JJ 507 – THERMODYNAMIC 2 - unit 3.pptx

8/19/2019 JJ 507 – THERMODYNAMIC 2 - unit 3.pptx

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UNI+ ,

IN+ERNAL- MBU/+I N

EN0INE



,.1 In erna* -$2'u% !$n

Eng!ne Perf$r2ancePara2e erInd!ca ed p$3erInd!ca ed 2ean e4ec !5e pre%%ure

(!2ep"Bra)e p$3erFr!c !$na* p$3erEng!ne $r6ueP!% $n 5e*$c! y/pec!7c fue* c$n%u2p !$nMec8an!ca* e9c!ency+8er2a* e9c!ency

$*u2e r!c e9c!ency



,.1.1 Ind!ca ed P$3er and Ind!ca ed MeanE4ec !5e Pre%%ure (!2ep"

The power produced by a ! "er a# co$bu%"!oe &! e depe d% o "he e'ec"!(e e%% o) co$pre%%!o *co$bu%"!o a d e+pa %!o proce%%e% ! "he cy#! der,

Thu%* whe "e%"! & a e &! e per)or$a ce* !" !%ece%%ary "o $ea%ure "he power wh!ch !% ac"ua##y

produced ! %!de "he cy#! der,

Th!% !% do e u%! & a de(!ce - ow a% a ! d!ca"or a d"he power $ea%ured !% ca##ed "he ! d!ca"ed power,

The purpo%e o) a y ! d!ca"or !% "o reproduce "here#a"!o %h!p be"wee "he pre%%ure a d "he (o#u$e o)"he wor-! & .u!d a% "he p!%"o $o(e% "hrou&h aco$p#e"e cyc#e ! "he cy#! der,



Figure 3.1 Indicator Diagram



Indicates mean effective pressure,

i

i

i L sA

P =

Where, s = stiffness of indicator spring, Nm 2/mm Ai = area of indicator diagram, mm 2

Li = length of the diagram, mm

(N/m 2

Indicated po!er of engine,

i.p = P i LAN’n ("#

Where, L = length of the piston stro"e, m$ = cross%sectional area of the piston, m 2

n = no. of c&linder



'2(1) N N =

')

N N =

For a * stro"e engine,

For a 2 stro"e engine ,

N = speed of rotation of cran"shaft, rev/min



E;a2p*e ,.1

I a "e%" o a / %"ro-e )our cy#! derau"o$ob!#e e &! e a ! d!ca"ord!a&ra$ !% "a-e a d )ou d "o ha(earea o) 170 $$ 2 a d #e &"h o) 2 $$,

The %pr! & ! "he ! d!ca"or ha% a%"!' e%% o) 0,3 bar4$$, De"er$! e "he! d!ca"ed $ea e'ec"!(e pre%%ure a d! d!ca"ed power o) "he e &! e a" acra -%ha)" %peed o) 200 re(4$! !)"he cy#! der% ha(e a bore o) 0 $$a d "he p!%"o %"ro-e !% 605 $$,



o#u"!o 8Da"a8/ %"ro-e e &! e* 9 /A! 9 170 $$ 2 * : ! 9 2 $$* % 9 0,3 bar4$$

N 9 200 re(4$!d 9 0 $$ 9 0,0 $* :9 605 $$ 9 0,605 $

i

ii

L sA

P =

2+ N/m1,-.3+

-.3+ ar 2

.0('-

=

=

=



2322

13.+*.(

*m x

d −

===π π

ond per N

N sec-.2'1232

'2(1

) ===

$rea of piston ($

For a * stro"e engine,

Indicated po!er of engine, i.p = P i LAN’n = (-.3+ 1 + ( .1 + (+. 3 1 %3 (2'.- (* = *1* #

= 41.4 kW



,.1.< Bra)e P$3er and Eng!ne+$r6ue

The power $ea%ured a" "he ou"pu" %ha)" o)"he e &! e !% - ow a% bra-e power, Thebra-e power !% $ea%ured u%! & a bra-e ordy a$o$e"er wh!ch pro(!de% a re%!%"a ce "o

e &! e by oppo%! & "he ro"a"!o o) "he %ha)",or ue is given &

= #4 (Nm !here, # = net load 4 = radius from the

a is rotationhe ra"e po!er is the

given &

'

N2π ("# !here, N = enginespeed

.p =



,6,2,6;ra-e $ea e'ec"!(e pre%%ure<b$ep=

M i

b

P P

imepbmep

η ==

hrefore,

.p = P b LAN’nIf,

n LAN

pb P b )

.=5o,



E;a2p*e ,.<

A )our cy#! der pe"ro# e &! e ha%%peed ra"e 2 00 re(4$! a d !" !%"e%"ed a" "h!% %peed a&a! %" a bra-ewh!ch ha% a "or>ue ar$ o) 0, 51 $,

The e" bra-e #oad !% 655 N, Ca#cu#a"e"he e &! e "or>ue a d bra-e power,



o#u"!o 8

' N2π

'

2(2 (++.2π

.p =

=

= 1'1 + Nm/s = 16.2 kNm/s = 16.2 kW

= #4 = 1++( .3+' = 55.2 Nm



,.1., Fr!c !$na* P$3er and Mec8an!ca* E9c!ency

he difference et!een the ip and the p is the friction po!er (fp ,and is that po!er re uired to overcome the frictional resistance ofthe engine part,

Frictional po!er, fp = ip 6 p

7echanical efficienc&,ipbp

M =η

he mechanical efficienc& of an internal com ustion engine ist&picall& et!een 8 and 0 8.



E;a2p*e ,.,

De"er$! e "he )r!c"!o power a d$echa !ca# e?c!e cy o) pe"ro# e &! eha% "he ! d!ca"ed power /6,/ -@ a d"he bra-e power 5, -@,Solution:

ip = *1.*"#

p = 3+.

"#fp = ip 6 p = *1.* 6 3+. = 5.6

kW



ip

bp M

=η

86.5%=

=

*.*1/.3+



,.1.= P!% $n e*$c! y

he mean piston speed can e determined & dividing thedistance moved & the piston in one complete cran"shaftrevolution & the time ta"en to travel that distance.

7ean pistonspeed '

2 LN =

!here, 9 = stro"e N = engine speed

(m/s



E;a2p*e ,.,

De"er$! e "he $ea p!%"o %peed )or e &! e

ha% "he %"ro-e #e &"h o) 605 $$ a d e &! e%peed o) 200 re(4$! ,

'2 LN

=

11.2m/s=

=

'

32(1 +.(2

5olution:

7ean pistonspeed



,.1.> +8er2a* E9c!ency and /pec!7c Fue*-$n%u2p !$n

suppliedenerg&bp

BT =η

( LCV mbp

f BT

=η

he po!er output of the engine is o tained from the chemical

energ& of the fuel supplied. he overall efficienc& of theengine is given & the ra"e thermal efficienc&,

;ra"e thermal efficienc&,

suppliedenerg&ip IT

=η

( LCV mip

f IT

=η

Indicated thermalefficienc&,



#here, f m = fuel mass flo! rate

9< = lo! calorific value of the fuel

herefore

M IT

BT

ipbp

η η

η ==∴



he specific fuel consumption (sfc is the mass flo! rate offuel consumed per unit po!er output, and is a criterion ofeconomical po!er production,

5pecific fuel consumption,

bp

m sfc f =

("g/"#h



E;a2p*e ,.>

$ four%c&linder petrol engine has a lo!er calorific value, 9< of**2 ">/"g and mass flo! rate of fuel of . 13-' "g/s. It hasindicated po!er of 1 .0 "# and ra"e po!er of 1'.2 "#.<alculate for the ra"e thermal efficienc&, indicated thermalefficienc& and the specific fuel consumption.



o#u"!o 8

( LCV m bp f

BT =η

26.7%=

=

**2(13-'.2.1'

( LCV mip

f IT =η

31%=

=

**2(13-'.0.1



bp

m sfc

f =

kWhkg x

kWskg x

/3 +.3'(1*0.

/1*0.2.1'

13-'.

+

+

==

=

=

−

−



,.1.? A!r@fue* Ra !$

The co "ro# o) "he a!r4)ue# ra"!o !% (ery!$por"a " w!"h re&ard "o e &! e per)or$a ce,

The a!r4)ue# ra"!o ! a e &! e "e%" !%de"er$! ed )ro$*

fuelof rateflo!mass

air of rateflo!mass=

f

o

m

m=

$ir/fuel

ratio,



,.1. $*u2e r!c E9c!ency

he po!er output of an I< engine depends directl& upon theamount of charge !hich can e induced into the c&linder. For I<engine, the volumetric efficienc& is the ratio of the volume of airinduced, measured at the free air conditions to the s!ept volume ofthe c&linder,

S

oV

V

V ..

=η s

o

mm

=

oV

.

sV .

om

sm

#here, = volume dra!n in per un

= s!ept volume of engine = actual mass of air

= mass of air that !ould fill the

s!ept volume at atmosphericcondition



E;a2p*e ,.>

$ *%stro"e four c&linder petrol engine !as tested in an

atmosphere at 1. 13 ar and 1+ <. he cran"shaft speed of2 rev/min if the c&linders have a ore of +- mm and the piston stro"e is 0 mm. he air%fuel ratio for petrol can eta"en 1*.+/1 and mass flo! rate of fuel is . 13-' "g/s.?stimate the volumetric efficienc& of the engine.

f

o

mm

=ratiofuel$ir

skg

m

m

o

o

/100+.

13-'.(+.1*13-'.

1*.+

=

=

=

/$*u !$n:



olume dra!n in per unit time,

sm

P

!T mV o

o

/1'3.113.1

2(2 -.(100+.

.

3

2

=

=

=

5!ept volume of engine ,

sm

ALnN V s

/21*.

'(2(*2(*(0.(+-.(

'(2

.

3

2

=

=

=

π



S

o

V V

V

.

.=η

76%=

=

(21*.(

(1'3.(



Distribution kJ/s %

?nerg& supplied @ 1

;ra"e po!er @ 1 @1/@?nerg& to enginecooling !ater

@2 @2/@

?nerg& to e haust gas @ 3 @3/@

?nerg& to surroundings @ * = @ 6 (@1 A @2 A @3 @*/@

he energ& distri ution can e summariBing in energ& alancesheet as elo!



( LCV m f

f m

4ate of heat energ&supplied =

9< = net calorific value of fuel,">/"g

= fuel massflo! rate,"g/s

( "i"o p"" # # cm −

"m

p"c

"o#

"i#

4ate of energ& reCected to engine cooling!ater =

= cooling !ater flo! rate, "g/s

= specific heat of cooling !ater,">/"g = cooling !ater outlet temperature,

= cooling !ater inlet temperature,



?nerg& to calorimeter cooling!ater = c"i"o p""c # # cm ( −

#here c indicates the calorimeter !ater flo! rate and temperature

( $ go pg g # # cm −?nerg& in e haust gases leaving the calorimeter per

second =

otal heat energ& in e haust gases = ?nerg& to calorimeter cooling !ater A ?nerg& in e haust gas leaving the calorimeter

JJ 507 – THERMODYNAMIC 2 - unit 3.pptx

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