diesel injection system

8/9/2019 Diesel Injection System

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DIESEL ENGINESThe diesel engine

requires compressionratios of 16:1 and higher.

Incoming air iscompressed until its

temperature reachesabout 1,000F (540C).

This is calledheat ofcompression.

As the piston reaches thetop of its compressionstroke, fuel is injectedinto the cylinder, where itis ignited by the hot air

Diesel combustion occurswhen fuel is injected into thehot, highly compressed air inthe cylinder.


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Diesel Injection System


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INDIRECT INJECTION In an indirect injection

(abbreviated IDI) dieselengine, fuel is injectedinto a small prechamber,

which is connected to thecylinder by a narrowopening.

The initial combustiontakes place in thisprechamber.

This has the eect ofslowing the rate ofcombustion, which tends

to reduce noise


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DIRECT INJECTION

A direct injectiondiesel engine

injects the fueldirectly into thecombustion

chamber.Many designs donot use a glow plug


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GLOW PLUGS Glow plugs are always used in diesel enginesequipped with a precombustion chamber andmay be used in direct injection diesel engines to

aid starting.Aglow plugis a heating element that uses 12volts from the battery and aids in the starting ofa cold engine.

As the temperature of the glow plug increases,the resistance of the heating element insideincreases, thereby reducing the current in

amperes needed by the glow plugs.


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Merits of Electronic controlleddiesel injection system

Quantity of fuel injection

Injection timing

Rate of injection during variousstage

Injection pressure

Speed of nozzle opening


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Types of Electronic controlled

diesel injection system Unit Injector System (UIS)

Rotary Distributor System (RDS)

Common Rail Injection System (CRS)


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Unit Injection System


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FUEL TANK AND LIFT PUMPA fuel tank used on a vehicle equipped witha diesel engine differs from the one usedwith a gasoline engine in several ways,including:

A larger filler neck for diesel fuel.

No evaporative emission control devicesor charcoal (carbon) canister.

The diesel fuel is drawn from the fuel tank

by alift pumpand delivers the fuel to theinjection pump. Between the fuel tank and the lift pump is awater-fuel separator.

Water is heavier than diesel fuel andsinks to the bottom of the searator.


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Four Stages of Combustion in CI Engines

-10 TC-20 10 20 30

Start of

injection

End of

injecction


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Combustion in CI Engine

The combustion process proceeds by the following stages:

Ignition delay (ab)- fuel is injected directly into the cylinder towardsthe end of the compression stroke.

The liquid fuel atomizes into small drops and penetrates into the

combustion chamber. The fuel vaporizes and mixes with the high-

temperature high-pressure air.Premixed combustion phase (bc) combustion of the fuel which has

mixed with the air to within the flammability limits !air at high-

temperature and high-pressure" during the ignition delay period

occurs rapidly in a few crank angles.

Mixing controlled combustion phase (cd) after premixed gas

consumed# the burning rate is controlled by the rate at which mixture

becomes available for burning.

The burning rate is controlled primarily by the fuel-air mixing

process.


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!ommon "ail Diesel Injection #ystem

The !ommon "ail Diesel Injection #ystem delivers a more controlled $uantityof atomised fuel, which leads to better fuel economy% a reduction in e&haustemissions% and a signi'cant decrease in engine noise during operation.


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Common rail diesel injection system

In the !ommon "ail system, an accumulator, orrail, is used to create a common reservoir of fuelunder a consistent controlled pressure that isseparate from the fuel injection points.

highpressure pump increases the fuel pressurein the accumulator up to *,+ bar .

The pressure is set by the engine control unit andis independent of the engine speed and $uantityof fuel being injected into any of the cylinders.

The fuel is then transferred through rigid pipes tothe fuel injectors, which inject the correct amountof fuel into the combustion chambers.


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Injectors for !"DI

The injectors used in !ommon "ail systems aretriggered e&ternally by an -lectronic Diesel !ontrol,or -D! unit.

-D! controls all the engine injection parametersincluding the pressure in the fuel rail and the timing

and duration of injection.

Diesel fuel injectors used in !ommon "ail injectionsystems operate dierently to conventional fuelinjectors used in the jerk pump system.

#ome common rail injectors are controlled by amagnetic solenoid on the injector.

ydraulic force from the pressure in the system isused to open and close the injector, but the

available pressure is controlled by the solenoid


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diesel injection system

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