Three-way catalyst diagnostics for advanced emissions control systems

Automotive emissions are stringently 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. This paper develops a method by which a dynamic TWC model can be used for diagnostic purposes. This diagnostic method is analyzed in the context of a hypothesis test that is based on the oxygen storage capacity of the TWC. The Neyman-Pearson criterion is used as the basis for this hypothesis test. It is initially applied in the case of a single sample where the variance of the data is assumed to be known. This is then expanded to a multiple-sample case through the use of Student´s t test. The improved fidelity of the t test is demonstrated, and it is shown that larger sample sizes provide further improvement in the quality of the hypothesis test.