The diesel particulate filter (DPF) is effective for particulate removal from diesel engine exhaust under a variety of conditions, but development of regeneration strategies remains an ongoing challenge, primarily because of low exhaust temperatures. This paper addresses two issues related to DPF regeneration: the thermal response of DPFs during regeneration events and the soot oxidation (i.e., regeneration) rate at varying temperature, flow rate, oxygen content, and unsteady inlet temperature.
The experiments are performed in a laboratory reactor, which provides gas temperature and composition similar to diesel engine exhaust. The catalyzed and uncatalyzed DPFs used in this study are first loaded with soot on an engine dynamometer at a fixed load and engine speed. During constant temperature regeneration experiments, the change in pressure drop is monitored to determine the extent of regeneration. Mass loss measurements are used to calculate the soot oxidation rate and apparent activation energy for each condition tested. The catalytic coating increases the mass loss rate at a given inlet temperature for each test condition, and also sharply decreases the minimum regeneration temperature. Oxygen content has a strong impact on the soot oxidation rate for the coated and uncoated DPFs.
The effect of time-varying inlet gas temperatures on DPF exit temperature are predicted using a numerical model. Comparisons between the model and experiments are favorable. The model shows that a time-varying inlet temperature has little effect on the DPF temperature for high DPF thermal inertia (i.e., the product of mass and heat capacity), low mass flow rate, and high wave frequency. At the experimental conditions examined in this paper, high frequency temperature changes have little effect on the regeneration of DPFs below the ignition temperature, but significant effect above the ignition temperature. A combined analysis of the results provides insight into the regeneration process and could lead to improved strategies involving thermal management of the particulate control system.