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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.

Thermocouples (TCs) are commonly used to measure exhaust gas temperature during automotive engineering experiments. To enhance the durability of TCs in the harsh exhaust gas environment, in many cases larger tip TCs (such as 1/8″ diameter) are used rather than smaller TCs. However, the signal from a larger thermocouple can differ significantly from that of small TC due to thermal capacitance of the tip, heat transfer to the exhaust pipe wall via conduction and radiation, and convection with exhaust gas. A model has been developed that calculates the effects of these factors and provides an estimate, for TCs of different sizes, of exhaust gas temperature. Experiments were performed to validate the model under transient (FTP) engine dynamometer conditions utilizing three popular TC sizes (1/32″, 1/16″, and 1/8″). Good correlation was found among predictions for various TC sizes.