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Basic Function of Diesel Engine

 The diesel engine (also known as a compression-ignition engine) is an internal

combustion engine that uses the heat of compression to initiate ignition and burn

the fuel that has been injected into the combustion chamber. This contrasts with

spark-ignition engines such as a petrol engine (gasoline engine) or gas

engine (using a gaseous fuel as opposed to gasoline), which use a spark plug to

ignite an air-fuel mixture.

 The diesel engine has the highest thermal eciency of any

standard internal or external combustion engine due to its ery high compression

ratio and inherent lean burn which enables heat dissipation by the excess air. !

small eciency loss is also aoided compared to two-stroke non-direct-injection

gasoline engines since unburn fuel is not present at ale oerlap and therefore

no fuel goes directly from the intake"injection to the exhaust. #ow-speed diesel

engines (as used in ships and other applications where oerall engine weight is

relatiely unimportant) can hae a thermal eciency that exceeds $%&.

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INTAKE STROKE

 The intake stroke begins at top dead center, and as the piston moes down, the

intake ale opens. The downward moement of the piston creates a acuum in

the cylinder, causing an air to be drawn through the intake port into the

combustion chamber. !s the piston reaches bottom dead center, the

intake ale closes.

COMPRESSION STROKE

 The compression stroke begins with the piston at bottom dead center and rising

up to compress the air. 'ince both the intake and exhaust ales are closed,there is no escape for the air, and it is compressed to a fraction of its original

olume. !s the piston reach T, the compression stroke ends.

POWER STROKE

 The piston begins the power stroke at T. !t this point, fuel is injected into

combustion chamber and ignited by the heat of the compression. The expanding

forces of burning gases force the piston downward.

EXHAST STROKE

 The exhaust stroke begins when the piston nears the end of the power stroke

and the exhaust ale is opened. !s the piston moes upward towards top dead

center, it pushes the burnt gases, resulting from the ignition of the fuel and air

mixture, out of the combustion chamber and through the exhaust port. !s the

piston reaches top dead center, ending the exhaust stroke, the

exhaust ale closes, and the intake ale opens to begin the intake stroke for

the next cycle. 

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Diesel Engine Co!"onent

Fun#a!ental O"e$ating P$inci"le of Diesel Engine

*ollowing is a step-by-step iew when you start up a diesel-powered ehicle.

%& 'ou tu$n t(e )e* in t(e ignition&

 Then you wait until the engine builds up enough heat in the cylinders for

satisfactory starting. (+ost ehicles hae a little light that says ait, but a

sultry computer oice may do the same job on some ehicles.) Turning the

key begins a process in which fuel is injected into the cylinders under such

high pressure that it heats the air in the cylinders all by itself. The time it

takes to warm things up has been dramatically reduced / probably no more

than 0.$ seconds in moderate weather.

iesel fuel is less olatile than gasoline and is easier to start if the

combustion chamber is preheated, so manufacturers originally installed little

glow plugs that worked o1 the battery to pre-warm the air in the cylinders

when you 2rst started the engine. 3etter fuel management techni4ues and

higher injection pressures now create enough heat to touch o1 the fuel

without glow plugs, but the plugs are still in there for emissions control5 The

extra heat they proide helps burn the fuel more eciently. 'ome ehicles

still hae these chambers, others don6t, but the results are still the same.

+& A ,Sta$t- lig(t goes on&

hen you see it, you step on the accelerator and turn the ignition key to

'tart.

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.& Fuel "u!"s #eli/e$ t(e fuel f$o! t(e fuel tan) to t(e engine&

7n its way, the fuel passes through a couple of fuel 2lters that clean it before

it can get to the fuel injector no88les. 9roper 2lter maintenance is especially

important in diesels because fuel contamination can clog up the tiny holes in

the injector no88les.

 A diesel fuel lter.

0& T(e fuel in1ection "u!" "$essu$i2es fuel into a #eli/e$* tu3e&

 This deliery tube is called arail

 and keeps it there under constant highpressure of :;,$%% pounds per s4uare inch (psi) or een higher while it

deliers the fuel to each cylinder at the proper time. (<asoline fuel injection

pressure may be just 0% to $% psi=) The fuel injectors feed the fuel as a 2ne

spray into the combustion chambers of the cylinders through no88les

controlled by the engine6s engine control unit (>?), which determines the

pressure, when the fuel spray occurs, how long it lasts, and other functions.

4& T(e fuel5 ai$5 an# ,6$e- !eet in t(e c*lin#e$s&

hile the preceding steps get the fuel where it needs to go, another process

runs simultaneously to get the air where it needs to be for the 2nal, 2erypower play.

7n conentional diesels, the air comes in through an air cleaner that6s 4uite

similar to those in gas-powered ehicles. @oweer, modern turbochargers

can ram greater olumes of air into the cylinders and may proide greater

power and fuel economy under optimum conditions. ! turbocharger can

increase the power on a diesel ehicle by $% percent while lowering its fuel

consumption by :% to :$ percent.

7& Co!3ustion s"$ea#s f$o! t(e s!alle$ a!ount of fuel t(at8s "lace#

un#e$ "$essu$e in t(e "$eco!3ustion c(a!3e$ to t(e fuel an# ai$ int(e co!3ustion c(a!3e$ itself&

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Antroduce !dance iesel >ngine ith >lectronic ontrol (ommon Bail

'ystem).

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P$inci"les

'olenoid or pie8oelectric ales make possible 2ne electronic control oer

the fuel injection time and 4uantity, and the higher pressure that the

common rail technology makes aailable proides better fuel atomisation.

 To lower engine noise, the engineCs electronic control unit can inject a

small amount of diesel just before the main injection eent (DpilotD

injection), thus reducing its explosieness and ibration, as well as

optimising injection timing and 4uantity for ariations in fuel 4uality, cold

starting and so on. 'ome adanced common rail fuel systems perform as

many as 2e injections per stroke.

ommon rail engines re4uire a ery short (E 0% seconds) to no heating-up

time, depending on ambient temperature, and produce lower engine noise

and emissions than older systems.

iesel engines hae historically used arious forms of fuel injection. Two

common types include the unit injection system and the distributor"inline

pump systems ('ee diesel engine and unit injector for more information).

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hile these older systems proided accurate fuel 4uantity and injection

timing control, they were limited by seeral factors5

•  They were cam drien, and injection pressure was proportional to

engine speed. This typically meant that the highest injection

pressure could only be achieed at the highest engine speed and

the maximum achieable injection pressure decreased as engine

speed decreased. This relationship is true with all pumps, een

those used on common rail systems. ith unit or distributor

systems, the injection pressure is tied to the instantaneous pressure

of a single pumping eent with no accumulator, and thus the

relationship is more prominent and troublesome.

•  They were limited in the number and timing of injection eents that

could be commanded during a single combustion eent. hile

multiple injection eents are possible with these older systems, it ismuch more dicult and costly to achiee.

• *or the typical distributor"inline system, the start of injection

occurred at a pre-determined pressure (often referred to as5 pop

pressure) and ended at a pre-determined pressure. This

characteristic resulted from DdummyD injectors in the cylinder head

which opened and closed at pressures determined by the spring

preload applied to the plunger in the injector. 7nce the pressure in

the injector reached a pre-determined leel, the plunger would lift

and injection would start.

An common a rail system, a high-pressure pump stores a reseroir of fuel

at high pressure / up to and aboe :,%%% bars (:%% +9aF :G,%%% psi). The

term Dcommon railD refers to the fact that all of the fuel injectors are

supplied by a common fuel rail which is nothing more than a pressure

accumulator where the fuel is stored at high pressure. This accumulator

supplies multiple fuel injectors with high-pressure fuel. This simpli2es the

purpose of the high-pressure pump in that it only needs to maintain a

commanded pressure at a target (either mechanically or electronically

controlled). The fuel injectors are typically >?-controlled. hen the fuel

injectors are electrically actiated, a hydraulic ale (consisting of a

no88le and plunger) is mechanically or hydraulically opened and fuel is

sprayed into the cylinders at the desired pressure. 'ince the fuel pressure

energy is stored remotely and the injectors are electrically actuated, the

injection pressure at the start and end of injection is ery near the

pressure in the accumulator (rail), thus producing a s4uare injection rate.

Af the accumulator, pump and plumbing are si8ed properly, the injection

pressure and rate will be the same for each of the multiple injection

eents.

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Fuel In1ection Pu!"

!n Anjection 9ump is the deice that pumps fuel into the cylinders of a

diesel engine. Traditionally, the injection pump is drien indirectly from thecrankshaft by gears, chains or a toothed belt (often the timing belt) that

also dries the camshaft. At rotates at half crankshaft speed in a

conentional four-stroke engine. Ats timing is such that the fuel is injected

only ery slightly before top dead centre of that cylinderCs compression

stroke. At is also common for the pump belt on gasoline engines to be

drien directly from the camshaft. An some systems injection pressures

can be as high as :%% +9a (;%,%%% 9'A).

%& Inline In1ection Pu!"

An-line injection pumps to meter,

and raise the pressure of the fuel.

 The basic principle is for a plunger

to act on a column of fuel, to lift an

injector needle o1 its seat.

Anside the pump is a pumping

element, and a deliery ale for

each cylinder of the engine. The

element has a barrel, and a plunger

that 2ts inside it. Their accurate 2t

and highly-polished 2nish ensures

only minimal fuel leakage past them, without needing positie seals. The

barrel usually has two holes, or ports, called the inlet port, and the spill

port. They connect the inside of the barrel with the gallery. The gallery

contains 2ltered fuel from the low-pressure system. !t the top of the

barrel is a deliery ale, deliery ale holder, and the pipe to carry fuel

to each cylinder.

 The upper end of the plunger has a ertical grooe, extending from its top

to an annular grooe. The top edge of this annular grooe is cut in a helix,

also called the control edge. 'ome pumps hae a helix cut on top of the

plunger.

! camshaft, cam follower and spring, moe the plunger in a reciprocating

motion.

hen the plunger is below the ports, fuel from the gallery enters the

barrel aboe the plunger. This ensures the barrel is full of fuel. !s thecamshaft rotates, the plunger is pushed past the ports. The highly

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polished surfaces cause a sealing e1ect, trapping the fuel aboe the

plunger. +oing the plunger further raises the pressure of the fuel. This

forces the fuel out past the deliery ale, along the fuel line to the

injector.

*uel Hows to the injector until the control edge uncoers the spill port. The

pressuri8ed fuel aboe the plunger then moes down the ertical grooe,

to the annular grooe, and into the spill port. The deliery ale stops fuel

leaking from the pipe back into the element. At reduces pressure in the

fuel line to ensure there is no dribbling by the injector.

 The deliery ale has a relief plunger, and a conical face which is held

against its matching seat by the deliery ale spring. The relief plunger

on the ale is a close 2t inside the bore of the deliery ale seat.

hen the fuel pressure rises, the deliery ale is lifted o1 its seat. hen

the plunger is clear of its bore, fuel Hows to the injector. hen injection

ceases, the pressure below the deliery ale drops to gallery pressure.

*uel pressure aboe the deliery ale forces the ale towards its seat.

 The relief ale enters the seat bore, sealing the olumes aboe and

below the deliery ale. *urther moement of the deliery ale towards

its seat, increases the olume in the injector pipe, and reduces the

pressure in there. This drop in pressure causes the injector needle to snap

shut, helping to preent fuel dribble from the injector. The conical face ofthe deliery ale then contacts the seat, further sealing the plunger from

the injector pipe.

Botating the plunger controls the length of the stroke for which the spill

port is coered. This is called the e1ectie stroke. At inHuences how much

fuel is deliered to the injector. ! short e1ectie stroke means a small

amount of fuel is injected. ! longer e1ectie stroke lets more fuel be

deliered. To stop the engine, the ertical grooe on the plunger is aligned

with the spill port, which stops pressure in the barrel rising.

 The plunger is rotated by a control sleee, a rack, and a pinion. +oing

the rack rotates the pinion, the control sleee, and then the plunger. The

rack6s moement is controlled by the goernor.

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+& Dist$i3uto$ T*"e Fuel In1ection Pu!"

 The distributor-type pump

uses a ane-typetransfer pump to 2ll the

single pumping element.

 This then raises fuel

pressure to injection

pressure.

! distribution system then distributes fuel to each

cylinder, in the 2ring order of the engine.

 The most common type in light automotie use is the 3osch I> pump.

! drie shaft drien from the engine, rotates a plunger, and a cam disc.

ams on the face of the disc hae as many lobes as cylinders in the

engine. ! plunger spring holds the cam disc against rollers that rotate on

their shafts.

 The lobes moe the plunger to-and-fro in its barrel, making it rotate, and

reciprocate, at the same time. Ats rotation operates the fuel inlet port to

the pumping chamber, and at the same time distributes pressuri8ed fuel

to the correct injector. The reciprocating motion pressuri8es the fuel in thepumping chamber.

 The plunger6s pumping action forces fuel through a deliery ale, to the

injector. This pump is for a ;-cylinder engine, so it has ; deliery ales.

 The barrel has 0 intake port and ; distribution ports. The plunger has a

central passage, a connecting passage to the distributing slit, and a cross-

drilling to a control sleee. !s the plunger rotates, each intake slit aligns

with the intake port, and the distributing slit with the distributing port.

!s the plunger rotates, the intake slit moes away from the intake port. !t

the same time, the plunger is acted on by the cams, causing it to moe

axially along the barrel, pressuri8ing the fuel in the pumping chamber.

 The distributing slit now uncoers the distribution port, and the

pressuri8ed fuel passes through deliery ale to the injector. *urther

rotation of the plunger closes o1 the distribution port, and opens the

intake port. !t the same time, the plunger spring moes the plunger back

along the barrel for the next pumping stroke.

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*or intake, fuel from the feed pump reaches the open intake port in the

barrel. The intake slit aligns with the intake port, and fuel 2lls the pumping

chamber and passages in the plunger.

*or injection, the plunger rotates to close o1 the intake port, and moes

along the barrel, to pressuri8e fuel in the pumping chamber. The

distributing slit aligns with the distribution port and the pressuri8ed fuel

forces the deliery ale o1 its seat, and reaches the injector. An this

phase, a cut-o1 port in the plunger is coered by the control sleee.

 To end fuel deliery, the plunger6s cut-o1 port moes out of the control

sleee, and lets pressuri8ed fuel spill back into the pump housing. This

reliees pressure in the pumping chamber, the deliery ale closes, and

injection ceases.

+etering the fuel is controlled by e1ectie stroke of the control sleee,

and that6s determined by the action of the goernor sliding the control

sleee along the plunger. 'liding it one way opens the cut-o1 port earlier,

and reduces e1ectie stroke. 'liding it this way delays its opening, and

increases e1ectie stroke.

 The goernor changes the position of the control sleee to ary the

4uantity of fuel deliered, according to throttle position and load.

hen the ignition is switched o1, an electrical solenoid closes o1 the

intake port, and stops fuel deliery.

Co!!on Rail

 The ommon Bail iesel Anjection 'ystem deliers a more controlled

4uantity of atomi8ed fuel, which leads to better fuel economyF a reduction

in exhaust emissionsF and a signi2cant decrease in engine noise during

operation.

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An the ommon Bail system, an accumulator, or rail, is used to create a

common reseroir of fuel under a consistent controlled pressure that is

separate from the fuel injection points.

! high-pressure pump increases the fuel pressure in the accumulator up to

0,J%% bar or :;,:%% 9'A. The pressure is set by the engine control unit and

is independent of the engine speed and 4uantity of fuel being injected into

any of the cylinders. The fuel is then transferred through rigid pipes to thefuel injectors, which inject the correct amount of fuel into the combustion

chambers.

 The injectors used in ommon Bail

systems are triggered externally by

an >lectronic iesel ontrol, or >

unit, which controls all the engine

injection parameters including thepressure in the fuel rail and the

timing and duration of injection.

iesel fuel injectors used in

ommon Bail injection systems

operate di1erently to conentional

fuel injectors used in the jerk pump

system, where the plungers are

controlled by the camshaft position

and speed. 'ome common rail injectors are controlled by a magneticsolenoid on the injector. @ydraulic force from the pressure in the system is

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used to open and close the injector, but the aailable pressure is

controlled by the solenoid triggered by the >lectronic iesel ontrol unit.

'ome injectors use 9ie8o crystal wafers to actuate the injectors. These

crystals expand rapidly when connected to an electric 2eld. An a 9ie8o

inline injector, the actuator is built into the injector body ery close to the

 jet needle and uses no mechanical

parts to switch injector needles.

 The electronic diesel control unit precisely meters the amount of fuel

injected, and improes atomi8ation of the fuel by controlling the injector

pulsations. This results in 4uieter, more fuel ecient enginesF cleaner

operationF and more power.

Fuel In1ecto$

 The fuel injectors are controlled by either a solenoid or pie8o actuator.

 They are energi8e se4uentially by the engine >+. The >+

simultaneously switches a lie oltage supply and an earth for each

injector. +ultiple injection processes per cylinder combustion are possible.

Co!!on Rail Diesel Fuel 

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A#/antages of co!!on $ail

• *uel pressure aailable on demand

• @igher injection pressure and 2ner atomi8ation of fuel

• Anjection pressure created independent of engine speed

• +ultiple injection per cylinder combustion are possible

Bene6t of Co!!on Rail

• Beduction of oerall exhaust emission

• Beduction of particulate emission

• Beduction of noise emission

• Amproe fuel eciency

• @igher performance