Engines START Four stroke petrol Two stroke petrol Diesel Click an engine to select

Engines

START

Four stroke petrol

Two stroke petrol

Diesel

Click an engine to select

Four Stroke Petrol Engine

Find out about the partsWatch an animation

How it works

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Different engine arrangements

http://auto.howstuffworks.com/engine4.htm

Four stroke petrol

Exhaust Valve

Spark Plug

Oil sump

Piston

Cylinder

Crank

Inlet Valve

Connecting Rod

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The Inlet Valve

The inlet valve is pushed down on its spring to open up a way for the petrol vapour and air mixture to go into the cylinder

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PARTS DEPARTMENTPARTS DEPARTMENT

Cylinder

The cylinder is where the fuel is burned.

The total volume of the cylinders is known as the ‘engine capacity’

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Connecting Rod

The connecting rod connects the piston which is moving up and down in a straight line to the crank which is rotating

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Exhaust Valve

The exhaust valve is pushed down on its spring to open up a way for the burnt fumes to leave the cylinder

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Spark Plug

The spark plug creates a spark at just the right time to ignite the petrol vapour and air mixture

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PistonThe piston moves up and down inside the cylinder.

When the fuel explodes the piston is pushed down

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Crank

The crank is the first part of the engine to move with rotating motion

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Oil sump

The oil used to reduce friction and keep the engine running smoothly collects in the sump at the bottom of the engine

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Fuel Injector

In a diesel engine the fuel is injected through these deveices at just the right moment

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How it works…

There are four stages to the cycle.Click on each engine to find out about each stage

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INDUCTION COMPRESSION

COMBUSTION EXHAUST

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Induction

The inlet valve opens

The piston is moving down

A mixture of petrol vapour and air is sucked into the cylinder

The inlet valve closes

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Compression

Both valves are now closed

The piston is moving up

A mixture of petrol vapour and air is being compressed (squashed)

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Combustion


The spark plug makes a spark which explodes the fuel

The piston and connecting rod are now pushed down, turning the crank shaft

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Exhaust

The exhaust valve opens


A waste fumes are pushed out of the cylinder

The exhaust valve closes

Different Engine Arrangements

IN-LINE

Most engines have four cylinders arranged vertically in a

straight line

V6

Some more powerful engine have 6 or eight cylinders arranged in a

‘V’ shape

FLAT4

Some engines have 4 cylinders arranged in a flat horizontal

way. Click each engine to see animations

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http://auto.howstuffworks.com/engine-inline.htm

http://auto.howstuffworks.com/engine-inline.htm

http://auto.howstuffworks.com/engine-v.htm

http://auto.howstuffworks.com/engine-flat.htm

Gallery

Four stroke petrol engines are usually used in cars, small propelor planes, and larger pleasure boats

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Four Stroke Diesel Engine

Find out about the parts

Watch an animation

How it works

GalleryBack

http://auto.howstuffworks.com/diesel1.htm

Fuel Injector

Cylinder

Connecting Rod

Four stroke diesel

Air Inlet Valve

Oil sumpCrank

Piston

Exhaust Valve

Back

How it works…

There are four stages to the cycle.Click on each engine to find out about each stage

Back

INDUCTION COMPRESSION

COMBUSTION EXHAUST

The inlet valve opens

The piston is moving down

Air is sucked into the cylinder

The inlet valve closesBack

Induction

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Compression



Diesel fuel is injected into the cylinder just before the piston reaches the top.

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CombustionBoth valves are now closed

There is no spark plug. Instead the air has been squashed so much that it is hot enough to ignite the fuel straight away

VIEW VIDEO CLIP

The piston and connecting rod are now pushed down, turning the crank shaft

These are video clips which show a piston being pushed very rapidly down a glass tube.

The squashed air heats up so quickly that a small piece of tissue paper at the bottom of the tube bursts into flames.

This is how a diesel engine ignites the fuel.

BackClick the pictures to play

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Exhaust

The exhaust valve opens


A waste fumes are pushed out of the cylinder

The exhaust valve closes

Gallery

Until recently diesel engines were only used on big vehicles, nowadays they are quite common in small cars.

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Two Stroke Petrol Engine

Find out about the partsWatch an animation

How it works

GalleryBack

Is two stroke better than four ?

Cylinder

Connecting Rod

Two stroke petrol

Crank

Piston

Back

Spark Plug

How it works…

Down Stroke… Combustion

Up Stroke… Compression

The two stroke engine fires once every revolution whereas the four stroke only fires once every other revolution.

There are just two parts to the cycle, the down stroke and the up stroke

Click on the pictures above to find out about each stroke

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The down stroke… Combustion

•This starts when the spark ignites the fuel pushing the piston down.

•Soon after starting to move down the exhaust port is uncovered and the exhaust gasses rush out

•In a two stroke engine the fuel,air,and oil mixture surrounds the crank.

•So as the piston moves down it squashes the fuel mixture. Continue

The down stroke continued…•As the piston moves down, the inlet port is uncovered and the squashed fuel mixture rushes into the cylinder.

•Notice that at this point both the exhaust and inlet port are both uncovered. It is possible for some fresh fuel to pass straight out of the exhaust port.

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The up stroke…Compression

Continue

•As the piston moves up it begins to squash or compress the fuel mixture above it.

The up stroke…Compression

•Once the inlet port has been covered the rising piston will cause a partial vacuum in the crank case below it.

•The drop in pressure in the crank case causes the reed valve on the inlet to be sucked open.

•A fresh fuel / air / oil mixture can now enter the crank case.

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Click on an expert to find out more

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•A two stroke engine fires once every revolution, whereas a four stroke engine only fires once every other revolution.

•This means it has a lot more power

•If you need a light weight engine with a lot of power, then two stroke is much better.

•This is important if the engine is on something that you have to lift, like a petrol hedge trimmer or chain saw.

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•A two stroke engine doesn’t have any valves and all the parts needed to drive the valves.

•With fewer moving parts the engine can be lighter, and will be more reliable.

•This is important in small portable engines, and makes two stroke engines ideal for scooters and small motor bikes

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•In a two stroke engine the fuel / air mixture has to surround the crank. This means there is no pool of oil in the sump to lubricate the moving parts.

•To overcome this special oil has to mixed with the fuel.

•This means that the engine will work equally well at all angles, even upside down. Important for small hand held machines like chain saws.

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•In a two stroke engine the fuel / air mixture has to surround the crank. This means there is no pool of oil in the sump to lubricate the moving parts.

•To overcome this special oil has to mixed with the fuel.

•This means that the engine will burn quite a lot of oil. Two stroke engines are often quite smoky. This doesn’t go down to well when we are trying avoid pollution.

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•Remember that there is one part of the cycle when both inlet and exhaust port are both open.

•New, un-burnt fuel can go straight out of the exhaust.

•This means that two stroke engines waste a lot of fuel. If you had a two stroke engine in your car you wouldn’t get very many miles to each litre of petrol.

•Petrol which has leaked out of two stoke boat engines is often seen floating on the water.

•All of this makes two stroke engines very environmentally unfriendly Back

Gallery

•Two stroke engines are ideal for small machinery which may have to operate at different angles and where it is important to keep the weight down.

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Documents

Engines START Four stroke petrol Two stroke petrol Diesel Click an engine to select