The higher the octane number, the more compression the fuel can withstand before detonating.
In contrast, fuels with lower octane numbers (but higher cetane numbers) are ideal for diesel engines.
Use of gasoline with lower octane numbers may lead to the problem of engine knocking.
Because some fuels are more knock-resistant than iso-octane, the definition has been extended to allow for octane numbers greater than 100.
Where the octane number is raised by blending in ethanol, energy content per volume is reduced.
The octane number is an empirical measure of the resistance of gasoline to combusting prematurely, known as knocking.
Gasoline is graded by octane number, which rates its resistance to premature ignition, or engine knocking.
The octane number on gasoline is a measure of the gasoline's tendency to cause "knocking" in the engine.
Because it has a high octane number, it is an important component of gasoline, composing a few percent of its mass.
Both of these processes raise the octane number of the substance.
