Combustion Intensification Mechanism in a Vortex-Tube Reactive Flow

The combustion intensification mechanism was revealed in a stratified vortex-tube combustor. The results show that a triple-flame structure is formed in this combustor and the peak heat release is located exactly at the triple-point position. The peak heat release rates in the five selected representative cases studied in this paper are all over 1.2 × 10⁹ W/m³. The stability limit is wide, and the lean stability limit is always lower than 0.2. The decreased mixing length and decreased velocity difference between the fuel and oxidant streams delay the mixing process and then bring about a stratified distribution of species. This is crucial for the generation of a triple-flame structure and the corresponding high species concentration in the vicinity of the reaction zone under lean conditions. The Damköhler numbers on the lines across the triple points were calculated with values above 1.0 in each of the cases, indicating that the species’ transport time is longer than the chemical reaction time. Therefore, the transport flux of species determines the final combustion strength. The synergistic coupling of the flowfield and species field gives rise toa large transport flux of the key species in the vicinity of the reaction zone. The results show that the corresponding fuel transport flux is large, with values all over 0.52 mole/(m² · s). This is the principal reason for the high combustion intensity in this combustor. The different transport fluxes of the critical species are responsible for the different chemical reaction strengths on the triple point in each of the different cases.