diesel injection

8/12/2019 Diesel Injection

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DIESEL INJECTIONSYSTEMS

unIT ii


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INTRODUCTION:The fuel-injection system is the most vital component

in the working of IC engine.

The engine performance, power o/p , economy etc isgreatly dependent on the effectiveness of the fuel-

injection system.Basically the purpose of caruretion ! fuel-injection is

the same i.e. preparation of the comustile charge.But in case of caruretion fuel is atomi"ed yprocesses relying on the air speed greater than fuel

speed at the fuel no""le , whereas in fuel-injection thefuel speed at the point of delivery is greater than theair speed to atomi"e the fuel.


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Diesel Fuel

If you have ever compared diesel fuel andgasoline, you know that they are different.

They certainly smell different.

#iesel fuel is heavier and oilier.

#iesel fuel evaporates much more slowly thangasoline -- its oiling point is actually higher thanthe oiling point of water.

$ou will often hear diesel fuel referred to as %dieseloil% ecause it is so oily.
http://auto.howstuffworks.com/gasoline.htmhttp://auto.howstuffworks.com/gasoline.htm


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DIESEL FUEL

#iesel fuel evaporates more slowly ecause it isheavier.

It contains more caron atoms in longer chains

than gasoline does &gasoline is typically C'()*,while diesel fuel is typically C+(*.

It takes less refiningto create diesel fuel, whichis why it is generally cheaper than gasoline.
http://auto.howstuffworks.com/oil-refining.htmhttp://auto.howstuffworks.com/oil-refining.htm


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DIESEL FUEL#iesel fuel must meet an entirely differentset of standards than gasoline.

The fuel in a diesel engine is not ignitedwith a spark, ut is ignited y the heatgenerated y high compression.

ll diesel fuel must e clean, e ale toflow at low temperatures, and e of theproper cetane rating.

Cleanliness.Low-temperature fluiit!.Cetane num"er.


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Diesel Fuel Characteristics

Cetane numer0easure of relative ease to initiatecomustion

(igher numer1 easier to ignite

2ctane numer for gas1 opposite(igher numer1 less tendency to ignite


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Cetane Number(igh cetane numer indicates good ignition 3uality &short delay period

4ow cetane numer indicates poor ignition 3uality &long delay period

5C engines re3uire a minimum cetane 6 of 7

#I engines re3uire a minimum cetane 6 of *

Cetane improver additive can improve ignition 3uality and reduce white smokeduring start up

Cetane numer is ased on the ignition characteristics of two hydrocarons1

Cetane- short delay period and ignites readily &+**

Alphamethylnaphthalene&08 - long delay period and poor ignition 3uality &*

It is the percentage y volume of normal cetane in a lend with 08


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FUEL CYCLE


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Requirements of a diesel inection

s!stem

The functional re3uirements of an injection system are listedelow9

+. Introduction of the fuel into the comustion chamershould take place within a precisely defined period of thecycle.

). The metering of amount of fuel injected per cycle shoulddone very accurately.

. The 3uantities of fuel metered should vary to meet thechanging load ! speed re3uirements.

. The injection rate should e such that it results in thedesired heat-release pattern.

7. The injected fuel must e roken into very fine droplets.


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:. 5roper spray pattern to ensure rapid mi;ing

of fuel ! air.


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For accom"lishin# these requirements the follo$in# functional

elements are required in a fuel inection s!stem%

+. 5>05I8? @4@0@8T1

To move the fuel from the fuel tank to cylinder ! piping etc.

. 0@T@AI8? @4@0@8T1 To measure ! supply the fuel at therate demanded y load ! speed.

. 0@T@AI8? C28TA241 To adjust the rate of metering elementsfor changes in load ! speed of the engine.

7. #ITAIB>TI8? @4@0@8T1To divide the metered fuel e3uallyamong the cylinder.

:. TI0I8? C28TA241 To adjust the start ! the stop of injection.


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DIESEL EN#INESIndirect and Direct Inection

& direct inection diesel en#ine

inects the fuel directl! into thecombustion chamber' (an!

desi#ns do not use a #lo$ "lu#'


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DIESEL EN#INESIndirect and Direct Inection

In an inire$t in%e$tion

&areviated IDI dieselengine, fuel is injected into asmall prechamer, which isconnected to the cylinder ya narrow opening.

The initial comustion takes

place in this prechamer. This has the effect of slowing

the rate of comustion,which tends to reduce noise.

&n indirect inection diesel en#ine uses a

"rechamber and a #lo$ "lu#'


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CL&SSIFIC&TION OF IN)ECTION

S*STE(S

#iesel injection systems can e divided into two asictypes. They are 1

ir injection system

olid injection system


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+' &ir inection s!stem

In this method fuel is forced into the cylinder y means ofcompressed air to a very high pressure. The rate of fueladmission can e controlled y varying the pressure of air .

The fuel is metered ! pumped to the fuel valve y a camshaft

driven fuel pump. The fuel valve is opened y means of amechanical linkage operated y the camshaft which controlsthe timing of injection . The fuel valve is also connected to ahigh pressure air line fed y a multi stage compressor whichsupplies air at a pressure of aout :* to


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#D8T?@9

It provides etter atomi"ation ! distriution of fuel.

(eavy ! viscous fuels, which are cheaper can also e injected.

#I#D8T?@9This method is not used now a day due to following reasons1

It re3uires a high pressure multi stage compression.

separate mechanical linkage is re3uired to time theoperation of fuel valve.

The fuel valve sealing re3uires considerale skill.

#ue to the compression ! the linkage the ulk of the engineincreases . This also results in reduced B.5 due to power loss

in operating the compression ! linkage.

In case of sticking of the fuel valve , the system ecomes3uite dangerous due to the presence of high pressure air.


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,' Solid inection s!stem

In this method fuel is injected directly into thecomustion chamer without primary atomi"ation istermed as solid injection. it is also termed asmechanical injection.

olid injection system can e classified into types1

>nit injector system.

Common rail system.#istriutor system.


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+'Unit inector s!stem:

The unit injector system is one in

which the pump ! injector arecomined in one housing.

@ach cylinder is provided with one ofthese unit injectors.

Euel is rought up to the injector y

a low pressure pump at proper time,a rocker arm actuates the plunger !thus injects the fuel into the cylinder.


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Aoger Frieger,

Electronic Unit Inector -EUI.


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,'Commmon rail s!stem:

In common rail system a high pressurefuel pump delivers fuel to anaccumulator, whose pressure is keptconstant with the help of a pressureregulating valve.

common rail or a pipe starts from theaccumulator ! leads to the different

distriuting elements for each cylinder.


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Eor each cylinder there is a separate metering !

timing element which is connected to an automaticinjector injecting fuel into the cylinder.

In the common rail system the supply pressure of

the fuel is independent of speed ! hence is notaffected y the fuel pump.

The amount of fuel entering the cylinder isregulated y varying the length of the push rodstroke.


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/i#h01ressure Common Rail

/i#h01ressure 1um"

ECU

Fuel Return

to Tan2

Common Rail

Inectors

S"ill

Control

3al4e


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5'Distributor s!stem:

In this system the pump whichpressuri"es the fuel also meters ! times

it .

The fuel pump after metering there3uired amount of fuel supplies it to

rotating distriutorat the correct timefor supply to each cylinder.


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The numer of injection strokes per cycle for

the pump is e3ual to the numer of cylinders.

ince there is only one metering element , a

uniform distriution is automatically ensured .

8ot only that , the cost of the fuel injection

system also reduces to a value less than two Gthird of that for individual pump system.


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NO66LE :8o""le is a part of an injector through

which the fuel is sprayed into thecomustion chamer.

Darious types of no""les used inC I engine are1


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I8?4@ (24@ 82HH4@1

ingle hole no""le are used in open comustion chamer. t the center of theno""le ody there is a single hole which is closed y the no""le valve.

The si"e of the hole is usually larger than *.)mm.The hole may e drilled centrally or at an angle to the centre line of the no""le. 0ain disadvantages of the ingle hole no""le are1 ingle hole no""le has tendency to drile.The spray angle is very narrow. This does not facilitate good mi;ing unless

higher air velocities are provided.


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0ulti-hole 8o""le1

In order to mi; the fuel properly

even with the slow air movementavailale with many opencomustion chamer ,a 0ulti-hole no""le.

The numer of holes varies from ! +=and the si"e from +.7mm to *.7mm.

dvantages9

i. ?ives good atomi"ation.

ii. #istriute fuel property even withlower air motion availale in opencomustion chamer.

. #isadvantages9

i. #riling /w injection.

ii. Dery high injection.

iii. Close tolerance in manufacture !hence costly.


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ELECTRONIC FUEL IN)ECTION

S*STE(-EFL.:

0odern diesel injection system use engine sensors, a computer andsolenoid operated fuel injectors to meter ! inject the right amount offuel into the engine cylinder. These system is called as electronic fuelinjection system&@E4 use electrical ! electronic devices to monitor !control engine operation.

n electronic control unit &@C> or computer receives electrical

signals in the form of current or voltage from various sensors. It thenuses the stored data to operate the injectors , ignition system ! otherengine related devices. s a result, less unurned fuel leaves theengine as emissions ! the vehicle gives etter mileage.


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>nder full load, the @C> will sense a wide open throttle, highintake manifold pressure,! high inlet air flow. The @C> will thenincrease the injector pulse width to enrich the mi;ture which willenale the engine to produce higher power.

>nder low load ! idling conditions, the @C> will shorten thepulse width y which the injectors are kept in the closed positionover a longer period of time. Because of this, air-fuel mi;ture willecome leaner ! will result in etter fuel economy.

@EI system has a cold start injector too. This is an e;tra injector

that sprays fuel into the center of the engine intake manifoldwhen the engine is cold. It server the same purpose as thecaruretor choke. The cold start injector ensures easy enginestart up in very cold weather.


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Typical sensors used in @EI system are asfollows1

@;haust gas &or o;ygen sensor. @ngine temperature sensor. ir flow sensor. ir inlet temperature sensor.Throttle position sensor. 0anifold pressure sensor. Camshaft position sensor. Fnock sensor.


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0erits of @EI system1

+ Better atomi"ation ! vapouri"ation will make the engine lessknock.

) 0anifold wetting is eliminated due to the fuel eing injectedinto or close to cylinder ! need not flow through the manifold.

tomi"ation of fuel is independent of cracking speed !therefore starting will e easier.

#istriution of fuel eing independent of vapouri"ation less

volatile fuel can e used.

7 5osition of the injection unit is not so critical ! therey theheight of the engine can e less.

#emerit of @EI system1+ (igh maintenance cost.

) #ifficulty in servicing.

5ossiility of malfunction of some sensors.


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COOLIN7 S*STE(S

In order to cool the engine a coolingmedium is re3uired. This can e either airor a li3uid.

There two types of cooling system forcooling the I C engine, these are1

ater or indirectcooling system.

ir cooling system.


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+' 8&TER OR INDIRECT COOLIN7

S*STE(

In this system mainly water is used and made tocirculate through the jackets provided around thecylinder, cylinder-head, valve ports and seatswhere it e;tracts most of the heat.

ater-cooling can e carried out y any one of thefollowing five methods1

#irect or non-return systemThermosyphon system

Eorced circulation cooling system @vaporative cooling system 5ressure cooling system


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#IA@CT 2A 828-A@T>A8 $T@0

This system is useful for large installationswhere plenty of water is availale. Thewater from a storage tank is directlysupplied through an inlet valve to the

engine cooling water jacket. The hot wateris not cooled for reuse ut simplydischarged.


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9' T/ER(OS*1/ON S*STE(


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T(@A02$5(28 $T@0

The asic principle of thermosyphon can e e;plained withrespect to figure. (eat is supplied to the fluid in the tank .Because of the relatively lower density, the hot fluidtravels up, its place eing taken up y comparatively coldfluid from the tank B through the pipe p).

The hot fluid flows through the pipe p+ to the tank Bwhere it gets cooled. Thus the fluid circulated through thesystem in the form of convection currents.

Eor engine application, tank represents the cylinderjackets while tank B represents a radiator and water acts

the circulating fluid.


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E2AC@# CIAC>4TI28 C224I8? $T@0

In Eorced cooling system apump is used to causepositive circulation ofwater in the water jacket.

usually the pump is eltdriven from the engine.


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The water or coolant is circulated throughjackets around the parts of the engine to e

cooled and kept in motion y a centrifugalpump which is driven y the engine.

The water is passed through the radiator

where it is cooled y air drawn through theradiator y a fan .

thermostat is used to control the watertemperature re3uired for cooling. This

system mainly consists of four components,vi"., a radiator, fan, water pump and athermostat.


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@D52ATID@ C224I8? $T@0

This system is used in stationary engines.In this , engine will e cooled ecause ofthe evaporation of the water in the cylinder

jackets into steam.


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This method of cooling utili"es the high latentheat of vapori"ation of water y allowing it toevaporate in the cylinder jackets.

The cooling circuit is such that coolant is

always li3uid ut the steam formed is flashedoff in the separate vessel. The makeup waterso formed is sent ack for cooling.

This system is used for cooling of many typesof industrial engines


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5A@>A@ C224I8? $T@0

In pressure cooling system moderatepressures, say upto ) ar, are commonlyused.


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s shown in the figure a cap is fitted on the radiator with two-valves, a safety valve which is loaded y a compression springand a vacuum valve.

hen the coolant is cold oth the valves are shut, ut as theengine warms up the coolant temperature rises until it reachesa certain value corresponding to the desired pressure then thesafety valve opens9 ut if the coolant temperature falls duringthe engine operation the valve will close again until thetemperature again rises to the e3uivalent pressure value.

hen the engine is switched off and the coolant cools downvacuum egins to form in the cooling system, ut when theinternal pressure falls elow atmospheric the vacuum valve isopened y the higher outside pressure and the cooling systemthen attains atmospheric pressure.


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,' &IR COOLIN7 S*STE(:

ir cooling is usually used for small enginesand for engines whose application givese;treme importance to weight such asaircraft engines. 2ther area for air-cooled

engines are industrial and agriculturalengines where there can e a strongojection to use of water as coolant.

Eor air cooling the cylinder head heattransfer area is increased y fining ! air ispassed over these fins to affect cooling.


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Two types of fins used to cover the cylinder.

The length of fins ! the spacing /w them is 3uite importantfor efficient cooling .

4arger inter-spacing /w the fins offers larger area for coolingair ut the heating of the air is less, so more cooling air isre3uired.

maller interspacing /w the fins results in smaller flow areafor cooling air ! hence air is heated more ! input to the

cooling air is less.

(owever, the pressure drop re3uired for flow is more. If thedistance /w two fins is 3uite small the laminar layer of theopposite area come in contact with each other ! the efficiencyof the fins is reduced very much. Therefore ,a spacing less

than ).7mm is not used.

The height of the fins controls the distance /w the twocylinders and hence, the si"e of the engine. >sually the finheight varies from +7 to )7mm.


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ROLE OF R&DI&TORS:

The function of the radiator is to reject coolantheat to the outside air.&y conduction ! forcedconvection ! not y radiation

The cooling effect in a radiator is achieved ydispersing the heated coolant into fine streamthrough the radiator core so that relatively small3uantities of coolant are rought in contact withlarge metal surface areas which in turn arecooled y a stream of air.

It should e noted that it is easier o transfer

heat from water to the metal surfacesthan frommetal surface to air.


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The radiator consists of an upper tank&header tank at the top ! a collector tank atthe ottom of the radiator core.

Two types of radiators in common use are 1

#own-flow type ! cross flow type.

In down-flow type ,water flow from top toottom ,ut in cross flow type the hot coolantis supplied to top of the supply tank, it flowsacross the radiator and is taken out from theottom of the collector tank. separateheader tank is usually provide at the upperend of the collector tank to prevent aeration.


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END

diesel injection

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