general engine

8/14/2019 General Engine

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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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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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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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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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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.

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