I C Engines E C Engines

Reciprocating Rotary Reciprocating Rotary

Stirling engine Gasoline

Engine Wankel

Engine

Open

Cycle

Gas

Turbine

Diesel

Engine

Steam Engine Steam

Turbine

Engine

Closed cycle Gas

Turbine

Heat Engines

1

Most widely used heat engines

INTERNAL

COMBUSTION

engine

GAS TURBINE

STEAM TURBINE

2

ADVANTAGES OF I C ENGINE

OVER THE OTHER ENGINES

Considerable mechanical simplicity and improved power plant efficiency

High working fluid temperatures can be employed resulting in higher thermal efficiency

weight to power ratio is less than that of the steam turbine

Small power output with reasonable thermal efficiency and cost

3

Disadvantages

Vibration

Not possible to use variety of fuels in these engines

Fuels are expensive

4

Applications

Automobiles

Motor cycles

Power boats

Ships

Slow speed aircrafts

Locomotives

Power units of relatively small output

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EXTERNAL COMBUSTION ENGINES –

Combustion takes place outside

the engine

INTERNAL COMBUSTION ENGINES –

Combustion takes place inside the

engine

6

Spark Ignition (SI) Compression Ignition (SI)

Reciprocating Engine

7

Engine Components

8

9

10

11

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Nomenclature

Cylinder Bore (d) – inner diameter of the working cylinder (mm)

Piston Area (A) – cross section area of bore (cm2)

Stroke (L) – distance through which a working piston moves between two successive reversals of its direction of motion (mm)

Stroke to Bore Ratio (L/d)

d<L - under-square Engine

d = L - Square Engine

d>L - Over Square Engine

Dead center – Position of working piston at the moment when the direction of the piston is reversed at the ether end of the stroke

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Nomenclature Continued Top Dead Center – Dead Center when piston is

farthest from crank shaft

Bottom Dead Center - Dead Center when piston is

nearest from crank shaft

Displacement or Swept Volume (VS)– Volume swept

by the piston when travelling from one dead center to

the other (cc)

Cubic Capacity or Engine Capacity – Displacement

volume ×No. of cylinders

Clearance Volume (VC) – Volume of combustion

chamber above piston when it is at top dead center

Compression ratio (r) - 𝑉𝑇

𝑉𝐶 =

𝑉𝐶+𝑉𝑆

𝑉𝐶

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Working Principle of Engines

https://www.youtube.com/watch?v=4W_NRHxek

aY

http://www.animatedengines.com/otto.html

http://www.animatedengines.com/diesel.html

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Working Principle of Four-

Stroke SI Engine

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Ideal p-V Diagram of a Four

Stroke SI Engine

A- Intake

B – Adiabatic compression

C – Const. volume heat addition

And Expansion

D – Exhaust

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Working Principle of Four-

Stroke CI Engine

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Ideal p-V Diagram of a Four

Stroke CI Engine

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Comparison of SI and CI

Engine Description SI Engine CI Engine

Working

Cycle

Otto Cycle or Constant

Volume heat addition

cycle

Diesel Cycle or Constant

Pressure heat addition

Fuel Used Gasoline(Volatile), Self

Ignition high

Diesel oil (non-volatile), Self

Ignition is low

Introduction

of Fuel

Mixture of fuel,

Carburetor and Ignition

System

Fuel is injected at high

pressure, Fuel Pump and

Injector

Load Control Control quantity of Air-

Fuel mixture

Control quantity of fuel, Air

quantity not controlled

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Comparison of SI and CI

Engine Continued Description SI Engine CI Engine

Ignition Ignition System with

Spark Plug, Primary

voltage given by

Magneto or a battery

Self Ignition due to high

temperature of air as a

result of high compression

Compression

ratio

6 to 10, Upper limit is

fixed by antiknock

quality of the fuel

16 to 20, Upper limit is

limited by weight

increase of Engine

Speed High speed (Light weight

and homogeneous

combustion)

Low speed (Heavy

weight and

heterogeneous

combustion)

Thermal

Efficiency

Lower (Lower CR) Higher (Higher CR)

Weight Lighter (Low Peak

Pressure)

Heavier (Higher Peak

Pressure)

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Two Stroke Engine

http://www.animatedengines.com/twostroke.html

https://www.youtube.com/watch?v=xV9jnWVeSB

4

https://www.youtube.com/watch?v=LuCUmQ9Fx

MU

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Indicator Diagram of a two

Stroke Engine

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Comparison of Four Stroke

and Two Stroke Engine Four Stroke Engine Two Stoke Engine

Four Stokes, two revolution of

crankshaft, One power stoke

in two revolution of CS

Two strokes, one revolution of crank

shaft, one power stoke in each

revolution of crank shaft

Heavier Flywheel Lighter Flywheel

Weight of engine per hp is

high

Weight of engine per hp is

comparatively low

There are inlet and exhaust

valves in the engine

There are inlet and exhaust ports

instead of valves

Thermal efficiency is high Thermal efficiency is comparatively

low

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Comparison of Four Stroke

and Two Stroke Engine conti’d

Four Stoke Engine Two Stoke Engine

Lesser cooling and lubrication,

Lower rate of wear and tear

Greater cooling and lubrication,

Higher rate of wear and tear

Initial cost of engine is more Initial cost is less

Volumetric Efficiency is higher Volumetric Efficiency is lower

Used where efficiency is

important (Buses, trucks, tractors,

aero planes etc.)

Used where Low cost.

Compactness and light weight

are important (mopeds, scooters,

motorcycle, hand sprayers etc.)

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Actual Indicator Diagram of a 2-stoke(a)

and 4-stroke (b) SI engine

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Theoretical Valve timing

Diagram

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Valve timing Diagram of Diesel Engine

https://www.youtube.com/watch?v=DBD

GOvsxpq8

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Valve timing Diagram of Petrol Engine

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Valve timing Diagram of Two

Stroke Engine

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CLASSFICATION OF IC ENGNES 1. Cycle of Operation

(i) Two Stroke engines

(ii) Four Stroke engines

2. According to cycle of Combustion

(i) Otto cycle engine (Combustion at constant volume)

(ii) Diesel Engine (Combustion at constant

Pressure)

(iii) Dual-combustion or Semi- Diesel cycle

engine(Combustion partly at constant

volume and partly at constant

pressure)

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CLASSFICATION OF IC ENGNES 3. According to arrangement of cylinder

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CLASSFICATION OF IC ENGNES

4. According to their uses

i. Stationary Engine

ii. Portable Engine

iii. Marine Engine

iv. Automobile Engine

v. Aero Engine

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CLASSFICATION OF IC ENGNES

5. According to the speed of engine

i. Low Speed

ii. Medium Speed

iii. High Speed

6. According to the method of Ignition

i. Spark-Ignition

ii. Compression-Ignition

7. According Method of cooling the Cylinder

i. Air-cooled

ii. Water-cooled

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CLASSFICATION OF IC ENGNES

8. According to method of governing

i. Hit and Miss governed

ii. Quality governed

iii. Quantity governed

9. According to valve arrangement

i. Over Head Valve

ii. L-head type

iii. T-head type

iv. F-head type

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Valve arrangements

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CLASSFICATION OF IC ENGNES

10.According to number of Cylinders

i. Single Cylinder

ii. Multi Cylinder

11.According Air intake process

I. Naturally aspirated

II. Supercharged

III. Turbo charged

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CLASSFICATION OF IC ENGNES

12. According to fuel employed

i. Oil Engine (Fuel Oil)

ii. Petrol Engine

iii. Gas engine (coal gas, producer gas, biogas, landfill gas)

iv. Kerosene Engine

v. LPG engine

vi. Alcohol-ethyl, methyl engine

vii. Duel fuel engine

viii. Gasohol

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CLASSFICATION OF IC ENGNES

13.Method of Fuel Input

i. Carbureted

ii. Multi point port fuel injection

iii. Throttle body fuel injection

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First Law Analysis of Engine Cycle

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Reciprocating Engine as an

Open System

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Performance Parameters

Mechanical efficiency

ηm = 𝑏𝑝 (𝑘𝐽/𝑠)

𝑖𝑝(𝑘𝐽/𝑠)

fp = 𝑖𝑝 − 𝑏𝑝

Indicated Thermal efficiency

ηith = 𝑖𝑝 (𝑘𝐽/𝑠)

𝑒𝑛𝑒𝑟𝑔𝑦 𝑖𝑛 𝑓𝑢𝑒𝑙 𝑝𝑒𝑟 𝑠𝑒𝑐𝑜𝑛𝑑(𝑘𝐽/𝑠)

Break Thermal efficiency

ηbth= 𝑏𝑝 (𝑘𝐽/𝑠)

𝑒𝑛𝑒𝑟𝑔𝑦 𝑖𝑛 𝑓𝑢𝑒𝑙 𝑝𝑒𝑟 𝑠𝑒𝑐𝑜𝑛𝑑(𝑘𝐽/𝑠)

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Performance Parameters

Volumetric Efficiency

ηv = 𝑚

𝑐𝑕𝑎𝑟𝑔𝑒

𝑚 𝑡𝑕𝑒𝑜𝑟𝑖𝑡𝑖𝑐𝑎𝑙

It is affected by

I. Density of fresh charge at intake

II. Pressure and temperature of outgoing burnt gas

III. Design and exhaust of manifolds

IV. Timing of opening and closing of intake and exhaust valve

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Performance Parameters Relative Efficiency or Efficiency Ratio – Thermal

efficiency of an actual cycle to that of ideal

cycle

ηrel = 𝐴𝑐𝑡𝑢𝑎𝑙 𝑡𝑕𝑒𝑟𝑚𝑎𝑙 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦

𝐴𝑖𝑟−𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦

Mean Effective Pressure – Average pressure inside

the cylinder of an internal combustion engine

based on the calculated or measured output

i. Indicated mean effective pressure (imep)

pim = 60000×𝑖𝑝

𝐿𝐴𝑛𝐾

ii. Break mean effective pressure (bmep)

pbm = 60000×𝑏𝑝

𝐿𝐴𝑛𝐾

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Performance Parameters

Mean Piston Speed

sp = 2LN

Specific Power Output – Power output

per unit piston area

Ps = bp/A

= constant ×Pbm ×sp

Specific Fuel Consumption

sfc = 𝐹𝑢𝑒𝑙 𝑐𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑡𝑖𝑚𝑒

𝑃𝑜𝑤𝑒𝑟

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Performance Parameters Inlet – Valve Mach Index

Z = 𝑔𝑎𝑠 𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑡𝑕𝑟𝑜𝑢𝑔𝑕 𝑡𝑕𝑒 𝑖𝑛𝑙𝑒𝑡 𝑣𝑎𝑙𝑣𝑒 (𝑢)

𝐼𝑛𝑙𝑒𝑡 𝑠𝑜𝑛𝑖𝑐 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 (α)

u = 𝐴𝑝𝑆𝑝

𝐶𝑖𝐴𝑖

Ap - Piston area

Sp - Mean piston speed

Ci - inlet valve average flow co-efficient

Ai - intake valve opening area

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Inlet-Valve Mach Index

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Performance Parameters Fuel – Air Ratio(F/A) or Air Fuel Ratio (A/F)

i. Stoichiometric fuel-air ratio or chemically

correct – a mixture that contains just enough air

for complete combustion of all the fuel in the

mixture is called a chemically correct or

stoichiometric fuel-air ratio

ii. Equivalence Ratio

Ф = 𝐴𝑐𝑡𝑢𝑎𝑙 𝑓𝑢𝑒𝑙−𝑎𝑖𝑟 𝑟𝑎𝑡𝑖𝑜

𝑆𝑡𝑜𝑖𝑐𝑕𝑖𝑜𝑚𝑒𝑡𝑟𝑖𝑐 𝑓𝑢𝑒𝑙−𝑎𝑖𝑟 𝑟𝑎𝑡𝑖𝑜

Ф = 1 chemically correct

Ф > 1 Rich mixture

Ф< 1 Lean mixture

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Performance Parameters Calorific Value or Heating Value or Heat of

Combustion – Thermal Energy released per unit quantity of the fuel when the fuel is burned completely and the product of combustion are cooled back to the initial temperature of the combustible mixture

i. Higher Calorific Value – when the products are cooled to 25 0C, practically all the water vapor resulting from combustion process is condensed. The heating value so obtained is called higher calorific value or gross calorific value

ii. Lower Calorific Value or net Calorific Value – Heat released when water vapor in the products of combustion is not condensed and remains the vapor form

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Reversible Process Delvers the most and

Consumes the least Work

50

Friction renders a Process

Irreversible

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Totally and Internally reversible

Process

52

Irreversible Compression and

Expansion

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Execution of Carnot Cycle in a

Closed System

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P-V Diagram of a Carnot

Cycle

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Questions Mean Effective Pressure

Pumping Losses

C-tane number

Ignition lag

Difference between diesel cycle and Otto cycle

Variation of specific heats

Battery ignition system and magneto ignition system

Effect of dissociation during combustion

Stratified charge engine

Expression for Thermal efficiency of Diesel Engine

Prove eff of otto is more than diesel cycle for same compression ratio

Qualities of fuel

Ignition timing

Variable compression engine

Chemical equilibrium

Effect of cut off

Effect of volatility

HUCR

Diff between four and two

Diff between SI and CI

Brake, Mechanical, Indicated, Volumetric Efficiency

Compression Ratio, Cut off Ratio, Expansion Ratio

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