Thermal Engineering - 1

1. I.C. ENGINES
1.1 Introduction. ..................................................................... 1.1
1.2 Basic Terms Connected With I.C. Engines ................. 1.1
1.3 Four Stroke SI (Petrol) Engine ..................................... 1.4
1.4 Four Stroke CI Engine ................................................... 1.6
1.5 Working of Two Stroke Cycle Engine .......................... 1.9
1.6 Working of Two Stroke Petrol Engine ......................... 1.10
1.7 Classification of IC Engines ........................................... 1.12
1.8 IC Engine Components – Functions And Materials .. 1.13
1.9 Valve Timing And Port Timing Diagrams................... 1.24
1.9.1 Valve Timing Diagram for a 4-Stroke Cycle
Petrol Engine.................................................................. 1.26
1.9.2 Valve Timing Diagram of 4-Stroke Diesel
Engine .... ........................................................................ 1.29
1.9.3 Port Timing Diagram of Two Stroke Cycle
Petrol Engine.................................................................. 1.29
1.9.4 Port timing Diagram for Two Stroke Cycle
Diesel Engine ................................................................. 1.32
1.10 Fuel Supply System ...................................................... 1.34
1.10.1 Fuel injection Systems for S.I. Engines.......... 1.34
1.10.2 Different types of Fuel Systems ....................... 1.35
1.10.3 Fuel Injection System In SI Engines.............. 1.36
1.10.4 Fuel Pump (for S.I. Engine) ............................ 1.36
1.11 Carburetor . ..................................................................... 1.37
1.12 Air Fuel Ratio ............................................................... 1.40
1.13 Various Compensation In Carburetors ....................... 1.40
1.14 Types of Carburetors..................................................... 1.43
1.15 Fuel Injection Systems For C.I Engines .................... 1.53
1.15.1 Fuel Pump (C.I. Engine) .................................. 1.53
1.16 Fuel Injection System ................................................... 1.55
Contents C.1
1.16.1 Fuel Injector ....................................................... 1.56
1.17 Ignition Systems. ........................................................... 1.57
1.17.1 Spark Plug ......................................................... 1.57
1.17.2 Types of Electronic ignition systems: .............. 1.65
1.18 Lubrication System........................................................ 1.69
1.18.1 Purpose of Lubrication...................................... 1.69
1.18.2 Systems of Lubrication...................................... 1.70
1.19 Cooling System............................................................... 1.73
1.19.1 Purpose of Cooling............................................. 1.73
1.19.2 Methods of Cooling IC Engine......................... 1.74
1.20 Fuels And Combustion.................................................. 1.77
1.20.1 Introduction ........................................................ 1.77
1.20.2 Classification of fuels: ....................................... 1.78
1.21 Solid Fuels ..................................................................... 1.79
1.22 Gaseous Fuels: ............................................................... 1.80
1.23 Fuel Properties ............................................................... 1.81
1.23.1 Determination of Calorific value of fuel by
Bomb Calorimeter.......................................................... 1.83
1.23.2 Determination of Higher Calorific value of
Gaseous fuel. .................................................................. 1.85
1.24 Combustion Stoichiometry ............................................ 1.88
1.25 Excess Air And Air Fuel Ratio Calculation .............. 1.95
2. Combustion in SI and CI Engine
2.1 Normal Combustion ......................................................... 2.1
2.1.1 Factors affecting normal combustion in S.I
Engines... ........................................................................ 2.3
2.1.2 Flame Front Propagation.................................... 2.4
2.3 Importance of Flame Speed And Effect of Engine
Variables ............ ..................................................................... 2.5
2.3.1 Factors affecting flame speed ............................. 2.5
2.2 Abnormal Combustion ..................................................... 2.8
2.2.1 Pre-ignition ...........................................................
C.2 Thermal Engineering - I
2.8
2.2.2 Knocking (or) Detonation (or) Pinking.............. 2.9
2.2.3 The phenomenon of knock in SI Engine.......... 2.10
2.2.4 Effects of knocking in SI Engine ...................... 2.13
2.2.5 Effect of engine variables on knock .................. 2.14
2.3 Fuel Requirement And Fuel Rating ............................. 2.18
2.3.1 Important properties of fuel in SI Engine ....... 2.18
2.3.2 Important characteristics of SI Engine fuel..... 2.18
2.3.5 Octane Number (ON) .......................................... 2.21
2.4 Anti-Knock Additives ....................................................... 2.23
2.4.1 Anti-knock Agents ................................................ 2.23
2.4.2 Effects of Anti knock additives .......................... 2.24
2.4.3 Factors affecting Detonation and Remedies ..... 2.25
2.5 Types of Combustion Chamber In SI Engine ............. 2.26
1. Overhead valve (or) I - Head combustion
chamber.. ........................................................................ 2.26
2. T-Head combustion chamber ................................... 2.27
3. L-head combustion chamber.................................... 2.27
4. F-head combustion chamber.................................... 2.28
2.6 Combustion in CI Engines ............................................. 2.28
1. Ignition Delay period ............................................... 2.29
2. Period of Rapid Combustion (or) Uncontrolled
Combustion..................................................................... 2.32
2.7 Factors That Affect Delay Period In Diesel Engine .. 2.32
2.7.1 Effect of variables on the Delay period............ 2.34
2.8 Knocking (or) Diesel Knock............................................ 2.35
2.8.1 The phenomenon of knock in CI engine........... 2.36
2.8.2 Comparison of knock on SI and CI Engines .. 2.38
2.8.3 Characteristics Tending to Reduce Detonation 2.40
2.9 Need For Air Movement In Diesel Engine.................. 2.40
2.10 Combustion Chamber Design For Compression
Ignition Engine . ..................................................................... 2.42
Contents C.3
1. Open combustion chamber....................................... 2.42
(a) Shallow depth chamber .......................................... 2.43
(b) Hemispherical chamber........................................... 2.43
(c) Cylindrical chamber ................................................ 2.43
(d) Toroidal chamber .................................................... 2.43
2. Divided combustion chamber type .......................... 2.45
(a) Turbulent combustion chamber ............................. 2.45
(b) Pre combustion chamber......................................... 2.46
(c) Energy-cell chamber................................................. 2.47
2.11 Diesel Fuel Requirement : For Compression
Ignition Engines ..................................................................... 2.50
1. Knocking characteristics........................................... 2.50
2. Volatility of the fuel ................................................. 2.51
3. Starting characteristics of the fuel ......................... 2.51
4. Smoke produced by fuel and its odour ................. 2.51
5. Viscosity of fuel......................................................... 2.51
6. Corrosion and wear.................................................. 2.51
7. Easy to handle.......................................................... 2.51
2.11.1 Cetane Number (CN)......................................... 2.52
2.11.2 Fuel Rating for CI Engine ............................... 2.52
3. Testing and Performance of Engines
3.1 Performance Calculations (or) Performance Test On
I.C. Engines ....... ..................................................................... 3.1
1. Indicator Diagram .................................................... 3.1
2. Indicated Power (IP) ................................................ 3.2
3. Mean Effective Pressure Pm .................................. 3.2
5. Brake Power (BP) ..................................................... 3.6
6. Different Arrangements used to find Brake
Power...... ........................................................................ 3.6
7. Friction Power (FP) .................................................. 3.9
8. Specific Fuel Consumption (S.F.C)......................... 3.9
9. Mechanical Efficiency mech  .................................. 3.10
C.4 Thermal Engineering - I
10. Thermal Efficiency.................................................. 3.10
11. Indicated Thermal Efficiency indicated .............. 3.10
12. Brake Thermal Efficiency Brake  ........................ 3.11
12. Relative Efficiency or Efficiency Ratio ................. 3.11
14. Volumetric Efficiency volumetric ........................ 3.11
3.2 Dynamometer.... ............................................................... 3.12
3.2.1 Hydraulic Dynamometer ..................................... 3.13
3.2.2 Eddy Current Dynamometer............................... 3.15
3.3 Measurement of Indicated Power of Multicylinder
Engine Morse Test . ............................................................... 3.21
3.4 Measurement of Air Consumption ................................ 3.31
3.5 Fuel Consumption ........................................................... 3.34
3.5.1 Volumetric type .................................................... 3.35
3.5.1.1 Burette method.................................................. 3.35
3.5.1.2 Automatic volumetric flow meter .................... 3.37
.........................................................................................
3.5.2 Gravimetric fuel flow measurement................... 3.38
Construction.................................................................... 3.39
3.5.3 Measurement of Heat Carried Away by
Cooling Water................................................................. 3.40
3.6 Exhaust Gas Composition............................................... 3.41
3.6.1 Oxides of Nitrogen............................................... 3.41
3.6.2 Carbon monoxide (CO)........................................ 3.43
3.6.3 Unburnt hydrocarbons......................................... 3.45
3.6.4 Aldehydes .............................................................. 3.47
3.7 Visible Emissions . ........................................................... 3.47
3.7.1 Smoke .................................................................... 3.47
3.7.1.1 Comparison method.......................................... 3.47
3.7.1.2 Obscuration method.......................................... 3.48
3.7.2 Measurement of Heat Carried Away by
Exhaust Gas ................................................................... 3.52
3.8 Heat Balance Sheet ......................................................... 3.52
Contents C.5
Solved Problems........................................................3....5..3-3.96
4. Air Compressors
4.1 Introduction. ..................................................................... 4.1
4.2 Classification of Air Compressors.................................. 4.2
4.3 Single Acting Reciprocating Air Compressor ............... 4.3
4.4 Double Acting Air Compressor ...................................... 4.4
4.5 Single Stage Compressor ................................................ 4.4
4.6 Multi Stage Compressor ................................................. 4.5
4.7 Working Principle of Reciprocating Air Compressors 4.5
4.7.1 Workdone during isothermal compression
PV  c without clearance volume............................... 4.7
4.7.2 Workdone during polytropic compression
[ PVn  constant ] without clearance volume .............. 4.8
4.7.3 Workdone During Isentropic Compression
PV  constant Without Clearance Volume............... 4.10
4.8 Minimum Workdone ........................................................ 4.11
4.9 Power Required To Run The Compressor ................... 4.11
Solved Problems........................................................4....1..2-4.15
4.9.1 Clearance Volume ................................................ 4.16
4.10 Workdone By Reciprocating Air Compressor With
Clearance Volume ... ............................................................... 4.16
4.11 Isothermal Efficiency of A Reciprocating Air
Compressor......... ..................................................................... 4.18
4.12 Volumetric Efficiency in A Reciprocating Air
Compressor......... ..................................................................... 4.18
4.12.1 Factors affecting volumetric efficiencies .......... 4.20
4.13 Important Technical Terms .......................................... 4.20
1. Volumetric Efficiency vol ........................................ 4.20
2. Clearance Ratio ‘k’.................................................... 4.21
3. Volume and Volume Rate........................................ 4.21
4. Indicated Power (I.P) and Brake Power (B.P) ..... 4.22
C.6 Thermal Engineering - I
5. Free Air Delivered (FAD) ........................................ 4.22
6. Mean Effective Pressure m.e.p .............................. 4.22
8. Swept Volume Vs.................................................... 4.23
9. Piston speed ............................................................. 4.23
4.14 Single Stage Solved Problems................................4...2..3. -4.66
4.15 Two Stage Compression................................................ 4.64
4.15.1. Complete (or) Perfect Intercooling................... 4.65
4.15.2 Incomplete (or) Imperfect Intercooling............. 4.65
4.15.3 Workdone when perfect and imperfect
intercooling. .................................................................... 4.66
4.15.4 Minimum Work Required for 2 Stages and
multi stages .................................................................... 4.66
4.16 Multistage Reciprocating Compressors ....................... 4.67
4.17 Various Types of Compressors Rotary Positive
Displacement Compressors ....................................................4.112
4.18 Roots Blower... ...............................................................4.112
4.19 Vane Type Blower of Compressor ...............................4.117
4.20. Centrifugal Compressor................................................4.125
4.21 Velocity And Pressure Variation .................................4.128
4.22 Static Temperature And Total Head (or)
Stagnation Temperature ........................................................4.129
4.23 Steady-flow Energy Equation.......................................4.132
4.24 Euler’s Equation - (Energy Transfer) .........................4.133
4.24.1 Velocity components at the entry and exit
of the rotor ..................................................................... 4.134
4.25 Impeller Blade Shape - Backward, Radial And
Forward Blade Impellers .....................................................4.137
4.26 Velocity Triangle And Work Done By The
Centrifugal Compressor..........................................................4.140
4.27 Important Formulae ......................................................4.142
1. Power required ........................................................ 4.142
2. Width of Blades of Impeller and Diffuser ............ 4.144
Contents C.7
3. Isentropic Efficiency of the Compressor ................. 4.145
4. Slip factor .................................................................. 4.147
5. Work factor ................................................................ 4.149
6. Pressure Co-efficient p .......................................... 4.149
7. Stage Work ................................................................ 4.149
8. Stage Pressure Rise .................................................. 4.151
9. Enthalpy-Entropy Diagram...................................... 4.151
10. Degree of Reaction.................................................. 4.153
11. Mass Flow Rate ...................................................... 4.153
Solved Problems...................................................4.....1..5..4..-4.165
4.28 Axial Flow Compressors ...............................................4.166
4.28.1 Working Principles of a Compressor Stage .... 4.167
4.28.2 Stage Velocity Triangles.................................... 4.169
4.28.3 Blade Loading, Flow Coefficients and
Specific Work.................................................................. 4.171
4.28.4 Static Pressure Rise in a Stage....................... 4.171
4.29 Degree of Reaction.........................................................4.175
4.30 Infinitesimal Stage Efficiency (or) Polytropic
Efficiency ............ .....................................................................4.176
4.31 Finite Stage Efficiency ..................................................4.178
4.38 Important Formulae ......................................................4.180
1. Flow coefficient f................................................... 4.180
2. Head or work coefficient h .................................. 4.180
3. Deflection co-efficient def ...................................... 4.181
4. Pressure co-efficient p ........................................... 4.181
5. Pressure ratio ............................................................ 4.181
6. Stagnation pressure ratio......................................... 4.181
7. Number of stages ...................................................... 4.181
4.32 Losses In Axial Flow Compressor Stage....................4.182
1. Profile losses on the surface of the blades:........... 4.183
2. Skin friction loss on the annulus walls: ............... 4.183
3. Secondary flow losses: .............................................. 4.183
C.8 Thermal Engineering - I
4.33 Surging ...... .....................................................................4.184
4.34 Stalling ...... .....................................................................4.186
4.35 Comparison Between Reciprocating And
Centrifugal Compressors........................................................4.187
4.36 Comparison Between Reciprocating And Rotary
Air Compressors .....................................................................4.188
4.37 Comparison Between Centrifugal And Axial Flow
Compressors....... .....................................................................4.189
Solved Problems...................................................4.....1..9..1..-4.208
5. Refrigeration
5.1 Introduction. ..................................................................... 5.1
5.1.1 Fundamentals of Refrigeration:.......................... 5.1
5.1.4 Types of Mechanical Refrigeration system........ 5.3
5.1.5 Unit of Refrigeration: (Ton of Refrigeration) ... 5.3
5.2 Air Refrigeration System................................................ 5.6
5.2.1 Air Refrigeration Cycles ...................................... 5.7
5.3 Reversed Carnot Cycle .................................................. 5.7
5.4 Bell-Coleman Cycle .......................................................... 5.17
5.5 Vapour Compression Refrigeration................................ 5.39
5.5.1 Different Conditions of the Vapour ................... 5.42
5.6 PH Chart..... ..................................................................... 5.56
Solved Problems........................................................5....5..7-5.65
5.7 Subcooling or Undercooling ............................................ 5.66
5.7.1 Effect of Subcooling............................................. 5.67
5.8 Super Heating .. ............................................................... 5.69
5.8.1 Effect of Super heating ....................................... 5.69
Solved Problems........................................................5....7..0-5.95
5.9 Performance Calculation - Factors Affecting
Performance of A Vapour Compression System ................ 5.99
5.10 Vapour Absorption System...........................................5.102
5.10.1 Working principle of vapour absorption ......... 5.103
Contents C.9
5.10.2 Practical vapour absorption system................. 5.104
5.11 Refrigerant .....................................................................5.106
5.11.1 Characteristics of good refrigerants................. 5.106
5.11.2 Refrigerants Number ......................................... 5.107
5.12 Ammonia - Water Absorption System........................5.108
5.12.1 Absorption Refrigeration: (Electrolux
Refrigerator).................................................................... 5.108
5.12.2 Lithium Bromide Absorption System .............. 5.109
5.13 Gas Liquefaction System ..............................................5.111
5.13.1 Hampson-Linde Gas Liquefaction System ...... 5.111
5.13.2 Claude System for Liquefying Gases .............. 5.112
5.13.3 Advantages and Limitations of vapour
absorption system: ......................................................... 5.113
5.14 Comparision Between Vapour Compression And
Vapour Absorption System....................................................5.114
5.15 Application of Cryogenic ...............................................5.114
(i) Application of Liquid Oxygen................................. 5.114
(ii) Application of Liquid Nitrogen ............................. 5.115
(iii) Application of Carbon-di-oxide ............................. 5.115
(iv) Application of Inert Gases .................................... 5.115
6. Actual Cycles and Their Analysis
6.1 Introduction. ..................................................................... 6.1
6.2 Comparison of Air-standard and Actual Cycles .......... 6.2
(a) The working medium.............................................. 6.3
(b) The nature of working substance.......................... 6.3
6.3 Time Loss.... ..................................................................... 6.4
6.4 Heat Loss Factors ........................................................... 6.6
6.5 Exhaust Blowdown........................................................... 6.8
6.6 Loss due to Gas Exchange Process .............................. 6.9
6.7 Volumetric Efficiency....................................................... 6.10
6.7.1 The amount of air-fuel ratio .............................. 6.10
C.10 Thermal Engineering - I
6.7.2 The design of intake and exhaust manifold
and port design ............................................................. 6.11
6.7.3 Compression ratios............................................... 6.11
6.7.4 The intake and exhaust valve timings ............. 6.11
6.8 Loss due to Rubbing Friction ........................................ 6.14
6.8.1 Surface finish ....................................................... 6.14
6.8.2 Lubricant properties ............................................ 6.14
6.8.3 Engine power........................................................ 6.15
6.8.4 Heat Dissipation .................................................. 6.15
6.8.5 Other miscellaneous components ........................ 6.15
6.9 Blowby Losses .. ............................................................... 6.16
6.9.1 Effects of blowby loss on efficiency ................... 6.16
6.9.2 Crankcase ventilation .......................................... 6.17
6.10 Actual and Fuel-Air Cycles of CI Engines ................ 6.19