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Internal Combustion Engines

Lecture-1

Ujjwal K Saha, Ph.D.Department of Mechanical Engineering

Indian Institute of Technology Guwahati

Prepared underQIP-CD Cell Project

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Heat EngineHeat Engine• Convert Thermal Energy in fuel into

Mechanical Energy for motion

EngineEngine

• Energy Conversion Device (One Form to the Other)

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Classifying Engines

• Classification is based on:– The location of the combustion

•Internal / External– The type of combustion

•Intermittent / Continuous– The type of internal motion

•Reciprocating•Rotational

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Internal Combustion Engines

• Combustion occurs Inside the engine• Internal combustion directly touches

the parts that must be moved in order to produce mechanical energy

• Examples: Lawnmower engines, Motorcycle engines, automotive engines

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External Combustion Engines

• Combustion occurs indirectly on the parts that must be moved

• Thermal energy heats another fluid (water), turns it into steam, and the steam pushes on a piston or part

Example: Steam locomotives, Boilers

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External Combustion

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Intermittent Combustion Engines

• Combustion within the engine STARTS and STOPS many times during operation

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Continuous Combustion Engine

• Combustion process that continues constantly without stopping

• It remains burning continuously• Examples:

– Turbine engines– Rocket engines– Jet engines

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• An internal combustion engine is defined as a device in which the chemical energy of the fuel is released inside the engine and used directly for mechanical work, as opposed to an external combustion engine in which a separate combustor is used to burn the fuel.

I C EnginesI C Engines

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History• The internal combustion

engine was first conceived and developed in the late 1800’s

• The man who is considered the inventor of the modern IC engine is pictured to the right ...Nikolaus Otto (1832-1891).

• Otto developed a four-stroke engine in 1876, most often referred to as a Spark Ignition, since a spark is needed to ignite the fuel air mixture.

Nikolaus Otto patented the 4-stroke engine when he was only 34!

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• Another important cycle is the Diesel cycle developed by Rudolph Diesel in 1897. This cycle is also known as a compression ignition engine.

• Almost all travel and transportation is powered by the IC engine: trains, automobiles, airplanes are just a few.

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Reciprocating Engines

• Motion produced from within the fuel (combustion) moves parts up an down

• Piston or internal parts are moved back and forth

• Examples: lawn mowers, cars, trucks, etc...

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Rotary Engines

• Has continuous rotation of the parts that are moving

• The combustion is pushing an internal part around in a circular path

Examples: Wankel enginesTurbine engines

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Forms of Kinetic Energy

• Reciprocation– motion that is defined on a linear path– up-and-down; back-and-forth

• Rotation– Motion that is defined on a circular

path– spinning; turning

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Kinetic Energy within Intermittent Combustion Engines

• Piston Movement– intermittent– Reciprocating– Not useful enough

• Crank shaft– Connected to piston– turns linear motion into rotation motion

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Thermodynamic Principles

• All internal combustion– Open cycle, heated engine

• Gasoline (Otto) engine– Spark ignition– Compresses air-fuel mixture

• Diesel engine– Compressed ignition– Compresses air only

17CROSS SECTION OF OVERHEAD VALVE FOUR CYCLE SI ENGINE

Name as many parts as you can

Your name:_________________

Parts of an Parts of an I C EngineI C Engine

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Structural Components

• Cylinder Block– Part of engine

frame that contains cylinders in which piston moves

– Supports liners & head

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Structural Components

• Cylinder Head/Assembly– Serves to admit, confine, and release

fuel/air– Cover to cylinder block– Supports valve train

• Crankcase– Engine frame section that houses the

crankshaft• Oil sump

– Reservoir for collecting and holding lube oil

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Moving Components

• Three Groups – according to motion– Reciprocating only (pistons and

valves)– Reciprocation & rotary

(connecting rods)– Rotary only (crankshafts and

camshafts)

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Moving Components• Piston

– Acted on by combustion gases

– Lightweight but strong/durable

• Piston Rings– Transfer heat from piston to

cylinder– Seal cylinder & distribute

lube oil• Piston Pin

– Pivot point connecting piston to connecting rod

• Connecting Rod– Connects piston & crankshaft– reciprocating rotating

motion

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Moving Components

• Crankshaft– Combines work done by each piston– Drives camshafts, generator, pumps, etc.

• Flywheel– Absorbs and releases kinetic energy of

piston strokes, and smoothens rotation of crankshaft

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Moving Components

• Valves– Intake: open to admit air

to cylinder (with fuel in Otto cycle)

– Exhaust: open to allow gases to be rejected

• Camshaft & Cams– Used to time the addition

of intake and exhaust valves

– Operates valves via pushrods & rocker arms

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Parts of an Parts of an I C EngineI C Engine

Air cleaner

Choke

Throttle

Intake manifold

Exhaust manifold

Piston ringsPiston

Wrist pinCylinder blockConnecting rod

Oil gallery to pistonOil gallery to head

CrankcaseCrankpin

Crankshaft

Cylinder head

Breather cap

Rocker armValve spring

Valve guidePushrod

Sparkplug

Combustion chamber

TappetDipstickCamCamshaft

Water jacketWet liner

Connecting rod bearing

Main bearing

Oil pan or sump

CROSS SECTION OF OVERHEAD VALVE FOUR CYCLE SI ENGINE

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Definitions

• Stroke - the number of times the piston travels the length of the cylinder

• Cycle - composed of 4 parts– Intake - working substance is introduced– Compression - working substance is

compressed by upward movement of the piston

– Power - ignition => forcing the piston down– Exhaust - removal of exhaust gases

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Definitions – contd.•• Top Dead Center Top Dead Center --

when the piston is at its highest point in the cylinder. The volume of the working fluid is a minimum.

•• Bottom Dead Center Bottom Dead Center --when the piston is at its lowest point in the cylinder. The volume of the working fluid is a maximum.

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Some Engine Terms•• BoreBore-- diameter of the cylinder

•• Engine DisplacementEngine Displacement-- the volume of air that is displaced by all the pistons during one upward stroke.

•• Compression RatioCompression Ratio-- the comparison of the cylinder volume when the piston is at BDC and the volume when the piston is at TDC.

•• Engine strokeEngine stroke– A stroke is a single traverse of the cylinder

by the piston (from TDC to BDC)– 1 revolution of crankshaft = 2 strokes of

piston

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Engine PowerEngine Power• IC engines can deliver power in the range

from 0.01 kW to 20 x 103 kW, depending on their displacement

• Number of Cylinders may vary from 1 to 20 with different geometric configurations.

A 4 stroke engine requires 2 full revolutions of the crankshaft to complete the cycle.

While the 2 stroke only requires 1 revolution of the shaft complete the same cycle.

4 and 2 Stroke Engines4 and 2 Stroke Engines

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Operation

• Increased pressure of combustion gases acts on piston, and is converted to rotary motion

• Can be 2 or 4 stroke engines– 2-stroke: 1 power stroke per 1

crankshaft rev– 4-stroke: 1 power stroke per 2

crankshaft rev

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Four Stroke SI Engine

• Induction Stroke: fill cylinder with fuel and air

• Compression Stroke: squeeze mixture

• Power Stroke: burn and extract work

• Exhaust Stroke: empty cylinder of exhaust

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Induction Stroke• Engine pulls piston out of cylinder• Low pressure inside cylinder• Atmospheric pressure pushes fuel

and air mixture into cylinder• Engine does work on the gases

during this stroke

• Engine pushes piston into cylinder• Mixture is compressed to high

pressure and temperature• Engine does work on the gases

during this stroke

Compression Stroke

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• Mixture burns to form hot gases• Gases push piston out of

cylinder• Gases expand to lower pressure

and temperature• Gases do work on engine during

this stroke

Power Stroke

Exhaust Stroke• Engine pushes piston into cylinder• High pressure inside cylinder• Pressure pushes burned gases out

of cylinder• Engine does work on the gases

during this stroke

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Ignition System

• Car stores energy in an electromagnet

• Energy is released as a high voltage pulse

• Electric spark ignites fuel and air mixture

• Two basic types of ignition– Battery – Magneto

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Four-Stroke Diesel Engine• Intake stroke

– Intake valve open, exhaust valve shut– Piston travels from TDC to BDC– Air drawn in

• Compression stroke– Intake and exhaust valves shut– Piston travels from BDC to TDC– Temperature and pressure of air increase

• Power stroke– Intake and exhaust valves shut– Fuel injected into cylinder and ignites– Piston forced from TDC to BDC

• Exhaust stroke– Intake valve shut, exhaust valve open– Piston moves from BDC to TDC– Combustion gases expelled

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SummarySummary

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CompressionStroke

PowerStroke

ExhaustStroke

AI

R

CombustionProducts

IntakeStroke

Air

Fuel Injector

Four Stroke Compression Ignition Engine

CompressionStroke

PowerStroke

ExhaustStroke

AI

R

CombustionProducts

Ignition

IntakeStroke

FUEL

Fuel/AirMixture

Four Stroke Spark Ignition Engine

SSuummmmaarryy

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Technologists, Addison Wisley.3.3. Fergusan CR, Fergusan CR, andand Kirkpatrick ATKirkpatrick AT,, (2001), Internal Combustion Engines, John

Wiley & Sons.4.4. Ganesan VGanesan V,, (2003), Internal Combustion Engines, Tata McGraw Hill.5.5. Gill PW, Smith JH, Gill PW, Smith JH, andand Ziurys EJZiurys EJ,, (1959), Fundamentals of I. C. Engines, Oxford

and IBH Pub Ltd. 6.6. Heisler H,Heisler H, (1999), Vehicle and Engine Technology, Arnold Publishers.7.7. Heywood JB,Heywood JB, (1989), Internal Combustion Engine Fundamentals, McGraw Hill.8.8. Heywood JB, Heywood JB, andand Sher E,Sher E, (1999), The Two-Stroke Cycle Engine, Taylor & Francis.9.9. Joel R, Joel R, (1996),(1996), Basic Engineering Thermodynamics, Addison-Wesley.10.10. Mathur ML, and Sharma RP,Mathur ML, and Sharma RP, (1994), A Course in Internal Combustion Engines,

Dhanpat Rai & Sons, New Delhi.11.11. Pulkrabek WW,Pulkrabek WW, (1997), Engineering Fundamentals of the I. C. Engine, Prentice Hall.12.12. Rogers GFC, Rogers GFC, andand Mayhew YRMayhew YR, (1992), Engineering Thermodynamics, Addison

Wisley. 13.13. Srinivasan S,Srinivasan S, (2001), Automotive Engines, Tata McGraw Hill.14.14. Stone R,Stone R, (1992), Internal Combustion Engines, The Macmillan Press Limited, London.15.15. Taylor CF,Taylor CF, (1985), The Internal-Combustion Engine in Theory and Practice, Vol. 1 & 2,

The MIT Press, Cambridge, Massachusetts.

References

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