12.12.6. State the function and/or purpose of the following within the carburettor:

12.12.4. Explain the basic principle of operation of a simple float-type carburettor.

Diagram

12.12.2. Explain the principle of carburation.

The device used to mix the fuel with the air is called the Carburettor
– the main fuel outlet of the carburettor is in the low pressure area at the centre of a venturi
– when air flows through the venturi the lowered pressure results in fuel being drawn or sucked from the jet
– the jet is calibrated so that it meters or delivers the required proportion of fuel into the air before the mixture enters the engine
– after it leaves the main jet, the fuel vaporises and and mixes with the air on its passage past the throttle butterfly and trhough the inlet manifold to the cylinders

12.10.6. Explain the basic principle of operation of a four stroke internal combustionengine. 

The four stroke engine operates on what is known as the Otto Cycle.
1. Intake – inlet valve open
2. Compression – both valves closed
3. Power – both valves closed – mixture ignited
4. Exhaust – exhaust valve open
(Diagram)

12.10.12. Explain the basic differences between compression ignition (diesel) engines and conventional ignition engines. 

In a diesel engine the fuel is injected directly into the cylinder during the compression stroke and ignites with the heat created by compression. There are no spark plugs.
In a conventional ignition engine fuel air mix enters via the inlet valve and is ignited by a spark plug during the compression stroke.

12.10.10. Explain the need for valve timing (i.e. valve lead, lag and overlap).

Because of the inertia of the fuel/ air mix travelling through the manifold to enter the cylinder, it has been found that better performance is obtained if the inlet valve is opened before top dead centre on the exhaust stroke ( valve lead). The exhaust valve is still open and only closes after the intake stroke has begun (valve lag). This lead on the inlet valve and overlap with both valves open allows the departing exhaust gases to help the inlet charge to start moving.The inlet valve closes after the start of the compression stroke (valve lag) because the inertia of the incoming gases means that they are still entering the cylinder for a time after the intake stroke is complete. Both valves are closed for the rest of the compression stroke and the power stroke, but the exhaust valve opens just before the end of the power stroke (valve lead).

12.10.8. Describe the correlation between engine rpm and power output.

Engine RPM – the higher the RPM the greater the power output

12.10.6. Explain the basic principle of operation of a four-stroke internal combustion engine. 

The four stroke engine operates on what is known as the Otto Cycle.
1. Intake – inlet valve open
2. Compression – both valves closed
3. Power – both valves closed – mixture ignited
4. Exhaust – exhaust valve open

12.10.4(j) . injectors. 

12.10.4(i) . spark plugs;