Insight into the effect of ammonia doping on the methane jet flame

Abstract

Ammonia (NH₃) is a carbon-free and high-hydrogen fuel with ease of storage and transport having low energy density, making it a promising alternative fuel. The combustion characteristics of NH₃ differ significantly from those of conventional fossil fuels, presenting significant barriers to its applications. Here, the effect of combustion characteristics of NH₃ doping with hydrocarbon fuel is investigated by employing Particle image velocimetry (PIV) experiments and CFD Simulation across various ratios of NH₃ doped in the premixed jet flame. The experimental findings indicate that NH₃ doping leads to a significant increase in flame height (from 5.15 cm to 10.51 cm with NH₃ doping), while the maximum flame temperature decreases with NH₃ doping (1972 °C to 1895 °C). Nevertheless, the flame temperature increases with flame height increase (1372 °C to 1537 °C) due to the decomposition of NH₃ into H₂, which combusts rapidly and releases additional heat, accompanied by a broader flame structure and more consistent heat distribution. This altered combustion characteristics and enhanced reactivity of the NH₃ hydrocarbon mixture which improves combustion efficiency and heat transfer within the flame zone. Additionally, the overall flame velocity decreased with NH₃ doping (7.13 m/s to 6.58 m/s), and higher velocities were observed in the upper flame regions due to an increased flame height. These results reveal that NH₃ doping enhances flame stability, facilitates complete combustion, and amplifies the understanding of mechanisms involved in NH₃ combustion thereby offering a pathway towards cleaner combustion technologies. Consequently, NH₃ can be utilized more efficiently in practical combustion devices, including internal combustion engines, aero engines, land-based gas turbines, furnaces, and boilers.