Non-thermal plasma-woody perovskite purifier for diesel engine exhaust

Woody perovskite-type catalysts are the sorts of porous catalysts with biomass morphology, in order to achieve the simultaneous purification of PM, NO_x, CO, and HC. Among them, the ratio of adsorbed oxygen (Oads)/lattice oxygen (Olatt) of perovskite-type catalysts can be improved to avoid the collapse and aggregation of perovskite-type catalysts. The reason was attributed to the presence of a large number of high-energy electrons, active particles, and active heavy particles in non-thermal plasma (NTP). In addition, the NTP can outstandingly improve the specific surface area and porosity of catalysts. The NTP can enhance the four-way purification performance of PM, NO_x, CO, and HC emitted by automobile exhausts over woody perovskite-type catalysts. Dielectric barrier discharge (DBD) can generate the NTP under atmospheric pressure conditions, indicating the broad application prospects in environmental protection and material processing. This study aims to enhance the performance of NTP synergistic woody perovskite-type catalysts, in order to purify the diesel engine exhaust. Firstly, a DBD reactor was designed, of which the corundum tubes and woody perovskite-type catalysts were used as the discharge medium. A two-dimensional simulation model was established for the DBD reactor. The plasma module of COMSOL software was employed to calculate the number density of active species under different parameter conditions of the reactor. After that, the optimal internal parameters of the reactor were obtained. Secondly, the overall mechanical structure of the non-thermal plasma-woody perovskite purifier was designed for the diesel engine exhaust. A numerical model was established to analyze the impact of different DBD arrangements on exhaust back pressure using pressure loss. Lastly, a test bench of the diesel engine was set to verify the purification performance of the purifier. According to the relevant regulations of automotive testing, the D2 (5 loads operating at rated speed) test cycle was selected from the ISO 8187 international standard, in order to test and verify the purifier. The model calculation indicated that when the input voltage of the exhaust purifier was 15 kV, the filling rate was 30%, the number density of active particles in the reactor reached the maximum, with an electron density of 10¹⁶/m³, the electron energy distribution in the reactor ranged from 10^1.1 to 10^1.5 eV, and the number densities of N₂⁺, -CO, and -N₂ reached 10¹⁸/m³, the number densities of -O reached 10¹³/m³, respectively. Once the number of DBD parallel connections was 20, and the DBD reactor length was 0.16 m, the exhaust back pressure of the purifier was 996.3 Pa. The experimental results showed that the exhaust back pressure of the purifier fully met the national standard requirements, in order to achieve the simultaneous purification of PM, NO_x, CO, and HC. Furthermore, the purification efficiencies of the purifier reached 92%, 64%, 72%, and 61%, respectively, when the engine speed was 2 600 r/min and the load was 50%. Once the purifier was used for no more than 75 h, the exhaust back pressure of the purifier was less than 3 kPa. Correlation analysis of experimental data revealed that the PM, CO and HC were promoted to reduce NO_x, thus leading to the oxidation of PM, CO, and HC. The finding can provide the theoretical reference for synergistic catalysis in the field of automotive exhaust purification.