Experimental analysis of non-premixed coflow combustion of hydrogen and natural gas with oxygen and air as oxidizers

This study presents an experimental evaluation of hydrogen and natural gas combustion under oxy-fuel and air-based conditions, using a coflow burner in both free and confined flame configurations. The experiments were conducted at a fixed thermal input of 0.5 kW based on the lower heating value, and ambient pressure of 0.854 bar, while varying the oxidizer-to-fuel ratio to analyze fuel-rich, stoichiometric, and fuel-lean regimes. The analysis includes flame morphology, radiation intensity, and exhaust emissions composition. Although hydrogen oxy-combustion flames were expected to be shorter due to higher reaction rates, the results showed that natural gas produced the shortest flames, highlighting the influence of fuel discharge velocity and diffusion coefficients on height of non-premixed flames. In confined conditions, hydrogen-rich flames exhibited a secondary reaction zone attached to the outlet of the confinement tube, this phenomenon is due to the preheated unburned H 2 reacting with the surrounding air. In addition, oxy-fuel flames demonstrated higher radiation intensity than air-based flames, with higher values under confined conditions. Finally, exhaust emission results revealed that oxy-fuel combustion generated higher NO x emissions than combustion with air, primarily due to elevated flame temperatures and extended residence times. • Assessment of the effect of the oxidizer-to-fuel ratio on flame morphology, radiative heat flux, and exhaust gas composition. • Natural gas flames were shorter than hydrogen flames under oxy-fuel combustion conditions. • Oxy-fuel flames exhibited higher radiation intensity than air flames, with additional enhancement under confined conditions. • NO x emissions increased under oxy-fuel combustion .