
IS NOT
• Steam power plant
• Solar power plant
• Nuclear power plant

1700s - STEAM ENGINES (external combustion engines)
1859 - OIL DISCOVERED
1860 - LENOIR ENGINE
- French gentleman, J.J.E. Lenoir, in 1860, developed the first IC engine for commercial use
- First marketable engine
- Fueled by coal gas and air mixture
- Lenoir engine (h = 5%)
1861 - OTTO built his first gas engine
1867 - OTTO IN PARTNERSHIP WITH EUGEN LANGEN,
- Improved the design and won a gold medal at the Paris Exposition
- Produced famous “Silent” engine, now called the “Otto Cycle”
HISTORY OF IC ENGINES

• Power: 2 hp @ 160 rpm; Weight: 1250 pounds
• Comp. ratio = 4 (knock limited), 14% efficiency (theory 38%)
• Today CR = 9 (still knock limited), 30% efficiency (theory 55%)
1867 - OTTO - LANGEN ENGINE (η = 11%, 90 RPM max.)
1876 - OTTO FOUR STROKE “SPARK IGNITION” ENGINE
- Premixed-charge, 4-stroke engine – Otto
- 1st Practical ICE

1880s - Two stroke engine
1892 - Diesel four stroke “compression ignition”engine
1897 - Non-premixed-charge engine - Diesel - Higher efficiency due to
Higher compression ratio(no knock problem)
No throttlingloss - use fuel/air ratio to control power
1901 - “2nd Industrial Revolution” will be fueled by oil
1921 - Tetraethyl lead anti-knock additivediscovered at General Motors
- Enabled higher compression ratio (thus more power,better efficiency) in Otto-type engines
1952 - A. J. Haagen-Smit, Caltech
NO + UHC + O2 + sunlight = NO2 + O3
(from exhaust) (brown) (irritating)
(UHC = unburned hydrocarbons)
1957 - Wenkel “rotary” engine
1960s - Emissions regulations
• Initial stop-gap measures -lean mixture, EGR, retard spark
• Poor performance & fuel economy

1973 & 1979 - The energy crises
1975 - Catalytic converters, unleaded fuel
- More “aromatics” (e.g., benzene) in gasoline - high octane but carcinogenic, soot-producing
1980s - Microcomputer control of engines
• Tailor operation for best emissions, efficiency
1990s - Reformulated gasoline
• Reduced need for aromatics, cleaner(?)
• Higher cost, lower kilometer per liter
• Then we found that Methyl tertiary butyl ether (MTBE) pollutes groundwater!
• Alternative “oxygenated” fuel additive -ethanol - very attractive
2000’s - hybrid vehicles
• Use small gasoline engine operating at maximum power (most efficient way to operate) or turned off if not
needed
• Use generator/batteries/motors to make/store/use surplus power from gasoline engine
• More efficient,but much more equipment on board -not clear if fuel savings justifyextra cost
• Plug-in hybrid: half-waybetween conventional hybridand electricvehicle

LARGEST INTERNAL COMBUSTION ENGINE
• Wartsila-Sulzer RTA96-C turbocharged two-stroke diesel,built in Finland,used in container ships
• Also one of the most efficient IC engines: 51%

14 CYLINDER DIESEL ENGINE (80 MW)
13
Max. Power 81, 221 kW (108,920 hp) @ 102 rpm
Max. Torque 7,603,850 Nm @ 102 RPM
Weight: 2300 tons
Length: 89 feet
Height: 44 feet

MOST POWERFUL INTERNAL COMBUSTION ENGINE
• Space Shuttle Solid Rocket Boosters are the most powerful
(≈ 42 millionhorsepower; not shaft power but kinetic energy of exhaust stream)

MOST POWERFUL INTERNAL COMBUSTION ENGINE
• Most powerful shaft-power engine:Siemens SGT5-8000H
16
Stationary gas turbine (340 MW = 456,000 HP) used for electrical power generation

WORLDS SMALLEST IC ENGINE
• Produced by engineers at the Universityof Birmingham
• World’s smallest petrol engine that is tinyenough to power a watch
• The mini-combustion engine can run for two years on a single dose of a light
fuel
• Produces 700 times more energy than a conventional battery despite having
a size less than a centimeter long
• If the technology matures, it could be used to power laptops and mobile
phones for months

PARTS OF AN IC ENGINE COMMON TO SI AND CI
18
Crankcase
Piston
Water Jacket
Cooling Water
Cylinder Head
Exhaust Valve
Valve Spring
Crankshaft
Connecting rod
Cylinder block
Combustion chamber
Cam
Intake Valve
Intake Manifold Exhaust Manifold

20
Spark Plug
Injector
Port Injection Direct Injection
COMMONLY USED FUEL INDUCTION TECHNIQUES FOR GASOLINE AND DIESEL ENGINES

GEOMETRY OF AN IC ENGINE
Displacement Volume
Volume displaced by the piston as it
travels through one stroke
21
LD
d
V
4
2π=
zLD
d
V .
4
2π=
Top Dead Center
Bottom Dead Center
Engine displacement volume
Displacement volume multiplied by no.
of cylinders (z)
Bore (B)
Diameter of the cylinder
Stroke (L)
Movement distance of the piston from one extreme
position to the other: TDC to BDC or BDC to TDC
Clearance volume
Minimum Volume in the combustion
chamber with piston at TDC

22
Compression Ratio (rc): The ratio between the volume
of the cylinder, when the piston is at the bottom of its
stroke (BDC), and the volume when the piston is at the
top of its stroke (TDC). This volume is called
“clearance volume” (Vc):
cV
d
V
cV
cV
d
V
cr +=
+
= 1
Typical values of the compression ratio are:
- SI Engines: 8 – 12
- CI Engines: 16 – 22

CLASSIFICATION OF INTERNAL
COMBUSTION ENGINES

IC Engine Classification Tree
24
IC ENGINES
Four Stroke
SI Engine CI Engine
Gasoline Gas
Two Stroke
Multi Fuel Divided Chamber
Carbureted Injection Pre Chamber Swirl Chamber
Battery Magneto
Water Cooled Air Cooled
Steady Non Steady
Premixed Non Premixed
Gas Turbine RocketRamjet
Turboshaft TurbojetTurbojet
Solid Fuel Liquid Fuel

MAIN CLASSIFICATION CRITERION
Fuel Type (Gasoline / Diesel)
Fuel delivery (Port / Direct)
Ignition Type (Spark/Compression)
Camshaft Type (DOHC / SOHC)
Construction Type (Inline / V)
Cooling Type (Air / Water)
Application (Car / Bus / Genset)
Operating Cycle (Otto / Dual)
Charge Pressure (Natural, Turbo)
Gas Exchange (2/4 Stroke)

CLASSIFICATION ON BASIS OF BASIC DESIGN
• Reciprocating
(a) Single Cylinder

MULTI CYLINDERS
In-line
All cylinders are arranged linearly
V
Cylinders are in two banks inclined
at an angle to each other and with
one crank-shaft
Radial/Rotary
the radial engine is an engine with more
than two cylinders in each row equally
spaced around the crank shaft
Opposed Cylinder
Banks located in the same plane on
opposite sides of the crankshaft
Opposed Piston
When a single cylinder houses two pistons,
each of which drives a separate crank shaft
• Cylinders may be vertical or horizontal
• Vertical engines needs smaller area
• When area is available horizontal engines may
be used

ROTARY ENGINES: WANKEL ENGINE
Single Rotor Multi - Rotor

RECIPROCATING ROTARY ENGINES
• A rotaryengine is characterized bya fixed crankshaft and cylinders that rotate
• The propeller is attached to the spinningcrankcase
• A fuel meteringcarburetor is attached to the hollowfixed crankshaft
- Air, fuel and castor oil (for lubrication), are drawn into the crankcase then pass through the intake pipes to the cylinders
- The exhaust is timed to exit at the bottom of the engine to minimize interference with the pilot
• This arrangement was common in World War I, when modern high-strength, heat resistant, steels were not
commonlyavailable
• Coolingwas accomplished byhavingthe cylinders spin
• Always odd number of cylinders
• Completelydifferentfrom the Wankel RotaryEngines
29
Fixed
Crankshaft
(viewed from the side)
Aircraft
Nose
Rotating
Cylinders

MECHANICAL ARRANGEMENT – RADIAL/ROTARY ENGINES
Cylinders
Crankcase
Valve
Gear
Valve
Pushrod
Spark
Plug
Propeller
Mount
Bolts

GAS TURBINE ENGINES
• The gas turbine group needs a compressors, its weight is smaller than reciprocating I.C.E. of the same power, its
efficiency is lower, the fuel relatively cheap, and it is suitable for air craft
31
Combustion
Chamber
Compressor
Fuel In
Turbine
Atmospheric Air Exhaust Gases
Shaft Output = Wnet
WCompresssor

• Gas turbine engines are,theoretically,extremelysimple.Theyhave three parts:
- Compressor - Compresses the incoming air to high pressure
- Combustion area - Burns the fuel and produces high-pressure, high-velocity gas
- Turbine - Extracts the energy from the high-pressure, high-velocity gas flowing from the combustion chamber
Compressor Combustion Turbine

WANKEL ROTARY PISTON ENGINE
33
• Rotary engine is a substitute for the reciprocating I.C.E. Wankel engine has a three lobe rotor which is
driven eccentrically in a casing in such a way that there are three separate volumes trapped between the
rotor and the casing
• These volumes perform induction, compression, combustion, expansion and exhaust process in
sequence
Rotary Engine

34
• Uses non-cylindrical combustion chamber.
• Provides one complete cycle per engine revolution without “short circuit” flow of 2-strokes (but still
need some oil injected at the rotor apexes)
• Simpler, fewer moving parts, higher RPM possible
• Very fuel-flexible - can incorporate catalyst in combustion chamber since fresh gas is moved into
chamber rather than being continually exposed to it (as in piston engine) - same design can use
gasoline, Diesel, methanol, etc.
• Very difficult to seal both vertices and flat sides of rotor
• Seal longevity a problem
• Large surface area to volume ratio means more heat losses
Advantages: Drawbacks:
• Higher power output Increased wear of rubbing parts
• No reciprocating mass Higher fuel consumption
• Simpler and lighter construction Requirement for better materials

Inlet
Port
Exhaust
Port
Casing
Spark
Plug
Output
Shaft
Rotating
Triangular
‘Piston’
Fixed (non-
rotating)
Pinion
This motion drives the
rotating crankshaft
Which in turn drives the output shaft
The piston rotates around the fixed pinion
Shape of the piston and the
casing also make the piston
move up and down by a small
amount as well
Rotating
‘Crankshaft’
Points of contact marked in yellow

Chamber A
Chamber C
Inlet
Port
Exhaust
Port
Chamber B
Wankel Engine – Engine Cycle

ENGINE CONFIGURATION
• After the type and size of engine have been determined, the number and disposition of the cylinders must be
decided.
• The main constraints influencingthe number and dispositionofthe cylinders are as follows:
1. The number of cylinders needed to produce a steady output
2. The minimum swept volume for efficient combustion
3. The number and disposition of cylinders for satisfactory balancing
4. The number of cylinders needed for an acceptable variation in the torque output

WORKING CYCLE (STROKES)
1. Four Stroke Cycle: (a) Naturally Aspirated : Admission of charge at near atmospheric pressure
(b) Supercharged/Turbocharged: Admission of charge at a pressure above atmospheric
2. Two Stroke Cycle: (a) Crankcase Scavenged
(b) UniflowScavenged
(i) Inlet valve/Exhaust Port
(ii) Inlet Port/Exhaust Valve
(iii) Inlet and Exhaust Valve
May be Naturally Aspirated / Turbocharged

FUEL USED
39
• Volatile liquid fuels: Petrol, Alcohol, benzene
- Fuel /Air mixture is usually ignited by a spark
- Spark ignition
• Viscous liquid fuels: Fuel oil, Heavy and light
diesel oil, Gas-oil, Bio-fuels
- Usually combustion of fuel takes place due to its
contact with high temperature compressed air
(self - ignition)
- Compression ignition
LIQUID FUELS
• Liquid Petroleum Gas ( LPG )
• Natural gas ( NG )
• Town gas
• Blast Furnace gas
- Ignition usually by a spark
GASEOUS FUELS
• DUAL FUEL ENGINES are operated with two types of fuels, either separately or mixed together
• Multi-fuel engines could be operated by a mixture of more than two fuels, gaseous; such as: Hydrogen, methane, L.P.G. etc.,
combined with one or more of liquid fuels, such as alcohol, ethers, esters, gasoline, diesel etc...

GENERAL FOUR STROKE CYCLE
40
Power or Expansion Stroke
(TDC to BDC)
Exhaust Stroke
(BDC to TDC)
Compression Stroke
(BDC to TDC)
Intake or Induction Stroke
(TDC to BDC)

1st Stroke - INTAKE stroke - 180° CA
Air – Fuel Mixture / Only Air enter into the cylinder
Intake Valve Open
2nd Stroke - Compression stroke - 360° CA
Air- Fuel / Air gets compressed
Inlet & Exhaust Valve Closed
3rd Stroke = Power stroke = 540° CA
Spark / Fuel is supplied; Combustion starts; Gases expand moving the piston downwards
Intake and Exhaust Valves are closed
4th Stroke - Exhaust stroke - 720° CA
Exhaust gases exit through exhaust valve
Exhaust Valve Open
Top Dead
Centre (TDC)
Bottom Dead
Centre (BDC)

FOUR STROKE SI CYCLE
42
(TDC to BDC)
Compression Stroke
(BDC to TDC)
Piston moves into the cylinder
compressing the fuel-air
mixture / only air to high
density, pressure and
temperature
At the end of the compression an electric spark ignites
the mixture starting the combustion process and
converting air and fuel into extremely hot burned gas
Fuel-air mixture is
drawn into the
cylinder

43
(TDC to BDC)
Exhaust Stroke
(BDC to TDC)
During this stroke the
mixture burns rapidly,
expanding gases drive
piston downwards
exhaust gases are expelled
from the cylinder ready
for the next induction
stroke. In this stroke
piston will move from BDC
to TDC

FEATURES OF 4 STROKE SI ENGINES
• Most common type of IC engine
• Simple, easy to manufacture, inexpensive materials
• Good power/weight ratio
• Excellent flexibility - works reasonably well over a wide range of engine speeds and loads
• Rapid response to changing speed/load demand
• “Acceptable” emissions
• Weaknesses
• Fuel economy (compared to Diesel, due lower compression ratio & throttling losses at part-load)
• Power/weight (compared to gas turbine)

FOUR STROKE CI
45
(TDC to BDC)
Exhaust Stroke
(BDC to TDC)
Compression Stroke
(BDC to TDC)
(TDC to BDC)

FOUR STROKE CI
46
(TDC to BDC)
Compression Stroke
(BDC to TDC)
Piston moves into the
cylinder, compressing the
only air to high density,
pressure and temperature
At the end of the compression fuel is injected at high
pressure, starting the combustion process and
converting air and fuel into extremely hot burned gas.
Only air is drawn into
the cylinder

FOUR STROKE CI
47
(TDC to BDC)
mixture burns rapidly,
expanding gases drive
piston downwards
Exhaust Stroke
(BDC to TDC)
exhaust gases are expelled
from the cylinder ready
for the next induction
stroke. In this stroke
piston will move from BDC
to TDC

TWO-STROKE CYCLE
• The two-stroke cycle of an internal combustion engine differs from the more common four-stroke cycle
by completing the same four operations (intake, compression, power, exhaust) in only two strokes (linear
movements of the piston) rather than four
• There is a power stroke per piston for every engine revolution, instead of every second revolution
• Two-stroke engines can be arranged to start and run in either direction
Poppet Intake Valve
Crankcase
Exhaust Port
Transfer Port
Compression causes
combustionPiston pushed down forces
fuel/air mixture into cylinder
48
Piston rising pulls fuel/air
mixture into crankcase

49
PowerCompression
Piston rises,
driven by flywheel
momentum
compresses the
fuel mixture
(At the same time, another
intake stroke is happening
beneath the piston)
At the top of the stroke
the spark plug ignites
the fuel mixture
The burning fuel expands,
driving the piston downward,
to complete the cycle

SHORT CIRCUITING OF FUEL IN 2 STROKE ENGINES
50
• Air and fuel mixture move out from the exhaust port when it is open
• This happens due to overlapping of the inlet and exhaust ports

• Transfer/Exhaust: Toward the end of the stroke, the piston exposes the transfer port, allowing the
compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder
- This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the
cylinder. Unfortunately, some of the fresh fuel mixture is usually expelled as well
51
the piston exposes the
transfer port
Piston moving downwards
towards the BDC,
near the end of the stroke
crankcase
cylinder exhaust gasses out
the exhaust port

MECHANICAL LAYOUT OF A TYPICAL 2 STROKE MOTORCYCLE ENGINE
52
Cooling Fins

A TYPICAL DIESEL 2 STROKE ENGINE
• Used in large engines, e.g. locomotives
– Air comes in directly through intake ports, not via crankcase
– Must be turbocharged or supercharged to provide pressure to
force air into cylinder
– Rather than ports - not necessary to have intake & exhaust paths
open at same time
– Only air, not fuel/air mixture enters through intake ports, “short
circuit” of intake gas out to exhaust is not a problem
– 2-stroke diesels have far fewer environmental problems than 2-
stroke gasoline engines
53
No oil mixed with air - crankcase
lubrication like 4-stroke
Exhaust valves

4- STROKE VS 2- STROKE ADVANTAGES
Advantages 4 - Stroke Engine
üHigh Volumetric Efficiency over a wide engine speed
range
üLow Sensitivity to Pressure Losses in the exhaust
system
üEffective Control of the Charging Efficiency trough
appropriate valve timingand intake system design
Advantages 2 – Stroke Engine
üVery Simple and Cheap engine design
üLow Weight
üLow Manufacturing Cost
üBetter Torsional Forces Pattern
ü2-stroke engines may not have valves, which
simplifies their construction and lowers their weight.
üFire once every revolution, while 4-stroke engines
fire once every other revolution. This gives two-
stroke engines a significant power boost.

4- STROKE VS 2- STROKE DISADVANTAGES
Disadvantages 4-Stroke Engine
üHigh Complexity of the Valve Control
üReduced Power Density because the work is
generated only every second shaft rotation
Disadvantages 2-Stroke Engine
üHigher fuel consumption
üHigher HC emissions (Poor scavenging)
üLower Mean Effective Pressure (Poor Volumetric
Efficiency)
üHigher Thermal Load
(No gas exchange stroke)
üPoor idle (High residual gas percentage into the
cylinder)
• More pollution because of 30% of the fuel is wasted.
• Less efficiency compared with four stroke engine.
• Requires special two stroke oil ("premix")

VALVE/PORT DESIGN
1. Poppet Valve
2. Rotary Valve
3. Reed Valve
4. Piston Controlled Porting
• Valve Location
1. The T-head
2. The L-head
3. The F-head
4. The I-head: (i) Over Head Valve (OHV)
(ii) Over Head Cam (OHC)

DIFFERENT TYPES OF VALVE LOCATION
57
L Head
SI Engines Only
I Head
SI & CI Engines
Current Practice
F Head
SI Promising
T Head
Obsolete

OVER HEAD VALVE ARRANGEMENT
58
Single Over Head Camshaft (SOHC)
Double Over Head Camshaft (DOHC)

VALVE OPERATION

OVERHEAD CAM VS. OVERHEAD VALVE

VALVE TIMING DIAGRAM
61
General Valve Timing Diagram

VALVE TIMING DIAGRAM OF FOUR STROKE ENGINES

UNDERSTANDING VALVE OVERLAP
63
Power Stroke Exhaust Stroke Intake Stroke Compression Stroke
00 1800 3600 5400 7200
Both Valve Open
Exhaust Valve
Starts to Open
Intake Valve
Closes
The duration of crank angle in which both inlet and exhaust valve remains open is called as valve overlap
It occurs at the end of exhaust stroke when the piston is about to reach TDC and continues for a few degree of crank angle after TDC
Exhaust
Gases Out

• Exhaust Blowdown : Late in the power stroke, the exhaust valve is opened and exhaust blowdown occurs
• Pressure and temperature in the cylinder are still high relative to the surroundings at this point, and a pressure
differential is created through the exhaust system which is open to atmospheric pressure
- This pressure differential causes much of the hot exhaust gas to be pushed out of the cylinder and through the
exhaust system when the piston is near BDC
- This exhaust gas carries awaya high amount ofenthalpy,which lowers the cycle thermal efficiency
- Opening the exhaust valve before BDC reduces the work obtained but is required because of the finite time
needed for exhaust blowdown
EXHAUST BLOWDOWN

FIRING ORDER
• Every engine cylinder must fire once in every cycle
• The order in which various cylinders of a multi cylinder engine fire is called the firing order
- For a four-stroke four- cylinder engine the ignition system must fire for every 180 degrees of crank rotation
- For a six- cylinder engine the time available is only120 degrees of crank rotation.
• The number of possibilities offiringorder depends upon the number of cylinders and throws of the crankshaft
• It is desirable to have the power impulses equally spaced and from the point of view of balancing this has led to
certain conventional arrangements ofcrankshaft throws

• Factors to be considered before deciding the optimum firing order of an engine
- Engine vibrations
- Engine coolingand
- Development ofback pressure
67
4
3
2
1
4
3
2
1
4
3
2
1
Without Firing Order With Firing Order 1 With Firing Order 2

GENERAL FIRING ORDER
• 4-Cylinder engines: 1-3-4-2 (commonly used); 1-2-4-3
• 6-Cylinder engine : 1-5-3-6-2-4 (commonly used);1-5-4-6-2-3;1-2-4-6-5-3; 1-2-3-6-5-4.
• 3 Cylinder engine: 1-3-2
• 8 Cylinder in-line engine: 1-6-2-5-8-3-7-4
• 8 Cylinder V engine: 1-5-4-8-6-3-7-2; 1-8-4-3-6-5-7-2; 1-6-2-5-8-3-7-4; 1-8-7-3-6-5-4-2; 1-5-4-2-
6-3-7-8.
Note: Cylinder No. 1 is taken from front of the in-line engines whereas in V shape front cylinder on right side-bank is considered
cylinder No.1 for fixing H.T. leads according to engine firing order.

69
ba
1
2 3
4
1 4
2 3
EFFECT OF FIRING ORDER ON ENGINE VIBRATIONS
Fire cylinder 1- A pressure p, generated in the cylinder number 1 will give rise to the forces shown in the figure
{pA x [b/(a + b)]} {pA x [a/(a + b)]}
Bearings A Bearings B
Load on A > B
Fire cylinder 2 – Imbalance in load on the two bearings would lead to imbalance and sever engine vibration
Fire cylinder 3 - after cylinder number 1, the load may be more or less evenlydistributed

• When the first cylinder is fired its temperature increases.
• If the next cylinder that fires is number 2, the portion of the engine between the cylinder number 1 and 2
gets overheated.
• If then the third cylinder is fired, overheating is shifted to the portion between the cylinders 2 and 4.
• The task of the cooling system becomes very difficult because it is then, required to cool more at one
place than at other places and this imposes great strain on the cooling system. If the third cylinder is fired
after the first the overheating problem can be controlled to a greater extent.
70
EFFECT OF FIRING ORDER ON ENGINE COOLING

• After firing the first cylinder, exhaust gases flow out to the exhaust pipe.
• If the next cylinder fired is the cylinder number 2, we find that before the gases exhausted by the first
cylinder go out of the exhaust pipe the gases exhausted from the second cylinder try to overtake them.
• This would require that the exhaust pipe be made bigger. Otherwise the back pressure in it would
increase and the possibility of back flow would arise.
• If instead of firing cylinder number 2, cylinder number 3 is fired. then by the time the gases exhausted by
the cylinder 3 come into the exhaust pipe, the gases from cylinder 1 would have sufficient time to travel
the distance between cylinder 1 and cylinder 3 and thus, the development of a high back pressure is
avoided.
71
EFFECT OF FIRING ORDER ON FLOW OF EXHAUST GASES

• With the analogy of human metabolism one can explain combustion of engine:
- Human metabolism = Oxidization of food converts chemical energy into Mechanical energy
- Food = Fuel
- Oxygen = Air
- Optimum air fuel ratio leads = Balanced diet leads
to optimum engine performance to healthy human life
- Cooling of engine via water, air or = Human body maintains its temperature by
any coolant to maintain its temperature perspiration, sweating
HUMAN ANALOGY

ASSIGNMENT

Internal combustion engines

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