The design of a diesel particulate trap system to fit a specific vehicular application requires significant expenditure, due to the high degree of interaction between the vehicle operation and trap behavior. The assistance of modeling in the design process is already well established. This paper presents the basic principles of a Computer Aided Engineering methodology aimed to assist the selection of the basic parameters of a Diesel Particulate Trap System by reducing the number of the necessary experimental tests. The computational modules currently supporting the CAE methodology are based on fundamental mathematical models, incorporating a small number of semi-empirical relations derived by experimental data on trap loading and catalytic regeneration, exhaust system heat transfer and trap backpressure effect on fuel consumption. The experimental data employed in the CAE system development, have been acquired from a case study involving a light duty van equipped with a cordierite filter and a Cerium based catalytic fuel additive. At this initial development phase, the capability of this methodology to assist optimization of filter sizing and positioning is demonstrated. The main optimization criteria in this process are fuel consumption penalty of the trap system and filter durability.