Introduction of I C Engines

INTERNAL COMBUSTION ENGINES
 Sub Code: ME0441 Credits:(4-0-0)
 Hrs / Week : 04 CIE : 50% SEE : 50 %
BY
Er.VIJAYAKUMARA.M
MTech in Thermal Engineering
Assistant Professor
Mechanical Engineering Department
The National Institute of Engineering
Mysore-570 008.
Karnataka, India
1

 TEXT BOOKS:
 1.I.C. engines by M.L. Mathur and R.P. Sharma, Dhanpat Rai
Publications -2012.
 2.Internal Combustion Engines by V.Ganeshan, Tata McGraw Hill,
3rd Ed. 2009.
 3.Fundamentals of Internal Combustion Engines by J.B.
Heywood, Tata McGraw Hill, 1988
 REFERENCE BOOKS:
 1.Engineering fundamentals of the I.C. Engine by Willard
W.Pulkrabek, Year 1998.
 2.Combustion Engine Process by Lichty Judge, Year 2000.
 3.A course in I.C.Engines by V.M. Domkundawar, Dhanpathrai
Publications -1999.
4.wikipedia.com
VIJAYAKUMARA M ME NIE MYSORE 2

 Objectives
 After studying this unit you should be able to
know
 How internal combustion engines are classified,
 Applied Thermal Engineering on which cycles
these engines work,
 How and how many times the piston has to
move to and fro to complete a cycle,
 What fuels are used in these engines and if there
are any harmful effects.

Introduction:
 An Engine is a device which transforms the chemical energy
of a fuel into thermal energy and uses this thermal energy to
produce mechanical work.
 Engines normally convert thermal energy into mechanical
work and therefore they are called heat engines.
 Heat engines can be broadly classified into :
 i) External combustion engines ( E C Engines)
 ii) Internal combustion engines ( I C Engines )

Heat Engines
Heat Engines
Open
cyclegas
turbine
Wankel
engine
Gasoline
engine
Diesel
engine
Steam
engine
Stirling
engine
Steam
turbine
Closed
Cycle gas
turbineVIJAYAKUMARA M ME NIE MYSORE 5

External combustion engines ( E C
Engines)
Figure 1 : External Combustion Engine

 Internal combustion engines can be classified as
Continuous IC engines and Intermittent IC engines.
 Continuous IC Engines
Figure 2: Continuous IC Engines
In continuous IC
engines products
of combustion of
the fuel enters into
the prime mover as
the working fluid.

Intermittent Internal Combustion Engine
Fig: Intermittent internal combustion engine

ADVANTAGES OF INTERNAL COMBUSTION
ENGINES
 1. Greater mechanical simplicity.
 2. Higher power output per unit weight because of absence of
auxiliary units like boiler , condenser and feed pump.
 3. Low initial cost
 4. Higher brake thermal efficiency as only a small fraction of
heat energy of the fuel is dissipated to cooling system.
 5. These units are compact and requires less space.
 6. Easy starting from cold conditions.

DISADVANTAGES OF INTERNAL
COMBUSTION ENGINES
 1. I C engines cannot use solid fuels which are cheaper. Only
liquid or gaseous fuel of given specification can be
efficiently used. These fuels are relatively more expensive.
 2. I C engines have reciprocating parts and hence balancing
of them is problem and they are also susceptible to
mechanical vibrations.

History
 Internal combustion engines date back to 1876 when Otto
first developed the spark-ignition engine and 1892 when
Rudolf Diesel invented the compression-ignition engine.
 Since that time these engines have continued to develop as
our knowledge of engine processes has increased, as new
technologies became available, as demand for new types of
engine arose, and as environmental constraints on engine
use changed.
 Internal combustion engines, and the industries that develop
and manufacture them and support their use, now play a
dominant role in the fields of power, propulsion, and
energy.

 The last twenty-five years or so have seen an explosive
growth in engine research and development as the issues of
air pollution, fuel cost, and market competitiveness have
become increasingly important.
 A more successful development-an atmospheric engine
introduced in 1867 by Nicolaus A. Otto (1832-1891) and
Eugen Langen (1833-1895)-used the pressure rise resulting
from combustion of the fuel-air charge early in the outward
stroke to accelerate a free piston and rack assembly so its
momentum would generate a vacuum in the cylinder.

 In 1892, the German engineer Rudolf Diesel (1858-1913)
outlined in his patent a new form of internal combustion
engine. His concept of initiating combustion by injecting a
liquid fuel into air heated solely by compression permitted
a doubling of efficiency over other internal combustion
engines.
 Much greater expansion ratios, without detonation or
knock, were now possible

CLASSIFICATION OF INTERNAL
COMBUSTION ENGINES.
 There are different types of IC engines that can be classified
on the following basis.
 1. According to thermodynamic cycle
 i) Otto cycle engine or Constant volume heat supplied cycle.
 ii) Diesel cycle engine or Constant pressure heat supplied
cycle
 iii) Dual-combustion cycle engine
 2. According to the fuel used:
 i) Petrol engine ii) Diesel engine iii) Gas engine
 3. According to the cycle of operation:
 i) Two stroke engine ii) Four stroke engine

 4. According to the method of ignition:
 i) Spark ignition (SI) engine ii) Compression ignition (CI )
engine
 5. According to the number of cylinders.
 i) Single cylinder engine ii) Multi cylinder engine
 6. According to the arrangement of cylinder:
 i) Horizontal engine ii) Vertical engine iii) V-engine
 v) In-line engine vi) Radial engine, etc.
 7. According to the method of cooling the cylinder:
 i) Air cooled engine ii) Water cooled engine

 8. According to their applications:
 i) Stationary engine ii) Automobile engine iii) Aero engine
 iv) Locomotive engine v) Marine engine, etc.

INTERNAL COMBUSTION ENGINE
PARTS AND THEIR FUNCTION
 1. Cylinder :- It is a container fitted with piston, where the
fuel is burnt and power is produced.
 2.Cylinder Head/Cylinder Cover:-One end of the cylinder
is closed by means of cylinder head. This consists of inlet
valve for admitting air fuel mixture and exhaust valve for
removing the products of combustion.
 3. Piston:- Piston is used to reciprocate inside the cylinder.
It transmits the energy to crankshaft through connecting
rod.
 4. Piston Rings:- These are used to maintain a pressure
tight seal between the piston and cylinder walls and also it
transfer the heat from the piston head to cylinder walls.

 5. Connecting Rod:- One end of the connecting rod is
connected to piston through piston pin while the other is
connected to crank through crank pin. It transmits the
reciprocatory motion of piston to rotary crank.
 6. Crank:- It is a lever between connecting rod and crank
shaft.
 7. Crank Shaft:- The function of crank shaft is to transform
reciprocating motion in to a rotary motion.
 8. Fly wheel:- Fly wheel is a rotating mass used as an energy
storing device.
 9. Crank Case:- It supports and covers the cylinder and the
crank shaft. It is used to store the lubricating oil.

IC ENGINE – TERMINOLOGY

 Bore: The inside diameter of the cylinder is called the
bore.
 Stroke: The linear distance along the cylinder axis
between the two limiting positions of the piston is called
stroke.
 Top Dead Centre (T.D.C) : The top most position of the
piston towards cover end side of the cylinder” is called top
dead centre. In case of horizontal engine, it is called as
inner dead centre
 Bottom Dead Centre (B.D.C):The lowest position of the
piston towards the crank end side of the cylinder is called
bottom dead centre. In case of horizontal engine, it is
called outer dead centre (O.D.C).

 Clearance Volume: The volume contained in the cylinder
above the top of the piston, when the piston is at the top
dead centre is called clearance volume.
 Compression ratio : It is the ratio of total cylinder volume
to clearance volume.

Four-Stroke Petrol Engine OR Four stroke
Spark Ignition Engine (S.I. engine)
 The four-stroke cycle petrol engines operate on Otto
(constant volume) cycle shown in Figure . Since ignition
in these engines is due to a spark, they are also called
spark ignition engines.
 The four different strokes are:
 i) Suction stroke
 ii) Compression stroke
 iii) Working or power
or expansion stroke
 iv) Exhaust stroke.

The construction and working of a four-
stroke petrol engine

stroke petrol engine

Four Stroke Diesel Engine (Four Stroke
Compression Ignition Engine— C.I.Engine)
 The four stroke cycle diesel
engine operates on diesel cycle
or constant pressure cycle.
 Since ignition in these engines
is due to the temperature of the
compressed air, they are also
called compression ignition
engines. The construction and
working of the four stroke
diesel engine is shown in
figures shows a theoretical
diesel cycle. The four strokes
are as follows:

stroke diesel engine

TWO STROKE CYCLE ENGINE
 In two stroke cycle engines, the suction and exhaust strokes
are eliminated.
 There are only two remaining strokes i.e., the compression
stroke and power stroke and these are usually called upward
stroke and downward stroke respectively.
 Also, instead of valves, there are inlet and exhaust ports in
two stroke cycle engines.
 The burnt exhaust gases are forced out through the exhaust
port by a fresh charge which enters the cylinder nearly at the
end of the working stroke through the inlet port.
 The process of removing burnt exhaust gases from the engine
cylinder is known as scavenging.

Two Stroke Cycle Petrol Engine
 The principle of two-stroke cycle petrol engine is shown
in Figure . Its two strokes are described as follows:

COMPARISON OF SI AND CI ENGINES
SI Engine CI Engine
• It works on Otto cycle.
• A fuel having higher self-ignition
temperature is desirable, such as petrol
(gasoline).
• Air and fuel mixture in gaseous form
is inducted through the carburettor in the
cylinder during the suction stroke.
• The throttle valve of the carburettor
controls the quantity of the charge. The
quality of the charge remains almost
fixed during normal running conditions
at variable speed and load. So it is a
quantity governed engine.
•
It works on Diesel or Dual combustion
cycle.
A fuel having lower self-ignition
temperature is desirable such as diesel
oil.
Only air is introduced into the cylinder
during the suction stroke and therefore
the carburettor is not required. Fuel is
injected at high pressure through fuel
injectors direct into the combustion
chamber.
The amount of air inducted is fixed but
the amount of fuel injected is varied by
regulating the quantity of fuel in the
pump. The air-fuel ratio is varied at
varying load. So, it is a quality governed
engine.

• Spark is required to bum the fuel.
For this, an ignition system with spark
plugs is required. Because of this it is
called a spark-ignition (SI) engine.
• A compression ratio of 6 to 10.5 is
employed.
The upper limit is fixed by the anti-
knock quality of fuel. The engine tends
to knock at higher compression ratios.
• Part load efficiency is poor, since
even at part load the air/fuel ratio is
not much varied. In order to improve
the part load efficiency of the SI
engine, the MPFI technique of fuel
supply is used in modem engines.
• The cost of the petrol is higher than
that of the diesel oil.
Combustion of fuel takes place on its
own with out any external ignition
system. Fuel bums in the presence of
highly compressed air inside the engine
cylinder.
A compression ratio of 14 to 22 is
employed. The upper limit of
compression ratio is limited by the
rapidly increasing weight of the
engine. Engine tends to knock at lower
compression ratios.
Part load efficiency is good. As the load
decreases, the fuel supply to the engine
can also be reduced and lean mixture
to the engine is then supplied.
The cost of diesel oil is less than that of
petrol. Moreover, as fuel is sold on
volume basis and diesel oil has higher
specific gravity, more weight is
obtained in one litre.

• Noise and vibration are less
because of less engine weight.
• The main pollutants are carbon
monoxide (CO), oxides of nitrogen
(NO.J and hydrocarbons (HC).
Noise and vibrations are more
because of heavier engine
components due to higher
compression ratio.
Apart from CO, NOx and HC, soot
or smoke particles are also emitted
to the atmosphere.

COMPARISON OF FOUR-STROKE AND
TWO-STROKE ENGINES

Actual Valve Timing Diagram
 The valve timing of an engine is set to give the best
possible performance. This means that the valves must be
opened and closed at very precise times.
 The traditional way of showing exactly when the valve
opens and closes is by the use of a valve-timing diagram.
 As can be seen the valves are opened and closed in relation
to the number of degrees of movement of the crankshaft.
 When comparing the diagrams for the petrol engine of
medium and high performance cars, it will be noticed that
the high performance car has larger valve opening periods,
especially the closing of the inlet valve which is later.

 This is so that at high operating speeds the increased lag
allows as much pressure energy as possible to be
generated in the cylinder by the incoming air and fuel
charge, prior to its further compression by the rising
piston.
 There is also an increase in the value of valve overlap for
the high performance engine. This means that at TDC both
inlet and exhaust valves will be open together for a longer
period of time giving a better breathing of the engine at
these higher engine speeds .

Actual Valve Timing Diagram

Valve timing diagram of 4 stroke petrol
engines
IVO – Inlet valve Opens
IVC – Inlet Valve Closes
IS – Ignition Starts
EVO – Exhaust Valve
Opens
EVC – Exhaust Valve
Closes
TDC – Top Dead Center
BDC – Bottom Dead
Center

Theoritical & Actual Valve Timing for 4
stroke Diesel Engine

 Valve timing diagram of a four stroke engine gives a clear
idea about the actual position of the piston during the
opening & closing of inlet & exhaust valves.
 In practice, the events of the four-stroke cycle do not start
and finish exactly at the two ends of the strokes - to
improve the breathing and exhausting, the inlet valve is
arranged to open before TDC and to close after BDC and
the exhaust valve opens before BDC and closes after
TDC.
 These early and late opening and closing events can be
shown on a valve timing diagram such as Fig.

 Valve lead :This is where a valve opens so many degrees
of crankshaft rotation before either TDC or BDC.
 Valve lag :This is where a valve closes so many degrees of
crankshaft rotation after TDC or BDC.
 Valve overlap : This is the condition when both the inlet
and the exhaust valves are open at the same time during so
many degrees of crankshaft rotation.

 Variable valve timing
 Variable valve timing is a development that has been
enabled by the use of electronic control which permits
valve timing to be changed while the engine is operating,
to suit low speed, intermediate speed and high speed
operation. The variations in inlet valve timing are
approximately as follows:
 Low speed inlet valves opened later to improve idling
performance;
 Intermediate speed inlet valves opened a few degrees
earlier to take advantage of manifold design and thus
improve cylinder filling and performance.
 High speed a larger degree of early opening of the inlet
valves. VIJAYAKUMARA M ME NIE MYSORE 51

Valve timing diagram of 4- stroke
single cylinder diesel engine.
IVO - 25 before TDC
IVC - 30 after BDC
EVO - 45 before BDC
EVC - 15 after TDC
FVO - 15 before TDC
FVC - 25 after TDC

 Valve timing diagram of 4- stroke single cylinder petrol
engine.(low speed)
 IVO - 10 before TDC
 IVC - 20after BDC
 EVO - 25 before BDC
 EVC - 5 after TDC
 Valve timing diagram of 4- stroke single cylinder petrol
engine.(high speed)
 IVO - 10 before TDC
 IVC - 50 after BDC
 EVO - 45before BDC
 EVC - 20 after TDC

 Port timing diagram of 4- stroke single cylinder petrol
engine
 EPO - 45before TDC
 EPC - 45 after BDC
 TPO - 35 before BDC
 TPC - 35 after TDC

Fuel air cycle and Actual cycle
 Air - standard cycle is based on several assumptions
 Consequently the performance levels are higher
 Ex: Thermal efficiency of an SI engine with Comp. Ratio
8:1 is 56% whereas actual is 28%.
 Deviation from actual performance attributed to a small
extent to progressive burning of fuel, incomplete
combustion, valve operation etc.
 Main reason is the assumptions made.

 Fuel air cycle
 The gases contain fuel, air, water vapour and residual gas
 Fuel - Air ratio varies during operation
 Consequently CO2, water vapour etc. change
 Specific heats increase with temp.
 Fuel, air, do not completely combine chemically at high
temp. (1600K) leads to presence of CO, H2, H and O2 at
equilibrium condition
 No. of molecules present after combustion depend and on
pressure and temperature after combustion.

Fuel air cycle – assumptions
 No chemical change in fuel or air prior to combustion
 Subsequent to combustion charge is always in chemical
equilibrium
 No heat exchange between cylinders and gas (Adiabatic),
compression and expansion are frictionless
 Fluid motion is ignored
 For constant volume fuel cycle,
 Fuel completed vapourised and mixed with air
 Instant burning at TDC (constant vol)

 Fuel air cycle - Composition of gas
 Air fuel ratio changes during operation
 Consequently the composition in exhaust changes (O2,
CO and water vapour)
 Fresh charge mixes with the burnt gases
 Amount of burnt gases in the cyl. depends on load and
speed
 All these are considered in fuel air cycle

 Fuel air cycle – Variable specific heats
 Gases except monoatomic show an increase of specific
heat with temp,
 Increase in sp. Ht. does not follow any particular law
 Upto 1500 K specific heat follows:
 Cp = a + kT, Cv = b + kT
 Where a, b and k are constants.
 Now R= Cp-Cv = a-b
 Above 1500 K specific heat follows:
 Cp = a1+k1T + k2𝑇2
, Cv = b1+k1T+k2𝑇2

 Fuel air cycle – Variable specific heats
 When temperature rises larges fraction of heat is required
to produce motion of atoms within molecules
 This is does not contribute to temperature rise
 Consequently final temp and pressure will be lower

 Fuel air cycle – Dissociation
 Disintegration of combustion products at high temp.
 Deemed as reverse process of combustion
 During dissociation heat is absorbed
 During combustion heat is released
 At 1000 C, CO2 will be CO, O2 and little of H2O
 CO2 + Heat < =>2 CO + O2 at 1000 C
 H2O + Heat < => 2 H2 + O2 at 1300C
 Heat released consequent to reversal at the end of power
stroke dissipates into exhaust (not as power)
 Dissociation not pronounced in CI due to excess air

 Fuel air cycle – No. of moles
 No. of molecules depends on fuel – air ratio, type/extent
of combustion
 Pressure depends on no. of molecules and consequently
on work

 Effect of dissociation on temp wrt air fuel ratio
 Rich mixture : Presence of CO and O2 in burnt gas tend
to prevent dissociation
 Lean mixture : Nearly no dissociation due to low temp.
 Stoichiometric : Dissociation pronounced
 Reduction to the tune of 300  C

 Fuel air cycle - Merits
 Fairly accurate estimate possible
 85% of the actual efficiency
 Peak pressure and Exhaust temp. estimate can be
reasonably close to actual engine
 Influence of many variables on engine performance
understood better

Actual cycle
 Deviates largely from Air- standard cycle and fuel-air
cycle
 Efficiency is much lower than Air – standard cycle

 Actual cycle
 ( Conditions common to Fuel – Air cycle)
 Air and fuel mixture combines with products of
combustion of previous cycle
 Change in chemical composition of working substance
 Variation of specific heats with temp.
 Change in composition, temp., and actual amount of fresh
charge because of residual gases

 Actual cycle
 (Conditions – Exclusive, Responsible for the difference
between Actual cycle and Fuel-air cycle
 Progressive combustion (not instantaneous)
 Heat transfer to and from working medium
 Exhaust blow-down (loss of work due to early EVO)
 Gas leakage, fluid friction

 Actual cycle
 Major influencing factors:
 Time loss factor- loss due to time required for mixing of
air and fuel as also for combustion
 Heat loss factor – loss of heat from gases to cylinder walls
 Exhaust blow-down factor – loss of work due to early
EVO in the power stroke

Performance Parameters
 (a) Power and Mechanical Efficiency.
 (b) Mean Effective Pressure and Torque.
 (c) Specific Output.
 (d) Volumetric Efficiency.
 (e) Fuel-air Ratio.
 (f) Specific Fuel Consumption.
 (g) Thermal Efficiency and Heat Balance.
 (h) Exhaust Smoke and Other Emissions.
 (i) Specific Weight.

 Power and Mechanical Efficiency
 The main purpose of running an engine is to obtain
mechanical power.
 Power is defined as the rate of doing work and is equal to
the product of force and linear velocity or the product of
torque and angular velocity.
 Thus, the measurement of power involves the
measurement of force(or torque) as well as speed. The
force or torque is measured with the help of a
dynamometer and the speed by a tachometer.
 The power developed by an engine and measured at the
output shaft is called the brake power (bp) and is given by,
 P=2NT/60
 where, T is torque in N-m and N is the rotational speed in
revolutions per minute.

 The total power developed by combustion of fuel in the
combustion chamber is, however, more than the bp and is
called indicated power (ip).
 Of the power developed by the engine, i.e. ip, some power
is consumed in overcoming the friction between moving
parts, some in the process of inducting the air and
removing the products of combustion from the engine
combustion chamber.

 Indicated Power IC Engine Testing
 It is the power developed in the cylinder and thus, forms
the basis of evaluation of combustion efficiency or the
heat release in the cylinder.
 IP= pim LANk/60
 where, pm = Mean effective pressure, N/m2,
 L = Length of the stroke, m,
 A = Area of the piston, m2,
 N = Rotational speed of the engine, rpm (It is N/2 for four
stroke engine) and
 k = Number of cylinders.
 Thus, we see that for a given engine the power output can
be measured in terms of mean effective pressure.

 The difference between the ip and bp is the indication of
the power lost in the mechanical components of the engine
(due to friction) and forms the basis of mechanical
efficiency; which is defined as follows :
 Mechanical efficiency=bp/ip
 The difference between ip and bp is called friction power
(fp).
 fp = ip − bp
 Mechanical efficiency= bp /(bp+fp)

 Mean Effective Pressure and Torque
 Mean effective pressure is defined as a hypothetical/average
pressure which is assumed to be acting on the piston
throughout the power stroke. Therefore,
 Pm=ip  60 / LANk
 where, Pm = Mean effective pressure, N/m2,
 Ip = Indicated power, Watt,
 L = Length of the stroke, m,
 A = Area of the piston, m2,
 N = Rotational speed of the engine, rpm (It is N/2 for four
stroke engine) and
 k = Number of cylinders.

 If the mean effective pressure is based on bp it is called the
brake mean effective pressure (bmep Pmb replace ip by
bp), and if based on ihp it is called indicated mean effective
pressure (imep). Similarly, the friction mean effective
pressure (fmep) can be defined as,
 fmep = imep-bmep
 The torque is related to mean effective pressure by the
relation
 P=2NT/60
 IP= pim LANk/60
 By equation
 2NT/60= bemp.A.L.Nk/60
 T=( bemp.A.L.k) / 2

 Specific Output
 Specific output of an engine is defined as the brake power
(output) per unit of piston displacement and is given by,
 Specific output=Bp /A × L
= Constant × bmep × rpm
 The specific output consists of two elements – the bmep
(force)available to work and the speed with which it is
working.
 Therefore, for the same piston displacement and bmep an
engine operating at higher speed will give more output.
 It is clear that the output of an engine can be increased by
increasing either speed or bmep. Increasing speed involves
increase in the mechanical stress of various engine parts
whereas increasing bmep requires better heat release and
more load on engine cylinder.

Volumetric Efficiency
 Volumetric efficiency of an engine is an indication of the
measure of the degree to which the engine fills its swept
volume.
 It is defined as the ratio of the mass of air inducted into the
engine cylinder during the suction stroke to the mass of the
air corresponding to the swept volume of the engine at
atmospheric pressure and temperature.
 Alternatively, it can be defined as the ratio of the actual
volume inhaled during suction stroke measured at intake
conditions to the swept volume of the piston.
 Volumetric efficiency, v =
 Mass of charge actually sucked in / Mass of charge
corresponding to the cylinder intake P and T conditions

 The amount of air taken inside the cylinder is dependent on the
volumetric efficiency of an engine and hence puts a limit on the
amount of fuel which can be efficiently burned and the power
output.
 For supercharged engine the volumetric efficiency has no
meaning as it comes out to be more than unity.
 Fuel-Air Ratio (F/A)
 Fuel-air ratio (F/A) is the ratio of the mass of fuel to the mass of
air in the fuel-air mixture. Air-fuel ratio (A/F) is reciprocal of
fuel-air ratio.
 Fuel-air ratio of the mixture affects the combustion
phenomenon in that it determines the flame propagation
velocity, the heat release in the combustion chamber, the
maximum temperature and the completeness of combustion.

 Relative fuel-air ratio is defined as the ratio of the actual
fuel-air ratio to that of the stoichiometric fuel-air ratio
required to burn the fuel supplied. Stoichiometric fuel-air
ratio is the ratio of fuel to air is one in which case fuel is
completely burned due to minimum quantity of air supplied.
 Relative fuel-air ratio, FR =(Actual fuel-Air ratio)/
 (Stoichiometric fuel -Air ratio)
 Brake Specific Fuel Consumption
 Specific fuel consumption is defined as the amount of fuel
consumed for each unit of brake power developed per hour.
It is a clear indication of the efficiency with which the engine
develops power from fuel.
 This parameter is widely used to compare the performance of
different engines.

Thermal Efficiency and Heat Balance
 Thermal efficiency of an engine is defined as the ratio of the
output to that of the chemical energy input in the form of fuel
supply. It may be based on brake or indicated output.
 It is the true indication of the efficiency with which the
chemical energy of fuel (input) is converted into mechanical
work.
 Thermal efficiency also accounts for combustion efficiency,
i.e., for the fact that whole of the chemical energy of the fuel
is not converted into heat energy during combustion.
 Brake thermal efficiency = bp / mf  Cv
 where, Cv = Calorific value of fuel, kJ/kg, and
 mf = Mass of fuel supplied, kg/sec.

 The energy input to the engine goes out in various forms – a
part is in the form of brake output, a part into exhaust, and
the rest is taken by cooling water and the lubricating oil.
 The break-up of the total energy input into these different
parts is called the heat balance.
 The main components in a heat balance are brake output,
coolant losses, heat going to exhaust, radiation and other
losses.
 Preparation of heat balance sheet gives us an idea about the
amount of energy wasted in various parts and allows us to
think of methods to reduce the losses so incurred.

Exhaust Smoke and Other Emissions
 Smoke and other exhaust emissions such as oxides of
nitrogen, unburned hydrocarbons, etc. are nuisance for the
public environment. With increasing emphasis on air
pollution control all efforts are being made to keep them as
minimum as it could be.
 Smoke is an indication of incomplete combustion. It limits
the output of an engine if air pollution control is the
consideration.
 Exhaust emissions have of late become a matter of grave
concern and with the enforcement of legislation on air
pollution in many countries; it has become necessary to view
them as performance parameters.

Specific Weight
 Specific weight is defined as the weight of the engine in
kilogram for each brake power developed and is an
indication of the engine bulk.
 Specific weight plays an important role in applications such
as power plants for aircrafts.

Introduction of I C Engines

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