Combustion Characteristics and Emissions of 99% Cracked 2 Ammonia Blends in a Gas Turbine Representative Swirl

This study presents the first systematic investigation of pressure-dependent combustion characteristics and emissions of highly cracked ammonia (99% cracking efficiency) in a gas turbine representative swirl burner. The research addresses a critical knowledge gap in understanding how operational pressure affects the combustion behaviour of cracked ammonia fuels, which are emerging as promising carbon-free alternatives for power generation.Experiments were conducted using a High Pressure Optical Combustor (HPOC) facility across a pressure range of 1.1 to 6 bar absolute, with air preheated to 500 K and a constant thermal power output of 22.7 kW maintained under lean conditions (equivalence ratio approximately 0.545). The fuel composition consisted of 17.5% hydrogen, 1.0% residual ammonia, and 81.5% nitrogen by volume, representing a realistic cracked ammonia blend for gas turbine applications.The investigation employed advanced optical diagnostics to capture NH₂* chemiluminescence, which serves as an indicator of radical formation and combustion intensity. Results demonstrated that NH₂* intensity increased monotonically with pressure from 1.1 to 6 bar, indicating enhanced radical production at higher collision frequencies. Concurrently, NOx emissions measurements revealed a distinctive pressure-dependent trend: emissions rose sharply from 90 ppmv at 1.1 bar to 189 ppmv at 4 bar before stabilising at higher pressures, forming a characteristic plateau that differs fundamentally from pure hydrogen combustion behaviour.To elucidate the underlying chemical mechanisms, a Chemical Reactor Network (CRN) model was developed and validated against experimental data using the Stagni et al. kinetic scheme. The model successfully captured the NOx plateau phenomenon and revealed that the stabilisation results from a balance between thermal NOx formation pathways and ammonia-mediated reduction reactions. Rate of production analysis identified pressure-dependent shifts in dominant reaction pathways, with thermal NOx mechanisms (N + O₂ → NO + O) contributing 35-42% across all pressures, while destruction pathways increased from 6% at 1.1 bar to 27% at 6 bar, explaining the emissions plateau.The findings demonstrate that pressure is a critical control parameter for managing NOx emissions in cracked ammonia combustion systems. The research provides essential data for the design and optimisation of low-emission gas turbine combustors capable of operating on ammonia-derived fuels, supporting the transition to carbon-free power generation while maintaining operational flexibility and emissions compliance. This work contributes fundamental knowledge to the emerging field of ammonia energy and offers practical insights for industrial implementation of cracked ammonia combustion technology

本研究首次系统性探究了裂解效率达99%的高度裂解氨在模拟燃气轮机旋流燃烧器中的压力依赖性燃烧特性与排放行为。当前学界对于运行压力如何影响裂解氨燃料的燃烧行为尚存在关键认知空白，而裂解氨作为极具潜力的无碳发电替代燃料正受到广泛关注。

本研究采用高压光学燃烧室（High Pressure Optical Combustor, HPOC）实验平台开展测试，实验压力范围覆盖1.1至6巴绝对压力，空气预热至500 K，在贫燃工况（当量比约为0.545）下维持恒定热功率输出22.7 kW。实验燃料按体积占比计包含17.5%氢气、1.0%残留氨与81.5%氮气，该组分契合燃气轮机应用场景下的典型裂解氨混合燃料配比。

本研究采用先进光学诊断技术采集NH₂*化学发光信号，该信号可作为自由基生成与燃烧强度的表征指标。实验结果显示，NH₂*发光强度随压力从1.1巴升至6巴呈单调上升趋势，表明更高的分子碰撞频率下自由基生成量有所提升。与此同时，氮氧化物（NOₓ）排放测量结果呈现出独特的压力依赖性规律：排放浓度从1.1巴下的90 ppmv（体积百万分浓度）急剧升至4巴时的189 ppmv，随后在更高压力下趋于平稳，形成了区别于纯氢燃烧行为的特征平台区。

为阐明背后的化学反应机理，本研究搭建了化学反应器网络（Chemical Reactor Network, CRN）模型，并基于Stagni等人的动力学机理对模型进行了实验验证。该模型成功复现了NOₓ排放平台现象，并揭示出该平台是热NOₓ生成路径与氨介导的还原反应之间动态平衡的结果。产率速率分析识别出主导反应路径随压力发生的偏移：热NOₓ生成机理（N + O₂ → NO + O）在所有压力下的贡献占比为35%至42%，而燃料破坏路径的占比则从1.1巴下的6%升至6巴时的27%，这一变化解释了排放平台的形成原因。

研究结果表明，压力是调控裂解氨燃烧系统中NOₓ排放的关键控制参数。本研究为设计和优化可使用氨衍生燃料的低排放燃气轮机燃烧室提供了关键数据，有助于在保障运行灵活性与排放合规性的前提下，推动无碳发电的转型进程。本研究为新兴的氨能源领域补充了基础认知，并为裂解氨燃烧技术的工业落地提供了实用参考。