Question

A fuel with a high octane number has less tendency to knock, whereas fuel with a high cetane number has more tendency to knock in an automobile engine.
A.True
B.False
C.Ambiguous
D.None of these

Answer 1

Hint : We must understand that fuels with a higher octane rating are used in high-performance gasoline engines that run with higher compression ratios. Fuels with lower octane numbers are best suited for diesel engines, because diesel engines do not compress the fuel.

Complete step by step solution :
We can remember that an octane number is a standard measure of the performance of an engine. If the octane number is higher, so the fuel can withstand higher compression.
Octane number is for gasoline or petrol fuels whereas cetane number is used for diesel fuel.
Octane number is determined by percentage of isooctane in the mixture of iso-octane and n-heptane. A petrol or gasoline with octane number of 80 represents that it is a mixture of 80% of isooctane and 20% of n-heptane. This percentage of compounds shows that the percentage of branched - chain alkane is more in mixture and so the knocking is less.
Cetane number is determined as the percentage of cetane in mixture of cetane and $α$-methyl naphthalene. A diesel fuel with cetane number 80 represents that mixturecontain 80% of cetane and 20% of $α$ - methyl naphthalene.
Higher the cetane number faster will be the ignition of fuel and it also produces higher knocking. Lower cetane number means fuel will ignite slowly and will produce lesser knocking.
Hence, we can conclude that the option A is the correct answer.

Note : We must understand that the knocking is simply known as eating sound. The knocking sound generates through the engine when the mixture of fuel and air or oxygen auto-ignites before the spark is generated.