Deflagration characteristics and molecular reaction mechanism of hydrogen-enriched natural gas at varying equivalence ratios inhibited by CO2/N2 dilution: A combined experimental and ReaxFF-MD study

• CO 2 suppresses deflagration via physical, chemical, and thermodynamic coupled modes. • A quantitative cross-scale framework links molecular transport to macroscopic deflagration. • Diffusion coefficient correlates positively with flame speed and explosion pressure. • CO 2 raises activation energy barrier roughly twice as much as N 2. • ReaxFF-MD reveals H-radical scavenging and CO 2 reduction dominance in rich flames. Blending hydrogen into natural gas infrastructure offers a pragmatic pathway toward a low-carbon energy transition, yet the inherently high reactivity of hydrogen markedly increases deflagration risks. Although CO 2 and N 2 are widely used suppressants, their cross-scale suppression mechanisms remain insufficiently quantified. Specifically, the mechanistic linkage between molecular-scale reaction dynamics and macroscopic flame propagation has not been systematically established. This study combined 60-L spherical deflagration experiments with ReaxFF-MD simulations to investigate the deflagration of multicomponent hydrogen-enriched natural gas at different equivalence ratios ( φ = 0.8–1.2) under 0–15 % CO 2 or N 2 dilution. At φ = 1.0 and 15 % dilution, CO 2 lowered maximum deflagration pressure by 30.7 % and maximum pressure rise rate by 89.3 %, compared with reductions of 17.4 % and 46.4 % for N 2 . ReaxFF-MD simulations revealed that CO 2 operates through three coupled modes: physical quenching reduces the diffusion coefficient; chemical H-radical scavenging via CO 2 + H → CO + OH depletes the chain-carrying radical pool and diverts carbon flux toward CO accumulation; and thermodynamic inhibition raises the apparent activation energy by 12.8 % at φ = 1.0, thereby retarding the overall oxidation kinetics. In contrast, N 2 acts exclusively through physical dilution. This study provides a quantitative framework linking molecular-level dynamics to macroscopic deflagration, providing a theoretical basis for safe HENG transport and efficient deflagration suppression.