Engine theory and operation

Section 1: Basic Engine Theory

A spark ignition engine is a type of internal combustion engine, usually fuelled by petrol, that uses an electric spark to ignite a fuel-air mixture.
The main parts of an engine include the cylinder, piston, connecting rod, crankshaft, spark plug, distributor, and valves.
The engine cycles refer to the sequence of events or stages that occur inside the engine. These stages include intake, compression, power (or combustion) and exhaust.
The engine takes in a fuel-air mixture during the intake stage, compresses it during the compression stage, ignites it via the spark plug during the power stage, and expels the exhaust gases during the exhaust stage.
This process is known as the four-stroke cycle, or Otto cycle, named after the inventor Nicholas Otto.

Section 2: Engine Components

Cylinder: The combustion of the fuel-air mixture occurs within the cylinder.
Piston: This moves up and down within the cylinder, creating different stages of the engine cycle.
Spark plug: Provides the spark for igniting the fuel-air mixture inside the cylinder.
Valves: Allow the intake of air and fuel into the cylinder and let out the exhaust gases.
Crankshaft: Converts the linear up and down motion of the piston into rotational motion that can drive a vehicle’s wheels.

Section 3: Engine Operation

The engine first draws in a mixture of air and fuel during the intake phase. The intake valve opens to let the mixture into the cylinder as the piston moves downward.
The intake valve closes during the compression phase, and the piston moves upwards to compress the fuel-air mixture.
In the combustion phase, the compressed mixture is ignited by a spark from the spark plug, which forces the piston down and creates power.
Finally, during the exhaust phase, the burnt gases are expelled from the cylinder through the exhaust valve.
The timing of valves and the ignition spark are controlled by the engine’s control unit and are critical for the efficient operation of the engine.

Section 4: Engine Systems

(Carburetion) A carburettor mixes air and fuel together for an internal combustion engine. The mixture is then ignited to produce power.
(Ignition) An ignition system generates a spark or ignites the fuel-air mixture to create combustion.
(Cooling) An engine cooling system dissipates the heat produced by combustion. This is typically accomplished via a water cooling system or an air cooling system.
(Lubrication) Lubrication systems reduce friction between the moving parts of the engine. This is achieved by supplying clean filtered oil to the interaction points.

Remember, understanding the basics of engine theory, components and operation is essential for maintaining and troubleshooting issues in spark ignition engines.