1. Engines
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2. Four stroke petrol
Two stroke petrol
Diesel
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3. Four Stroke Petrol Engine
Find out about the parts
Watch an animation
How it works
Different engine arrangements
Gallery
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4. Four stroke petrol Exhaust Valve Inlet Valve Spark Plug Cylinder
Piston
Connecting Rod
Crank
Oil sump
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5. PARTS DEPARTMENT
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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6. Cylinder The cylinder is where the fuel is burned.
PARTS 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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7. PARTS DEPARTMENT
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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8. PARTS DEPARTMENT
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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9. PARTS DEPARTMENT
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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10. Piston The piston moves up and down inside the cylinder.
PARTS DEPARTMENT
Piston
The piston moves up and down inside the cylinder.
When the fuel explodes the piston is pushed down
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11. PARTS DEPARTMENT
Crank
The crank is the first part of the engine to move with rotating motion
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12. PARTS DEPARTMENT
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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13. PARTS DEPARTMENT
Fuel Injector
In a diesel engine the fuel is injected through these deveices at just the right moment
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14. How it works… There are four stages to the cycle.
INDUCTION
COMPRESSION
COMBUSTION
EXHAUST
There are four stages to the cycle.
Click on each engine to find out about each stage
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15. 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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16. 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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17. Combustion Both valves are now closed
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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18. Exhaust The exhaust valve opens The piston is moving up
A waste fumes are pushed out of the cylinder
The exhaust valve closes
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19. 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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20. Gallery
Four stroke petrol engines are usually used in cars, small propelor planes, and larger pleasure boats
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21. Four Stroke Diesel Engine
Find out about the parts
Watch an animation
How it works
Gallery
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22. Four stroke diesel Fuel Injector Air Inlet Valve Exhaust Valve
Cylinder
Connecting Rod
Piston
Crank
Oil sump
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23. How it works… There are four stages to the cycle.
INDUCTION
COMPRESSION
COMBUSTION
EXHAUST
There are four stages to the cycle.
Click on each engine to find out about each stage
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24. Induction The inlet valve opens The piston is moving down
Air is sucked into the cylinder
The inlet valve closes
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25. Compression Both valves are now closed The piston is moving up
Diesel fuel is injected into the cylinder just before the piston reaches the top.
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26. Combustion Both 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
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27. This is how a diesel engine ignites the fuel.
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.
Click the pictures to play
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28. Exhaust The exhaust valve opens The piston is moving up
A waste fumes are pushed out of the cylinder
The exhaust valve closes
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29. Gallery
Until recently diesel engines were only used on big vehicles, nowadays they are quite common in small cars.
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30. Two Stroke Petrol Engine
Find out about the parts
Watch an animation
How it works
Is two stroke better than four ?
Gallery
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31. Two stroke petrol
Spark Plug
Piston
Cylinder
Connecting Rod
Crank
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32. Up Stroke… Compression
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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33. 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.
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34. 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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35. The up stroke…Compression
As the piston moves up it begins to squash or compress the fuel mixture above it.
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36. 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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37. Is two stroke better than four ?
Click on an expert to find out more
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38. Is two stroke better than four ?
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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39. Is two stroke better than four ?
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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40. Is two stroke better than four ?
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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41. Is two stroke better than four ?
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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42. Is two stroke better than four ?
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
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43. 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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