A new jet-stabilized burner concept for industrial gas turbines - a numerical study

Kurzfassung

In existing heavy-duty gas turbines and aero engines, the need to reduce emissions led to the application of lean premixed combustion technology. In such fuel-lean combustion chambers, pressure amplitudes can occur caused by unsteady heat release, provoking component damages. For this reason, it is essential to gain a more accurate understanding of the combustion processes. To avoid thermoacoustic instabilities and flashbacks in these systems, the jet-stabilized combustor design was introduced as an alternative to state-of-the-art swirl type combustors. With this concept, the flame is stabilized by hot combustion products that recirculate upstream, in order to promote the mixing between the unburned fuel and the oxidizer. A more uniform temperature distribution is obtained leading to decreased emissions compared to other combustion systems. The idea to apply the jet-stabilized combustor in industrial gas turbines is a new concept that the current study wants to support. For this purpose, numerical combustion investigations of a jet-stabilized hydrogen burner with finite-rate combustion model and k-omega SST turbulence model were carried out with given operating conditions. The DLR in-house code ThetaCOM or THETA was used to perform RANS calculations of several combustor designs. In the first part of the paper, several geometry modifications were studied in order to find out which one reaches the best performances for industrial applications. The main focus was to investigate different main nozzle diameters for both air and fuel mass flows and the results for each nozzle geometry analyzed are presented here. The main nozzle design that showed the best air-fuel mixing within the nozzle was then taken and implemented in the entire combustor geometry. As next step, with the chosen main nozzle design, RANS simulations of the entire combustor were carried out to test the performances and the interactions between the main nozzles also together with the pilot geometry. The outcomes obtained for the full burner are shown in the paper proposing a combustor design that could be adopted in current industrial gas turbines.