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A transient one-dimensional model developed to simulate the thermal and conversion characteristics of adiabatic monolithic converters operating under warm-up conditions is presented. The model takes into account the gas-solid heat and mass transfer, axial heat, conduction, chemical reactions and the related heat release. The model has been used to analyze the transient response of an axisymmetric catalytic converter during a warm-up as a function of catalyst design parameters and operating conditions in order to observe their effects on the lightoff behaviour. The experimental test was carried out in two steps: the first on a sample for lightoff test and the second on two-stroke 150 cc engine with Pt/Rh metal-supported catalyst and full open-throttle condition. The simulated temperatures are close to test results. The predicted conversion efficiencies are qualitatively acceptable.

The emission standards compliance is really becoming effective generally for all the class of engines and particularly for two-stroke SI. While for larger capacity and more valuable applications, such as scooters, snowmobiles, marine engines, the state of the art appears consolidated with the use of direct fuel injection systems, the engines dedicated to very light and simple applications need a different approach in terms of simplicity and cost. Aiming in this direction a system including a self - sustained air injection system in the exhaust and oxidation catalysts was prepared. The influence of the main design parameters governing the system performances and their mathematical relationships were experimentally studied with the aid of a DOE (Design of Experiment) technique methodology.