ERI: High-pressure spectroscopy of ammonia combustion species for carbon-free supercritical and detonative power and propulsion

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). More efficient energy conversion at extreme pressures is increasingly important as both the U.S. transportation and power generation sectors transition to a low-carbon future to reduce environmental impact and increase U.S. energy security. Unfortunately, extreme-pressure combustion of carbon-free fuels, such as ammonia, is not well-understood. The main goal of this project is to better understand chemical reactions of high-pressure ammonia by measuring important combustion gases formed during controlled ignition experiments, and at fast enough measurement rates to capture the behavior of many short-lived gases. To perform these measurements, a new laser diagnostic technique will be developed to measure these gases at higher pressures and faster measurement rates than ever before. Successful execution of the project will provide (1) new diagnostic tools for measuring ammonia combustion gases at extreme pressures, with broader application to both energy and rocket propulsion systems, and (2) new understanding of pollution formation at high temperatures and pressures. It is envisioned that knowledge gained from this project will help accelerate development of carbon-free power generation technologies in the U.S. The project will also build state-of-the-art combustion research capability at UTSA, a Minority Serving Institution with close proximity to U.S. energy and aerospace industries, and complementary educational activities will enhance UTSA’s emerging aerospace curriculum with relevant laboratory research projects. The research objective of this proposal is to exploit non-ideal spectroscopic phenomena for measurement of supercritical and detonation combustion flows of next-generation carbon-free fuels, most specifically ammonia. The proposed research combines advancements in low-cost compact mid-infrared photonics with physics-informed spectroscopic models to quantitatively interpret otherwise convoluted high-pressure absorbance spectra at measurement rates which sufficiently capture time-evolution of intermediate species in supercritical and detonation regimes. In this project, high-pressure absorption spectroscopy of ammonia combustion gases will be investigated using both a heated optical gas cell and high-enthalpy shock tube. Thermodynamically scalable models will be developed to predict absorbance spectra of these species for temperatures and pressures relevant to detonation and supercritical combustion. The models will subsequently be used to perform novel high-speed quantitative measurements of the target species during supercritical ignition and detonation combustion of ammonia mixtures in shock and detonation tubes at UTSA. Data collected during the project effort will be incorporated into graduate and undergraduate engineering courses at UTSA to better prepare students for next-generation research and development in the engineering workforce.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.