Experiments and Kinetic Modeling of Diffusion Flame Extinction of 2-Methylfuran, 2,5-Dimethylfuran, and Binary Mixtures with Isooctane

This work presents an experimental and numerical study of extinction properties of 2,5-dimethylfuran (DMF) and 2-methylfuran (MF) in counterflow diffusion flames at atmospheric pressure. The impact of addition of isooctane to the fuels is presented with two degrees of blends (25:75 and 50:50). The analysis was carried out for different levels of fuel loading ranging from 0.10 to 0.24 (volumetric) with the rest of the component being N-2 as a carrier gas. Extinction limits are observed to increase with an increase in fuel loading, and the resistance to extinction follows the order MF > isooctane > DMF. Numerical predictions using the Tianjin mechanism are within 10% of the measurements for MF cases, while the Galway mechanism tends to underpredict at higher fuel loading conditions. For DMF flames, both the mechanisms perform relatively well at X-F <= 0.14; however, they underpredict as the fuel loading is increased. Addition of isooctane to DMF led to an increase in the extinction limits at low fuel loading conditions, but the impact of blending diminished at higher fuel loading conditions. On the other hand, addition of isooctane had a minimum impact on MF flame's extinction limit at low fuel loading conditions, while it led to a reduction in the resistance to extinction at higher fuel loadings. Numerical simulations by a mechanism proposed for the isooctane-DMF-MF blend predict similar effects of blending, however, consistently tend to underpredict at higher fuel loading conditions. Quantitative reaction path diagrams show that the H-abstraction step is the dominant fuel consumption route for near-extinction MF and DMF flames. With an increase in fuel loading, the role of C5H5 in the H-abstraction process increases in DMF/air flames. Reaction sensitivity analysis shows an increase in the importance of C5H5 kinetics in X-F = 0.24 DMF flames as compared to X-F = 0.14 along with the ring-opening step converting DMF to 3,4-hexadiene-2-one. In MF/air flames, the degree of change in sensitivities with fuel loading was found to be significantly low as compared to the DMF/air flames. Finally, reaction rate analysis was carried out to reveal that the slower consumption of MF causes the underprediction of the extinction strain rate by the Galway mechanism as compared to the Tianjin mechanism.