What is the basic ingredient that gives fuel petrol engine an anti knock ? what element is it ?

Question

What is the basic ingredient that gives fuel petrol engine an anti knock ? what element is it ?

Answer 1

The anti knock is the ability of fuel to resist combustion due to pressure.

Fuels with higher auto ignition pressures are generally added, (like octane) to create a better resistance to this.

Answer 2

more or higher octane rating. a low octane fuel can cause engine "knock" or "ping".

Answer 3

Decades ago, they used to use Tetraethyl Lead, this is why you have the terms Leaded and unleaded gasoline.

One big reason they used this was that it was too expensive to make very high octane fuel , usually over 92.   In those old days  LEAD (pb)  was the element you may be searching for.

It's a synthesized organic lead.