(106017702) thermal engineering lecture 2.doc

8/14/2019 (106017702) thermal engineering lecture 2.doc

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Paavai Department of

UNIT-II 2.

ME1251 THERMAL ENGINEERING

UNIT II

INTERNAL COMBUTION ENGINES


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CONTENTS

TECHNICAL TERMS

2.1 Classification of IC engine

2.2 Components of I.C engine 1.Cylinder loc!

2." T#eoretical $al$e timing diagram of fo%r stro!e engine

2.& Comparison of t'o stro!e and fo%r stro!e engines

2.( Simple Car%retor

2.) *iesel +%mp and In,ector system

2.- *iesel !noc!ing and detonation

2. Ignition System2.1/ Comparison et'een 0attery and Magneto Ignition System

2.11 L%rication System

2.12 Cooling System

2.12.1 Air Cooled System

2.12.2 ater Cooling System

2.1" Emission ormation in C.I. Engine

2.1& +rinciple C.I. Engine E3#a%st Constit%ents

2.14 Sample prolems

2.1( Sol$ed +rolems

2.1) T'o Mar!s 5ni$ersity 6%estions

2.1- 5ni$ersity Essay 6%estions


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TECHNICAL TERMS

1. IC Engines: Air and f%el mi3t%re flo's t#ro%g# inlet $al$e and e3#a%st lea$es t#ro%g#

e3#a%st $al$e Con$erts reciprocating motion to rotary motion %sing piston and cran!

s#aft

2. TDC: Top *ead Center7 +osition of t#e piston '#ere it forms t#e smallest $ol%me8

3. BDC: 0ottom *ead Center7 +osition of t#e piston '#ere it forms t#e largest $ol%me

4. Str!e: Stro!e means *istance et'een T*C and 0*C

5. Bre: 0ore *iameter of t#e piston 9internal diameter of t#e cylinder:

". C#e$r$n%e '(e: T#e clearance $ol%me means minim%m $ol%me formed is called

t#e clearance

). C(*ressin r$ti: T#e compression ratio means ratio of total cylinder $ol%me to

clearance $ol%me.

+. ME,: Mean effecti$e press%re7 A const. t#eoretical press%re t#at if acts on piston

prod%ces 'or! same as t#at d%ring an act%al cycle net ; ME+ 3 +iston area 3 Stro!e

-. C((n #$'ts / engines $re7

R ec ipro ca ti n g 7

T' o< stro!e e n g in e

o% r< stro ! e e n g ine 9=tto c y c le :

S i3 < stro!e e n g ine

*i e s e l e n g ine

At!inson c y c l e

Mill er cyc le

10. T S t r ! e E n g ine:

Engines ased on t#e t'o


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12. , ist n : A cylindrical component ma!ing an %p and do'n mo$ement in t#e cylinder

13. C ( ' st i n % $ ( e r : A portion ao$e t#e cylinder in '#ic# t#e com%stion of

t#e f%el


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UNITII

INTERNAL COMBUTION ENGINES

2.1 C#$ssi/i%$tin / IC engine:

Normally IC engines are classified into

1.C.I engines and

2.S.I engines

Some of t#e important classifications are gi$en elo'>

1. N%mer of stro!es medi%m> and #ig# speed engines

1/. According to t#e application A%tomoti$e> Marine> Locomoti$e> Aircraft

etc.>

2.2 C(*nents / I.C engine 1.C#iner #%!:

T#e cylinder loc! is t#e main ody of t#e engine> t#e str%ct%re t#at s%pports

all t#e ot#er components of t#e engine. In t#e case of t#e single cylinder engine t#e

cylinder loc! #o%ses t#e cylinder> '#ile in t#e case of m%lti


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#en t#e $e#icle r%ns> large amo%nts of #eat are generated 'it#in t#e cylinder

loc!. To remo$e t#is #eat t#e cylinder loc! and t#e cylinder #ead are cooled y 'ater

flo'ing t#ro%g# t#e 'ater ,ac!ets 'it#in larger engines s%c# as t#ose fo%nd in cars and

tr%c!s. or smaller $e#icles li!e motorcycles> fins are pro$ided on t#e cylinder loc! and

on t#e cylinder #ead to cool t#em. T#e ottom portion of t#e cylinder loc! is called a

cran!case. it#in t#e cran!case is '#ere l%ricating oil> '#ic# is %sed for l%ricating

$ario%s mo$ing parts of t#e engine> is stored.

C#iner:

As t#e name s%ggests it is a cylindrical s#aped $essel fitted in t#e cylinder

loc!. T#is cylinder can e remo$ed from t#e cylinder loc! and mac#ined '#ene$er

re@%ired to. It is also called a liner or slee$e. Inside t#e cylinder t#e piston mo$es %p and

do'n> '#ic# is called t#e reciprocating motion of t#e piston. 0%rning of f%el occ%rs at

t#e top of t#e cylinder> d%e to '#ic# t#e reciprocating motion of t#e piston is prod%ced.

T#e s%rface of t#e cylinder is finis#ed to a #ig# finis#> so t#at t#ere is minimal friction

et'een t#e piston and t#e cylinder.

,istn:

T#e piston is t#e ro%nd cylindrical component t#at performs a reciprocating

motion inside t#e cylinder. #ile t#e cylinder itself is t#e female part> t#e piston is t#e

male part. T#e piston fits perfectly inside t#e cylinder. +iston rings are fitted o$er t#e

piston. T#e gap et'een t#e piston and t#e cylinder is filled y t#e piston rings and

l%ricating oil. T#e piston is %s%ally made %p of al%min%m

. ,istn rings:

T#e piston rings are t#in rings fitted in t#e slots made along t#e s%rface of t#e

piston. It pro$ides a tig#t seal et'een t#e piston and t#e cylinder 'alls t#at pre$ents


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lea!ing of t#e com%stion gases from one side to t#e ot#er. T#is ens%res t#at t#at motion

of t#e piston prod%ces as close as to t#e po'er generated from inside t#e cylinder.

C('stin %$(er:

It is in t#e com%stion c#amer '#ere t#e act%al %rning of f%el occ%rs. It is t#e

%ppermost portion of t#e cylinder enclosed y t#e cylinder #ead and t#e piston. #en t#e

f%el is %rnt> m%c# t#ermal energy is prod%ced '#ic# generates e3cessi$ely #ig#

press%res ca%sing t#e reciprocating motion of t#e piston.

In#et ($ni/#:

T#ro%g# t#e inlet manifold t#e air or air


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T#e small end of t#e connecting rod is connected to t#e piston y g%dgeon pin> '#ile t#e

ig end is connected to cran!s#aft y cran! pin

.Cr$n!s$/t:

T#e cran!s#aft performs t#e rotary motion. It is connected to t#e a3le of t#e

'#eels '#ic# mo$e as t#e cran!s#aft rotates. T#e reciprocating motion of t#e piston is

con$erted into t#e rotary motion of t#e cran!s#aft 'it# t#e #elp of connecting rod. T#e

cran!s#aft is located in t#e cran!case and it rotates in t#e %s#ings.

C$(s$/t:

It ta!es dri$ing force from cran!s#aft t#ro%g# gear train or c#ain and operates t#e

inlet $al$e as 'ell as e3#a%st $al$e 'it# t#e #elp of cam follo'ers> p%s# rod and roc!er

arms.

2.3 Tereti%$# &$#&e ti(ing i$gr$( / /'r str!e engine:


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2.3.1 A%t'$# &$#&e ti(ing i$gr$( / /'r str!e engine:

2.3.2Tereti%$# *rt ti(ing i$gr$( / t str!e engine:


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2.4 C(*$risn / t str!e $n /'r str!e engines:

T$#e 2.1 C(*$risn / t str!e $n /'r str!e engines

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2." Si(*#e C$r'retr:

T#e f%nction of a car%retor is to $aporie t#e petrol 9gasoline: y means of

engine s%ction and to s%pply t#e re@%ired air and f%el 9petrol: mi3t%re to t#e engine cylinder.

*%ring t#e s%ction stro!e> air flo's from atmosp#ere into t#e cylinder. As t#e air passes t#ro%g#

t#e ent%re> $elocity of air increases and its press%re falls elo' t#e atmosp#ere. T#e press%re at

t#e nole tip is also elo' t#e atmosp#eric press%re. T#e press%re on t#e f%el s%rface of t#e f%el

tan! is atmosp#eric. *%e to '#ic# a press%re difference is created> '#ic# ca%ses t#e flo' of f%el

t#ro%g# t#e f%el ,et into t#e air stream. As t#e f%el and air pass a#ead of t#e ent%re> t#e f%el gets

$aporied and re@%ired %niform mi3t%re is s%pplied to t#e engine. T#e @%antity of f%el s%pplied

to t#e engine depends %pon t#e opening of t#rottle $al$e '#ic# is go$erned y t#e go$ernor.

T#e main parts of a simple car%retor are7

7#$t %$(er: T#e le$el of f%el in t#e float c#amer is maintained slig#tly elo' t#e tip of t#e

nole. If t#e le$el of petrol is ao$e t#en t#e petrol 'ill r%n from t#e nole and drip from t#e


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UNIT-II 2.

car%retor. If t#e petrol le$el is !ept lo' t#an t#e tip of t#e nole t#en part of press%re #ead is

lost in lifting t#e petrol %p to t#e tip of nole. Benerally it is !ept at 4mm from t#e le$el of

petrol in t#e float c#amer. T#e le$el of t#e f%el is !ept constant 'it# t#e #elp of float and needle

$al$e. T#e needle $al$e closes t#e inlet s%pply from main tan! if t#e le$el rises ao$e t#e

re@%ired le$el. If t#e le$el of f%el decreases t#en t#e needle $al$e opens t#e s%pply. Benerally t#e

f%el le$el is !ept 4mm elo' t#e nole tip.

9ent'ri: #en t#e mi3t%re passes t#ro%g# t#e narro'est section its $elocity increases and

press%re falls elo' t#e atmosp#eric. As it passes t#ro%g# t#e di$ergent section> press%re

increases again.

Trtt#e &$#&e: It controls t#e @%antity of air and f%el mi3t%re s%pplied to t#e engine t#ro%g#

inta!e manifold and also t#e #ead %nder '#ic# t#e f%el flo's.

C!e: It pro$ides an e3tra ric# mi3t%re d%ring to t#e engine starting and in cold 'eat#er to

'arm %p t#e engine. T#e c#o!e $al$e is nearly closed d%ring clod starting and 'arming. It

creates a #ig# $ac%%m near t#e f%el ,et '#ic# ca%ses flo' of more f%el from t#e ,et.

2.) Diese# ,'(* $n Ine%tr sste(:


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2.+ Diese# !n%!ing $n etn$tin:

e already !no' t#at if t#e delay period is long> a large amo%nt of f%el 'ill e in,ected

and acc%m%lated in t#e c#amer. T#e a%to ignition of t#is large amo%nt of f%el may ca%se #ig#

rate of press%re rise and #ig# ma3im%m press%re '#ic# may ca%se !noc!ing in diesel engines. A

long delay period not only increases t#e amo%nt of f%el in,ected y t#e moment of ignition> %t

also impro$e t#e #omogeneity of t#e f%el air mi3t%re and its c#emical preparedness for e3plosion

type self ignition similar to detonation in SI engines. It is $ery instr%cti$e to compare t#e

p#enomenon of detonation is SI ens%es 'it# t#at of !noc!ing in CI engines. T#ere is no do%t

t#at t#ese t'o p#enomena are f%ndamentally similar. 0ot# are processes of a%to ignition s%,ect

to t#e ignition time lag c#aracteristic of t#e f%el air mi3t%re. Ho'e$er> differences in t#e

!noc!ing p#enomena of t#e SI engine and t#e CI engine s#o%ld also e care f%lly e noted7 1. In

t#e SI engine> t#e detonation occ%rs near t#e end of com%stion '#ere as in t#e CI engine

detonation occ%rs near t#e eginning of com%stion as s#o'n in fig. (.1/. 2. T#e detonation in

t#e SI engine is of a #omogeneo%s c#arge ca%sing $ery #ig# rate of press%re rise and $ery #ig#

ma3im%m press%re. In t#e CI engine t#e f%el and air are in perfectly mi3ed and #ence t#e rate ofpress%re rise is normally lo'er t#an t#at in t#e detonating part of t#e c#arge in t#e SI engine. ".

Since in t#e CI engine t#e f%el is in,ected in to t#e cylinder only at t#e end of t#e compression

stro!e t#ere is no @%estion of pre ignition or pre mat%re ignition as in t#e SI engine. &. In t#e SI

engine it is relati$ely easy to disting%is# et'een !noc!ing and non< !noc!ing operation as t#e


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#%man ear easily find t#e distinction. Ho'e$er> in t#e case of t#e CI engine t#e normal ignition

is itself y a%to ignition and #ence no CI engines #a$e a s%fficiently #ig# rate of press%re rise per

degree cran! angle to ca%se a%dile noise. #en s%c# noise ecomes e3cessi$e or t#ere is

e3cessi$e $iration in engine str%ct%re> in t#e opinion of t#e oser$er> t#e engine is sending to

!noc!. It is clear t#at personal ,%dgment is in$ol$ed #ere. T#%s in t#e CI engine t#ere is no

definite distinction et'een normal and !noc!ing com%stion. T#e ma3im%m rate of press%re

rise in t#e CI engine may reac# as #ig# as 1/ar per cran! degree angle.

It is most important to note t#at factors t#at tend to red%ce detonation in t#e SI engine increase

!noc!ing in CI engine and $ice $ersa eca%se of t#e follo'ing reason. T#e detonation of

!noc!ing in t#e SI engine is d%e to sim%ltaneo%s a%to ignition of t#e last part of t#e c#arge. To

eliminate detonation in t#e SI engine 'e 'ant to pre$ent all toget#er t#e a%to ignition of t#e last

part of t#e c#arge and t#erefore desire a long delay period and #ig# self ignition temperat%re of

t#e f%el. To eliminate !noc!ing t#e CI engine 'e 'ant to ac#ie$e a%to ignitions early as possile

t#erefore desire a s#ort delay period and lo' self ignition temperat%re of t#e f%el. Tale (.2 gi$es

t#e factors '#ic# red%ce !noc!ing in t#e SI and CI engines

T$#e 2.2: actors tending to red%ce !noc!ing in SI and CI engine


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It is also clear from t#e tale and disc%ssion t#at a good CI engine f%el is a ad SI engine f%el

and a good SI engine is ad CI engine f%el. In ot#er 'ords diesel oil #as lo' self ignition

temperat%re and s#ort time lag '#ere as petrol #a$e #ig# self ignition temperat%re and a long

ignition lag. In terms of f%el rating diesel oil #as #ig# cetane n%mer 9&/ D (/: and lo' octane

n%mer 9ao%t "/: and petrol #as #ig# octane n%mer 9-/ D /: and lo' cetane n%mer 91-:.

2.- Ignitin Sste(:

0asically Con$ectional Ignition systems are of 2 types 7 9a: 0attery or Coil

Ignition System> and 9: Magneto Ignition System. 0ot# t#ese con$entional> ignition systems

'or! on m%t%al electromagnetic ind%ction principle. 0attery ignition system 'as generally %sed

in & inetic HondaF Honda Scooty> iero> etc.:. In t#is case ( or 12

atteries 'ill s%pply necessary c%rrent in t#e primary 'inding. Magneto ignition system is

mainly %sed in 2 ignition s'itc#> a%to contact rea!er> capacitor> distri%tor rotor> distri%tor contact points> spar! pl%gs>

etc. Note t#at t#e ig%re &.1 s#o's t#e ignition system for & #ere t#ere

are &


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a. It consists of ( or 12 attery> ammeter> ignition s'itc#> primary 'inding it #as

2//


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closes t#e circ%it & t#e magnetic field egins to collapse. 0eca%se of t#is collapsing magnetic field> c%rrent

'ill e ind%ced in t#e secondary 'inding. And eca%se of more t%rns 9G 21/// t%rns: of

secondary> $oltage goes %nto 2-///


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2.11 L'ri%$tin Sste(:

2.11.1 S*#$s:


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T#e splas# system is no longer %sed in a%tomoti$e engines. It is 'idely %sed in

small fo%r o%toard marine operation> and so on. In t#e splas#

l%ricating system > oil is splas#ed %p from t#e oil pan or oil trays in t#e lo'er part of t#e

cran!case. T#e oil is t#ro'n %p'ard as droplets or fine mist and pro$ides ade@%ate l%rication to

$al$e mec#anisms> piston pins> cylinder 'alls> and piston rings. In t#e engine> dippers on t#e

connecting


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2.11.2 C(in$tin S*#$s $n 7r%e 7ee:

In a comination splas# and force feed > oil is deli$ered to some parts y means

of splas#ing and ot#er parts t#ro%g# oil passages %nder press%re from t#e oil p%mp. T#e oil from

t#e p%mp enters t#e oil galleries. rom t#e oil galleries> it flo's to t#e main earings and

cams#aft earings. T#e main earings #a$e oil


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2.11.3 7r%e 7ee :

A some'#at more complete press%riation of l%rication is ac#ie$ed in t#e force


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2.11.4 7'## 7r%e 7ee:

In a f%ll force t#e main earings> rod earings> cams#aft

earings> and t#e complete $al$e mec#anism are l%ricated y oil %nder press%re. In addition> t#e

f%ll force creating an oil

passage from t#e connecting rod earing to t#e piston pin earing. T#is passage not only feeds

t#e piston pin earings %t also pro$ides l%rication for t#e pistons and cylinder 'alls. T#is

system is %sed in $irt%ally all engines t#at are e@%ipped 'it# f%ll

cylinder #ead> etc. Heat generated d%e to com%stion in t#e engine cylinder 'ill e cond%cted to

t#e fins and '#en t#e air flo's o$er t#e fins> #eat 'ill e dissipated to air. T#e amo%nt of #eat

dissipated to air depends %pon 7 9a: Amo%nt of air flo'ing t#ro%g# t#e fins. 9: in s%rface area. I

T#ermal cond%cti$ity of metal %sed for fins.


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A&$nt$ges / Air C#e Sste( ollo'ing are t#e ad$antages of air cooled system7 9a:

Radiatorp%mp is asent #ence t#e system is lig#t. 9: In case of 'ater cooling system t#ere are

lea!ages> %t in t#is case t#ere are no lea!ages. I Coolant and antifreee sol%tions are not

re@%ired. 9d: T#is system can e %sed in cold climates> '#ere if 'ater is %sed it may freee.

Dis$&$nt$ges / Air C#e Sste( 9a: Comparati$ely it is less efficient. 9: It is %sed only in

aero planes and motorcycle engines '#ere t#e engines are e3posed to air directly.

2.12.2 ;$ter C#ing Sste(7

In t#is met#od> cooling 'ater ,ac!ets are pro$ided aro%nd t#e cylinder> cylinder

#ead> $al$e seats etc. T#e 'ater '#en circ%lated t#ro%g# t#e ,ac!ets> it asors #eat of

com%stion. T#is #ot 'ater 'ill t#en e cooling in t#e radiator partially y a fan and partially y

t#e flo' de$eloped y t#e for'ard motion of t#e $e#icle. T#e cooled 'ater is again recirc%lated

t#ro%g# t#e 'ater ,ac!ets

Ter( Si*n Sste(: In t#is system t#e circ%lation of 'ater is d%e to difference in

temperat%re 9i.e. difference in densities: of 'ater. So in t#is system p%mp is not re@%ired %t

'ater is circ%lated eca%se of density difference only.


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,'(* Cir%'#$tin Sste(: In t#is system circ%lation of 'ater is otained y a p%mp. T#is

p%mp is dri$en y means of engine o%tp%t s#aft t#ro%g#


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follo'ing 7 9a: Specific %el Cons%mption. 9: 0ra!e Mean Effecti$e +ress%re. I Specific +o'er

=%tp%t. 9d: Specific eig#t. 9e: E3#a%st Smo!e and =t#er Emissions. T#e partic%lar application

of t#e engine decides t#e relati$e importance of t#ese performance parameters. or E3ample 7

or an aircraft engine specific 'eig#t is more important '#ereas for an ind%strial engine specific

f%el cons%mption is more important. or t#e e$al%ation of an engine performance fe' more

parameters are c#osen and t#e effect of $ario%s operating conditions> design concepts and

modifications on t#ese parameters are st%died. T#e asic performance parameters are t#e

follo'ing 7 9a: +o'er and Mec#anical Efficiency. 9: Mean Effecti$e +ress%re and Tor@%e. I

Specific =%tp%t. 9d: ol%metric Efficiency. 9e: %el #o'e$er> more

t#an t#e p and is called indicated po'er 9ip:. =f t#e po'er de$eloped y t#e engine> i.e. ip>

some po'er is cons%med in o$ercoming t#e friction et'een mo$ing parts> some in t#e process

of ind%cting t#e air and remo$ing t#e prod%cts of com%stion from t#e engine com%stion

c#amer.

Ini%$te ,er: It is t#e po'er de$eloped in t#e cylinder and t#%s> forms t#e asis of

e$al%ation of com%stion efficiency or t#e #eat release in t#e cylinder. #ere> I.+; +mLAN(/

pm ; Mean effecti$e press%re> Nm2> L ; Lengt# of t#e stro!e> m> A ; Area of t#e piston> m2> N

; Rotational speed of t#e engine> rpm 9It is N2 for fo%r stro!e engine:> and ! ; N%mer of

cylinders. T#%s> 'e see t#at for a gi$en engine t#e po'er o%tp%t can e meas%red in terms of

mean effecti$e press%re. T#e difference et'een t#e ip and p is t#e indication of t#e po'er lost


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in t#e mec#anical components of t#e engine 9d%e to friction: and forms t#e asis of mec#anical

efficiencyF '#ic# is defined as follo's 7 Mec#anical efficiency;pip T#e difference et'een ip

and p is called friction po'er 9fp:. p ; ip K p Mec#anical efficiency; .p9pfp:

Me$n E//e%ti&e ,ress're $n Tr +m ; Mean effecti$e press%re> Nm2> Ip ;

Indicated po'er> att> L ; Lengt# of t#e stro!e> m> A ; Area of t#e piston> m2> N ; Rotational

speed of t#e engine> rpm 9It is N2 for fo%r stro!e engine:> and ! ; N%mer of cylinders. If t#e

mean effecti$e press%re is ased on p it is called t#e ra!e mean effecti$e press%re9 +m:> and if

ased on i#p it is called indicated mean effecti$e press%re 9imep:. Similarly> t#e friction meaneffecti$e press%re 9fmep: can e defined as> fmep ; imep D mep

T#e tor@%e is related to mean effecti$e press%re y t#e relation 0.+;2Jnt(/ I.+;+mLAN!(/

2Jnt(/;mep.A.L.9N!(/:O or> T;9mep.A.L.!:2P

T#%s> t#e tor@%e and t#e mean effecti$e press%re are related y t#e engine sie. A large engine

prod%ces more tor@%e for t#e same mean effecti$e press%re. or t#is reason> tor@%e is not t#e

meas%re of t#e aility of an engine to %tilie its displacement for prod%cing po'er from f%el. It is

t#e mean effecti$e press%re '#ic# gi$es an indication of engine displacement %tiliation for t#is

con$ersion. Hig#er t#e mean effecti$e press%re> #ig#er 'ill e t#e po'er de$eloped y t#e

engine for a gi$en displacement. Again 'e see t#at t#e po'er of an engine is dependent on its

sie and speed. T#erefore> it is not possile to compare engines on t#e asis of eit#er po'er or

tor@%e. Mean effecti$e press%re is t#e tr%e indication of t#e relati$e performance of different

engines.

S*e%i/i% O't*'t: Specific o%tp%t of an engine is defined as t#e ra!e po'er 9o%tp%t: per %nit of

piston displacement and is gi$en y> Specific o%tp%t;0.+A.L Constant ; mep Q rpm T#e

specific o%tp%t consists of t'o elements D t#e mep 9force: a$ailale to 'or! and t#e speed 'it#


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UNIT-II 2.


'#ic# it is 'or!ing. T#erefore> for t#e same piston displacement and mep an engine operating

at #ig#er speed 'ill gi$e more o%tp%t. It is clear t#at t#e o%tp%t of an engine can e increased

y increasing eit#er speed or mep. Increasing speed in$ol$es increase in t#e mec#anical stress

of $ario%s engine parts '#ereas increasing mep re@%ires etter #eat release and more load on

engine cylinder.

9#'(etri% E//i%ien%: ol%metric efficiency of an engine is an indication of t#e meas%re of t#e

degree to '#ic# t#e engine fills its s'ept $ol%me. It is defined as t#e ratio of t#e mass of air

ind%cted into t#e engine cylinder d%ring t#e s%ction stro!e to t#e mass of t#e air corresponding to

t#e s'ept $ol%me of t#e engine at atmosp#eric press%re and temperat%re. Alternati$ely> it can e

defined as t#e ratio of t#e act%al $ol%me in#aled d%ring s%ction stro!e meas%red at inta!econditions to t#e s'ept $ol%me of t#e piston. ol%metric efficiency> #$ ; Mass of c#arge

act%ally s%c!ed in Mass of c#arge corresponding to t#e cylinder inta!e T#e amo%nt of air ta!en

inside t#e cylinder is dependent on t#e $ol%metric efficiency of an engine and #ence p%ts a limit

on t#e amo%nt of f%el '#ic# can e efficiently %rned and t#e po'er o%tp%t. or s%perc#arged

engine t#e $ol%metric efficiency #as no meaning as it comes o%t to e more t#an %nity.

7'e#Air R$ti =7>A?: %el


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UNIT-II 2.


;9Act%al %el< Air ratio:9Stoic#iometric f%el


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UNIT-II 2.


Ter($# E//i%ien% $n He$t B$#$n%e: T#ermal efficiency of an engine is defined as t#e ratio

of t#e o%tp%t to t#at of t#e c#emical energy inp%t in t#e form of f%el s%pply. It may e ased on

ra!e or indicated o%tp%t. It is t#e tr%e indication of t#e efficiency 'it# '#ic# t#e c#emical

energy of f%el 9inp%t: is con$erted into mec#anical 'or!. T#ermal efficiency also acco%nts for

com%stion efficiency> i.e.> for t#e fact t#at '#ole of t#e c#emical energy of t#e f%el is not

con$erted into #eat energy d%ring com%stion. 0ra!e t#ermal efficiency ; 0.+mf C$ '#ere>

C$ ; Calorific $al%e of f%el> ,!g> and mf ; Mass of f%el s%pplied> !gsec. T#e energy inp%t to

t#e engine goes o%t in $ario%s forms D a part is in t#e form of ra!e o%tp%t> a part into e3#a%st>

and t#e rest is ta!en y cooling 'ater and t#e l%ricating oil. T#e rea! coolant losses> #eat going to e3#a%st> radiation and ot#er losses.

+reparation of #eat alance s#eet gi$es %s an idea ao%t t#e amo%nt of energy 'asted in $ario%s

parts and allo's %s to t#in! of met#ods to red%ce t#e losses so inc%rred.

E6$'st S(!e $n Oter E(issins: Smo!e and ot#er e3#a%st emissions s%c# as o3ides of

nitrogen> %n%rned #ydrocarons> etc. are n%isance for t#e p%lic en$ironment. it# increasing

emp#asis on air poll%tion control all efforts are eing made to !eep t#em as minim%m as it co%ld

e. Smo!e is an indication of incomplete com%stion. It limits t#e o%tp%t of an engine if air

poll%tion control is t#e consideration.

E(issin 7r($tin Me%$nis(s: =S.I? T#is section disc%sses t#e formation of HC> C=> No3>

C=2> and alde#ydes and e3plains t#e effects of design parameters.

Hr%$rn E(issins:

HC emissions are $ario%s compo%nds of #ydrogen> caron> and sometimes

o3ygen. T#ey are %rned or partially %rned f%el andor oil. HC emissions contri%te to

p#otoc#emical smog> oone> and eye irritation. T#ere are se$eral formation mec#anisms for HC>

and it is con$enient to t#in! ao%t 'ays HC can a$oid com%stion and 'ays HC can e

remo$edF 'e 'ill disc%ss eac# elo'. =f co%rse> most of t#e HC inp%t is f%el> and most of it is

%rned d%ring normal com%stion. Ho'e$er> some HC a$oids o3idation d%ring t#is process.

T#e processes y '#ic# f%el compo%nds escape %rning d%ring normal S.I. com%stion are7


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UNIT-II 2.


1. %el $apor


36/45

UNIT-II 2.


2.13 E(issin 7r($tin in C.I. Engine:

or many years> diesel engines #a$e #ad a rep%tation of gi$ing poor

performance and prod%cing lac! smo!e> an %npleasant odor> and considerale noise. Ho'e$er>

it 'o%ld find it diffic%lt to disting%is# today8 s modern diesel car from its gasoline

co%nterpart. or diesel engines t#e emp#asis is to red%ce emissions of No3 and partic%lates>

'#ere t#ese

emissions are typically #ig#er t#an t#ose from e@%i$alent port in,ected gasoline engines e@%ipped

'it# t#ree diesel engines #a$e #ad a

rep%tation of gi$ing poor performance and prod%cing lac! smo!e> an %npleasant odor> and

considerale noise. Ho'e$er> it 'o%ld find it diffic%lt to disting%is# today8 s modern diesel car

from its gasoline co%nterpart. Concerning C= and HC emissions> diesel engines #a$e an in#erent

ad$antages> t#erefore t#e emp#asis is to red%ce emissions of No3 and partic%lates> '#ere t#ese

emissions are typically #ig#er t#an t#ose from e@%i$alent port in,ected gasoline engines e@%ipped

'it# t#ree Indicated

+o'er> rictional +o'er> 0ra!e T#ermal Efficiency> Indicated T#ermal Efficiency> Mec#anical

Efficiency> Relati$e Efficiency> ol%metric Efficiency> 0ra!e Specific %el Cons%mption>

Indicated Specific %el Cons%mption> Indicated mean effecti$e press%re> 0ra!e mean effecti$e

press%re.


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UNIT-II 2.


2.15 S$(*#e *r#e(s:

1. ollo'ing data relates to & cylinder> single stro!e petrol engine. A ratio y 'eig#t 1(71.

Calorific $al%e of t#e f%el; &42// ,!g> mec#anical efficiency;-2V.Air standard

efficiency;42V> relati$e efficiency;)/V> $ol%metric efficiency;)-V> L*;1.24> s%ction

condition;1 ar>24/C. Speed;2&// rpm and po'er at ra!es;)2!'. Calc%late

1. Compression ratio

2. Indicated T#ermal Efficiency

". 0ra!e specific f%el cons%mption

&. 0ore and Stro!e.

2. A si3 cylinder> & stro!e SI engine #a$ing a piston displacement of )//cm" per cylinder

de$eloped )-' at "2// rpm and cons%med 2) !g of petrol per #o%r. T#e calorific $al%e of t#e

f%el is &&MW!g. Estimate 1.T#e $ol%metric efficiency of t#e engine if t#e air "2oC. 2. 0ra!e t#ermal efficiency and ra!e tor@%e. or air R;/.2-)

W!g.


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UNIT-II 2.


2.1" S#&e ,r#e(s:

1. A trial carried o%t in a fo%r stro!e single cylinder gas engine ga$e t#e follo'ing res%lts.

Cylinder dia;"//mm> Engine stro!e;4//mm> Clearance $ol%me;()4/cc> E3plosions per

min%te;1// Net 'or! load on t#e ra!e;1/!g 0ra!e dia;1.4m Rope

dia;24mm> Speed of t#e engine;2&/rpm> Bas %sed;"/ > Calorific $al%e of gas;2/414

W . *etermine compression ratio>mec#anical efficiency>indicated t#ermal efficiency>air

standard efficiency>relati$e efficiency>ass%me

BIEN *ATA7

;2&./"V

9&:.Relati$e Efficiency 9Xrel:7 speed of t#e engine is 24//rpm> 0.+ ; 2/> Air inta!e orifice diameter

; "4mm>+ress%re across t#e orifice ; 1&/mm of 'ater coefficient of disc#arge of orifice ; /.(>

piston diameter ; 14/mm> stro!e lengt# ; 1//mm> *ensity of t#e f%el ; /.-4gmcc > r;(.4> C$ of

f%el ; &2///Wg> 0arometric press%re ; )(/mm of Hg > Room temperat%re ; 2&oc

*etermine7

9i: ol%metric efficiency on t#e air asis alone

9ii: Air


42/45

9iii: T#e ra!e mean effecti$e press%re

9i$: T#e relati$e efficiency on t#e ra!e t#ermal efficiency

S#'tin:

1/."&m of 'ater ; 1/1."24Nm2

+ress%re #ead

+o ; /.1&m of 'ater

+o ; 1")2Nm2

*ensity of gas 9Y: ; +RT

Y ; 1.1--)gm"

+ress%re #ead 9#:

6air ;

# ; 11).(44)m

; /./2))& m"sec

No. of. S%ction stro!es per second

Air cons%mptions per stro!e

; /.//1""2m"

Stro!e $ol%me 9s: ; m"

ol%metric efficiency 9X$ol: ;

X$ol ; )4."-2V


43/45

$ol%me of air cons%med air ; 6air ; /./2))&m"sec

; /./2))& m

"

#rMass of air cons%med 9ma: ; ; .-(&

; 11-.)1g#r

%el cons%mption ; ///cc#r

Mass of t#e f%el cons%med 9mf: ; ///Q/.-4 ; ).(4g#r

Air f%el ratio

0ra!e po'er 90.+: ; 2/ ; +m Q l Q a Q n Q !

+m

; 4&".2&Nm2

Air standard efficiency 9Xair: ;

;

; 42.)/"V

0ra!e t#ermal efficiency 9X0T: ; 22.&V

Relati$e efficiency on ra!e t#ermal efficiency asis 9X rel: ; X0T Xair

; /.22&//.42)/"

Xrel ; &2.42V

2.1) T;O MAR@ UNI9ERSIT UESTIONS:

1. Classify IC engine according to cycle of l%rication system and field of application.

Types of l%rication system

2. List t#e $ario%s components of IC engines.


44/45

". Name t#e asic t#ermodynamic cycles of t#e t'o types of internal com%stion reciprocating

engines.

&. Mention t#e important re@%ites of liner material.

4. State t#e p%rpose of pro$iding piston in IC engines.

(. *efine t#e terms as applied to reciprocating I.C. engines ?Mean effecti$e press%re? and

Compression ratio?.

). #at is meant y #ig#est %sef%l compression ratioZ

-. #at are t#e types of piston ringsZ

. #at is t#e %se of connecting rodZ

1/. #at is t#e %se of fly'#eelZ

2.1+ UNI9ERSIT ESSA UESTIONS

1. E3plain f%ll press%re l%rication system I.C Engine. 91(:


45/45

2. E3plain t#e 'ater cooling system in I.C Engine. 91(:

". E3plain t#e 2 types of Ignition system In 4.1 Engine. 91(:

&. *ra' and e3plain t#e $al$e timing diagram of & stro!es *iesel Engine. 91(:

4. *ra' and e3plain t#e port timing diagram of 2stro!e +etrol Engine. 91(:

(. E3plain 'it# neat s!etc# t#e e3#a%st gas analysis. 91(:

). T#e follo'ing res%lts refer to a test on a petrol engine Indicated po'er ; "/ '> 0ra!e po'er

; 2( '> Engine speed ; 1/// rpm %el ra!e po'er #o%r ; /."4 !g Calorific $al%e of f%el

; &"//!,!g .Calc%late t#e indicated T#ermal efficiency> t#e ra!e T#ermal efficiency and

Mec#anical efficiency 91(:

-. A fo%r cylinder 2 stro!e cycle petrol engine de$elops 2".4 !' ra!e po'er at 24// rpm. T#e

mean effecti$e press%re on eac# piston in -. 4 ar and mec#anical efficiency in -4V Calc%late

t#e diameter and stro!e of eac# cylinder ass%ming t#e lengt# of stro!e e@%al to 1.4 times t#e

diameter of cylinder. 91(:

. T#e follo'ing data to a partic%lar t'in cylinder t'o stro!e diesel engine. 0ore 14 cm stro!e.

2/ cm. speed &// rpm. Indicated mean effecti$e press%re & ar> dead 'eig#t on t#e ra!e

dr%m (4/ N. spring alance reading 24 N *iameter of t#e ra!e dr%m 1 m .%el cons%mption

/./)4 !gmin and calorific $al%e of t#e f%el is &&4// W!g. *etermine 1. Indicated +o'er 2.

0ra!e +o'er ". Mec#anical efficiency &. Indicated t#ermal efficiency and 4. 0ra!e t#ermal

efficiency 91(:

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