Non-Invasive Differential Thermocouple Method for the Evaluation of Catalyst Performance 2008-01-0454

A simple non-invasive thermocouple method is described and demonstrated that provides catalyst performance information. The thermocouple circuit consists of a Chromel wire attached to the stainless steel exhaust system before the catalyst and another Chromel wire after the catalyst. The exhaust system stainless steel functions as the other dissimilar metal component of a differential thermocouple. Measured electromotive force (EMF) between the thermocouple leads is proportional to the temperature difference across the catalyst and allows assessment of the performance of the catalyst between the thermocouple junctions. By measuring the difference directly, rather than measuring at two locations and using the difference between high temperatures at the two locations, one obtains a relatively accurate measurement even without calibration. A series of experiments were carried out to demonstrate the catalyst monitoring capabilities of this methodology. The results show excellent characteristics and capabilities of the new method to provide temperature difference data and indicate the quality of catalyst function. Possible applications for this exhaust system temperature measurement method include replacement or supplementation of the current OBD2 system, monitoring of catalyst function during aging, and as a diagnostic procedure for technicians investigating MIL light reports.