Abstract
The performance in the downstream swirling and upward swirling combustors with different swirler locations was evaluated. Unlike the axial recirculation formed by the interaction between swirling and direct flows in the downstream swirling combustor, upward swirling combustor exhibits simultaneous radial and axial recirculation. In the primary cavity and its downstream region of downstream swirling combustor, the central vortex core continuously decreases radially, presenting a cone shape with its tip downward. The central vortex core remains essentially unchanged axially in the upward swirling combustor. The flame stretch rate value is primarily influenced by both temperature and velocity gradient, with the flame stretch rate in the downstream swirling combustor being much larger than that in the upward swirling combustor. The range with high flame stretch rate decreases as the length of the primary cavity (L) increases, and a larger L weakens the flame stretching. Outlet NO emission in the upward swirling combustor is much lower than that in the downstream swirling combustor. The influence of the change in the mixture residence time in the high temperature region caused by L on the reduction of NO emission is far less significant than the impact of high temperature on NO emission, ultimately leading to an increase in NO emission.
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