Recursive Sequential Combustion: A Concept Study About a Momentum-Enhanced Blend of the Reactants With Recirculated Burnt Gases

Over the last decade, new concepts have evolved to promote a significant azimuthal flow in annular combustors of gas turbines. The benefits are better flame propagation at ignition, positive flame-flame interaction, and better interaction with the burnt gases. Other advantages in terms of size, congestion and conditioning of the turbine inlet flow are also significant. The technical challenges reported by the literature are often related to the higher thermal stress of the flames on the walls compared to a conventional frame. Other sources of inspiration for this work are the principles of burnt gas recirculation, sequential combustion and flameless combustion. This contribution focuses on a novel tangential burner arrangement inspired by the previous references. It offers a synthesis of key features and properties of the latter and goes even further. Here, a significant part of the burnt gases produced by one burner intentionally enters the inlet of the next burner, and so on along the azimuthal direction. This takes advantage of the closed loop aspect of an annular combustor when considering the toroidal direction. It also proposes a solution to the thermal load problem. We named this principle Recursive Sequential Combustion (RSC). While the flame alignment is organised along the generatrix of the combustor’s annulus, one difficulty lies in the design of the lateral feeds of reactants and the lateral exit of the exhaust gases. A double-spiral combustor design is proposed, which has similarities with the Swiss Roll Combustor concept. It directs the flow in the toroidal direction, as well as it creates the favourable conditions for a dynamically stabilised premixed flame centred along the torus’ generatrix at some distance from the walls. This design maximises the interaction between the fresh reactants and the burnt gases. The technical challenge is to find the right balance in terms of momentum flux of the incoming and outgoing flows to keep the flame in the middle of the torus. If this concept is successful, a lean flame could be operated with an unmatched trade-off between stability, flexibility and low-emissions (including soot). The paper reports about the RSC concept, the design, and the early results.