ISO 17507-2:2025
PKI method
The PKI method in ISO 17507-2:2025 calculates the PKI methane number for a given gas composition.
Calculation flow
Compositions entered by volume, mole, or mass are converted to mole fractions according to ISO 14912:2025 and normalized before the method limits are checked. The standard first calculates the propane knock index (PKI) from the composition. A separate equation then converts PKI to the PKI methane number.
The calculation preserves full numerical precision internally. Rounding is applied only when values are presented to the user. Inputs outside the component or result ranges of the method are reported as errors rather than extrapolated silently.
Input guidance
The shared gas-composition model performs the ISO 14912:2025 conversion before the normalized mole composition is passed to the PKI method.
If your analysis reports Hexanes+, enter the full value as n-Hexane, as specified by the PKI method.
Implementation and validation
This calculator implements the PKI method described in ISO 17507-2:2025, including its equations, component limits, and result limits. Both the calculated propane knock index and methane number agree closely with the published values for all 12 reference mixtures. The validation page shows the results and differences for each comparison.