Effect of Natural Gas Blend Enrichment with Hydrogen on Laminar Burning Velocity and Flame Stability

Present study deals with the effect of enrichment with H₂ on the laminar burning velocity (LBV) and flame stability of various multicomponent NG–air mixtures. In the present work, constant pressure outwardly propagating spherical flame method is used to experimentally evaluate the LBV and burned gas Markstein length (L_b) of various fuel–air mixtures. The chemical kinetic analysis is performed with the help of CHEMKIN-PRO^® simulation software by using various detailed chemical kinetics mechanisms. All the experiments and simulations are performed at an initial pressure and temperature of 0.1 MPa and 300 ± 3 K, respectively. The addition of H₂ to NG blends increases the concentration of active radicals (H, O, and OH) in the reaction zone, and hence, enhances the combustion chemistry of the H₂-enriched NG blend. The effect is most prominent for the NG6–H₂ blend, which has the highest mole fraction of CH₄. The addition H₂ in the lean fuel–air mixtures reduces their Lewis number and thus may make the flames unstable. However, the NG5–H₂ blend, which has the highest mole fraction of C₃H₈, maintains a positive L_b over a wider range of equivalence ratios (0.7–1.4). The predictions of LBV using GRI-MECH 3.0 is the closest to the experimental results for the blends with 75% H₂ in the fuel when compared with those using San Diego and USC-II mechanisms.