Technical Paper
Converting Raw Thermocouple Measurements to Those Measured with a Thermocouple of a Different Size
2009-04-20
2009-01-1113
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.