The sequential combustion concept, where the first combustion stage is supported by a standard lean premixed flame, and the second stage relies on an autoignition-dominated flame forms the focus of the present contribution.
The flame is anchored by establishing a positive static temperature gradient within the burner. The advantage of such a concept is that it can be easily incorporated into an integrated combustor-nozzle guide vane.
A critical challenge is that, in order to set up the static temperature gradient, the flow has to be accelerated to a relatively high Mach number, ca. 0.7, and then decelerated in a diffusing section where the flame is located. Achieving fuel/air premixing and combustion, while achieving acceptable pressure drops is not trivial at the high velocities. Additionally, the dynamic stability of the concept is not clear and needs to be investigated.
Within the present work, compressible CFD is used to investigate the pressure drop characteristics within the system. It is demonstrated that for the system a total pressure drop of < 6% can be achieved. To realize this, the premixing section includes multi-point fuel injection coupled with mixing devices.
Investigation of the flame response with 2D CFD to harmonic perturbations in inlet temperature shows that the flame transfer function (FTF) is characterized by amplitude growing linearly with frequency. The rate of growth with frequency of the FTF amplitude is rather high reaching up to sixty times the imposed relative fluctuation of inlet temperature at a frequency of 600Hz