Test on diesel particulate filter regeneration using non-thermal plasma technology aided by exhaust waste heat

Abstract: Diesel engines are widely applied in the field of transportation and manufacturing because of their dynamic and economic performance. Compared to gasoline engine, the hydrocarbon (HC) and carbon monoxide (CO) emissions from diesel engine are much lower. However, diesel engine emits huge quantities of particulate matter (PM) which pose a great threat to human health and environmental protection. As emission regulations are becoming gradually stricter, it is imperative to stringently control diesel PM emission with a feasible after-treatment technic. The technology of diesel particulate filter (DPF) is considered as the most effective mean to reduce diesel PM emission. The key of DPF technology is regeneration of the DPF, which is to timely remove the carbon deposit captured by DPF. Non-thermal plasma (NTP) technology is a promising method to control diesel emission. Reactive species generated by NTP reactor can activate complicated chemical reactions under common condition. Therefore, NTP technology has been used to remove PM deposited in DPF and become a new research hotspot in the field of DPF regeneration. Other studies have shown DPF could be effectively regenerated by NTP when the regeneration temperature was precisely controlled by an extra heater. In this work, an experimental system of DPF regeneration was constructed to investigate the regeneration effect in which DPF was not heated by an external heat source. Aided by the exhaust waste heat after engine outage, an experimental study on DPF regeneration was conducted by using a dielectric barrier discharge (DBD) NTP reactor. In the process of DPF regeneration, reactive species and PM generated exothermic oxidation reactions. Infrared gas analyzer was used to measure the volume fraction of CO and CO2 that were the main oxidation products in DPF regeneration. Twelve pairs of thermocouples were distributed in the interior of DPF to monitor the temperature change in the regeneration process. Based on NTP technology aided by exhaust waste heat, the regeneration process was investigated by analyzing the concentration change of oxidation products and the temperature change of each measuring point. Engine exhaust pipe was equipped with pitot tubes to measure the exhaust backpressure before and after regeneration. The regeneration effect was evaluated by backpressure variation of DPF after regeneration. In addition, an auxiliary test was conducted to explore the decomposition law of O3 versus temperature, contributing to the analysis of regeneration process. Thermogravimetric analysis (TGA) was performed to compare the physicochemical properties of deposit before and after NTP treatment. Results showed that NTP technology aided by exhaust waste heat exerted a good regeneration effect on DPF without an external heat source, dramatically lowering the backpressure of DPF by 69%. With the decrease of temperature, the decomposition of O3 in NTP was weakened. Therefore oxidation reaction of PM was intensified, causing the rising of the internal temperature of DPF instead of dropping. In the regeneration process, the oxidation area extended from the front of DPF to the back. The most vigorous oxidation reaction occurred at the radial midpoint of DPF and the remnant PM after regeneration on the axial section of DPF showed a ? shape. The soluble organic fraction (SOF) in the remnant deposit reduced after DPF regeneration. NTP treatment reduced the activation energy of PM both in SOF and in dry soot (DS). In the whole regeneration process, the mass of carbon in the PM decomposed was more than 6 g. This work proves the feasibility of the DPF regeneration by NTP without an external heat source, and provides experimental basis for vehicle application of the NTP technology.