Engines START
Four stroke petrol Two stroke petrol Diesel Click an engine to select
Four Stroke Petrol Engine Find out about the parts Watch an animation How it works Different engine arrangements Gallery Back
Four stroke petrol Exhaust Valve Inlet Valve Spark Plug Cylinder Piston Connecting Rod Crank Oil sump Back
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 Back
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’ Back
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 Back
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 Back
PARTS DEPARTMENT Spark Plug The spark plug creates a spark at just the right time to ignite the petrol vapour and air mixture Back
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 Back
PARTS DEPARTMENT Crank The crank is the first part of the engine to move with rotating motion Back
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 Back
PARTS DEPARTMENT Fuel Injector In a diesel engine the fuel is injected through these deveices at just the right moment Back
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 Back
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 Back
Compression Both valves are now closed The piston is moving up A mixture of petrol vapour and air is being compressed (squashed) Back
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 Back
Exhaust The exhaust valve opens The piston is moving up A waste fumes are pushed out of the cylinder The exhaust valve closes Back
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 Back
Gallery Four stroke petrol engines are usually used in cars, small propelor planes, and larger pleasure boats Back
Four Stroke Diesel Engine Find out about the parts Watch an animation How it works Gallery Back
Four stroke diesel Fuel Injector Air Inlet Valve Exhaust Valve Cylinder Connecting Rod Piston Crank Oil sump Back
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 Back
Induction The inlet valve opens The piston is moving down Air is sucked into the cylinder The inlet valve closes Back
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. Back
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 Back
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 Back
Exhaust The exhaust valve opens The piston is moving up A waste fumes are pushed out of the cylinder The exhaust valve closes Back
Gallery Until recently diesel engines were only used on big vehicles, nowadays they are quite common in small cars. Back
Two Stroke Petrol Engine Find out about the parts Watch an animation How it works Is two stroke better than four ? Gallery Back
Two stroke petrol Spark Plug Piston Cylinder Connecting Rod Crank Back
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 Back
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. Back
The up stroke…Compression As the piston moves up it begins to squash or compress the fuel mixture above it. Continue
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. Back
Is two stroke better than four ? Click on an expert to find out more Back
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. Back
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 Back
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. Back
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. Back
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 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. Back