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Instability and Flame-Pressure Coupling in Downward Propagating Premixed H2/CO/CO2/Air Flames
Zhanglin Yang1, Qiaosheng Zhang1, Zhidong Guo2
1College of Mechanical and Automotive Engineering, ChuZhou Polytechnic, Chuzhou 239000, P. R. China.
ACS Omega
|July 24, 2026
Summary
Increasing hydrogen in syngas flames causes significant instability and pressure changes. Higher hydrogen volume fractions (HVF) lead to flame wrinkling, intense pressure fluctuations, and acoustic coupling, increasing explosion risks.
Area of Science:
- Combustion Science
- Chemical Engineering
- Fluid Dynamics
Background:
- Downward propagating premixed flames of hydrogen (H₂)/carbon monoxide (CO)/carbon dioxide (CO₂)/air mixtures are crucial in various industrial applications.
- Understanding flame instability and pressure coupling is vital for safety and efficiency in combustion systems.
Purpose of the Study:
- To investigate the effects of varying hydrogen volume fractions (HVF) on the instability and flame-pressure coupling of H₂/CO/CO₂/air flames.
- To analyze flame morphology, overpressure development, thermoacoustic characteristics, and reaction sensitivity under different HVFs.
Main Methods:
- Experimental investigation of downward propagating premixed H₂/CO/CO₂/air flames.
- Systematic variation of hydrogen volume fractions (HVF).
- Analysis of flame morphology, pressure oscillations, dominant frequencies, and reaction pathways through sensitivity analysis.
Main Results:
- Increasing HVF transitions flame propagation from laminar to instability-controlled, characterized by wrinkling and cellular structures.
- Overpressure responses intensify with higher HVF, shifting from low-frequency oscillations to strong nonlinear pressure fluctuations.
- Flame-acoustic coupling is enhanced, with dominant frequencies shifting to longitudinal acoustic modes at HVF ≥ 10%.
Conclusions:
- A critical transition region for instability and reactivity is identified around 10%-15% HVF.
- CO oxidation remains key, but chain-branching reactions become more dominant at higher HVFs, driving flame acceleration.
- Findings offer insights into hydrogen-enriched syngas combustion risks in confined environments.
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