Gas dilution method based on critical flow orifices in gas analysis for hydrogen fuel quality

Objective The aim is to solve the analysis problems on the accurate determination of micro-trace impurity components in the high-quality development of China's hydrogen energy industry.

Methods For the quality analysis of hydrogen fuel, a gas dilution method based on the principle of critical flow orifices was established. As the major component of the sample to be tested is hydrogen rather than nitrogen, the math module of flow response factor is studied to investigate the influences on the flow of different gases.

Results The dilution ratio of this method could achieve over 1∶1 000 with a relative expand uncertainty of better than 1%. The gas reference materials, namely formaldehyde and methane in hydrogen, are prepared in a 10^-9 molar fraction level dynamically. The measured repeatability of concentrations of the gas reference materials is no more than 7%. The linear correlation coefficient R² of each diluted concentration is more than 0.999.

Conclusions The analysis results of formaldehyde in nitrogen and in hydrogen respectively conclude that the math module of flow response factor is reliable, and the accuracy of this gas dilution method will be improved after a correction by flow response factor.