An experimental and computational investigation of microwave regeneration of diesel particulate traps.

As the number and power ratings of diesel engines in both on-road and off-road applications are increasing, concern over the health effects of the exhaust emissions, especially diesel particulate matter (DPM) is becoming more significant. One of the most effective exhaust after-treatment methods is to use ceramic traps to control DPM emissions. Periodic cleaning of traps (regeneration) is essential as the flow resistance progressively increases during filtration of DPM. However, the existing regeneration technologies for ceramic particulate traps are uneconomical and/or cause structural damage to the ceramic trap element. Microwave energy offers the advantage of selectively heating only the DPM, since the ceramic material is nearly transparent to them. The present study investigated fundamental and experimental aspects of employing microwave energy to regenerable diesel particulate traps. The three-phase investigation was aimed at determining the thermal and microwave characteristics of DPM; development of a Microwave Enhanced Trap Oxidizer System (METOS), for on-line and off-line regeneration; development of test protocols and safety systems; and implementation of a two-dimensional mathematical model of the microwave heating of particulate traps. Custom designed and fabricated soot filtration and off-line regeneration systems were used for conducting tests on METOS. Accurate diesel soot loading of the Corning EX80 ceramic trap was made possible with the development of an automated exhaust bypass system. In this study, regeneration efficiencies were determined gravimetrically. Microwave systems employed magnetrons with 1 kW output power, which are readily available in consumer ovens. A parametric study on METOS indicated that the optimal parameter choice was a trade-off between the maximum regeneration efficiency and prolonged filter life. The optimal parameters for these microwave systems were a soot loading of 24 g, a microwave heating period of 12.5 min, and an airflow rate of 5 scfm (141.6 slpm). Several novel regeneration schemes, which including filter-positioning, reverse trap configuration, pulsation, air supply during microwave heating, and soot quality testing were implemented. This study has successfully demonstrated the operation of a viable Microwave Enhanced Trap Oxidizer System (METOS) and confirmed that DPM can be preferentially heated in a ceramic trap