Abstract <p>The gas parameters near the flame leading edge in the boundary layer behind a rib and behind a backward-facing step with ethanol evaporation and combustion were compared to study combustion stabilization mechanisms. It is shown that at an air flow velocity of ~11 m/s, an attached flame is formed behind the backward-facing step and the ethanol evaporation intensity is lower than behind the rib with a separated flame. At the flame leading edge behind the obstacles, there is a region where maximum heat release occurs at the mixture ignition temperature and the static and dynamic pressures are equal. It is shown that under conditions of gas flow with combustion and separation behind the rib, the maximum contribution of turbulent momentum transfer reaches ~30–40% of the averaged convective momentum transfer and the contribution of molecular transfer is 2–3%.</p>