Combustor – Turbine Stator Interaction in Hydrogen Fuelled Micro Gas Turbine

Authors

Roberta De Robbio - University of Naples Federico II, Italy
Maria Cristina Cameretti - University of Naples Federico II, Italy
Alessandro Cappiello - University of Naples Federico II, Italy
Raffaele Tuccillo - University of Naples Federico II, Italy

Abstract

The current trend to global decarbonization induces micro-gas turbine (MGT) manufacturers to experience the employment of alternative, carbon-neutral or carbon-free fuels. Consequently, the most widely diffused natural gas supply is going to be replaced, in next years, by syngas fuelling or hydrogen based gaseous mixtures. In both cases combustion instabilities or, more generally, unsteady phenomena can be expected because of some typical features of these fuels, say: -        The reduced calorific value of syngases, which results in combustion regimes with low flame speed levels close to quenching conditions. -        The enhanced flame speed in hydrogen-based combustion with increased flammability of the fuel-air mixture, so inducing possible flash-back phenomena. Unstable or unsteady, pulsating combustion regimes represent a source of pressure and entropy wave propagation towards the downstream turbine. The latter can result in a superimposition of the pulsating flow pattern to the periodic unsteadiness that is usually due to the stator – rotor interaction. The final effect is a performance decay because of the irregular torque at power shaft and of the non-uniform conditions at the turbine guide vanes inlet. Power shaft torsional oscillation and increased sound pressure level can be also induced. Based on their previous experiences in the CFD analysis of microturbine combustors [ 1, 2] and on the unsteady stator – rotor matching in radial flow turbines [3, 4], the authors discuss in this paper the effect that some critical combustion regimes, in a reverse flow MGT burner, exert on the combustor – stator interaction. Being the turbulent combustion the main source of wave propagation to the guide vanes, a preliminary assessment of flow analysis aims at the selection of the more appropriate turbulence model: in this sense, the results of k-omega model are compared with those of detached and large eddy simulation, in terms of main frequency and amplitude of the pulsating flow properties. Next, the unsteady stator – rotor interactions are compared for 3 cases, the first one related to conventional natural gas combustion, the other one to syngas or hydrogen fuelling. The turbulence – chemistry interaction is analyzed by means of a flamelet generated manifold scheme under the hypothesis of partially premixed combustion. The combined solution of C-equations allows identification of the fluctuations of the flame front location, which is considered the main origin of pulsating reacting flow. [1]   Cameretti, Cappiello, De Robbio, Tuccillo. (2020) "Comparison between Hydrogen and Syngas Fuels in an Integrated Micro Gas Turbine/Solar Field with Storage”, Energies 2020, 13(18), 4764; https://doi.org/10.3390/en13184764 [2]   Tuccillo, Cameretti, De Robbio, Reale, Chiariello. (2019) "Methane-Hydrogen Blends in Micro Gas Turbines: Comparison of Different Combustor Concepts." Proceedings of the ASME Turbo Expo 2019 Volume 8. V008T26A003. ASME. DOI: https://doi.org/10.1115/GT2019-90229 [3]   Cappiello, Tuccillo. (2022). "Influence of Supersonic Nozzle Design Parameters on the Unsteady Stator–Rotor Interaction in Radial-Inflow Turbines for Organic Rankine Cycles." ASME. J. Turbomach. Vol. 144(10): 101005. https://doi.org/10.1115/1.4054068 [4]   Cappiello, Tuccillo. (2022) Design Parameter Influence on Losses and Downstream Flow Field Uniformity in Supersonic ORC Radial-Inflow Turbine Stators, Int. J. Turbomach. Propuls. Power 2021, 6(3), 38; https://doi.org/10.3390/ijtpp6030038