Fuel Injection system IITD

8/18/2019 Fuel Injection system IITD

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Fuel Injection Systems for CI Engines

P M V Subbarao

Professor

Mechanical Engineering Department

Methods to Facilitate High

Compression Ratio ….


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Coal dust injection system of Rudolph Diesel. AIR

INJ ECTION

(After .!. patent No. "#$%& of '%".)

Compressed air tan* A

+opper , -Comustion chamer , C

Rotary /al/e, D

Injection /al/e, E

Orifice, 0


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Type of 0uel 1s Comustion !trate2y

3 Occurrence of +eat Addition in !I En2ine , A Child Care

E/ent.

3 +i2hly /olatile 4ith +i2h self I2nition Temperature, !par*

I2nition. I2nition after thorou2h mi5in2 of air and fuel.

3 Occurrence of +eat Addition in CI En2ine, A Teen Care

E/ent.

36ess 1olatile 4ith lo4 self I2nition Temperature,Compression I2nition7 Almost simultaneous mi5in2 8

I2nition.


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Colour Coded E/olution of Diesel !pray


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Onset of The Ine/itale Dan2er


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The Comple5 Nature of 9oun2 Teen


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!imultaneous Occurrence of :ultiple ;rocess in CI En2ines

-10

Start of

injection

End of

injecction


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!chematic of a diesel spray 8 Transport ;rocess


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E/ents in CI Comustion


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0uel Injection !ystem for CI En2ines

3 The fuel is to e introduced into the cylinder of a diesel en2ine

throu2h a no


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Ecolo2ical A4areness , European !tandards


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De/elopment of Injection ;ressure 8 Injection

!ystem in CI En2ines


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Common Rail Diesel Injection !ystem

The Common Rail Diesel Injection !ystem deli/ers a more controlled

?uantity of atomised fuel7 4hich leads to etter fuel economyB a

reduction in e5haust emissionsB and a si2nificant decrease in en2inenoise durin o eration.


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+istory of CRDI

3 The common rail system prototype 4as de/eloped in the

'&=s y Roert +uer of !4it


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Electronically Controlled CRDI


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Common rail diesel injection system

3 In the Common Rail system7 an accumulator7 or rail7 is used

to create a common reser/oir of fuel under a consistent

controlled pressure that is separate from the fuel injection

points.

3 A hi2h@pressure pump increases the fuel pressure in theaccumulator up to '7&== ar .

3 The pressure is set y the en2ine control unit and is

independent of the en2ine speed and ?uantity of fuel ein2

injected into any of the cylinders.3 The fuel is then transferred throu2h ri2id pipes to the fuel

injectors7 4hich inject the correct amount of fuel into the

comustion chamers.


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Injectors for CRDI

3 The injectors used in Common Rail systems are tri22ered

e5ternally y an Electronic Diesel Control7 (EDC) unit.

3 EDC controls all the en2ine injection parameters includin2 the

pressure in the fuel rail and the timin2 and duration of injection.

3Diesel fuel injectors used in Common Rail injection systemsoperate differently to con/entional fuel injectors used in the jer*

pump system.

3 !ome common rail injectors are controlled y a ma2netic

solenoid on the injector.

3 +ydraulic force from the pressure in the system is used to open

and close the injector7 ut the a/ailale pressure is controlled y

the solenoid tri22ered y the Electronic Diesel Control unit.


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3 !ome injectors use ;ie


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The Desi2n Al2orithm to 0acilitate 0luid Dynamics

3 The asic concept of the desi2n model is as follo4s.

3 The fuel injected into a comustion chamer is di/ided into

many


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0luid Dynamics 0actors

eometric 0eatures


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!pray de/elopment

3 After fuel is injected into the cylinder7 spray rea*@up

ta*es place in fe4 cran*shaft an2les follo4ed y 4all

impin2ement.

3 In these sta2es7 the mo/ement of the fuel jet follo4s

different la4s.

3 -efore rea*@up7 the jet follo4s the ener2y conser/ation

la4 and the intial /elocity of jet is as follo4s,


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Diesel fuel injection no


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Actuation of Injector No


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:ass flo4 rate throu2h No


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0uel E5itin2 into +i2h ;ressure8 Temperature Air

En/iroment , An une5plored 0luid :echanics


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Coefficient of Dischar2e

Nuric*Hs Numer7 K

$'

'

p p

p p K v

−

−=

pv is the vapor pressure of the fuel.


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Optimal Desi2n of No


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!pray 0ormation

3 !pray formation is e5plained as -rea*up :echanism7

descried as,

3 !tretchin2 of fuel li2ament into sheets or streams.

3 Appearance of ripples and protuerances.

3 0ormation of small li2aments or holes in sheets.

3 Collapse of li2aments or holes in sheets.3 0urther rea*up due to /iration of droplets.

3 A22lomeration or sheddin2 from lar2e drops.

3 The flo4 parameters of a jet,

3 Jet Reynolds numer

3 Jet 4eer numer

3 Ohnesor2e numer


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!pray !tructure


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Distriution of Droplets in A !pray


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here

σ is the li?uid surface tension7µ6 is the li?uid /iscosity7 ρ

A

is the air density7

ρ 6 is the li?uid density7∆ p67 is the injection pressure differential across the no


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;ost -rea*@up inematics

3 After rea*@up7 the fuel jet eha/es as a 2as jet and follo4s

the moment conser/ation la4.

3 jet centreline (um ) is

Accordin2 to the cylindrical free turulent jet theory, the /elocity

distriution at the jet cross@section is


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4here u is the velocity of fuel reaching the point r! ").

ce is the entrainment factor.

The spray an2le θ

The /elocity of the fuel


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;enetration of 0uel !pray

3 The spray penetration len2th and spray penetration rate from a

fuel injector are the parameters used to jud2e fuel spray performance.

3 The merits of hi2h or lo4 penetration lar2ely depend on en2ine

desi2n and 2eometry.

3 !horter spray penetration may e of an ad/anta2e 4here itreduces fuel impin2ement7 ut in lar2er en2ines may inhiit

ma5imum air utilisation.


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Influence of Injection ;ressure on !pray ;enetration

6en2th , +! Diesel

Infl ence of Amient ;ress re on !pra ;enetration


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Influence of Amient ;ressure on !pray ;enetration

6en2th , +! Diesel


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:odel to Desi2n a !pray


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!OI , ''o -TDC


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Impin2ement of !pray

3 After the fuel jet has impin2ed the opposite chamer 4all7

the mo/ement of the 4all jet is complicated.

3 :any e5perimental formulae ha/e een su22ested in the

desi2n methodolo2ies.

3 One such formulae used to calculate the /elocity of the


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!pray 1elocity Distriution in A T4o +ole No


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!pray 1elocity Distriution in A T4o +ole No


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Air entrainment and mi5in2

3 The rate of air entrainment into each


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f p g

lo4 airfuel ratios.

3 The relationship 2i/en ao/e also impro/es the predicti/e

aility of the model for transient operatin2 conditions7 for

4hich the airfuel ratio is lo4 and the fresh air in the

cylinder may e consumed y entrainment of fuel


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Idealized spray vaporization

3 The spray is di/ided into an initial KcoolL and KhotK


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The e/aporation in forced con/ection

3 The e/aporation constant in forced con/ection

{ }GM'".== Re$>&.=' Sc+= β β

( ) (c

%

p f += 'ln

%=

ρ β

here7 * is the thermal conducti/ity of the 2as7

C p is the specific heat of the gas!

ρ f is the density of the fuel and (the transfer num#er


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I2nition Delay

3 The sum of times re?uired for su process.

3 The most 4idely reported correlation relatin2 the i2nition

delay to the amient 2as condition is 2i/en y the relation

4here P is the i2nition delay7 ;2 and T2 are the amient 2as mean

pressure and temperature efore autoi2nition ta*es place7

A7 - and n are e5perimental constants.


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Arhenius@type e?uation for I2nition Delay

3 An Arhenius type e?uation for I2nition delay is,

×= −

−

−

$ p p g

ref

cyl id &===e5p'==.#

=#.'

".$

G φ τ

=

$ pcyl

pid &===e5p'% $λ τ

λ p ,;remi5ed air fuel ratio.


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!ymptoms to e !ensed to ;redict Auto I2nition


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Effect of as Temperature on I2nition Delay

ff f i l i i i l


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Effect of E?ui/alence Ratio on I2nition Delay

The flammaility limits /ersus the numer of caron


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The flammaility limits /ersus the numer of caron

atoms in al*anes



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!ystem in CI En2ines

0 l I j i !


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0uel Injection !ystem

3 The fuel is to e introduced into the cylinder of a diesel en2ine

throu2h a no


61/72

p

Types of CI En2ine Injection !ystems


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Types of CI En2ine Injection !ystems

3 0uel@Injection !ystems

3 nit Injector !ystem (I!) !in2le@Cylinder CI En2ine.

3 nit ;ump !ystem (;!) :ulti@cylinder CI En2ine.

3 Common Rail Injection !ystem (CR!) :ulti@cylinder CI

En2ine.

3 The nit Injector !ystem (I!) and the nit ;ump !ystem (;!)

are amon2 the most si2nificant inno/ations in this field.

3 They inject precisely the ri2ht amount of fuel indi/idually into

each cylinder7 at /ery hi2h pressure7 and at e5actly the ri2ht

moment in time.

3 This results in consideraly more efficient comustion than is the

case 4ith con/entional injection systems.

3 This7 in turn7 e?uates to hi2her output7 less fuel consumption7 and

lo4er le/els of noise and e5haust@2as emissions.

nit Injector !ystem


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nit Injector !ystem


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Actuation of Injector No


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j

nit ;ump Diesel Injection !ystem


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nit ;ump Diesel Injection !ystem

Common Rail Diesel Injection !ystem


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The Common Rail Diesel Injection !ystem deli/ers a more controlled

?uantity of atomised fuel7 4hich leads to etter fuel economyB a

reduction in e5haust emissionsB and a si2nificant decrease in en2ine

noise durin o eration.


70/72

Common rail diesel injection system

3 In the Common Rail system7 an accumulator7 or rail7 is usedto create a common reser/oir of fuel under a consistent

controlled pressure that is separate from the fuel injection

points.

3 A hi2h@pressure pump increases the fuel pressure in theaccumulator up to '7&== ar .

3 The pressure is set y the en2ine control unit and is

independent of the en2ine speed and ?uantity of fuel ein2

injected into any of the cylinders.

3 The fuel is then transferred throu2h ri2id pipes to the fuel

injectors7 4hich inject the correct amount of fuel into the

comustion chamers.

Injectors for CRDI


71/72

j

3 The injectors used in Common Rail systems are tri22ered

e5ternally y an Electronic Diesel Control7 or EDC unit.

3 EDC controls all the en2ine injection parameters includin2 the

pressure in the fuel rail and the timin2 and duration of injection.

3 Diesel fuel injectors used in Common Rail injection systems

operate differently to con/entional fuel injectors used in the jer*

pump system.

3 !ome common rail injectors are controlled y a ma2netic

solenoid on the injector.

3 +ydraulic force from the pressure in the system is used to open

and close the injector7 ut the a/ailale pressure is controlled y

the solenoid tri22ered y the Electronic Diesel Control unit.


72/72

3 !ome injectors use ;ie

Fuel Injection system IITD

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