Hydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback. The ENABLEH2 project aims to demonstrate the feasibility of such a switch to hydrogen for civil aviation, within which the micromix combustion, as a key enabling technology, will be matured to TRL3. The micromix combustor comprises thousands of small diffusion flames where air and fuel are mixed in a cross-flow pattern. This technology is based on the idea of minimizing the scale of mixing to maximize mixing intensity. The high-reactivity and wide flammability limits of hydrogen in a micromix combustor can produce short and low-temperature small diffusion flames in lean overall equivalence ratios.

In order to mature the hydrogen micromix combustion technology, high-quality numerical simulations of the resulting short, thin and highly dynamic hydrogen flames, as well as predictions of combustion species, are essential. In fact, one of the biggest challenges for current CFD has been to accurately model this combustion phenomenon.

The Flamelet Generated Manifold (FGM) model is one of the most promising combustion models with a low computational cost due to its reliance on pre-tabulated combustion chemistry, instead of directly integrating detailed chemistry mechanisms. However, this trade for a lower computational cost may have an impact on the solution, especially when considering a fuel such as hydrogen. Therefore, it is necessary to compare the FGM model to another combustion modelling approaches which use a more detailed complex chemistry approach.

The main focus of this paper is to compare the results of LES simulations obtained with the FGM model, to those obtained with more complex chemistry models, for hydrogen Micromix flames, using STAR-CCM+ to determine the most suitable numerical approach required for the design of injection systems for ultra-low NOx. Since hydrogen fluid characteristics and reaction rates are significantly influenced by temperatures and pressures and in order to quantify the predictive accuracy and to establish best practices for CFD modelling of H2/air combustion, the simulations results will be validated and calibrated against high-quality experimental data, at high pressures and temperatures.

 


Comparison of Tabulated and Complex Chemistry Turbulent-Chemistry Interaction Models With High Fidelity Large Eddy Simulations on Hydrogen Flames

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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