Enhanced low-temperature particulate matter oxidation through optimised DBD-generated NO₂: From statistical modelling to real-exhaust application

This study investigated the design, optimisation, and performance evaluation of a dielectric barrier discharge (DBD) reactor for the selective synthesis of NO 2 from ambient air and its subsequent application as a low-temperature oxidant for particulate matter (PM) abatement. Utilising a Central Composite Design (CCD) within a Response Surface Methodology (RSM) framework, the synergistic effects of discharge frequency and applied voltage on NO 2 formation were quantified. This yielded a robust quadratic model (R 2 =98.53%, R 2 (pred) = 92.90%), identifying 1500 Hz and 10 kV as the optimal parameters for maximising NO 2 generation capacity within the defined design space. Experimental validation at this peak condition produced 162.41 ppm of NO 2 against a predicted 175.09 ppm (a 7.24% deviation), thereby confirming the model's reliability for benchmarking reactor performance. Specific Energy Density (SED) analysis indicated that while NO 2 concentrations scaled with frequency, the energy-normalised yield reached saturation between 500 and 750 Hz, suggesting an efficient operational window for energy-conscious applications. Downstream integration with gasoline direct injection (GDI) engine exhaust at 500 Hz generated moderate NO 2 levels (7–11 mg/kWh), achieving significant PM reduction of approximately 2.2 mg/kWh. These findings establish a practical framework for implementing plasma-based oxidants in environmental engineering, demonstrating the efficacy of RSM in streamlining complex chemical reactor optimisations.