As HUCR value is only applicable to a particular engine and a given set of operating conditions another method has been devised to give an anti knock measure of the fuel. This method is determination of the octane number of the fuel.
In octane number test the performance of unknown gasoline is compared with that a series of reference fuels consisting of mixtures of iso-octane and n-heptane. Iso-octane is low boiling point branched chain compound and has a very slight tendency to knock and hence arbitrarily assigned an octane number of 100. n-heptane detonates rapidly and hence has been assigned an octane number of zero.
These fuels are known as the Primary Reference Fuels (PRF) and the octane number of unknown fuel is defined as the percent-age of iso-octane in Primary Reference Fuel that gives the same knock intensity. Thus a gasoline that gives the same knock intensity as 90PRF (90% vol iso-octane, 10% vol n-heptane) in a test is said to have an octane number of 90.
Picture beside show that Suzuki Thunder EN125 with compression ratio 9.2 that must use 92 octane number of fuel to get the highest efficiency of fuel consumption 100%.
If we knew compression ratio of machine, we can selected fuel octane number by multiple compression ratio with 10 for example Indonesian fuel
-Premium (octan 88) for compression ratio 7:1 (7) until 9:1 (9)
-Pertamax (octan 92) for compression ratio 9 until 10
-Pertamax Plus (octan 95) for compression ratio 10 until 11
Honda Jazz has compression ratio 10.1 is suitable for fuel Pertamax Plus. another example Suzuki Karimun has compression ratio 8.8 so premium is enough.
Refference:
From http://suzuki-thunder.indonesianforum.net/t33-moto-moto-gede-moge-moto-besar-vs-moto-kecil
Mathur & Sharma, A Course in Internal Combustion Engine, Dhanpat Rai & Son 1980
Next compression ratio and detonation http://mechanic-info.blogspot.com/2011/05/compression-ration.html
