Prospects for the Development of Reference Materials of the Wobbe Index

The thermophysical properties of gaseous fuel are essential for its industrial applications. The trueness of gas volumetric calorific values is currently ensured using certified reference materials for the net volumetric calorific value of pure gases and gas mixtures traceable to GET 16-2018. However, when determining the Wobbe index, a need arises to measure the relative gas density to air with traceability to GET 18-2014. This study aims to improve the accuracy of the pycnometer method for measuring gas density to establish metrological support for Wobbe index measurements. This method was used to estimate the uncertainty budget of gas density measurements. The mass determination of analyzed gas was found to make the greatest contribution to the combined uncertainty. To minimize the uncertainty, the pycnometer internal volume was increased and determined using the modified procedure. A pycnometer (imitator) having an increased volume and original design was produced. The modified method was tested to improve Wobbe index measurement accuracy. The study results provide a wider possibility of establishing metrological characteristics in the metrological support of Wobbe index analyzers, as well as enabling the application of the procedure for controlling the measurement accuracy of relative gas density to air.