The OCTANE NUMBER associated with a motor fuel (as the CETANE NUMBER associated with a Diesel fuel) is a measure of the performance of that fuel. The number corresponds to the preignition properties of the fuels as compared with standard fuel mixtures. Pure isooctane is defined as having an octane number of 100, while heptane is defined as having an octane number of 0. A series of standards containing heptane, isooctane, and toluene are used to define a scale between these two bounds. The ASTM Standard Procedures for determination of octane numbers require the use of knock engines.

The operational principle of the OCTANE-IM based on the analysis of a fuel dielectric permeability. Due to original design of sensor and innovative technique of dielectric permeability measurement OCTANE-IM provides excellent repeatability and long-term stability of reading.

But measure of dielectric permeability is a secondary technique, in that results are generated through regression equations that model the output of some primary method of analysis. In the case of octane testing, the primary method of analysis is the knock engine. A secondary method can never show better accuracy than the precision of the primary method. In the case of knock engine testing, the limitations are as summarized in Table.
In this context:

• reproducibility describes the ability of an engine to generate the same result for a given' fuel after being shut down, then restarted and used by a new technician

• repeatability describes the ability of an engine to generate the same result for a fuel sample in successive tests.

Fuels from different refineries may have a difference in typical dependence of dielectric permeability — octane (cetane) number, made of pure isooctane and heptane. So it may be necessary make an individual calibration, taking a certain fuels as standards, testing them by knock engine. OCTANE-IM provides an easy way to make calibration and can manage up to 10 individual calibrations.