Collaborative Research: Quantifying Secondary Electron Emission for Predictive Electrode Boundary Conditions in Plasma-Assisted Combustion

Plasma-assisted combustion is a new technology that can improve combustion efficiency. It can also enable use of difficult-to-burn fuels such as ammonia. However, predicting the performance of plasma-assisted combustion requires models that take into account how plasma interacts with surfaces. This project will use a combination of modeling and experiments to identify the fundamental physics driving interactions of plasma with surfaces. The research outcomes will be critical tools that better simulate plasma-assisted combustion and the ignition of various fuels. These results will apply broadly to a variety of applications in aerospace, energy, and advanced manufacturing. The project will train graduate and undergraduate students, providing them with expertise in advanced laser diagnostics and computational modeling. The goal of this project is to quantify the effective secondary electron emission coefficient under conditions relevant to plasma-assisted combustion, including high surface temperatures and nitrogen-oxygen mixtures. Current simulations use coefficient values that are significantly smaller than those inferred from experiments, creating a discrepancy likely driven by excited metastable species. To resolve this, the project will utilize a coupled experimental and computational approach. The experiments will employ novel techniques to measure current-voltage characteristics and isolate the critical cathode sheath voltage, while simultaneously measuring metastable and radical species using advanced laser diagnostics. Concurrently, the computations will develop a new hybrid fluid-kinetic framework that integrates a nonlocal kinetic sheath model. This framework will utilize a thermodynamically consistent theoretical framework for electron heating due to vibrationally excited states that accurately accounts for the additional heating when the vibrational temperature is higher than the gas temperature. Furthermore, a semiclassical theory for heavy-particle kinetics will be implemented to determine more accurately the rates of the reactions involving electronically excited states. By matching simulated characteristics to experimental measurements, the project will derive and validate the first physics-based correlations for secondary electron emission in a combustor environment. 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.