Fig. 1. Schematic diagram of hydrocarbon fuel combustion and soot sampling

Fig. 2. The consistency check of the Raman spectrum experiment: the normalized comparison of three sample results

Fig. 3. Normalized spectral

Fig. 4. Raman spectrum peak fitting effect diagram

Fig. 5. A_D1/A_G variation diagram of soot particles in hydrogen-doped methane ethylene flame
(a): Along flame height; (b): At different methane ratios

Fig. 6. Asymmetrical vibrational expansion and contraction of CH₂ aliphatic hydrocarbon functional group in methane hydrogen-doped ethylene flame soot
(a): Along flame height; (b): At different methane ratios

Fig. 7. Changes of double-substituted C—H between hydrogen-doped methane and ethylene flame soot aromatic functional groups
(a): Along flame height; (b): At different methane ratios