Hydrogen-Enriched Ammonia Combustion

Ammonia-hydrogen blend combustion is a promising innovation in clean energy, combining the strengths of ammonia as an energy-dense carrier and hydrogen as a highly reactive fuel. Ammonia, a carbon-free compound, offers excellent storage and transport advantages compared to hydrogen due to its higher energy density and liquid form under relatively mild conditions. However, its standalone use in combustion is challenged by low flame speed, high ignition energy, and a narrow flammability range, leading to inefficient and unstable combustion. By blending ammonia with hydrogen, these limitations are addressed, significantly enhancing its performance as a practical fuel.

When hydrogen is added to ammonia, it accelerates the combustion process by producing reactive radicals like H, OH, and O. These radicals promote the oxidation of ammonia, speeding up chemical reactions and stabilizing the flame. This improvement widens the flammability range and lowers the ignition energy required, allowing for more reliable and efficient combustion. Hydrogen’s faster flame speed compensates for ammonia’s slow propagation, ensuring a stable and consistent burn. Additionally, the presence of hydrogen reduces the risk of unburned ammonia emissions, which are both toxic and harmful to the environment.

The blending ratio plays a critical role in determining the efficiency and emissions of the combustion process. Low hydrogen fractions can enhance flame stability without drastically increasing combustion temperatures, while higher hydrogen content results in greater efficiency and energy output. However, elevated temperatures can lead to higher nitrogen oxide (NOx) emissions, a key environmental concern. Addressing this requires advanced mitigation strategies such as staged combustion, selective catalytic reduction (SCR), and exhaust gas recirculation (EGR) to minimize NOx formation.

Applications for ammonia-hydrogen blends span power generation, transportation, and maritime sectors. Gas turbines and internal combustion engines are being adapted to use these blends, providing a carbon-free alternative to fossil fuels. In the maritime industry, the blend shows potential as a bunker fuel to meet stringent emission regulations. Ongoing research focuses on optimizing combustion kinetics, designing advanced burners, and integrating safety measures for handling these fuels. Ammonia-hydrogen blends represent a critical step toward sustainable, carbon-neutral energy systems, offering flexibility, efficiency, and reduced emissions in diverse applications.

Recent publications on the area

1. Towards sustainable hydrogen and ammonia internal combustion engines: Challenges and opportunities

https://doi.org/10.1016/j.fuel.2024.131090

2. Ammonia and hydrogen blending effects on combustion stabilities in optical SI engines

https://doi.org/10.1016/j.enconman.2023.116827

3. Assessment of combustion development and pollutant emissions of a spark ignition engine fueled by ammonia and ammonia-hydrogen blends

https://doi.org/10.1016/j.ijhydene.2024.08.210

4.?Visualization and simulation study of ammonia blending with hydrogen as combustion application in lean-burn condition

https://doi.org/10.1016/j.fuel.2023.129812

5. Effects of hydrogen blending ratio on combustion and emission characteristics of an ammonia/hydrogen compound injection engine under different excess air coefficients

https://doi.org/10.1016/j.ijhydene.2023.10.049

6. Comparative analysis of ammonia/hydrogen fuel blends combustion in a high swirl gas turbine combustor with different cooling angles

https://doi.org/10.1016/j.ijhydene.2023.07.166

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