Flame Speed Measurements of Ammonia–Hydrogen Mixtures for Gas-Turbines

Recent findings from the U.S. Energy Information Administration project an increase in domestic fossil fuel consumption (e.g., petroleum and natural gas) and global greenhouse gas emissions through 2050 (Nalley, S., 2021, “International Energy Outlook 2021 (IEO2021),” IEO2021 Release, CSIS, Center for Strategic and International Studies, Washington, DC, Technical Presentation, pp. 2–12). Consequently, advanced combustion research aims to identify fuels to mitigate fossil fuel consumption while minimizing exhaust emissions. Ammonia (NH₃) is one of these candidates, as it has historically been shown to provide high energy potential and zero-carbon emission (CO and CO₂) (Hayakawa, A., Goto, T., Mimoto, R., Arakawa, Y., Kudo, T., and Kobayashi, H., 2015, “Laminar Burning Velocity and Markstein Length of Ammonia/Air Premixed Flames at Various Pressures,” Fuel, 159, pp. 98–106). As a hydrogen (H₂) carrier, NH₃ serves as a possible solution to the U.S. Department of Energy's Hydrogen Program Plan by providing efficient H₂ storage and conservation capabilities (U.S. Department of Energy, 2020, “Department of Energy Hydrogen Program Plan,” U.S. Department of Energy, Washington, DC, Report No. DOE/EE-2128). As a result, applied turbine-combustion research of NH₃ and H₂ fuel has been conducted to identify combustion performance parameters that aid in the design of sustainable turbomachinery (Chiong, M.-C., Chong, C., Ng, J., Mashruk, S., Chong, W., Samiran, N., Mong, G., and Medina, A., 2021, “Advancements of Combustion Technologies in the Ammonia-Fuelled Engines,” Energy Convers. Manage., 244, p. 114460). One of these key combustion parameters is the laminar burning speed (LBS). While abundant literature exists on the combustion of NH₃ and H₂ fuels, there is not sufficient evidence in high-pressure environments to provide a comprehensive understanding of NH₃ and H₂ combustion phenomena in turbine-combustor settings. To advance the state of the knowledge, NH₃ and H₂ mixtures were ignited in a spherical chamber across a range of equivalence ratios at 296 K and 5 atm to understand their flame characteristics and LBS which was determined using a multizone constant volume method. The experimental conditions were selected according to primary turbine-combustor conditions, as much research is needed to support NH₃–H₂ applicability in turbomachinery for power generation. The effect of H₂ addition to NH₃ fuel was observed by comparing the LBS for various NH₃–H₂ mixture compositions. Experimental results revealed increased LBS values for H₂ enriched NH₃, with the maximum LBS occurring at stoichiometry. The experimental data were accurately predicted by the University of Central Florida (UCF) NH₃–H₂ mechanism developed for this investigation, while NUI 1.1 simulations overestimated recorded LBS data by a significant margin. This study demonstrates and quantifies the enhancing effect of H₂ addition to NH₃ fuels via LBS and strengthens the literature surrounding NH₃–H₂ combustion reactions for future work.