Study on laminar flame speed and flame structure of syngas with varied compositions using OH-PLIF and spectrograph

Various Bunsen flame information of premixed syngas/air mixtures was systematically collected. A CCD camera was used to capture the flame images. The OH-PLIF technique was applied to obtain the flame OH distribution and overall flame radiation spectra were measured with a spectrograph. Experiments were conducted on a temperature un-controlled burner and syngas over a wide range of H2/CO ratios (from 0.25 to 4) and equivalence ratios (from 0.5 to 1.2). Results show that increasing hydrogen fraction (XH2XH2) extends the blow-off limit significantly. The measured laminar flame speed using cone-angle method based on CCD flame imaging and OH-PLIF images increases remarkably with the increase of XH2XH2, and these measurements agrees well with kinetic modeling predictions through Li's mechanism when the temperature for computation is corrected. Kinetic study shows that as XH2XH2 increases, the production of H and OH radicals is accelerated. Additionally, the main H radical production reaction (or OH radical consumption reactions) changes from R29 (CO + OH = CO2 + H) to R3 (H2 + OH = H2O + H) as XH2XH2 increases. Sensitivity analysis was conducted to access the dominant reactions when XH2XH2 increases. The difference on flame color for different XH2XH2 mixtures is due to their difference in radiation spectrum of the intermediate radicals produced in combustion.

► Flame speed and flame structure of syngas were obtained using OH-PLIF technique.
► Flame speeds are accurately simulated with the corrected temperature.
► Dominate reactions on laminar flame speed change as hydrogen changes in syngas.
► Change in flame color results from radiation spectrum of intermediate radicals.