Enhancing diluted syngas combustion via oxygen-enriched pre-chamber jet ignition

Biomass-derived syngas is regarded as a promising renewable fuel with significant potential for reducing emissions in combustion engines, whereas its highly variable H₂/CO composition and CO₂/N₂ dilution severely deteriorate flame propagation and combustion stability. Although oxygen enrichment and pre-chamber jet ignition have individually demonstrated potential for improving low-reactivity fuel combustion, their combined effects on the fundamental and practical combustion characteristics of syngas remain poorly understood. This work experimentally investigates the laminar burning characteristics and pre-chamber combustion behavior of CO₂/N₂ diluted low-H 2 syngas under oxygen-enriched conditions. Laminar burning velocities were measured in a constant volume chamber at oxygen concentrations of 21–40% and equivalence ratios of 0.5–1.4, while pre-chamber jet ignition and flame propagation under ultra-lean conditions were visualized using high-speed Schlieren imaging. Results show that oxygen enrichment proves highly effective in enhancing flame propagation and offsetting CO₂/N₂ dilution inhibition. Elevating oxygen concentration from 21% to 40% increases the peak laminar burning velocity by up to 106.6%. Compared with CO₂ dilution, N₂-diluted syngas exhibits a stronger dependence of laminar burning velocity on equivalence ratio, reflecting different thermal-diffusive and chemical effects. Furthermore, the pre-chamber jet significantly enhances ignition stability for diluted syngas across a wide range of equivalence ratios, extending the ultra-lean operating limit to an equivalence ratio of 0.4 under 30% and 40% oxygen concentrations. The enhanced main chamber combustion under oxygen-enriched pre-chamber ignition exhibits a positive correlation with laminar burning velocity. These findings demonstrate an experimental relationship between fundamental flame propagation characteristics and practical pre-chamber combustion performance, providing valuable insights for designing and optimizing advanced syngas-fueled engine systems.