The model results show that the laminar burning velocity of the hydrogen-methane mixtures is not the linearregression of those of the pure fuels since it results substantially less than the proportional averaging of thevalues for the fuel constituents. Moreover, the effect of hydrogen addition in terms of enhancement of themixture laminar burning velocity with respect to the methane is relevant only at very high values of thehydrogen content in the hybrid mixtures (> 70 %2mol.).The performed sensitivity analysis shows that these results can be attributed to kinetics and in particular tothe concentration of H radicals: depending on the hydrogen content in the fuels mixture, the production ofthe H radicals can affect the limiting reaction step for methane combustion. Two regimes are identified in thehydrogen-methane combustion. The first regime is controlled by the methane reactivity, the hydrogen beingnot able to significantly affect the laminar burning velocity (hydrogen combustion has a relevant role as its high content in the hybrid fuel leads to a significant H radicalspool, thus enhancing the reaction rate of the more slowly combusting methane.
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