Hydrocarbon traps for gasoline engines are promising candidates for cold start emission control, provided that their design is based on a “systems approach”. In this paper, an existing CAE methodology for exhaust after-treatment is expanded to include HC trap technology. The flow, heat transfer and chemical kinetics in a typical complex system, comprising a “barrel type” adsorber and two conventional catalysts are studied. A mathematical model is developed and applied for the computation of the flow and pressure distribution, as well as transient heat transfer in the barrel type adsorber. A physically relevant model is used to simulate HC adsorption desorption on the adsorbing material. The model is used in combination with an existing 2-d 3-way catalyst model to simulate different HC trap concepts. The aim is to understand and quantify the particular thermal response and HC retention behavior of hydrocarbon adsorber systems. Illustrative results with variable geometric parameters under realistic input conditions are presented.