Session: 04-25 Combustion Dynamics - Hydrogen Flames I

Paper Number: 152452

An Extended Artificially Thickened Flame Model for Turbulent Hydrogen and Hydrogen-Enriched Flames With Intrinsic Instabilities Under Gas Turbine Relevant Conditions 

Hydrogen is a zero-carbon fuel that has been the focus of extensive research as a potential alternative for gas turbine combustion, paving the way to net-zero emissions, The adoption of hydrogen introduces major challenges due to its high reactivity and large diffusivity. The latter leads to preferential diffusion and for lean conditions to the characteristic intrinsic thermo-diffusive (TD) instabilities. These characteristics directly impact the safe operation of gas turbines, as these instabilities can more than quadruple the flame speed, significantly increasing the risk of flashback. Computational Fluid Dynamics (CFD) is essential for the design of new gas turbines and to ensure efficient and safe operation. However, existing CFD models for simulating the interaction between chemistry and turbulence do not account for these intrinsic TD instabilities. This underlines the need for new models that capture hydrogen's distinct combustion properties.

A commonly used model for the turbulence-chemistry interaction is the artificially thickened flame (ATF) approach. However, as shown in the literature, the ATF approach successfully applied for hydrocarbon flames cannot predict the consumption speed of hydrogen flames even in simplified configurations. In our previous work, we derived an extended efficiency function to include the effects of intrinsic TD instabilities in laminar flames.  In this work, this efficiency function is extended to turbulent gas-turbine relevant conditions. This includes hydrogen blends to address challenges associated with fuel flexibility.

To this end, a general formulation that characterizes the effects of intrinsic instabilities is proposed, enabling the efficiency function of the ATF approach to be applied across a wide range of conditions. The generalization focuses on application-relevant conditions and encompasses elevated pressures and temperatures as well as hydrogen blended with either ammonia or methane. The model extension is validated a posteriori in multi-dimensional configurations for an extensive variation of conditions, showing excellent agreement with reference results. Thereafter, the model is applied to more complex geometries, showcasing its ability to accurately predict the complex flame characteristics under technically relevant conditions.

Finally, the model is applied to a turbulent jet flame under selected conditions and evaluated against reference DNS data. The proposed model represents a significant advancement by enabling the widely used ATF approach to correctly predict the flame speed of thermo-diffusively unstable flames in complex geometries and under challenging conditions, i.e. elevated pressure and temperature. We consider this model as an essential building block to enable predictive CFD simulations urgently needed for the development of more efficient and environmentally friendly propulsion and power generation systems.

Presenting Author: Vinzenz Schuh Technical University Darmstadt

Presenting Author Biography: 2018: Bachelor in Mechanical Engineering at Technical University Darmstadt
2022: Master in Mechanical Engineering at Technical University Darmstadt
2022: Master in Computational Engineering at Technical University Darmstadt
since 2022: PhD student at Technical University Darmstadt

Authors:

Vinzenz Schuh Technical University Darmstadt
Driss Kaddar Technical University Darmstadt
Antonia Bähr Technical University Darmstadt
Mathis Bode Forschungszentrum Jülich GmbH
Christian Hasse Technical University Darmstadt
Hendrik Nicolai Technical University Darmstadt