Hydrogen-enriched combustion of CO₂-diluted landfill gas: a Damköhler-number stability framework for power plant life extension

The CH₄ content of the LFG declines progressively while CO₂ increases, degrading combustion stability until engines can no longer sustain reliable operation below a CH₄ threshold of approximately 40 volume percent (vol.%). This paper investigates the combustion physics behind this degradation and evaluates hydrogen enrichment as a mitigation strategy that projects to extend plant operational life by more than a decade beyond the conventional shut-off point, under the assumptions and the empirically calibrated stability mapping. A custom numerical solver was developed in MATLAB and was validated against the canonical coflow diffusion flame benchmark experiments. Parametric simulations systematically varied the CO₂ fraction from 0 to 60 vol.% and the hydrogen (H₂) enrichment level from 0 to 40 vol.%, yielding quantitative maps of adiabatic flame temperature, equivalent flame speed, ignition delay, and radical pool concentrations. Increasing CO₂ from 0 to 60 vol.% reduces Da (Damköhler number) by 83%, doubles ignition delay to 3.16 ms, and depresses the OH radical pool by 49%; 30 vol.% H₂ enrichment fully restores stable operation (Da ≥ 5 in the laminar flame model), projecting, under the stated assumptions and pending engine-level validation, a 14-year plant-life extension and doubling CO₂-equivalent avoidance to 60,700 tonnes. A complementary techno-economic analysis, based on a 30-year discounted cash flow (DCF) model applied to a 1.5-million-tonne reference Brazilian landfill, indicates that the physically-derived H₂ enrichment schedule is projected to double total electricity generation (from 48,200 to 92,100 MWh).