Course Contents

1. Chapter One:- Introduction

2. Chapter Two:- Thermodynamics Cycles
3. Chapter Three:- performance equation and engine
characteristics
4. Chapter Four:- Fuel for IC Engines
5. Chapter Five :- Combustion and combustion chamber
Design
6. Chapter Six:- Ignition System
7. Chapter Seven:- Fuel Injection System
8. Chapter Eight:- Cooling And Lubricating System

122
Performance parameter of Ic-Engine
Chemical Energy Thermal Energy Mechanical Work

losses

Energy in fuel Heat Heat not wholly convertible

to drive the piston

• Losses to coolant
• Losses radiation
• Losses exhaust

 The remaining is convert to power (to drive the piston)

and this is called Indicated power.
123
124
Brake Power
 The amount of usable power the engine produce.
 brake power starts low at low engine speed and increase
steadily with speed until a high engine speed reaches.
 At high speed of engine attained brake power drops-
off.
 because of :-
 Frictional power - increase due to increasing Engine
speed
 Torque – decrease due to increasing engine speed

125
Indicated power
 The amount of power produce at piston due to gasses
forces of combustion of air-fuel mixture.

Torque
 Turning effort when the piston moves from TDC to BDC
 It is applying torque to the Engine crankshaft (through
connecting rod)
 Grater amount of Torque is get when
* Higher combustion pressure – due to harder push on the piston
* Higher volumetric efficiency – In Intermediate speed

126
Cont..
 In Higher Engine Speed
 Volumetric Efficiency drops-off - there is not enough time
for the cylinder to become filed up with air fuel mixture.
 less fuel-air mixture burns that produce less combustion
pressure.
 Less combustion pressure will be less push of the piston.
 so the Engine Torque is Less.
• Torque is a good indicator of an engine ability to do work.
where; Wb = brake power
n = number of rev per cycle
Wb
  ;
2 n=1 ; for 2-stoke Engine
n=2 ; for 4-stroke Engine

127
128
 Mean effective pressure (mep)
is that the pressure in the cylinder of an engine is
continuously changing during the cycle.
is a good parameter to compare engines for design/output
because it is independent of engine size and speed.
w  (mep)v Where W= work of one cycle
W w= specific work of one cycle
mep 
V d
V d = displacement volume
 Indicated mean effective pressure (Imep)

Im ep  W i
V d

 Brake mean effective pressure (Bemp)

Bmep  W b
V d

129
Cont…
 Torque and power
Wb Bemp *V d
  ;....W b 
2 n
Bemp *V d For 2-stroke cycle n=1
 
2 n
For 4-stroke cycle n=2

130
Cont…
 Many modern automobile engines have maximum torque in the
200 to 300 N-m range at engine speeds usually around 4000 to
6000 RPM.
 The point of maximum torque is called maximum brake torque
speed (MBT). A major goal in the design of a modern
automobile engine is to flatten
 To have less torque at both high and low speed. CI engines
generally have greater torque than SI engines.
 Large engines often have very high torque values with MBT at
relatively low speed.
 Power is defined as the rate of work of the engine. If n = number
of revolutions per cycle, and N = engine speed, then:

131
f

.
Where .; 1 _____
 fmeb *U p* Ap
W f 2n
.
_____
. 1
 bmeb *U p* Ap
W b 2n
_____

U p
 2SN
2
D
V d
 A * S ; where A
p p

4

132
Cont…
 Specific Power (SP):- measure the effectiveness with which piston area
is used regardless of cylinder size.
SP= Wb/ Ap
 Specific Volume (SV):- indicate the relative effectiveness with which
engine space is utilized.
SV = Vd / Wb
 specific weight (SW):- indicate the relative economy with which material
is used
SW = (engine weight)/Wb

where: Wb = brake power

Ap = piston face area of all pistons
Vd = displacement volume

133
Efficiency
 Engine Efficiency
 Is the relation between the power deliver and the power that
could be obtained, without losses.
 calculated in two ways
1. Thermal Efficiency
2. Mechanical Efficiency
1. Thermal Efficiency :- is the ratio of power produced to the
energy is the fuel burned to produce this power.
P
 
th
Q in
IP
 Indicated Thermal Efficiency  
ith
Q in

BP
 Brake Thermal Efficiency  
bth
Q in
134
Cont…
2. Mechanical Efficiency
BP bemp
 m  IP  imeb
Volumetric efficiency
 The power output of an engine depends directly on the
amount of charge that can be induced in the cylinder.
 Referred to as the breathing capacity of the engine
 Is the ratio of the volume of air induced to the swept
volume of the cylinder.
 Is ratio of actually enter air-fuel mixture to the amount of
air-fuel that could possibly enter.

135
Cont…
 Improving Volumetric Efficiency
 By increasing the number of intake valve per
cylinder.
 By made large Intake valve.
 By opening the Intake Valve wider.

136
Cont…
 Fuel Consumption
 specific fuel consumption:- is defined as the fuel flow
rate per unit power output. .

Sfc 
m f

. P
m  rate of fuel flow into engine
f

 SFC:- is a measure of how efficiency the fuel supplied

to the engine is used to produce power.
 a low volume of specific fuel consumption is
desirable, since for a given power level fuel is
consumed.
 classified in to two:- Brake specific fuel consumption
and indicated specific fuel consumption.
137
Cont…
 Brake Specific Fuel Consumption(BSFC)
.

bSfc 
m f

bp
 BSfc is decrease with engine size; fuel
consumption is less with larger engine.
 because less heat loss due to the higher
volume to surface area of ratio the
combustion chamber.
 BSfc is decrease as engine speeds increases due to
the shorter time for heat losses during each cycle.
 BSfc is decrease as compression ratio is increases
due to grater Efficiency.
138
Cont…
 BSfc increases at higher engine speed because of higher
frictional losses.

Example 2.2
139
Course Contents
1. Chapter One:- Introduction
2. Chapter Two:- Thermodynamics Cycles
3. Chapter Three:- performance equation and engine
characteristics
4. Chapter Four:- Fuel for IC Engines
5. Chapter Five :- Combustion and combustion chamber
Design
6. Chapter Six:- Ignition System
7. Chapter Seven:- Fuel Injection System
8. Chapter Eight:- Cooling And Lubricating System

140
Fuels
 Why we study about Fuel for I.C Engine
 Fuel properties affect the combustion process in the engine
and its operation
 Engines are designed to run on fuels that meet certain
standards in terms of chemical and physical properties
• The engine convert the Heat Energy in to useful work.

141
142
 Fuels for Engines
 I.C Engines can be operated on different Types of Fuels
1. Gaseous
2. Liquid
3. Originally solid also but now very rarely used.
 May be
1. Naturally available or
2. Artificially derived

143
 Solid Fuels
 Solid fuels have little practical application at the present
because of
 Problem of handling
 Disposing of the solid residue or ash
 Feeding are quite cumbersome
 Therefore this fuels have become unsuitable for I.C Engine
application.

144
 Gaseous Fuels
 Gaseous Fuels are ideal and pose very few problems in
using them in I.C engine
 Main gaseous fuels for engines are:
 Natural gas – from nature.
 Liquefied Petroleum Gas - from refineries.
 Producer gas - from coal
 Biogas - from biomass.
 Hydrogen – from many sources.

145
Contd.
 Advantages of Gaseous Fuels
 Mix more homogeneously with air
 Eliminate the distribution and starting problems
 Disadvantage
 Storage and handling Problem
 Therefore gaseous fuels are commonly used for stationary
power plants located near the source of available of the
fuel.
 Some of the gaseous fuel can be liquefied under pressure
for reducing the storage volume but this arrangement is
very expensive

146
Contd…
 Most IC engines obtain their energy from the
combustion of a hydrocarbon fuel with air, which
converts chemical energy of the fuel to internal energy
in the gases within the engine.
 The balanced chemical equation of the simplest
hydrocarbon fuel, methane CH4, burning with
stoichiometric oxygen is:
CH4 + 2 02 ~ C02 + 2 H20
 It takes two moles of oxygen to react with one mole of
fuel, and this gives one mole of carbon dioxide and two
moles of water vapour.
147
Contd…
 Air –fuel mixture.
AF  ma  M N
a a

mf M N
f f

148
Contd…
 Air is used as the source of oxygen to react with fuel.
Atmospheric air is made up of about:
 78% nitrogen by mole
 21 % oxygen
 1% argon traces of C02, Ne, CH4, He, H20, etc.
 To simplify calculations without causing any large error,
the neutral Argon in air is assumed to be combined with the
neutral Nitrogen, and atmospheric air then can be modelled
as being made up of 21% Oxygen and 79% Nitrogen.
 For every 0.21 moles of oxygen there is also 0.79 moles of
nitrogen.

149
Contd…
 For one mole of oxygen there are 0.79/0.21 moles of
nitrogen.
 For every mole of oxygen needed for combustion, 4.76
moles of air must be supplied: one mole of oxygen plus
3.76 moles of nitrogen.
 Stoichiometric combustion of methane with air is then:
CH4 + 2 O2 + 2(3.76) N2 ~ C02 + 2 H20 + 2(3.76) N2
 And of isooctane with air is:
C8H18 + 12.5 02 + 12.5(3.76) N2 ~ 8 C02 + 9 H20 +
12.5(3.76) N2

150
Contd…
 Molecular weights can be found in Table below. The
molecular weight of 29 will be used for air.
 Like Oxygen Molecular 32*0.21=6.72 and Nitrogen Molecular
28*0.79=22.12, the summation is 28.84 approximately 29 will
be used for air.

151
Contd…

Example

152
Contd…

153
Contd…

154
Contd…

155
Contd…
 Combustion efficiency as a function of fuel equivalence ratio.
Efficiency for engines operating lean is generally on the order of
98%. When an engine operates fuel rich, there is not enough
oxygen to react with all the fuel, and combustion efficiency
decreases.
 CI engines operate lean and typically have high combustion
efficiency.

156
Contd…
 Heat into the engine that gets converted to output work
can be given as:

157
158
159
Families of hydrocarbon
1. Paraffin's(alkane)(CnH2n+2)
 Straight Chain Compounds Like Methane, Ethane,
Propane, Etc. Or
 Branched Chain Compounds (Isomers) Like Iso-butane,
Iso-heptane (Like 2,2,3 Tri-methyl Butane Or “Triptane”)
And Iso-octane (Like 2,2,4 Tri-methyl Pentane).

160
Contd.
2. Olefins (Alkene): (CnH2n)
 Open chain unsaturated hydrocarbons with one or more
double bond like ethane or propylene which also have
straight and branched chain compounds.
 Both types of olefins produce gum when reacted with
oxygen which can block fuel filters.

161
Contd…
3. Diolefins CnH2n-2(Alkadiene):
 similar to olefins, except that they have two double
carbon-carbon bonds.
4. Napthenes or Cycloparaffins: (CnH2n)
 Have same general formula as mono olefins but are
saturated compounds with a ring structure.
 Examples are Cyclobutane, Butycylcolhexane, Decalin
etc.

162
Contd...
5. Aromatics: (CnH2n-6)
 Ring structured unsaturated hydrocarbons with double
bonds but more stable than the paraffinic double bond
hydrocarbons.
 Examples are benzene, toluene, naphthalene, and
anthracenes.

163
Characteristics of Some Hydrocarbon Families

164
 General Characteristics
 The above families of hydrocarbons exhibit general
characteristics due to their molecular structure which
are summarized below
 Normal paraffin's exhibit the poorest antiknock quality
when used in an SI engine.
 But the antiknock quality improves with the increasing
 Number of carbon atoms and
 The compactness of the molecular structure.
 The aromatics offer the best resistance to knocking in
SI Engines

165
Contd.
 For CI engines, the order is reversed i.e.
 The normal paraffin's are the best fuels and
 Aromatics are the least desirable,
 As the number of atoms in the molecular structure
increases, the boiling temperature increases.
 Thus fuels with fewer atoms in the molecule tend to be
more volatile.
 The heating value generally increases as the proportion of
hydrogen atoms to carbon atoms in the molecule increases
due to the higher heating value of hydrogen than carbon.
 Thus, paraffins have the highest heating value and the
aromatics the least.

166
Self-Ignition Characteristics of Fuels
 If the temperature of an air-fuel mixture is raised
high enough, the mixture will self-ignite without
the need of a spark plug or other external igniters.
 The temperature above which this occurs is called
the self-ignition temperature (SIT).

167
Course Contents
1. Chapter One:- Introduction
2. Chapter Two:- Thermodynamics Cycles
3. Chapter Three:- performance equation and engine
characteristics
4. Chapter Four:- Fuel for IC Engines
5. Chapter Five :- Combustion and combustion chamber
Design
6. Chapter Six:- Ignition System
7. Chapter Seven:- Fuel Injection System
8. Chapter Eight:- Cooling And Lubricating System

168