Problems Encountered Using IrRh-Ir Thermocouples for Measuring Combustion Gas Temperatures

This paper discusses some of the problems encountered in using IrRh-Ir thermocouples for measuring jet engine combustion gas temperatures up to 3500 F, such as water cooled supports and compensated lead wires.

The IrRh-Ir thermocouples are subject to errors common to all immersion type probes of the sensor not attaining gas temperature such as radiation, conduction and recovery factor.

Discrepancies in calculated combustion efficiency determined by IrRh-Ir and Pt Rh-Pt measured temperatures are presented and discussed. Data taken across a combustor with a unique traverse probe that featured a dual head consisting of a IrRh-Ir bare thermocouple and a A1₂O₃ coated IrRh-Ir thermocouple is presented, compared with gas analysis and the catalytic effect offered as the most probable explanation.