Petrol
In its crude state, petroleum is a virtually useless material. However when refined, the hydrocarbons it contains supply almost half the world's current energy needs and are the starting chemicals from which about 90% of the worlds organic chemicals are made. Fractional distillation is the process by which the different fractions in crude petroleum are separated according to their boiling points.
One of the fractions obtained is naphtha. Further fractionation of naphtha yields petrol (C - C alkanes). In the internal combustion engine, a piston compresses a mixture of air and petrol vapour. At the point of maximum compression, an electrical spark ignites the petrol/air mixture and rapid combustion occurs. A typical reaction would be the combustion of octane:
The hot gaseous products expand against the piston and force it downwards. This mechanical energy is transmitted to the drive wheels of the car, enabling it to move.
Petrol also contains various additives such as lubricants, rust inhibitors and anti-knock agent. Some hydrocarbons have a tendency to ignite spontaneously before maximum compression is achieved. This premature explosion, known as knocking, still forces the piston downwards and powers the vehicle. However, the chemical energy in the petrol is less efficiently converted into mechanical energy. As a result, the vehicle will do fewer miles per gallon. Knocking also causes a rough ride and excessive engine wear as the explosion is occurring as the piston is still moving up in its cylinder.
In its crude state, petroleum is a virtually useless material. However when refined, the hydrocarbons it contains supply almost half the world's current energy needs and are the starting chemicals from which about 90% of the worlds organic chemicals are made. Fractional distillation is the process by which the different fractions in crude petroleum are separated according to their boiling points.
One of the fractions obtained is naphtha. Further fractionation of naphtha yields petrol (C - C alkanes). In the internal combustion engine, a piston compresses a mixture of air and petrol vapour. At the point of maximum compression, an electrical spark ignites the petrol/air mixture and rapid combustion occurs. A typical reaction would be the combustion of octane:
The hot gaseous products expand against the piston and force it downwards. This mechanical energy is transmitted to the drive wheels of the car, enabling it to move.
Petrol also contains various additives such as lubricants, rust inhibitors and anti-knock agent. Some hydrocarbons have a tendency to ignite spontaneously before maximum compression is achieved. This premature explosion, known as knocking, still forces the piston downwards and powers the vehicle. However, the chemical energy in the petrol is less efficiently converted into mechanical energy. As a result, the vehicle will do fewer miles per gallon. Knocking also causes a rough ride and excessive engine wear as the explosion is occurring as the piston is still moving up in its cylinder.
