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 (XH₂) 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 XH₂, 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 XH ₂ 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 XH₂ increases. Sensitivity analysis was conducted to access the dominant reactions when XH₂ increases. The difference on flame color for different XH₂ mixtures is due to their difference in radiation spectrum of the intermediate radicals produced in combustion.