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History
The Diesel engine wasinvented by RudolfDiesel around 1892, thiswas 16 years after the
petrol engine wasdeveloped.
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Diesel Engine Operation
A Diesel engines operationsequence is as follows:
Stroke 1 (intake) only airenters cylinder.
Stroke 2 (compression) air is compressed to highextent, raising temperature.
Stroke 3 (power) diesel isinjected, high air temperature
ignites diesel.
Stroke 4 (exhaust) burntgases are expelled from theengine.
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Differences in a Petrol & Diesel Engine
All things being the same the diesel engine generallyhas some particularly different traits from the petrolengine.
They are :
Diesels have more sound & vibrations.Diesels are heavier.And diesels have more fuel economy.
There are also more differences in thatDiesel engines generally use glow plugs.
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Differences in a Petrol & Diesel Engine
Diesels have more sound and vibrations.
The higher compression ratios lead to a much
higher operating pressure inside the cylinders, thishigh pressure makes the engine produce moresound and vibrations.
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Differences in a Petrol & Diesel Engine
Diesels are heavier.
Due to the higher pressure inside the cylinder thecylinder blocks are made more robust thus leadingto a heavier weight.
For this reason also diesel engines almost never usealuminium cylinder blocks.
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Differences in a Petrol & Diesel Engine
Diesels have more fuel economy.
The two main reasons for this are:
Diesels have a higher compression ratio thusleading to a higher efficiency and also
Diesel fuel has a higher energy density than petrol.
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Differences in a Petrol & Diesel Engine
Diesels generally use glow plugs.
As seen earlier diesel engines, compress the air to ahigh extent to raise the temperature for diesel toburn.
However in very cold conditions when the initial airtemperature is very low, mostly for I.D.I engines thecompression does not raise the temp. sufficiently thusstarting is difficult.
To avoid this a glow plug is present in the cylinder. Itis just an electrical heater wire that comes on for afew seconds before engine starting.
Glow plugs generally last the life of the engine andneed no replacement.
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Differences in Operation
As was seen earlier one of the major differences isthat in diesel engines only air is taken through theintake port and the fuel is injected later into thecylinder.
Based on the injection there are two main types ofengines today
d) Direct Injection
e) Indirect Injection
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Direct Injection
In a direct injectiondiesel engine, fuel isinjected directly intothe cylinder.
Injector
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Direct Injection
Here the burning is more uniform.
The advantages of this are:
The power developed is high.
The efficiency is high.
The emissions are low.
However there are some drawbacks, these are The sound levels & vibrations are
generally higher.
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Indirect Injection
To avoid the drawbackof the direct system asystem called indirectinjection is also used.
Here diesel engine fuel
is injected into a smallpre-chamber which isconnected to thecylinder by a narrow
opening. The initial combustion
takes place in this pre-chamber slowing the
rate of combustion.
InjectorPre Combustion
Chamber
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Indirect Injection
The advantages of this are
The sound and vibrations are reduced
The Disadvantages of this are The Power developed is low
The efficiency is low
The Emissions are high
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Differences
Considering all other factors equal, direct andindirect injection engines are said to have thefollowing differences.
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Future Trend
As can be seen the benefits of the direct injectionfar outweigh the drawbacks.
Thus world over indirect injection is on its way
out, as manufacturers are more and more usingdirect injection.
As its only draw back of higher sound levels canbe easily addressed.
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Regular Direct Injection
In this system a fuel pump, pumps fuel and alsodistributes it to each injector.
This system is mechanically controlled or can becomputer controlled.
ENGINE
FUEL PUMP
Injectors
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Common Rail Direct Injection
In this system a fuel pump only pumps fuel into arail.
In this system the injection has to be computercontrolled as the pump is not metering fuel.
ENGINE
FUEL PUMP
Injectors
Common Rail
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Forced Induction
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Forced Induction
Air enters into the cylinder via suction. i.e. thepiston moves down and creates a vacuum drawingair into the cylinder.
Forced induction is where a device pushes in moreair (than the piston will draw in) into the cylinder.Usually about 20 to 40 % more.
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Types Of Forced Induction
There are two major ways in which forcedinduction can be done.
Turbo Charging or Super Charging
In Turbo Charging the device is driven by engineexhaust gases.
In Super Charging the device is directly driven ofthe engine.
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Turbo Charging - How it Works
A turbocharger contains two fans in separatechambers, mounted on opposite ends of a commonshaft.
Engine exhaust flows onto one of the fans (called
turbine), causing it to turn & rotate the shaft. This rotates the second fan on the opposite side of
the shaft (called compressor) which is mounted inthe engines intake system.
When the second fan turns, it compresses the airentering the engines air intake manifold.
This boost of intake air works to improve theengines performance.
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Exhaust Gas
Turbo
Air InEngine
ToMuffler
CompressedAir
Turbo Charging - How it Works
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Intercooling
When air is compressed it heats up, & this heat
causes it to expand back a little.
Thus after air is compressed by a turbo, it heats up& expands a little back again, so some engines use adevice called an intercooler to cool the compressed
air and thus get more air molecules in.
Exhaust Gas
Turbo
Engine
ToMuffler
CompressedAir
Air In
Intercooler
Cool &Compressed Air
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Intercooling
The intercooler is very much a radiator wherecompressed air flows inside small pipes, and outsideair moves past the fins surrounding these pipes.