Study of Catalytic Regeneration Mechanisms in Diesel Particulate Filters Using Coupled Reaction-Diffusion Modeling

Diesel particulate filters are today widely accepted as a viable technology for drastically reducing particulate emissions from diesel engines. Current applications are based on some form of catalytic assistance for the filter regeneration purposes, either in the form of a fuel borne catalyst or by employing catalyzed filters. This paper presents an experimental and computational study of the prevailing reaction mechanisms in the catalyst supported DPF systems. The knowledge of the soot reaction kinetics in uncatalyzed filters with O₂ and NO₂ is a prerequisite in this respect. Next, the reaction rates in the case of using a Ce-based fuel-borne catalyst are evaluated. Emphasis is given on the importance of oxygen diffusion effects during uncontrolled regeneration. Finally, the regeneration mechanisms in a catalyst coated filter are studied. In this case, experiments and simulations are carried out for controlled and uncontrolled regenerations, revealing differences in the governing reaction-diffusion processes. The diffusion of NO₂, which appears important for low temperature regenerations is studied parametrically in more detail. Concluding, each configuration exhibits different characteristics regarding the reaction mechanism and its temperature dependence, with important implications for the system designer of diesel catalytic after-treatment systems.