Combustion characteristics of hydrogen-enriched natural gas under elevated temperature and pressure

Laminar flame characteristics of natural gas-hydrogen-air mixtures were studied in a constant volume combustion bomb at elevated temperature and pressure (T₀=450 K, p₀=0.75 MPa). Unstretched laminar burning velocities of natural gas-hydrogen-air mixture with various hydrogen fractions at different equivalence ratios were obtained, and flame stability was analyzed. The results showed that at elevated initial condition, laminar burning velocity increases with the increase of hydrogen fraction, while Markstein length decreases with the increase of hydrogen fraction which decreases flame stability. The unstretched laminar burning velocity give a peak value at certain equivalence ratio, and the corresponding equivalence ratio moves to the rich mixture direction with the increase of hydrogen fraction. Markstein length tends to increase with the increase of equivalence ratio at different hydrogen fractions, and this indicates the increase of flame stability with the increase of equivalence ratio.