This document provides an overview of fundamentals of compression ignition engines. It begins with classifications of engines based on physical state of mixture and ignition type. It then discusses engine components, the diesel cycle, combustion processes, abnormal combustion, and developments to improve emissions such as common rail direct injection and exhaust gas recirculation. The goal is to introduce key concepts regarding compression ignition engines including working, thermodynamics and developments to control emissions.

1. FUNDAMENTALS OF COMPRESSION
IGNITION ENGINES
S. A. Anand Kumar
Research Scholar
Madras Institute of Technology - Chennai

2. Overview
 Historical Review of IC Engines
 Classification of Engines
 Brief Intro on IC Engine
 Diesel Cycle
 Thermochemistry of fuels
 Combustion in C.I Engine
 Abnormal Combustion
 Turbulence
 Emission
 Developments in Diesel Engine
 Reference

3. o The modern reciprocating internal
combustion engines have their origin in the
Otto and Diesel Engines invented in the later
part of 19th century.
o The main engine components comprising of
piston, cylinder, crank-slider crankshaft,
connecting rod, valves and valve train, intake
and exhaust system remain functionally
overall similar since those in the early
engines although great advancements in
their design and materials have taken place
during the last 100 years or so.

5. Classification of Engines

6. Classification of IC Engines
A. Physical State of Mixture
o Homogeneous Charge
Premixed outside( conventional gasoline and gas engines with fuel inducted in the intake manifold)
o Heterogeneous Charge
Premixed in-cylinder: In- cylinder direct injection and port fuel injection
B. Ignition Type
o Spark ignition
o Compression ignition
C. Mode of Combustion
o Flame propagation
o Spray combustion

7. Classification of IC Engines
Method of ignition has been adopted as the main criterion of
classification as in the conventional type IC engines it governs
• Fuel type
• Mixture preparation methods
• Progression of combustion process
• Combustion chamber design
• Engine load control and
• Operating and emission characteristics

8. Basic Terminologies
• Bore (d)
• Stroke (L)
• Top Dead Centre (TDC)
• Bottom Dead Centre (BDC)
• Clearance Volume (Vc)
• Swept Volume (Vs)
• Cylinder Volume (V)
• Compression Ratio (r)

9. Working of an Internal Combustion Engine

10. Working of an Internal Combustion Engine

11. Engine Components

12. Engine Components
Sl.No Component Material
1 Cylinder Block High grade cast iron High compressive strength
2 Cylinder Head Cast iron / Aluminium Made of single block
3 Piston Aluminium alloy / cast iron Light and strong
4 Connecting Rod Nickel, chromium, chrome vanadium steel Withstand the thrust
5 Crank Shaft Spheroidal graphitic cast iron / nickel alloy castings Good service life
6 Flywheel Cast/nodular iron Depends on application
7 Crankcase Cast iron / cast Aluminium
8 Cam Shaft Chilled iron castings Good wear resistance
9 Valves Steel alloys
10 Manifold Aluminium alloy
11 Piston rings Cast iron of fine grains Not affected by working heat
12 Engine Bearing Steel / bronze Support all rotating objects
13 Gudgeon pin/ Piston pin Hardened steel
14 Push rod Steel

13. Diesel Cycle

14. Thermochemistry of fuels
 The gas species that make up the working fluids in internal combustion engines (e.g.,
oxygen, nitrogen, fuel vapor, carbon di oxide, water vapor etc.) can usually be treated as ideal
gases.
 Oxygen is the reactive component of air. For each mole oxygen in air there are 3.773
moles of nitrogen.
Gas ppm by volume Molecular weight Mole fraction Molar Ratio
O2 209,500 31.998 0.2095 1
N2 780,900 28.012 0.7905 3.773
Ar 9,300 39.948
CO2 300 44.009
Air 1,000,000 28.962 1.0000 4.773

15. Thermochemistry of fuels

17. Combustion Stoichiometry

18. Combustion in Compression Ignition Engine

19. Combustion in Compression Ignition Engine
o Liquid fuel injected into compressed charge.
o Fuel evaporates and mixes with hot air
oAuto-ignition with rapid burning of fuel-air that is pre-mixed during the
ignition delay period.
oThis is followed by diffusion burning as the fuel and air mix.

20. Steps of combustion process

21. Auto ignition process
Physical Delay Chemical Delay
 Drop Atomization
 Evaporation
 Fuel/Air mixing
 Chain Initiation
 Chain Propagation
 Branching Reactions

22. Pressure – Crank angle diagram

23. Heat Release Curve

24. Diesel Spray and Flame Characteristics

25. Combustion Photography

26. Abnormal Combustion
 The ignition characteristics of the fuel affect the ignition delay.
 The ignition quality of a fuel is defined by it’s cetane number.
 For low cetane fuels the ignition delay is long and most of the injected fuel is
accumulated in the cylinder before autoignition.
 This leads to rapid combustion.
 Under extreme cases, this produces an audible knocking sound referred to as diesel
knock.

27. Abnormal Combustion

28. Factors Affecting Knocking
To reduce the possibility of knock, the elements of fuel and air should
have
A high temperature
A high density
A short ignition delay
A reactive composition

29. Turbulence
Increases the rate of
• Heat Transfer
• Evaporation
• Mixing
• Combustion

30. Types of Air motion
Swirl Squish Tumble

31. Emission
• C + O2 CO2 + 3.76 N2
• 12 Kg of C + 32 kg of O2 + 106 kg of N2 44 kg of CO2 + 106 kg of N2

32. Emission from C.I Engine
Smoke
• Blue Smoke (Lube oil)
• White Smoke (unburnt fuel)
• Black Smoke (unburnt carbon)
Particulate Matter
Oxides of Nitrogen (NOX)

33. Emission Formation Mechanism
 Smoke / Particulate matter
o Incomplete Combustion
 Oxides of Nitrogen
o Availability of oxygen
o Prevailing High temperature in the combustion chamber

34. Emission vs Air Fuel Ratio

35. Emission Control
 Particulate Traps
 Oxidation Catalytic Convertor (for PM)
 Reduction Catalytic Convertor (for NOX)
 Selective Catalytic Reduction (for NOX)

36. Developments in Diesel Engine
For effective control, power output and emission control in diesel engines several
developments are carried out
• Engine Modifications
o Combustion Chamber Design
o Sound Attenuation
• Advanced Fuel Systems
o Common Rail Direct Injection System
• Digital vs Analog Control Systems
• Emission Treatments
o Exhaust Gas Recirculation
o Selective Catalytic Reduction

37. Common Rail Direct Injection System

38. Exhaust Gas Recirculation System

39. Selective Catalytic Reduction System

40. Reference
Sl. No Title Author
1 Internal Combustion Engine Fundamentals John B Heywood
2 Fundamentals of Internal Combustion Engines H N Gupta
3 Internal Combustion Engine - Handbook Richard van Basshuysen and
Fred Schafer

41. Thank You . . .