Abstract
The results of recent experiments on the thermal properties of diesel particulate matter (DPM) are reported. These data were collected in connection with the design of a microwave system for the regeneration of the diesel particulate traps for diesel engines, hoping for a selective heating of the DPM by microwaves. The DPM was collected from a Caterpillar 3304 diesel engine that was operated over a range of steady-state and transient duty cycles. The thermal parameters were determined from thermogravimetric and differential scanning calorimetry experiments, carried out in air and argon, from room temperature to about 800°C. These experiments showed that the decomposition of the diesel particulate is an exothermic process beginning at about 350°C with an activation energy of about 30 kcal/mol. The residual matter left after the decomposition was analyzed using X-ray diffraction, its major components being CaSO4, α-Fe2O3, and CaC2. Because the rate of energy absorbed from the microwaves is proportional toε×, the imaginary part of the dielectric constant, we measured ε× for DPM and the ceramic trap material at 8.7 GHz. The measured value of ε× for DPM = 7.4 ± 1.5, and it is 105 times larger than ε× ≈ 6 × 10-5 measured for the ceramic trap material, confirming the idea of selective heating of DPM by microwaves. Finally, design aspects of the microwave-enhanced trap oxidizer system (METOS), which is now being tested, are outlined.