Mechanical Engineering - IC Engines and Nuclear Power Plants - Discussion

The antiknock value of an SI engine fuel is determined by comparing its antiknock property with a mixture of two reference fuels, iso-octane(C8H18) and normal Heptane(C7H16).

Octane rating or octane number is a standard measure of the performance of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are used in high performance petrol engines that require larger compression ratios. In contrast, fuels with lower octane numbers (but higher cetane numbers) are ideal for diesel engines, because diesel engines (also referred to as compression-ignition engines) do not compress the fuel but rather compress only air and then inject the fuel into the air heated up by compression, whereas petrol engines (also referred to as gasoline engines) rely on ignition of air and fuel compressed together as a mixture without ignition, which is then ignited at the end of the compression stroke using spark plugs. Therefore, high compressibility of the fuel matters greatly for only petrol engines. Use of gasoline (also known as petrol) with lower octane numbers may lead to the problem of engine knocking.

For spark plug engine petrol or fuel used is determined by its octane number which is percentage of iso octane in the heptane,

ISO octane is anti knocking agent and heptane is knocking agent.

What is petrol chemical formula?

What do mean by knocking agent?

What is knock rating of spark ignition engines?

Knocking agent is dependent of combustion.

I think the answer should be A this is the basic definition of octane number.

Given answer is correct.

Alpha methylnapthalene is related to cetane number, which is a measure for diesel engines.