COMPARISON OF TRANSIENT-RESPONSE OF EXHAUST-GAS SENSORS BASED ON THIN-FILMS OF SELECTED METAL-OXIDES

New concepts of engine control are required to meet the increasingly stringent standards for the reduction of pollutants in the exhaust gas. These new concepts can be realized by new fast sensors for lambda measurement by means of which the transient operating condition of a combustion engine and the fluctuation between the individual cylinders of the engine can be recorded. The most suitable materials for a fast exhaust-gas sensor are thin films made from different metal oxides (e.g.. SrTiO3, BaTiO3 or CeO2). As bench tests show, use of these materials allows a lambda measurement to be made in a wide range (0.9 < lambda < 1.1). In order to permit a cylinder-selective and stroke-selective measurement, the sensors are placed directly behind the outlet valve of the engine (position I), at the point of junction of the exhaust manifold (position II) and several centimetres towards the exhaust cycles of the engine. Nevertheless, the signals indicate that apart from position I directly behind the outlet valve. the exhaust gases of the different cylinders are mixed. This is caused by the valve operation times and the different running times of the gas from the outlet to the sensor.