Hydrogen-enriched methane combustion in a swirl vortex-tube combustor

The hydrogen-enrichment combustion performance was investigated numerically by employing methane mixed with different volume proportions of hydrogen, wherein a vortex-tube combustor was employed to achieve a steady combustion process. Results show that this combustion technique indicates good adaptability to hydrogen-enrichment combustion together with an ultra-steady combustion process. The lean stability limit is always within 0.15, which decreases further with the increase of hydrogen content, whilst the amplitude of pressure fluctuation △p is always within 500 Pa with a uniform flame front. The generated non-premixed property flame structure can guarantee a high concentration of components in the reaction zone, which improves the local concentration of species and yields a large stability limit. The strong vortex flow can decrease the local flow velocity to inhibit flame blow-out and yield a large tangential velocity component. The high combustion intensity generates a large density gradient. The large density gradient and large tangential velocity promote the laminarization of the flow, resulting in a large Richardson number R_i* that is always much greater than 1.0. The laminarization of the flow field provides good aero-dynamic and thermo-dynamic stability. Further, the thermo-acoustic coupling is ultra-weak as well, and therein the Ra(x) is always smaller than 0.0024, indicating good flame-dynamic stability. In summary, the resultant good aero-dynamic, thermo-dynamic, and flame-dynamic stabilities of this vortex-tube combustor are the principal reasons for the super-steady hydrogen-enrichment combustion.