A numerical study of the three-way parametric effect of fuel blend, confinement ratio, and operating pressure on swirl stabilised syngas combustion emissions

Reducing pollutant emissions from high-pressure combustion in the power and industrial sectors calls for a shift toward low-carbon fuels such as syngas, a hydrogen (H 2 )–carbon monoxide (CO) mixture whose combustion behaviour is highly sensitive to operating conditions. This study numerically examines the effect of operating pressure (1, 4, 8 bar), confinement ratio (CR 1.5, 2, 3), and fuel blend (75H 2 :25CO, 25H 2 :75CO) on the flow, swirl, and emissions of a swirl-stabilised burner, using a validated Reynolds Stress Model (RSM) coupled with the Eddy Dissipation Concept (EDC) and a 14-species/30-reaction Davis mechanism. Monte Carlo-verified swirl-number and recirculation-zone tracking (CoV 2.5–6.7%) show CR as the dominant driver of jet penetration, while pressure exerts a nonlinear, compressive effect strongest for CO-rich blends via axial momentum flux. Higher pressure and CR shift reaction zones and OH concentration upstream, with H 2 -rich blends burning out fastest and anchoring most stably at CR3, per an OH-centroid stability metric. Despite H 2 's higher heating value, the CO-rich blend delivers 8.4% higher total heat release from greater mass throughput. Chemkin analysis identifies H + O 2 = O + OH as the dominant OH-forming reaction, with pressure sensitivity diverging between blends. Quantitatively, 25H 2 :75CO reaches 1–5% higher peak temperatures but 34–99% higher CO emissions than 75H 2 :25CO; raising pressure from 1 to 8 bar cuts CO by up to 96% but raises NO x by 65–90%, while increasing CR from 1.5 to 3 lowers CO by up to 98%. CO and NO x are jointly minimised at 1 bar and CR3, the optimal low-emission configuration.