Numerical Investigation of Hydrogen-Induced Modulation of Flame Structure and Soot Formation in Turbulent Jet Diffusion Flames With Participating Radiation

Abstract

Abstract. Hydrogen blending in hydrocarbon flames has been proposed as a viable strategy for cleaner combustion in sustainable energy systems. The present numerical analysis is conducted to elucidate the effect of hydrogen (H2) addition (0–20% on mass basis) on the flame structure characteristics, mixing behavior, and soot formation processes involving nucleation, coagulation, surface growth, and oxidation in a turbulent methane–air jet flame with participating media radiative heat transfer effect. The results reveal that hydrogen addition shortens the flame, reduces flame width, and elevates the peak temperature up to an optimum enrichment level of approximately 16% H2, beyond which the hydrogen blending effect on flame length shortening diminishes. The contracted flame, enhanced mixing rate, and altered radical pool distribution, such as O, H, OH, and C2H2 lead to distinct nucleation–coagulation behavior near the flame centerline in reaction zone and far-field regions. Moreover, the H2 addition suppresses soot surface growth significantly by 85–90% through restricting the formation of surface radicals. This causes a similar substantial decrease in overall soot generation, indicating that surface growth is the decisive mechanism for soot formation for composite fuel. The increased OH radical concentration with hydrogen addition further accelerates soot oxidation, yielding a decrease in total soot volume fraction. Finally, the present study proposes a precise quantitative metric for the soot-free length fraction to characterize the spatial extent of soot suppression with hydrogen enrichment. Overall, these findings provide insight into how hydrogen addition modifies thermal and mixing characteristics to govern soot suppression in diffusion flames.