Performance of Internal Combustion Engine

7/21/2019 Performance of Internal Combustion Engine

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Performance of InternalCombustion Engine

By

Kumar Avinash

Thermal Engineering


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INTRODCTION

!ith a gro"ing #eman# for trans%ortation ICengines have gaine# lot of im%ortancein automobile in#ustry& It is therefore

necessary to %ro#uce e'cient an# economicalengines& !hile #evelo%ing an IC engine it isre(uire# to ta)e in consi#eration all the%arameters a*ecting the engines #esign an#

%erformance hence it becomes necessary tocon#uct tests on the engine an# #eterminethe measures to be ta)en to im%rove theengines %erformance&


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Performance of an Engine is an in#icationof the #egree of success "ith "hich it is#oing its assigne# "or) i&e& the conversionof chemical energy containe# in the fuelinto the useful mechanical "or)&

The #egree of success is measure# on thebasis of the follo"ing %arameters +

,a- .%eci/c fuel consum%tion

,b- Bra)e mean e*ective %ressure

,c- .%eci/c %o"er out%ut ,#- .%eci/c "eight

,e- E0haust smo)e an# otheremission


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In evaluation of engine %erformance certain

basic %arameters are chosen an# stu#ie#&

The basic %erformance %arameters are + ,a-Po"er an# mechanical e'ciency 1

,b- 2ean e*ective %ressure an# tor(ue 1

,c- .%eci/c out%ut 1

,#- 3olumetric e'ciency 1

,e- 4uel5Air ratio 1

,f- .%eci/c fuel consum%tion

,g- Thermal e'ciency an# heat balance 1

,h-E0haust smo)e an# other emissions 1,i- .%eci/c "eight&


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Po"er an# 2echanical e'ciency

An IC engine is use# to %ro#uce mechanical

%o"er by combustion of fuel& Po"er is referre# toas the rate at "hich "or) is #one& Po"er ise0%resse# as the %ro#uct of force an# linearvelocity or %ro#uct of tor(ue an# angular velocity&In or#er to measure %o"er one nee#s to measure

tor(ue or force an# s%ee#& The force or tor(ue ismeasure# by Dynamometer an# s%ee#by Tachometer& The %o"er #evelo%e# by anengine an# measure# at the out%ut shaft is calle#

the bra)e %o"er ,b%- an# is given bybp 678 NT9:;

"here< Tis tor(ue in N5m an# Nis the rotational s%ee# in& revolutions %er minute&


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The total %o"er #evelo%e# bycombustion of fuel in the combustion

chamber is< ho"ever< more than thebpan# is calle# in#icate# %o"er ,ip-&Of the %o"er #evelo%e# by the

engine< i&e& ip< some %o"er isconsume# in overcoming the frictionbet"een moving %arts< some in the%rocess of in#ucting the air an#removing the %ro#ucts of combustionfrom the engine combustionchamber&


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BASIC MEASUREMENTS

4ollo"ing measurements are to be #one to

evaluate the %erformance of an engine +a- .%ee#

b- 4uel consum%tionc- Air consum%tion

#- .mo)e #ensity

e- Bra)e horse5%o"er

f- In#icate# horse %o"er an# friction horse %o"er

g- =eat going to cooling "ater

h- =eat going to e0haust

i- E0haust gas analysis&


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.%ee#

A "i#e variety of s%ee# measuring #evices areavailable in the mar)et& They range from a mechanicaltachometer to #igital an# triggere# electrical

tachometers&

A mechanical tachometer or an electrical tachometercan also be use# for measuring the s%ee#&

The electrical tachometer has a three5%hase

%ermanent5magnet alternator to "hich a voltmeter isattache#& The out%ut of the alternator is a linear

function of the s%ee# an# is #irectly in#icate# on thevoltmeter #ial& Both electrical an# mechanical ty%es oftachometers are a*ecte# by the tem%erature variations

an# are not very accurate&


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4uel Consum%tion

4uel consum%tion is measure# in t"o "ays +

a-3olumetric ty%e +By #etermining the volume >o" in agiven time interval an# multi%lying it by the s%eci/c

gravity of the fuel "hich shoul# be measure# occasionallyto get an accurate value& 3olumetric ty%e >o"meterinclu#es Burette metho#< Automatic Burrette >o"meteran# Turbine >o"meter &

b- ?ravimetric ty%e +By measuring the time re(uire# for

consum%tion of a given mass of fuel& There are threety%es of gravimetric ty%e systems "hich are commerciallyavailable inclu#e Actual "eighing of fuel consume#< 4ourOri/ce 4lo"meter< etc&


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2easurements of Air5Consum%tion

In IC engines


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2easurement of E0haust.mo)e

2etho#s are +

a- =artri#ge smo)emeter + "or)s on the light e0tinction%rinci%le&

b- Bosch smo)emeter + a /0e# (uantity of e0haust gas is

%asse# through a /0e# /lter %a%er an# the #ensity ofthe smo)e stains on the %a%er are evaluate# o%tically&

c- 3on Bran# smo)emeter + a /lter ta%e is continuouslymove# at a uniform rate to "hich the e0haust from

the engine is fe#& The smo)e stains #evelo%e# on the/lter %a%er are sense# by a recor#ing hea#& Thesignal obtaine# from the recor#ing hea# is calibrate#to give smo)e #ensity&


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Instruments to measure E0haust Emission+

a)Flame Ionization Detector (FID) A hy#rogen5air >ame contains a negligible amount of

ions& =o"ever< if even trace amounts of an organiccom%oun# such as =C are intro#uce# into the >ameects the limiting in>uence of the air5fuel ratioan# of the (uality of combustion&.imilarly< there is

a slight curvature at light loa#s& This is %erha%s#ue to #i'culty in inecting accurately an#consistently very small (uantities of fuel %er cycle&


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More Tet

A%%licable only to multicylin#er engines&

In this test< the engine is /rst run at there(uire# s%ee# an# the out%ut is measure#&

Then< one cylin#er is cut out by short circuitingthe s%ar) %lug or by #isconnecting the inectoras the case may be& n#er this con#ition allother cylin#ers motor this cut5out cylin#er&The out%ut is measure# by )ee%ing the s%ee#constant at its original value&

The #i*erence in the out%uts is a measure ofthe in#icate# horse %o"er of the cut5outcylin#er&


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Thus< for each cylin#er the ipis obtaine# an# is a##e#together to /n# the total ipof the engine&

ipn6bpn Jfp.

ip for ,n L- cylin#ers is given by ipnM L6 bpnM LJ fp.

.ince< the engine is running at the same s%ee# it is(uite reasonable to assume that fhp remains

constant& 4rom E(s& ,&L- an# ,&L-< "e see that the ihpof

the nthcylin#er is given by

,ip-nth6 bpn bpnM L&

an# the total ipof the engine is


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Motorin# Tet

In the motoring test< the engine is /rst run u% to the#esire# s%ee# by its o"n %o"er an# allo"e# to remain at

the given s%ee# an# loa# con#itions for some time so

that oil< "ater< an# engine com%onent tem%eraturesreach stable con#itions&

The %o"er of the engine #uring this %erio# is absorbe#

by a s"inging /el# ty%e electric #ynamometer< "hich ismost suitable for this test&

The fuel su%%ly is then cut5o* an# by suitable electric5s"itching #evices the #ynamometer is converte# to run

as a motor to #rive for motor the engine at the sames%ee# at "hich it "as %reviously running&

The %o"er su%%ly to the motor is measure# "hich is ameasure of the fhpof the engine& During the motoringtest the "ater su%%ly is also cut5o* so that the actual

o%erating tem%eratures are maintaine#&


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Comment on Metho- o Meaurin#

fpa-The !illan line metho# an# 2orse

tests are very chea% an# easy tocon#uct&

)2otoring test gives a very goo# insightinto the various causes of losses an# isa much more %o"erful tool&

)2otoring metho# usually gives a highervalue for fhpas com%are# to that givenby the !illians line metho#&


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B,$'B/ ,$SS

Blo"by is the esca%e of unburne# air5fuel mi0ture an# burne# gases fromthe combustion chamber< %ast the

%iston rings< an# into the cran)5case&=igh blo"by is (uite harmful in that itresults in higher ring tem%eratures

an# contamination of lubricating oil&


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&ERF$RMANCE $F SIEN"INES The %erformance of an engine is

usually stu#ie# by heat balance5sheet&The main com%onents of the heatbalance are +

=eat e(uivalent to the e*ective ,bra)e-"or) of the engine

Documents

Performance of Internal Combustion Engine