Effects of hydrogen content and pressure on lean premixed hydrogen/methane Bunsen flames

Hydrogen/methane (H2/CH4) blends serve as a transitional fuel for gas turbines, offering a pathway toward cleaner energy by reducing carbon emissions while leveraging existing natural gas infrastructure. Understanding the effects of H2 content and pressure on the flame shape is essential for safe operation and opti­mising combustion performance. In this work, turbulent lean premixed Bunsen H2/CH4 flames are studied using large eddy simulation (LES), focusing on the flame brush length ( fl ) and thickness ( fb ) along the centreline. The results have been compared with available measurements for validation. The findings indicate that increasing H2 content leads to shorter and thinner flames, while the pressure effects are minimal. At the lower H2 content (≤ 30% by volume), the change in fl is relatively small, whereas at the higher H2 content ( > 30% by volume), fl decreases linearly with increasing H2 content. Similarly, the values of fb decrease as H2 content is increased. This phenomenon is primarily due to the increased turbulent flame speed ( sT ) resulting from enhanced fuel reactivity. The limited pressure effects on fl and fb are attributed to the consistent sT , maintained by the synergistic interactions between chemical reactions and turbulent char­acteristics. Furthermore, this study highlights the transition of the flame regime from the corrugated flamelet regime to the thin reaction zone regime along the axial direction. This transition occurs further upstream in flames with higher H2 content, driven by the increased flame speed. Additionally, the reaction progress variable contours and profiles show that the H2 addition also leads to a radial thinning of the flame, while pressure has little effect on the overall flame shapes.