Propane-syngas premixed flames in a heat-flux burner: Effect of H2/CO enrichment on laminar burning velocity, temperature profiles, and mechanism sensitivity

Abstract

Blending syngas with propane offers a versatile approach to tune combustion behavior, merging the high reactivity and clean burning properties of syngas with the stability and energy density of propane enabling flexible syngas adoption in the current combustion systems. Premixed propane-syngas flames were investigated at 298 K and 1 bar over an equivalence-ratio range of phi = 0.6-1.5 to quantify the Laminar Burning Velocity (LBV) and flame temperature. The LBV was measured using a heat-flux burner (quasi-adiabatic, planar flame), and temperature profiles at Heights Above the Burner (HAB) of 1-20 mm were recorded using a type-S thermocouple and corrected for radiative losses via a steady-state convection-radiation balance (epsilon = 0.205-0.235). Equimolar and non-equimolar H2/CO syngas blends, with syngas fractions up to 80% of the fuel, were examined. Numerical predictions were obtained using a one-dimensional freely propagating flame model with the USC II, San Diego, Aramco 2.0, C3MechLite, and NUIG 1.1 kinetic mechanisms; the San Diego mechanism best reproduces lean LBV, whereas USC II performs better under rich conditions. Increasing syngas content increases LBV at all phi and shifts the LBV peak from phi = 1.0 to phi =1.1 at high syngas fractions; at phi =1.5, LBV increases by 145% as the syngas fraction rises from 20% to 80%. The peak flame temperature (Tpeak) increases by 2.9% at phi = 0.8 and by 12.5% at phi = 1.4 for 80% equimolar syngas, with H2-rich syngas yielding higher values than CO-rich blends. Sensitivity and radical-profile analyses indicate that H-atom branching (H + O2 = O + OH) and OHassisted CO oxidation promote LBV, whereas HO2 formation and H-recombination pathways limit the gains, consistent with the observed mechanism-to-mechanism differences under rich conditions. Syngas addition also moves the flame front closer to the burner (HAB approximate to 1 mm versus 2 mm for propane), consistent with improved rich-side stabilization. Overall, the dataset provides a combined experimental-numerical benchmark of LBV and temperature profiles for propane flames enriched with syngas (H2/CO), including both equimolar and nonequimolar blends up to 80% of the fuel for model validation and syngas-utilization studies.