This paper focuses on the potential use of ammonia as a carbon-free fuel, and covers recent advances in the development of ammonia combustion technology and its underlying chemistry. Fulfilling the COP21 Paris Agreement requires the de-carbonization of energy generation, through utilization of carbon-neutral and overall carbon-free fuels produced from renewable sources. Hydrogen is one of such fuels, which is a potential energy carrier for reducing greenhouse-gas emissions. However, its shipment for long distances and storage for long times present challenges. Ammonia on the other hand, comprises 17.8% of hydrogen by mass and can be produced from renewable hydrogen and nitrogen separated from air. Furthermore, thermal properties of ammonia are similar to those of propane in terms of boiling temperature and condensation pressure, making it attractive as a hydrogen and energy carrier. Ammonia has been produced and utilized for the past 100 years as a fertilizer, chemical raw material, and refrigerant. Ammonia can be used as a fuel but there are several challenges in ammonia combustion, such as low flammability, high NOx emission, and low radiation intensity. Overcoming these challenges requires further research into ammonia flame dynamics and chemistry. This paper discusses recent successful applications of ammonia fuel, in gas turbines, co-fired with pulverize coal, and in industrial furnaces. These applications have been implemented under the Japanese ‘Cross-ministerial Strategic Innovation Promotion Program (SIP): Energy Carriers’. In addition, fundamental aspects of ammonia combustion are discussed including characteristics of laminar premixed flames, counterflow twin-flames, and turbulent premixed flames stabilized by a nozzle burner at high pressure. Furthermore, this paper discusses details of the chemistry of ammonia combustion related to NOx production, processes for reducing NOx, and validation of several ammonia oxidation kinetics models. Finally, LES results for a gas-turbine-like swirl-burner are presented, for the purpose of developing low-NOx single-fuelled ammonia gas turbine combustors.

本文着重于氨作为无碳燃料的潜在用途，并涵盖了氨燃烧技术及其基础化学的最新进展。要实现COP21巴黎协议，就必须通过利用可再生能源生产的碳中性和整体无碳燃料，使能源生产脱碳。氢是此类燃料之一，它是减少温室气体排放的潜在能源载体。然而，其远距离运输和长时间存储提出了挑战。另一方面，氨以质量计包含17.8％的氢，并且可以由与空气分离的可再生氢和氮产生。此外，在沸腾温度和冷凝压力方面，氨的热性质与丙烷相似，使其作为氢和能量载体具有吸引力。在过去的100年中，氨已被生产并用作肥料，化学原料和制冷剂。氨可以用作燃料，但是氨燃烧存在一些挑战，例如低易燃性，高NOx排放和低辐射强度。克服这些挑战需要对氨火焰动力学和化学进行进一步研究。本文讨论了氨燃料在燃气轮机中与煤粉共燃的最新成功应用，以及在工业炉中的成功应用。这些应用程序已在日本“跨部级战略创新促进计划（SIP）：能源载体”中实施。此外，还讨论了氨燃烧的基本方面，包括层流预混火焰的特性，逆流双火焰和湍流的预混火焰由喷嘴燃烧器在高压下稳定。此外，本文讨论了与NOx产生有关的氨燃烧化学的详细信息，还原NOx的过程以及几种氨氧化动力学模型的验证。最后，为了开发低NOx单燃料氨燃气轮机燃烧器，给出了类似燃气轮机旋流燃烧器的LES结果。