Investigation of Mixing Mechanisms to Enable Premixed Hydrogen Combustion

Future aeroengine combustors operating in highly swirled premixed mode with a hydrogen/air mixture are central to this paper. Evaluating the operating condition and performance of such engines and combining the propulsion performance with the combustion characteristics is essential. In this paper, the focus lies in establishing a method to determine realistic operating conditions for the retrofit of existing aeroengines with premixed hydrogen combustion. The pursued method, a combustor performance map, satisfies four key requirements: (1) the mass conservation into the combustor, (2) the thermal power requirement for the engine, (3) the combustor power budget, and (4) the combustor energy budget. To obtain the map, several steps are undertaken with emphasis on the mixing mechanisms as a key component to enable the premixed combustion mode as well as to improve thermal efficiency of the combustion process. Hydrogen/air chemical kinetic simulations are employed and included into the method via one-dimensional flame analyses for considered lean mixtures in order to observe the influence of equivalence ratio on various flame characteristics. The mixing mechanisms required to enable premixed hydrogen combustion in future propulsion systems are investigated for a given combustor architecture. Specifically, the two mixing problems to be addressed in future research are: the swirling mixing of gaseous hydrogen and air in the injector unit, and the mixing of the dilution hole airstream with the combustion products in the downstream portion of the chamber. A digital model of a typical combustor in an aeroengine is utilized to conduct non-reacting numerical simulations that include hydrogen/air mixtures and to discuss the mixing process inside the swirling injector unit. Four unique injector approaches are considered with the help of the performance map operating point identification process. The developed baseline premixed combustor geometry provides a platform to further analyze the discussed mixing mechanisms in future work.