(210b) Microwave Regeneration of Diesel Particulate Filter

Wall-flow diesel particulate filters (DPFs) require periodic regeneration for continuous operation. While microwave heating has been considered a potential active regeneration method for the DPFs, past studies on the technology have identified several technical problems leading to filter failure. The problems are mainly associated with the use of inappropriate filter materials for the microwave system and the generation of local hotspots due to uneven microwave heating, resulting in the physical damage to the filters. The objective of this study was to develop and demonstrate the technology employing a microwave-absorbing filter material coupled with an effective waveguide design for the reliable regeneration of DPFs. In this study, a well-equipped diesel emission control laboratory was established to conduct the experiments. The experimental facilities included a 6-kw diesel generator, an exhaust flow control system, a diesel particulate filter system, a microwave energy supply system, a soot-sampling system, a differential-pressure measurement system, and a temperature measurement system. In the DPF set up, a silicone carbide wall-flow monolith filter was enclosed in a quartz filter holder. A commercial 1.4-kw microwave oven was modified to accommodate the quartz holder and a waveguide was engineered to evenly supply the microwave energy to the enclosed filter to achieve filter regeneration. In the experiments, the diesel engine exhaust was lined up to flow through the filter with a fixed flow rate. The microwave regeneration was triggered after a specific soot loading was generated based on the differential pressure drop reading. The results have indicated that the designed system has been able to achieve uniform temperature profiles both in the radial and the vertical DPF positions. The oxygen concentration has been found to play an important role in regeneration kinetics. The soot filtration efficiency has remained to be comparably high after more than five cycles of microwave regeneration with no apparent physical damage to the DPF being observed.