Estimating Actual Exhaust Gas Temperature from Raw Thermocouple Measurements Acquired During Transient and Steady State Engine Dynamometer Tests 2007-01-0335

Thermocouples are commonly used to measure exhaust gas temperature during automotive engineering experiments. In most cases, the raw measurements are used directly as an absolute indication of the actual exhaust gas temperature. However, in reality, the signal from a TC is only an indication of its own tip temperature. The TC indicated tip temperature can deviate significantly from the actual gas temperature due to factors such as thermal capacitance of the tip itself, and heat transfer to the exhaust pipe wall through conduction and radiation. A model has been developed that calculates the effects of these factors to provide an estimate of the actual exhaust gas temperature. Experiments were performed to validate the model under both transient and steady state engine dynamometer conditions utilizing three popular sizes of TCs. Good correlation among predictions for various TC sizes confirms the model's accuracy. This tool enhances the quality of exhaust gas temperature measurements and provides a useful alternative to the practice of using fragile (low durability) small tip TCs for experiments requiring fast-response temperature measurements