Mechanical Engineering
Graduate Seminar
NOTICE OF SEMINAR PRESENTATION
CANDIDATE: Shiyuan Tang
DEGREE SOUGHT: MASc
DATE: 9/25/2026
TIME: 11:30am
PLACE: Room 1101 CEI
TITLE: Effect of Excess Air Ratio on Lean NOx Trap Regeneration Using Dimethyl Ether as the Reductant
Abstract
Automotive manufacturers are required to meet increasingly stringent emission regulations, including Euro 7 and the U.S. EPA 2027 standards. Among the regulated pollutants, nitrogen oxides (NOx) remain a major challenge for compression-ignition (CI) engines. Aftertreatment technologies such as Selective Catalytic Reduction (SCR) and Lean NOx Trap (LNT) are widely applied and have demonstrated NOx reduction efficiencies of over 90% under well-controlled boundary conditions. Lean NOx Trap operation alternates between periodic lean NOx storage and rich NOx regeneration, where reductant injection is required but can introduce an energy penalty, unconverted NOx slip, and undesirable byproducts. Renewable fuels, particularly oxygenated ethers, have been demonstrated as effective reductants for LNT regeneration. Dimethyl ether (DME) has received considerable attention due to its availability, established production pathways, and favorable cost. However, the strong exothermic oxidation of DME can elevate the catalyst bed temperature and reduce nitrate stability, causing additional NOx slip after injection ceases. This phenomenon is commonly attributed to thermal NOx release. This study employs lean-rich cycling experiments on an established heated flow bench using DME as a reductant to investigate NOx thermal release phenomenon. Results indicate that NOx conversion efficiency generally increases under richer conditions, while the 0.88 g DME case (λ = 1.11) exhibits the strongest thermal release behavior with high regeneration effectiveness but reduced conversion efficiency. Additional experiments varying injection duration at the same reductant quantity show that the 15 s injection produces lower NOx slip, higher NOx conversion efficiency, and more favorable product selectivity. These results demonstrate that optimizing the injection duration strategy can mitigate insufficient reductant exposure, reduce thermal NOx release, and improve LNT regeneration performance, providing a more favorable balance among regeneration effectiveness, conversion efficiency, and product selectivity.