Flame control by low-temperature hydrogen injection in a trapped vortex combustor

The transition to hydrogen as a primary fuel in aviation requires innovative strategies to mitigate challenges associated with flashback in combustion systems. Due to its low volumetric energy density, hydrogen is preferably stored at cryogenic temperatures (T ≤ 100 K). Since stoichiometric hydrogen/air laminar premixed flames have been observed to sustain combustion even at temperatures as low as 100 K, low-temperature injection can be used as a strategy to control flashback and stabilize the flame. This study investigates the performance of low-temperature rich premixed hydrogen/air combustion within a model Rich-Quench-Lean (RQL) combustor configuration equipped with a Trapped Vortex Cavity (TVC). Large Eddy Simulations (LES) with Eulerian Stochastic Field (ESF) approach are conducted for this purpose. The LES are first validated against a recent experimental campaign involving high-speed chemiluminescence diagnostics. Subsequently, parametric studies explore the operating limits and flashback resistance of rich hydrogen flames under varying low-temperature conditions. Results indicate a strong sensitivity of the flame position within the TVC to the injection temperature. The strong reduction in laminar flame speed observed in experiments, however, is counteracted by the increase in turbulent/laminar flame speed ratio, adding to the complexity of the problem. Insights on how to control the flame dynamics in the cavity are provided within this study with the purpose of optimizing RQL-TVC designs for robust, low-emission, and flashback-resistant operation in hydrogen-based propulsion systems.