High-pressure combustion of realistic landfill gas: Laminar burning velocity, Markstein length, and chemical-kinetic analysis of CH4–CO2–N2 mixtures

Abstract

© 2026 The Author(s).Landfill gas (LFG) is a renewable yet highly diluted fuel whose variable composition and operation at elevated pressures pose significant challenges for stable and efficient combustion. In this work, the laminar burning velocity (LBV) and Markstein length of realistic CH4–CO2–N2 mixtures were investigated experimentally and numerically at 298 K, at pressures up to 5 bar, and for equivalence ratios ranging from 0.6 to 1.3, with special focus on the lean region where new burners concepts are expected operate and where data is quite scarce. Two surrogate fuels containing 65% and 55% CH4 were formulated while maintaining a constant CO2:N2 ratio to isolate the effect of total dilution. Experimental LBVs were determined using the outwardly propagating spherical flame method and compared with detailed chemical-kinetic mechanisms. Among the mechanisms evaluated, Konnov Mech 0.6 provided the best agreement with experimental data at 1 bar. The results show that increasing pressure and dilution both significantly reduce the LBV; however, they act through distinct mechanisms. Dilution primarily suppresses flame propagation through thermal effects, reducing adiabatic flame temperature and overall reaction rates, whereas pressure enhances competition between chain-branching and termination reactions, leading to reduced radical concentrations. Sensitivity and pathway analyses identified the reaction H + O2 ⇌ O + OH as the dominant promoting step controlling flame propagation under all conditions. The Markstein length was found to increase from lean to rich mixtures and to decrease with increasing pressure, indicating enhanced flame instability at elevated pressures. The present study provides new high-pressure experimental data and a detailed mechanistic interpretation of LFG combustion, contributing to improved modeling and the design of energy systems operating with low-calorific-value fuels.

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