Dynamic modeling of a three-way catalyst for SI engine exhaust emission control

Automotive emissions are severely regulated. Since 1980, a three-way catalyst (TWC) has been used to convert harmful emissions of hydrocarbons, carbon monoxide, and oxides of nitrogen into less harmful gases in order to meet these regulations. The TWC's efficiency of conversion of these gases is primarily dependent on the mass ratio of air to fuel (A/F) in the mixture leaving the exhaust manifold and entering the catalyst, the velocity of the exhaust mass, and the temperature of the catalyst. The goal of the paper is to develop a dynamic control-oriented model of a TWC. First, the measurement capabilities are described. Then, a simplified, dynamic catalyst model that can be determined on the basis of medium bandwidth A/F measurements and low bandwidth temperature and emission measurements is developed and validated.