Experimental and kinetic of hydrogen blending effects on lean flammability limit of gasoline fuels

This study investigates the effects of hydrogen (H₂) bending on lean flammability limits (LFL) of gasoline using a constant volume combustion bomb apparatus at an initial temperature (T) of 453 K under atmospheric conditions. To enable stable engine operation with lean mixtures, the influencing mechanisms of H₂ on gasoline's LFL were further examined through chemical kinetic analyses. The experimental results reveal that H₂ addition markedly extends LFL of gasoline, though this effect is nonlinear. At lower blending ratios, H₂ addition produces a linear increase in LFL, while higher blending ratios yield a more pronounced enhancement. Kinetic analysis demonstrates that as the equivalence ratio decreases, the effect of flame thickness (reaction zone) causes the distribution of H radicals in TRF/H₂ blends to shift from a single peak to a double peak. This study proposes a novel method for determining LFL of TRF/H₂ blends by observing the transition in H radical distribution from bimodal to unimodal, reflecting a significant shift in flame structure and an increase in combustion stability and propagation speed. Compared to traditional methods, which rely on chain-branching (H+O₂ = O+OH) and chain-termination (H+O₂ (+M) = HO₂ (+M)) reactions to estimate LFL, the new approach demonstrates superior alignment with experimental data.