Exhaust gas temperature is often measured with a device such as thermocouple or RTD (Resistance Temperature Detector). An alternative method to determine the gas temperature would be to use an existing gas sensor heating mechanism to perform as a temperature sensor. A planar type FLOH (Fast Light Off HEGO-Heated Exhausted Gas Oxygen) sensor under transient vehicle speed/load conditions is suited to this function and was modeled to predict the exhaust gas temperature. The numerical input to the model includes exhaust flow rate, heater voltage, and heater current.
Laboratory experiments have been performed to produce an equation relating the resistance of the heater and the temperature of the sensor (heater), which provides a method to indirectly determine HEGO sensor temperature. Emission tests at the vehicle dynamometer were then used for comparison purposes and additional laboratory measurements were made to supply some of the geometric and physical properties of the sensor, which could not be directly measured.
Results show reasonable agreement between the model estimates of temperature and experimental measurements with an independent thermocouple from a vehicle during an EPA-75 (Bag 3) emission test, demonstrating the model's capability of yielding acceptable predictions.