Emission and combustion characteristics of ammonia/methane mixtures for carbon reduction and alternative fuel development

The reduction of fossil fuel consumption is of great importance in achieving the targets set forth in the Paris Agreement. One solution to reduce carbon emissions is the utilization of renewable energy sources and alternative fuels, despite the variability that comes with them. Energy storage and vectors are essential in overcoming variability and achieving a faster transition to renewable sources. Ammonia is increasingly being used as an energy vector due to its suitability for transport and utilization in existing combustion systems, even more so than hydrogen. Existing natural gas burners can be modified without extensive adaptations for ammonia/methane mixtures and pure ammonia. To determine combustion parameters and evaluate emission properties, a combination of computational fluid dynamics (CFD) and experimental research is commonly used. This study focuses on generating laminar flame speed and autoignition ammonia/methane mixture databases as input data for combustion CFD modeling, employing LOGE™ software and developed methods with correlation functions. Databases are used as lookup tables for autoignition criteria and laminar flame speed in 3D CFD coherent flame model. Three-zone extended coherent flame model (ECFM-3Z) is used in this study as a CFD combustion model. The generated databases are validated against experimental data from premixed burner and shock tube experiments. A database for autoignition was generated using non-dimensional constant pressure reactors and the San Diego mechanism. The grid for the autoignition database is defined by five parameters: pressure, temperature, equivalence ratio, exhaust gas recirculation, and ammonia/methane ratio. The laminar flame speed database was generated with one-dimensional freely propagating reactors and the same mechanism. Special attention and new developed modelling approach was given to define appropriate correlation methods for unsuccessfully calculated data in unstable regimes. Thus, the first CFD-ready lookup database (345 k auto-ignition points + 18 k laminar-flame-speed points) for NH3/CH4 blends is presented, enabling rapid yet accurate decarbonisation studies.