ERROR ANALYSIS OF THERMOCOUPLE DYNAMIC PERFORMANCES EXPERIMENTAL DETERMINING IN ENGINE CONDITIONS USING STEP RESPONCE

Abstract

The turbine inlet temperature is one of the major thermodynamic parameters that determine specific thrust and specific fuel consumption of the turbine engine. The gas temperature also influences the temperature of the engine parts, hence thermal stresses and the ability of materials to support static and cyclic loads. Therefore, the temperature limitation is one of the main tasks of the engine automatic control system. Because of a significant influence of the gas temperature on parameters of the working process, strength, and life-time of parts, the temperature must be limited with high precision. The paper is focused on dynamic parameters of the temperature measurement channel, which contains consequently linked engine, thermocouple, and the dynamic corrector. Errors of the corrector tuning, which mainly depend on the error of thermocouple time constant setting, cause dynamic errors in the temperature determining and the corresponding errors of automatic control. The paper considers the influence of the corrector tuning error on a dynamic error of the temperature determination. The equations are derived that relate the dynamic error with dynamic parameters of the engine and dynamic parameters of the temperature measurement channel. These equations can be used in the synthesis of this channel, which satisfies the set requirements to the temperature determining precision. The simplest case is considered when the thermocouple is represented as an inertial dynamic link, which single dynamic parameter is the time constant. Then the above-mentioned equations relate the thermocouple time constant with the error of temperature measurement and allow formulating requirements to a precision of its experimental determination. The final part of the paper considers the error of thermocouple time constant experimental determining. The relations are derived that allow analyzing this error under influence of such parameters as the measuring error, interval of observations, measuring frequency and dynamic properties of the engine and the thermocouple.

Keywords

• газотурбинный двигатель
• термопара
• динамическая погрешность
• математическая модель
• идентификация