Marion Wedemann

Catalyst State Observation via the Perturbation of a Microwave Cavity Resonator

The state of the three-way catalyst (TWC) of a gasoline engine is commonly estimated by measuring the air-to-fuel ratio in the exhaust gas. This indirect method suffers from several disadvantages that one could avoid by directly observing the catalyst state and in particular its oxygen loading. We have investigated an RF approach to this direct measurement problem which is based on the fact that the TWC and its stainless steel canning form a filled cavity resonator. It will be shown that the resonator is perturbed when the TWC changes its conductivity as a function of oxygen loading and that the characteristics of the resonator S-parameters mirror the oxidation/reduction state of the catalyst. Index Terms – Three-way catalyst, TWC, state observation, in situ, cavity resonator, perturbation