Addressing the measurement problem in the gas turbine

The fitted array of sensors in a gas turbine provides the only means in which the operator or maintenance contractor can assess the performance, health aspects and contractual features of a gas turbine in operation. Yet sensors cannot be fitted in the sensitive region of the engine between the combustor and the turbine discharge plane due to the hostile environment in the gas path. In application to aero-engines, the intrusive nature of sensors in the gas path cannot be tolerated since their presence can create component mis-match. Further, there is the danger of instrument breakage leading to mechanical damage in the engine. This paper demonstrates that measured values are subject to errors which render their use in performance calculations unreliable. Additionally, the limited number of sensors that can be fitted preclude a complete analysis of the engine health and performance. The paper demonstrates, with results, a solution to these problems. Software has been developed to overcome these engineering difficulties and consequently forms the basis of reliable performance and health monitoring throughout the life of the engine. Known as Pathan, the software has already been used on a beta programme on several industrial gas turbine engines. Consequently, it may now be applied to aero and marine gas turbines.