Stabilization mechanism revelation of a novel vortex-tube combustion technique: LES with sgs-pdf approach

Abstract

The paper revealed the in-depth stabilization mechanisms of a novel vortex-tube combustion technique by using ethanol as fuel, which is implemented by a stratified vortex-tube combustor (SVC). The stability properties of the SVC are investigated, showing that the SVC has a wide stability limit and low-pressure fluctuation amplitudes with a uniform flame front. The equivalence ratio at the lean flammability limit is always below 0.2, and the amplitude of pressure fluctuation is less than 2000 Pa, indicating a highly steady combustion process. The non-premixed flame structure guarantees high mass concentrations near the reaction zone, while the vortex flow also decreases the local flow velocity, inhibiting flame blow-out, thus providing good self-adjusting capacity under various global equivalence ratios. The vortex–flame interaction transports the interior high-enthalpy burnt gas to the exterior unburnt gas region, thereby promoting ignition. The exterior unburnt gas is also transported to the flame front where it promotes reaction and yields an intensified combustion. The large tangential velocity and density gradient result in the large values of Richardson number, which suggests that laminarization of the flow occurs and results in good aero-dynamic and thermo-dynamic stabilities. The small values of the Rayleigh number indicate good flame-dynamic stability. Therefore, the resultant good self-adjusting capacity and three types of dynamic stabilities are the intrinsic causes of the ultra-steady combustion process in this combustor.