Enhancing Ammonia Reactivity with UV Light: Excited-State Kinetics

Ammonia has significant potential as a fuel for future energy applications but suffers from low reactivity. A possible remedy to this deficiency is the largely unexplored technique of ultraviolet-enhanced combustion, which utilizes ultraviolet (UV) light to accelerate combustion. While UV light sources have been used in many other applications to control chemical reactions, it has not yet been applied to control ammonia reaction pathways, especially the formation and destruction of intermediate species. The goal of this project is to quantify the rate process of ammonia decomposition in the presence of an ultraviolet light source. Through a combination of high-temperature laboratory experiments, and theory, this project will explore the fundamental reaction rates of this promising technique for application to ammonia combustion, which will pave a pathway to higher-efficiency engines and turbines that run on ammonia. The research will be disseminated to the general public through a series of hands-on activities intended to convey basic scientific principles of utilization of UV light in controlling chemical reactions. Additionally, a series of workshops will help train graduate and undergraduate students on how to present science to the public. The project goal will be achieved through three objectives. First, temperature- and pressure-dependent ultraviolet absorption coefficients of ammonia will be measured at ambient to high temperatures. Second, ammonia time histories will be measured during pyrolysis of ammonia in a shock tube, both with and without ultraviolet light. Third, theory-based rate constants will be calculated for both ground- and excited-state ammonia kinetics. Successfully completing these objectives will yield a detailed kinetic mechanism for ultraviolet-enhanced ammonia pyrolysis and will advance the predictive capabilities for modeling such processes—with the goal of eventually being applied to ultraviolet-enhanced ammonia oxidation. The outreach activities (including presentations at a local children’s museum using hands-on activities) will generate interest in STEM fields among the next generation of scientists, and the design/implementation of these activities will then be shared online for a broader reach. 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.