Analysis of soot formation of CH4 and C2H4 with H2 addition via ReaxFF molecular dynamics and pyrolysis-gas chromatography/mass spectrometry

A combined numerical and experimental investigation of the different chemical effects of H-2 (CE-H-2) on soot formation was conducted by applying the reactive molecular dynamics simulation (ReaxFF MD) and the pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) diagnostic technique. In addition, the detailed chemical reaction pathway for the different CE-H-2 was explored in the combustion of methane (CH4) and ethylene (C2H4) fuels. It was found that both the experimental and numerical results reflected the evolution of polycyclic aromatic hydrocarbons (PAHs) and initial soot particles and the different CE-H-2 on PAHs/soot formation. The primary reason for the different CE-H-2 was that the hydrogen addition led to the production of a large number of hydrogen atoms, which promoted acetylene (C2H2) formation during the methane combustion through the chemical reactions C2H5 + H <-> C2H4 + H-2 and C2H4 + H <-> C2H3 + H-2, but inhibited acetylene formation during the ethylene combustion through the chemical reaction C2H3 <-> C2H2 + H. The hydrogen addition only increased the number of 6-membered rings in the largest PAH/soot particle of methane combustion but decreased the numbers of all ringed compounds in the largest PAH/soot particle of ethylene combustion. Moreover, the CE-H-2 promoted methane pyrolysis but inhibited ethylene pyrolysis.

Automated summary

The study reveals different chemical effects of H-2 on soot formation, with hydrogen addition promoting acetylene formation during methane combustion but inhibiting it during ethylene combustion. Furthermore, H-2 increases 6-membered rings in the largest PAH/soot particle in methane combustion while decreasing the number of ringed compounds in ethylene combustion. Hydrogen addition also promotes methane pyrolysis and inhibits ethylene pyrolysis.