One of the main challenges in developing cost-effective diesel particulate filters is to guarantee a thermally safe regeneration under all possible conditions on the road. Uncontrolled regenerations occur when the soot reaction rate is so high that the cooling effect of the incoming exhaust gas is insufficient to keep the temperature below the required limit for material integrity. These conditions occur when the engine switches to idle while the filter is already hot enough to initiate soot oxidation, typically following engine operation at high torque and speed or active filter regeneration.
The purpose of this work is to investigate engine management techniques to reduce the reaction rate during typical failure mode regenerations. A purely experimental investigation faces many difficulties, especially regarding measurement accuracy, repeatability in filter soot loading, and repeatability in the regeneration protocol. Therefore, the present study is guided by advanced regeneration modeling, which is supported for calibration and validation purposes by careful experimental measurements on the engine bench.
The study covers both uncoated and catalyzed filters. The model used is a previously developed and validated 3-dimensional regeneration model including heterogeneous catalytic reactions for all types of coatings, including NOx storage functionality. The engine management techniques for peak temperature limitation involve engine speed, air path and injection control during the idle mode. Experiments are performed with and without protection measures to verify the model agreement in both conditions. In a next step, the validated model is used to study the acceptable soot mass limit for various calibrations of control measures.