Laminar flame speed measurements and flame structure differences of syngas(H₂/CO)-air mixture in lean and rich conditions

In this study, the laminar flame speeds are measured by the angle method based on the Schlieren images and the numerical simulations including chemical kinetic analysis used CHEMKIN package with USC-II mechanism. A large range of syngas mixture compositions such as H₂:CO=10:90, 25:75, 50:50, 75:25 and equivalence ratios from lean condition of 0.5 to rich condition of 5.0 have been conducted. The experimental results of flame speed are in good agreement with previous other research data and numerical simulation. Also, it is shown that the experimental measurements of laminar flame speed linearly increased with the increment of H₂ content although the flame speed of hydrogen is faster about ten times order than that of carbon monoxide. This phenomenon is attributed to the rapid production of hydrogen related radicals such as H and OH radicals at the early stage of combustion, which is confirmed the linear increase of H radical concentrations on kinetic simulation. Particular concerns in this study are the characteristics of flame speed and flame structure differences from lean condition for rich condition. The decrease of OH radicals and double peaks are observed with H₂ content in rich condition once H₂ fraction exceeds over threshold.