Prospects for the Development of Reference Materials of the Wobbe Index

Abstract

The thermophysical properties of gaseous fuel, including the calorific value and the Wobbe index, are one of its main properties for industrial use. The correctness of measurements of the volumetric energy of gas combustion is currently ensured by using sets of certified reference materials of the lowest volumetric energy of combustion based on pure gases: hydrogen, methane, ethane and propane GSO 11662–2020 / GSO 11665–2020 and gaseous mixtures GSO 11904–2022 / GSO 11907–2022 with metrological traceability to GET 16–2018. However, it becomes necessary to measure the gas relative density to air with established traceability to GET 18–2014 when determining the Wobbe index.The purpose of this research is to improve the accuracy of the pycnometer method for measuring the density of gases for further development and creation of metrological assurance in the field of measuring the Wobbe index.In the course of the research, an analysis of existing methods for determining the gas density was performed, as a result of which the pycnometer method set forth in GOST 17310–2002, GOST 34721–2021 was taken as the basis for the developed method. The uncertainty budget of gas density measurements was estimated using the pycnometer method. It has been established that the mass determination of the gas under study makes the greatest contribution to the total uncertainty. It was decided to increase the internal volume of the pycnometer and use a modified method for determining its volume to minimize the uncertainty.An imitator of a pycnometer with an increased volume was manufactured in an original design to solve the task of developing a modified pycnometer method for measuring the gas density. A gravimetrically produced gaseous mixture of the following composition was chosen for testing the developed method: CO2 –  40.22 mol. %, CH4 –  rest.The theoretical significance of the results obtained lies in approbation of a modified pycnometer method to improve the measurement accuracy of such a gaseous fuel property as the Wobbe index. In the process of developing a modified pycnometer method, the measurement algorithm was tested, the density values of the studied gas were obtained, and the uncertainty budget of density measurements was estimated.The practical significance of the results of this research will expand the possibility of establishing metrological characteristics during the metrological assurance of Wobbe index analyzers, as well as apply the developed method in future accuracy control of the measurement results of the gas relative density to air.