In order to comply with the stringent future emission mandates of automotive diesel engines it is essential to deploy a suitable combination of after treatment devices like diesel oxidation catalyst (DOC), diesel particulate filter (DPF) and DeNox converter (Lean NOx Trap (LNT) or Selective Catalytic reduction (SCR) system). Since arriving at a suitable strategy through experiments will involve deploying a lot of resources, development of well-tuned simulation models that can reduce time and cost is important. In the first phase of this study experiments were conducted on a single cylinder light duty diesel engine fitted with a diesel oxidation catalyst (DOC) at thirteen steady state mode points identified in the NEDC (New European Driving cycle) cycle. Inlet and exit pressures and temperatures, exhaust emission concentrations and catalyst bed temperature were measured. A one dimensional simulation model was developed in the commercial software AVL BOOST. Eight of the experimental data sets from the 13 modes were taken for fine tuning the chemical kinetic rate parameters and friction factor of the model. The prediction of the model was validated at the remaining five experimental data points keeping the kinetic and friction parameters the same. The model could predict the conversion efficiency and pressure drop across the DOC within 1.5%. The influence of the length and diameter of the DOC was studied using the model which indicated that increasing the diameter is more effective than increasing the length based on the conversion efficiency and pressure drop. It was also found that increasing the diameter will enable the reduction in the DOC volume without any sacrifice in the conversion efficiency while the pressure drop can also be reduced simultaneously. The developed model can be used to size the DOC based given the requirements of space and conversion efficiency. © 2019 SAE International. All Rights Reserved.