How engines work

Most internal combustion engines work on what is called the 4 stroke cycle. Combustion takes place in a steel or aluminium cylinder with an aluminium piston inside it. This piston can slide up and down for one complete working cycle. The piston moves 4 strokes 2 up and 2 down.

How the 4 stroke engine works

Intake

As a piston moves down in the cylinder a valve opens and the piston draws a mixture of petrol and air into the cylinder. Towards the end of the stroke the inlet valve closes.

Compression

The piston moves up and because both valves are closed the petrol and air mixture is squeezed in to a small space between the top of the piston and the top of the cylinder.

Power

When the piston is almost at the top of the compression stroke the spark plug ignites the mixture which burns very rapidly and expands this forces the piston down and gives the power to turn the crankshaft.

Exhaust

Towards the end of the power stroke the exhaust valve opens and the piston moves up again it pushes out exhaust gases which are left after the mixture has burnt.

Catalytic converters are designed to reduce the amount of poisonous gases that are released into the atmosphere. Inside is a honeycomb structure with a surface area of two football pitches. All of this inside a box about 30cm x 23cm. Waste gases pas through the catalytic converter which causes a chemical reaction that changes most of the poisonous gases and makes them less harmful.

The battery

The battery is a store for electricity made up of a series of cells. Each cell is basically two plates of lead in a solution of diluted sulphuric acid which produces an electrical current of two volts. Six cells joined together will make a twelve volt battery. The cells works by the sulphuric acid splitting into two parts from positively charged hydrogen and negatively charged sulphate which moves towards the positive and negative plates. This movement of electrons is a basis of the flow of electricity. The positive plate is lead peroxide (pb02) and the hydrogen combines with this and the sulphuric acid (h2so4) to form lead sulphate (pbso4) and water. The negative plate is spongy lead (pb) and the sulphate combines with this to form lead sulphate (pbso4). As both plates become covered with lead sulphate and the sulphate acid becomes water the reaction slows down and eventually stops. Charging the battery is the reverse of this process.