Fuel mixing effects on flame propagation were investigated with hydrogen and methane, whose flames, respectively, propagate through two different kinds of mechanisms. The calculated burning velocities did not show linearity with the hydrogen content in the fuel. The addition of only 5% of methane to hydrogen reduces the burning velocity by 20%, notoriously inhibiting the combustion of the mixture. This is caused by obstruction of the harmonious progression of two key chain-branching reactions, resulting in a decrease in hydrogen atom production at the flame front. However, the upstream flux, at the ignition point, of chemical energy due to diffusion of hydrogen atoms from the flame front and the integrated amount of heat released in the low-temperature region did show linearity with the burning velocity. Therefore, it was found that even for flames of mixed fuels whose components burn individually through different propagation mechanisms, the burning velocity can be expressed as a simple linear function of the upstream chemical energy flux or of the amount of heat released in the low-temperature region.
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