Progress of Ammonia Combustion Study towards Carbon Neutrality

Abstract

Towards carbon neutrality by 2050, an utilization of ammonia not only as hydrogen energy carrier but also as carbon free fuel is anticipated. The Green Growth Strategy Through Achieving Carbon Neutrality in 2050 which consists of 14 important targets were formulated in December 2020 and updated in June 2021. Fuel ammonia plays an important role in the strategy. In this manuscript, recent progress on ammonia combustion study obtained at the High Speed Reacting Flow laboratory, Institute of Fluid Science, Tohoku University were summarized. To clarify fundamental combustion characteristics of ammonia flame, laminar burning velocities were experimentally obtained up to 0.5 MPa and 500 K from spherically propagating flames. Also, product gas characteristics of ammonia/hydrogen/air flames stabilized in a stagnation flow were investigated experimentally and numerically. It was observed that large amount of N₂O was produced for the equivalence ratio of 0.6, and important reactions for N₂O production and reduction were identified. Results of liquid ammonia spray were also described briefly. The detailed spray characteristics were observed using 2-phase Structured Laser Illumination Planar Imaging (2p-SLIPI) and clarified that the spray characteristics of liquid ammonia spray were different from those of water spray. Then, the experiments of ammonia spray combustion were performed using a laboratory-scale swirl combustor. The stability map and product gas characteristics of liquid ammonia spray flames were obtained.