حسين واشقاني فراهاني

With increasing focus on the development of clean fuels to reduce pollutants, hydrogen, due to its high potential in mitigating environmental impacts, has become one of the key topics of research. However, operational challenges in lean-fuel systems, particularly combustion instability, highlight the necessity of parametric studies to ensure stable performance with alternative fuels. In this study, the thermoacoustic instability of pure hydrogen an‎d methane in a laboratory combustion chamber called the Rijke tube was numerically investigated using the unsteady Reynolds-averaged Navier–Stokes (URANS) method. The present investigation focused on two distinct instability behaviors, namely beating an‎d limit-cycle oscillations. Key results indicate that for both fuels, increasing the equivalence ratio an‎d moving toward richer mixtures significantly reduces the intensity of thermoacoustic instability. Additionally, increasing the thermal power from 1.42 kW to 1.7 kW leads to a transition from the beating state to limit-cycle oscillations. Comparative analysis shows that methane flames in lean-fuel conditions produce stronger oscillations, whereas hydrogen exhibits a wider instability range under richer-fuel conditions. Advanced modal analysis using the Dynamic Mode Decomposition (DMD) method identified dominant longitudinal acoustic modes an‎d local oscillations near the fuel nozzle that influence the flame structure. Specifically, hydrogen, due to its higher reactivity an‎d diffusivity, sustains instability over a wider range of equivalence ratios, while methane shows more intense oscillations under lean-fuel conditions. The findings of this study highlight the role of fuel properties in determining the onset an‎d nature of thermoacoustic instabilities in reactive flow systems an‎d clarify the sensitivity of system behavior in transitioning from fossil fuels to clean fuels.

احتراق , ترموآكوستيك

thermoacoustic , combustion

Hossein Vasheghani Farahani

Amir Mahdi Tahsini