NSF-BSF: Plasma Reformed Ammonia as a Carbon Free Fuel: Study of Nanosecond-Pulsed Discharge Kinetics and Combustion Enhancement

可再生能源系统（如风能、水力、太阳能）将在供应世界电力方面发挥主导作用，但在实现从化石燃料中独立出来之前，必须有成本效益高的方法来储存可再生能源，并在难以脱碳的运输部门利用它。氨（NH3）可以使用可再生能源合成，并且可以很容易地作为液体储存/运输，作为一种无碳低成本的化学储能介质和重型货运/海洋应用的潜在燃料，已经引起了人们的极大兴趣。虽然将氨作为储能解决方案和燃料的关注是必要的，但其低反应性和在燃烧过程中产生一氧化氮排放的倾向是广泛采用的关键障碍。通过NSF-BSF的联合项目，科罗拉多州立大学和以色列理工学院的研究人员正在合作开发等离子体辅助氨重整策略所需的科学理解，以使氨在最先进的燃烧装置中使用。这项工作的主要成果包括一个经过验证的氨等离子体化学模型和一个经过验证的在发动机相关条件下等离子体改造氨混合物的燃烧模拟策略。研究成果将有利于能源和交通部门，这两个行业加起来占全球温室气体排放量的73%，通过支持高保真模型的开发，缩短下一代无碳能源转换设备的设计周期。来自NSF/BSF的这一独特的资助机会将有助于促进利用以色列理工学院等离子体改造和科罗拉多州立大学燃烧和激光诊断方面的独特专业知识的国际合作，并将支持高影响力的教育和跨国界的多样性建设活动。研究结果将在出版物和会议上分享，并将纳入合作机构的本科和研究生联合课程。这项研究将定期在K-12外展活动中突出。提案小组的初步等离子体和燃烧动力学模型表明，在广泛的操作条件下，NRP等离子体重整混合物的可燃性和火焰速度可以与传统燃料相媲美。研究了等离子体反应器内的详细动力学，包括确定NH2自由基对减少NO燃烧排放的关键作用。这项工作旨在通过实验验证来阐述这些建模结果，为未来基于系统的开发和优化工作奠定基础。工作计划的主要内容是：(1)在新建的NRP等离子体反应器内进行重整物测量，以验证和完善现有的NH3等离子体动力学模型；(2)通过腔衰落光谱（CRDS）在NRP内进行NH2测量，以阐明NH2在等离子体动力学和NOx还原中的作用；(3)在相关条件下使用激光点燃快速压缩机测量所得NH3重整物混合物的点火延迟和火焰速度。这些工作将解决当前文献中的空白，包括：(1)详细研究等离子体脉冲频率、振幅和反应器压力/温度对NRP反应器中NH3和NH3/空气重整效率的相对影响，构成动力学建模工作的验证数据集；(2)首次直接测量了ns脉冲系统中NH2自由基的形成，并与动力学模型进行了定量比较；(3)将NH3/H2/O2/N2重整混合物的点火延迟和火焰速度扩展到当前文献中稀疏的温度/压力区，具有微量NO/NO2，变化等效比和诱导湍流，为支持NH3燃烧化学机理和多维模拟开发提供了宝贵的数据集。对NRP等离子体反应器及其转化气体燃烧特性的进一步了解将为开发和优化包括内燃机和燃气轮机在内的各种氨-电转换系统奠定基础，否则这些系统只能通过繁琐的经验迭代进行。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Renewable energy systems (e.g., wind, hydro, solar) are primed to play the dominant role in supplying the world’s power, but before independence from fossil fuels can be achieved there must be cost-effective ways to store the renewable energy and utilize it in hard to decarbonize transportation sectors. Ammonia (NH3), which can be synthesized using renewable energy and can easily be stored/transported as a liquid, has garnered significant interest as a carbon-free low-cost chemical energy storage medium and potential fuel for heavy duty freight/marine applications. While the attention being paid to ammonia as an energy storage solution and fuel is warranted, its low reactivity and propensity to produce nitric oxide emissions during combustion represent critical impediments to widescale adoption. Through the joint NSF-BSF program, researchers at Colorado State University and Technion - Israel Institute of Technology are partnering to progress the scientific understanding needed to develop plasma assisted ammonia reforming strategies to enable the use of ammonia in state-of-the-art combustion devices. Key outcomes from the proposed effort include a validated ammonia-plasma chemistry model and a validated combustion simulation strategy for the plasma-reformed ammonia mixtures at engine relevant conditions. The research output will benefit both the energy and transportation sectors – industries which together account for 73% of greenhouse gas emissions worldwide – by supporting the development of high-fidelity models required to shorten the design cycles of next generation carbon-free energy conversion devices. This unique funding opportunity from NSF/BSF will help foster international collaboration leveraging the unique expertise in plasma reformation at Technion and combustion and laser diagnostics at Colorado State University and will support high impact educational and diversity building activities across borders. Findings will be shared in publications, at conferences, and will be integrated into joint undergraduate and graduate coursework at the collaborating institutions. The research will be regularly highlighted in K-12 outreach events.Preliminary plasma- and combustion-kinetic modeling by the proposal team has suggested that the ignitability and flame speed of NRP plasma reformate blends could be comparable to those of conventional fuels across a wide range of operating conditions. Detailed kinetics within the plasma reactor have been examined, including identifying the key role of the NH2 radical for reduction of NO combustion emissions. This work aims to expound upon these modeling results via experimental validation to build a foundation for future system-based development and optimization efforts. The main elements of the work plan are: (1) reformate species measurements within a newly constructed NRP plasma reactor to validate and refine existing NH3 plasma kinetic models, (2) NH2 measurements within the NRP by cavity ring-down spectroscopy (CRDS) to elucidate NH2’s role in plasma kinetics and NOx reduction, and (3) ignition delay and flame speed measurements of the resulting NH3 reformate blends at relevant conditions using a laser-ignited rapid compression machine. These efforts will address gaps in the current literature including: (1) the detailed study of the relative impact of plasma pulse frequency, amplitude, and reactor pressure/temperature on NH3 and NH3/air reformation efficiency in an NRP reactor, constituting a validation dataset for kinetic modeling efforts; (2) the first direct measurement of NH2 radical formation in ns-pulsed systems for quantitative comparison with kinetic models; and (3) the expansion of ignition delay and flame speed measurements of NH3/H2/O2/N2 reformate blends into temperature/pressure regimes that are sparse in current literature, with trace NO/NO2, varying equivalence ratio, and induced turbulence, providing an invaluable dataset to support NH3 combustion chemical mechanism and multi-dimensional simulation development. The improved understanding of NRP plasma reactors and the combustion characteristics of their reformate gases will set the foundation for the development and optimization of a variety of ammonia-to-power conversion systems including internal combustion engines and gas turbines, which could otherwise only progress through cumbersome empirical iteration.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.