Experimental and modelling study of the effect of elevated pressure on ethane and propane flames

Laminar burning velocities, S_L, of ethane + air and propane + air flames within an equivalence ratio range between 0.8 and 1.3 were determined at atmospheric and elevated pressures up to 4 atm. Measurements were performed in non-stretched flames, stabilized on a perforated plate burner at adiabatic conditions, created using the heat flux method. Initial unburnt gas temperature was 298 K. These new experimental results were compared with available literature data and predictions using three kinetic schemes: USC Mech II, San Diego mechanism and Aramco Mech 1.3. The models behave differently in reproducing S_L of ethane and propane flames with closer agreement between Aramco Mech 1.3 and the present measurements. The pressure dependence of the laminar burning velocities was analysed using the expression S_L = S_L0(P/P₀)^β. Large deviations of the derived power exponent, β, were observed for different experimental datasets and between model predictions and the measurements. To elucidate these differences in the performance of the three mechanisms, sensitivity analyses of the burning velocity and of the power exponent β were performed. It was demonstrated that the power exponent β may serve as an independent target for model validation and improvement. When comparing β coefficients derived from the present and previous measurements of S_L in methane, ethane, propane and n-pentane flames using the heat flux method, important similarities were found at lean conditions with large disparity in rich mixtures. Neither experiments nor modelling support the linear dependence of the power exponent β with equivalence ratio for flames of alkanes.