Fuels and Octane Number(Complete)

Question 1

What are the main fuels?

Answer 1

Methane- Natural gas.
Propane- Bottled gas.
Butane- Lighter fuel.

Question 2

What are mercaptans?

Answer 2

They are added to field to give off an odour and detect leaks to keep things safe.

Question 3

How are long chains converted into short chains?

Provide an example.

Answer 3

By catalytic cracking.
Catalytic cracking of decane:
C10H22= C5H12 + C3H6 + C2H4.

Question 4

What does octane number mean?

Answer 4

The measure of a fuels tendency to be able to resist knocking.

Question 5

What is knocking and what is its effects?

Answer 5

Knocking is premature ignition.

It reduces power.

Question 6

What are the two reference chemicals when referring to octane number and what are their octane numbers?

Answer 6

Heptane:
C7H16
Octane number- 0

2,2,4 trimethylpentane:
C8H18
Octane number- 100

Question 7

What are the factors that influence octane number?

Answer 7

Chain length:
The shorter the chain length the higher the octane number.
Degree of branching:
The more branched the chain, the higher the octane number.
Cyclic:
Higher than the corresponding straight chain.

Question 8

What are the factors that improve octane number?

Answer 8

Catalytic cracking: 
Splits long chains into short chains.
Isomerisation:
Creates more branched chains.
Dehydrocyclisation:
Creates a ring by removing the terminal h's and creating a single bond between the two end carbons.
Adding Additives;
Tetraethyl lead- banned due to toxicity.
Benzene- octane number- 106.
Adding oxygenates.
Ethanol- Octane number- 113.
MTBE- Methyl Tertiary Butyl Ether.

Question 9

What does MTBE stand for?

Answer 9

Methyl Tertiary Butyl Ether.

Question 10

Lead compounds were used in the past to increase the octane number of fuels. Why are lead compounds unsuitable as additives for petrol used in modern cars?

Answer 10

Because Pb/ lead is a catalytic poison and destroys the catalytic converter.