This work investigates the effects of hydrogen blending on soot formation and flame structure in a laboratory-scale Rich- Quench-Lean (RQL) burner using ethylene-hydrogen mixtures (0-50 vol.% hydrogen) at constant carbon mass flow rate. Laserinduced incandescence and single-ring and multi-cyclic polyaromatic hydrocarbon (PAH) planar laser-induced fluorescence were employed to quantify soot and PAH distributions respectively, while𝑂𝐻∗ chemiluminescence was used to detect the flame structures and reaction zone location. Hydrogen addition progressively reduced soot by c.a. 9, 36, and 68% at 10, 30, and 50 vol.% blending, respectively, with multi-cyclic PAHs decreasing more than single-ring aromatics. The single-ring aromatics were confined to the early parts of the fuel jet, while the multicyclic PAHs spread more downstream. Increasing the percentage of air flowing through the dilution jets results in significant shortening of the flame and reduction in soot, irrespective of the hydrogen content, and to a smaller difference between single-ring aromatics and multi-cyclic PAH distributions, possibly due to the reduction of the residence time in rich mixtures. An additional case with helium instead of hydrogen helped to isolate chemical effects from aerodynamic effects. The results suggests that the chemical effects of hydrogen addition dominate over thermal effects. This study shows that hydrogen addition can control particulate emissions. The dataset enables validation of turbulent combustion models for soot.
Tan et al. (2026) studied this question.