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Modeling the Emissions Control Performance of a Catalyzed Diesel Particulate Filter (CDPF) System for Light Duty Diesel Applications
Abstract:
The use of catalyzed diesel particulate filter (CDPF) systems in light duty diesel (LDD) vehicles is becoming increasingly common. The primary functions of the system are to remove carbon monoxide (CO) and hydrocarbons (HC) from the vehicle exhaust stream, while simultaneously reducing the level of particulate matter (PM) emissions to ambient background levels. These systems can comprise either a separate diesel oxidation catalyst (DOC) and a downstream CDPF, or a single unit CDPF with the DOC functions incorporated within the CDPF. The single CDPF unit provides higher regeneration efficiency as it is located nearer to the engine and also cost benefits, as only a single unit is required compared to the alternative separate DOC and CDPF arrangement.
A model describing the performance of the single unit CDPF for emissions control has been developed, with particular emphasis on achieving predictions of the CO and HC emissions over transient vehicle drive cycles. The model comprises a 1-D DPF model, with a description of soot accumulation and removal, and CO, HC and NO oxidation over the catalyst coated on the filter wall. Langmuir-Hinshelwood expressions were employed to describe the CDPF reaction kinetics.
The model has been validated using transient European (ECE/EUDC) drive cycle data. The model has been developed to incorporate diffusion of the exhaust components to the catalyst surface, akin to mass transfer in a monolith substrate. This enabled a study of the effect of precious metal catalyst loading and precious metal catalyst distribution within the filter on the CDPF emissions performance. The model can be used as a tool to aid optimized CDPF catalyst design as well as sizing and positioning of a CDPF on different vehicle applications.