Question

State whether the given statement is true or false.
Statement: Lower the octane number, better will be the fuel.
A. True
B. False

Answer 1

Octane rating is defined as a measure of the resistance of gasoline and other fuels to detonation (engine knocking) in spark ignition internal combustion engines.

Complete answer:
First let us discuss the octane number.
Fuel with octane number is required to prevent engine knock. Knock occurs when unburnt fuel/air mixture auto ignites-essentially a small explosion in the engine.
Octane ratings are used for measuring fuel stability. These ratings are based on the pressure at which a fuel will spontaneously combust in a testing engine. The octane number is actually the simple average of two different octane rating methods—motor octane rating (MOR) and research octane rating (RON)—that differ primarily in the specifics of the operating conditions. The higher an octane number, the more stable the fuel.
Retail gasoline stations sell three main grades of gasoline based on the octane level:
1. Regular (the lowest octane fuel–generally 87)
2. Midgrade (the middle range octane fuel–generally 89–90)
3. Premium (the highest octane fuel–generally 91–94)
Engines are designed to burn fuel in a controlled combustion. A flame starts at the spark plug and burns throughout the cylinder until all of the fuel in the cylinder is burned. In comparison, spontaneous combustion, also called auto-ignition, detonation, or knock, happens when rising temperature and pressure from the primary combustion causes unburned fuel to ignite. This uncontrolled secondary combustion causes pressure in the cylinder to spike and causes the knock to occur.
The competition between the intended (controlled) and unintended (spontaneous) combustion causes the energy from the burning fuel to disperse unevenly, which can cause damage and place high pressure on the engine's piston before it enters the power stroke (the part of the cycle when the piston's motion is generating power).
High-performance engines typically have higher compression ratios and are therefore more prone to detonation, so they require higher octane fuel. A lower-performance engine will not generally perform better with high-octane fuel, since the compression ratio has been fixed by the engine design.

**So our statement is true.

Note:**
Octane rating does not relate to the energy content of the fuel. It is only a measure of the fuel's tendency to burn rather than explode.