Monsalve Guaracao, Jorge MarioJorge MarioMonsalve GuaracaoVölz, UweUweVölzJongmanns, MarcelMarcelJongmannsBetz, BjörnBjörnBetzLanga, SergiuSergiuLangaRuffert, ChristineChristineRuffertAmelung, JörgJörgAmelungWiersig, MarcusMarcusWiersig2025-02-252025-02-252024-07-12https://publica.fraunhofer.de/handle/publica/48424010.5194/jsss-13-179-2024Abstract. The implementation of the "power-to-gas" concept, where hydrogen and natural gas are blended and transported in the existing network, requires a quick, on-site method to monitor the content of hydrogen in the mixture. We evaluate a rapid characterisation of this mixture based on the measurement of the speed of sound, using micromachined ultrasonic transducers (MUTs). Two MUT-based prototypes were implemented to analyse a mixture of natural gas and hydrogen under controlled conditions. Changes in the hydrogen content below 2 mol % (in a mixture that was adjusted between 6 mol % and 16 mol %) were discriminated by both devices, including the uncertainty due to the temperature compensation and the time-delay estimation. The obtained values of the speed of sound were consistent with those calculated from independent, non-acoustic measurements performed with a gas chromatograph and a density sensor. An MUT-based flow meter is thus capable of reporting both gas intake and the molar fraction of hydrogen, provided that the source of natural gas is kept constant.enjournal article