11/02/2026
By Marley O'Neil

The Francis College of Engineering, Department of Mechanical and Industrial Engineering (Energy Engineering - Renewable concentration), invites you to attend a doctoral dissertation defense by Yicheng Zhang titled "Direct Nitrogen Oxides Abatement Via Atmospheric Pressure Conventional and Membrane Dielectric Barrier Discharge Plasma."

Details

  • Defense date: Monday, Nov. 16, 2026
  • Time: 10:30 a.m. – 12:30 p.m.
  • Location: ETIC 445

Committee members

  • Advisor: Juan Pablo Trelles, Ph.D., Mechanical and Industrial Engineering, University of Massachusetts Lowell
  • Dimitris Assanis, Ph.D., Professor, Mechanical Engineering, Stony Brook University
  • Noah Van Dam, Ph.D., Mechanical and Industrial Engineering, University of Massachusetts Lowell
  • J. Hunter Mack, Ph.D., Mechanical and Industrial Engineering, University of Massachusetts Lowell

Abstract

The transportation sector, especially long-haul aviation and maritime transport, is increasingly adopting alternative fuels, including hydrogen-ammonia blends, to strengthen long-term energy security and achieve decarbonization targets. However, the combustion of these low-carbon fuels results in elevated nitrogen oxide (NOx) emissions, particularly under cold-start conditions. Selective catalytic reduction (SCR), which utilizes catalysts and reducing agents, is commonly used to reduce NOx to nitrogen and water vapor, yet generally requires elevated activation temperatures. Dielectric barrier discharge (DBD) plasma offers a compelling low-temperature, rapid-response approach for dynamic NOx abatement, potentially complementing SCR systems.

This dissertation evaluates and compares the performance of conventional DBD and a novel membrane DBD (mDBD) for direct NOx decomposition. Initial baseline evaluations using simulated exhausts consisting of NOx diluted in nitrogen demonstrate that both DBD and mDBD can achieve more than 90% NOx abatement at high specific energy intensities (SEI > 2 kJ/L), while mDBD shows 10% to 15% greater abatement under high-throughput, low-SEI conditions (< 0.8 kJ/L). Species-resolved chemical analysis revealed preferential reduction of NO2 across both systems, indicating that overall NO reduction is inherently constrained by competitive NO2 back-reactions. Optical emission spectroscopy confirmed comparable gas temperatures in both configurations, isolating the performance discrepancy to physical and kinetic mechanisms rather than thermal effects. The superior effectiveness of the mDBD configuration is attributed to two key factors: (1) gas flow through the membrane promotes more frequent and uniformly distributed microdischarges that enhance plasma-gas flow interaction and (2) gas distribution through the membrane significantly increases gas residence time, favoring NOx reduction reactions.

Subsequent investigations evaluated the treatment of oxygen-enriched (2% to 10%) simulated exhausts via mDBD plasma corresponding to lean-burn combustion scenarios. Connecting experimental diagnostics with nonlinear electric circuit and two-temperature fluid dynamic modeling further confirmed a distinct shift in discharge behavior: as applied power increased, the plasma transitioned from a highly localized filamentary discharge to a stable, volume-filling glow regime. This transition dictated a critical operational trade-off in NOx abatement. High-power diffuse discharges maximize NOx conversion, approaching more than 90% in the absence of oxygen, but yield lower energy efficiency. In contrast, low-power filamentary discharges maximized energy efficiency, reaching up to 4 mg NOx/kJ, three times higher than high-power glow discharges, at the expense of decreased bulk conversion. The introduction of elevated oxygen levels (> 6%) hindered net NOx removal by accelerating O-radical-driven NO regeneration pathways. The use of a green membrane provided only a temporary improvement; with extended use, performance stabilized near the baseline established by the seasoned membrane.

This research demonstrates the potential of mDBD plasma as a rapid-response, on-demand complementary technology for SCR systems, helping to address the treatment gap during cold starts.