Effect of Injection Orifice Geometry on the combustion efficiency of a swirl stabilized Methane/Air combustor, at atmospheric pressure

In this work, the effect of transverse injector orifice geometry on the combustion efficiency of a swirl-stabilized Methane/Air combustor, at atmospheric pressure, is investigated numerically. Four fuel injector orifice geometries: circular, triangular, elliptical, and slot were tested in this experiment. For all orifice geometries, except for the slot, 8 orifices were used. For the slot geometry, four orifices were used where each had an area equivalent to two circular orifices. The total orifice outlet area was conserved for each geometry modification. For the purpose of repeatability, as well as to reduce the number of dynamic variables, the swirl intensity was kept constant with a swirl number of 1.0 across all four geometries. Analysis of the reacting flowfield was performed using Unsteady Reynolds Averaged Navier-Stokes (URANS) equations with realizable k-epsilon as the turbulence model. Although the isosceles-triangle orifice improved the combustion efficiency in the near-field, the weakening of the Central Recirculation Zone (CRZ) led to an overall decrease in combustion efficiency compared to the baseline case. For the circular and elliptical orifice, the swirl jet showed increased velocity and spread angle, which led to a tighter recirculation zone that successfully recirculated the unburnt fuel to promote complete combustion. This study shows that although nearfield performance may be positively affected by the orifice geometry, optimal performance is contingent on the presence of an optimal swirling flow and the resulting recirculation zone.