The octane number refers to compressibility of fuel before spontaneous combustion. Four-stroke powerhouses handle four different stages namely suction, compression, explosion (work), and discharge. Approximately 99% of the existing engines are the same system.
An important factor for proper compression phase is the type of fuel, which occurs when the gasoline and air mixture is compressed to the specific extent by piston.
This mixture is combusted following the compression phase with a spark. The resulting compression is measured with a number known as the “compression ratio”. In old engines, the compression ratio is 5:1 (5 to 1) or 6:1 and in new engines this figure reach to 10:1 or 12:1, respectively.
When the mixture of fuel and air mixture which is extremely flammable is combusted in less compression before the sparker ignition, the engine would be knocked, because before the piston reaches the highest level, it drives it down with an opposite force, which is known as knocking. This knocking can damage engine parts including the gudgeon pin, piston, conrod, etc.
A solution for increasing the output power of vehicle engines is improving their compaction rate. However, compaction ratio is only improved by increasing the fuel resistance to spontaneous combustion as a result of compression. Therefore, with the advancement of automobile manufacturing technologies the compaction ratio increased from 5 to 12.
Octane number definition and scale: The octane number is an agreed-upon number showing anti-knock properties of a fuel.
Isooctane has an octane number of 100 as the best fuel, whereas N-heptane has an octane number of zero as the worst fuel. An important characteristic of automobile and airplane gasoline is its octane number or slow-burning degree. Combusting of gasoline in the engine must be slow and without sudden explosion. Hence, knowing the gasoline octane number is necessary before use. Additives are used for increasing octane number (slow-burning).
The octane numbers of regular gasoline is 87, premium gasoline is 94 and avgas is 91-145, respectively. This scale was defined when isooctane was the best fuel but nowadays, better fuels by higher octane numbers more than 100 have been discovered.
Generally, the octane number of branchless hydrocarbons are low, the saturated cyclic one is average and the branched chain hydrocarbon and aromatic compounds are high respectively.
The general method for obtaining an octane number: The gasoline octane number can be calculated by both theoretical or research (RON) and the scientific or motor octane (MON) methods. The differences for applying each method are in related condition and experimental parameters on considered gasoline.
SNP Octan Booster Datasheets