A wide range air-fuel ratio sensor with a plate-type structure

A new wide range air-fuel (A/F) ratio sensor has been constructed with a plate-type structure using a single YSZ (Yttria Stabilized Zirconia) solid electrolyte plate shared by the electrochemical oxygen storage, pumping, and sensing cells. The sensing characteristic was tested in fuel lean (O-2-CO2-N-2) and fuel rich (CO-CO2-N-2) condition and compared with that of simulation. The operation pumping voltage could be set beyond the limiting current region when the reference voltage was fixed at 450 mV. This improper sensing characteristic was a result of the fact that the electrochemical oxygen sensing and pumping cells share a single electrolyte and one of the electrodes. A model to explain this sharing effect was set up and a new operating method for this sensor was suggested, which varied the reference voltage in proportion to the pumping voltage. The detecting range of this A/F ratio sensor extended up to very high concentrations of oxidizing and reducing gases by adopting variable reference voltage.