Effects of Hydrogen Addition on the Standoff Distance of Premixed Burner-Stabilized Flames of Various Hydrocarbon Fuels

The quenching distance of premixed hydrocarbon flames is of significant importance for studying flame/wall interactions and for understanding the unburned hydrocarbon emissions of internal combustion engines. Motivated by the fact that the standoff distance of premixed burner-stabilized flames could be used to investigate the behavior of head-on quenching distance of freely propagating flames despite the different physics involved, a parametric investigation on the standoff distances of methane, ethane, and propane burner-stabilized flames was conducted numerically using a detailed chemical kinetic mechanism, with a focus on the effects of hydrogen addition. Specifically, the minimum standoff distance was found to quantitatively correlate with the head-on quenching distance of premixed flames. The variations of the minimum standoff distance as a function of hydrogen fractions were then investigated in detail. The results showed that as hydrogen fraction increased, the minimum standoff distances decreased monotonously for all the hydrocarbon/air flames, with the reduction being most significant for methane fuel. Accompanying kinetic analysis showed that hydrogen addition enhances the heat release process, which promotes the reduction of minimum standoff distance. Subsequently, the dependences of the minimum standoff distance on fuel dilution, equivalence ratios, unburned gas temperatures, and pressures were explored. In addition, the potential to study the parametric dependence on unburned hydrocarbons emissions induced by near-wall flame quenching using the burner-stabilized flame model was discussed. The current study provides a useful approach to quantify the quenching distance of premixed flames, which has practical applications in internal combustion engines. Moreover, the dependence of standoff distance on hydrogen addition and other varying flame parameters can now be more fundamentally understood with the help of detailed chemical kinetics.