A numerical investigation into the stabilization of hydrogen enriched n-dodecane premixed flames

Abstract

The aviation industry uses heavy hydrocarbon fuels, which release carbon-based emissions upon combustion and could suffer from flame stabilization issues due to their high Lewis numbers at lean conditions. Hydrogen is emerging as an alternative fuel which can help mitigate these issues. A viable strategy is to blend liquid hydrocarbons with hydrogen, which could strengthen the flame in positively stretched regions and help reduce carbon-based emissions. In order to investigate this, we carry out a numerical study for different blends of n-dodecane, which is a surrogate fuel for kerosene and jet fuel, with hydrogen in air. Equivalence ratios and unburnt temperatures of different blends are selected such that the laminar burning velocity remains the same. This condition allows for a more precise characterization of Lewis number effects manifested at the flame base and tip. It is found that up to 60 % addition of H2 into n-dodecane by volume, no major difference is observable with respect to the flame stabilization process. The positively curved flame base burns weakly while the negatively curved flame tip is strengthened due to thermal diffusivity being greater than mass diffusivity. With a further increase in the percentage of hydrogen, the flame base starts to burn stronger with the flame moving closer to the flame holder. However, the flame tip does not become weak as n-dodecane continues to burn there. As positive stretch and negative curvature increase the consumption rate for H2 and n-dodecane flames, respectively, for the blend with 95 % hydrogen and 5 % n-dodecane, a flame is observed with the flame base and the flame tip both burning strong. Overall, this demonstrates that introducing hydrogen at concentrations exceeding 60 % by volume significantly enhances flame stabilization by bringing the flame closer to the flame holder, potentially expanding flame stabilization boundaries.