jj 507 – thermodynamic 2 - unit 3.pptx
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8/19/2019 JJ 507 – THERMODYNAMIC 2 - unit 3.pptx
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UNI+ ,
IN+ERNAL- MBU/+I N
EN0INE
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,.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
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,.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,
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Figure 3.1 Indicator Diagram
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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
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'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
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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 $$,
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o#u"!o 8Da"a8/ %"ro-e e &! e* 9 /A! 9 170 $$ 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('-
=
=
=
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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
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,.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 =
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,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,
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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 $,
The e" bra-e #oad !% 655 N, Ca#cu#a"e"he e &! e "or>ue a d bra-e power,
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o#u"!o 8
' N2π
'
2(2 (++.2π
.p =
=
= 1'1 + Nm/s = 16.2 kNm/s = 16.2 kW
= #4 = 1++( .3+' = 55.2 Nm
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,.1., Fr!c !$na* P$3er and Mec8an!ca* E9c!ency
he difference et!een the ip and the p is the friction po!er (fp ,and is that po!er re uired to overcome the frictional resistance ofthe engine part,
Frictional po!er, fp = ip 6 p
7echanical efficienc&,ipbp
M =η
he mechanical efficienc& of an internal com ustion engine ist&picall& et!een 8 and 0 8.
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E;a2p*e ,.,
De"er$! 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
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ip
bp M
=η
86.5%=
=
*.*1/.3+
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,.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
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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$! ,
'2 LN
=
11.2m/s=
=
'
32(1 +.(2
5olution:
7ean pistonspeed
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,.1.> +8er2a* E9c!ency and /pec!7c Fue*-$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&,
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#here, f m = fuel mass flo! rate
9< = lo! calorific value of the fuel
herefore
M IT
BT
ipbp
η η
η ==∴
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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
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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.
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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
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bp
m sfc
f =
kWhkg x
kWskg x
/3 +.3'(1*0.
/1*0.2.1'
13-'.
+
+
==
=
=
−
−
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,.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,
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,.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
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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:
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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
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S
o
V V
V
.
.=η
76%=
=
(21*.(
(1'3.(
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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!
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( 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,
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?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