Method for protecting a gas turbine engine against surge

Abstract

The invention relates to methods for protecting a gas turbine engine against axial compressor surge. The present method consists in monitoring the pressure in the compressor using at least three pressure sensors disposed two stages of an axial compressor away from a combustion chamber, and analyzing the sensor readings using an engine control system, while simultaneously monitoring and controlling the speed of the rotor of the compressor. Taking the rate of change of the pressure over time, the pressure oscillation frequency and the amplitude of the oscillations and comparing the current values thereof with threshold values, the engine control system generates a surge signal and takes steps to eliminate a surge by reducing the amount of fuel fed into the combustion chamber or increasing the rotor speed by activating a starter until the amplitude and frequency of the pressure oscillations according to the sensor readings fall below the threshold values. The invention makes it possible to improve the operational reliability of a gas turbine engine and increase the lifespan of the engine by eliminating surge in a wide range of operating modes, as well as by making it possible to predict the occurrence of surge events.

Description

[0001] Method of protecting a gas turbine engine from surge

[0002] The invention relates to methods for protecting a gas turbine engine from surge in an axial compressor. It can be used to detect, eliminate and prevent surge.

[0003] There are known methods of protecting a gas turbine engine from surge based on: measuring the pressure at the air inlet to the compressor, behind the compressor; temperature in various engine designs with subsequent elimination of this phenomenon using: various gas flow bypass systems, using special gas chambers, changing the operating mode of the combustion chamber with a change in the compressor rotor speed as a dependent parameter.

[0004] These methods have a number of disadvantages, including: an increase in the dimensions of the engine structure and its weight, high inertia of the measurement system, low service life of the measuring elements, especially when using them to measure temperature and pressure in hot zones of the engine structure.

[0005] A method of compressor surge protection is known (patent RU 2382909 C2). In which the technical result is achieved by using a set of parameters for surge diagnostics, the simultaneous intensive change of which occurs only in the case of surge, whereas when the engine operating mode changes, a complex change of these parameters does not occur. The method for diagnosing compressor surge includes measuring the pressure behind the compressor and the compressor rotor speed, calculating the value of the time derivative of the pressure behind the compressor and comparing it with a specified threshold value, taking into account the sign.Additionally, the temperature of the gases behind the turbine is measured, the value of the ratio of the temperature of the gases behind the turbine to the rotation frequency of the compressor rotor is calculated and compared with the threshold value, a conclusion about the presence of surge is made in the event that the values ​​of the time derivative of the pressure behind the compressor and the ratio of the temperature of the gases behind the turbine to the rotation frequency of the compressor rotor simultaneously exceed their threshold values.

[0006] The disadvantage of this method is the need to install temperature sensors behind the turbine, in the hot zone of combustion products flow, and pressure sensors are also placed behind the compressor, which necessitates the creation of a special measurement zone after the compressor. A method for protecting against compressor surge is known (patent RU 2453733 C2).In the method of compressor surge protection, the rate of change of the flow rate through the compressor or the rate of change of the pressure difference on the inlet narrowing device (confuser) and the acceleration of the compressor rotor speed are determined; if the acceleration of the compressor rotor speed exceeds the preset value, or the rate of flow rate drop through the compressor with the opposite sign is greater than the preset value, a "Pre-surge" signal is generated, after which the countdown of the surge signal time and the countdown of the pre-surge signal retention time are started; if a new "Pre-surge" signal arrives during the "Pre-surge" signal retention time, the retention time is restarted; if by the end of the "Surge" signal countdown, the pre-surge signal retention time has not been counted to the end, a "Surge" signal is generated. In this case, the "Surge" signal can be generated if the number of occurrences of the "Pre-surge" signal during the specified time of occurrence of the first "Pre-surge" signal exceeds the critical value.The invention makes it possible to increase the reliability of surge recognition at the very beginning of its occurrence.

[0007] The disadvantage of the given method is the need to measure parameters in a large number of characteristic sections of the flow path; in addition, only measuring the rate of change of flow or pressure may not provide sufficiently complete information about the occurrence of surge due to the inertia of the measurement system, for example, at a high frequency of resonant oscillations of the parameters of the working process.

[0008] A method for protecting a gas turbine engine during surge at start-up is known (patent RU 2403454 C1) accepted for a number of features as the closest analogue. The technical problem of the invention is to increase the reliability of protecting a compressor of a gas turbine engine by detecting its unstable operation at early stages of the start-up mode. The essence of the invention is that in the method for protecting a gas turbine engine during surge at start-up mode, the current values ​​of temperature behind the low-pressure turbine, the rotation frequency of the high-pressure rotor are measured, the ratio of the first derivatives of the said values ​​is calculated, the said ratio is compared with its threshold value and a signal of unstable operation of the compressor is generated. A disadvantage of the known method is the need to install temperature sensors in the hot zone, as a consequence of their low service life, the inertia of the measurement system, and monitoring the surge phenomenon only at engine start-up.

[0009] The purpose of this invention is to increase the reliability of determining gas-dynamic phenomena in an engine compressor when there is a risk of surge and to eliminate the causes of surge on a running gas turbine engine without the need to restart it.

[0010] The set goal is achieved by monitoring the compressor pressure using pressure sensors placed two stages of the axial compressor from the combustion chamber in a quantity of at least three, the sensor readings are analyzed by the engine control system at the same time as the compressor rotor speed is monitored and controlled. Installing pressure sensors two stages before the combustion chamber, in a relatively cold zone of the compressor flow path allows extending their service life. Based on the rate of pressure change over time, the frequency of pressure fluctuations and the amplitude of oscillations, comparing the current values ​​with the threshold, the automatic engine control system generates a surge signal and takes measures to eliminate it. This technical solution assumes two ways of the control system's response to surge to eliminate it.The first method involves reducing the amount of fuel supplied to the combustion chamber, which will reduce the thermal power of the engine and reduce the compressor speed. It is most appropriate to use this method in the cruising mode of the engine when surge occurs as a result of external factors of various nature and in the mode of reducing engine power. The second method involves increasing the compressor rotor speed by engaging the starter. The method is applicable at the stage of starting a gas turbine engine or restarting after a stop. Measures to eliminate surge phenomena are applied until the frequency and amplitude of pressure fluctuations according to sensor readings decrease below threshold values.

[0011] The essence of the invention is explained by the drawing. Fig. 1 shows a section of the general view of a low-thrust dual-circuit turbojet engine. Position 1 marks the position of the pressure sensors two compressor stages before the combustion chamber. Position 2 marks the position of the starter. Position 3 shows the position of the injectors in the combustion chamber. Position 4 is the working wheel of the penultimate compressor stage. Position 5 is the working wheel of the last stage of the axial compressor.

[0012] Thus, this invention makes it possible to increase the reliability of the gas turbine engine, to increase its service life both by eliminating surge phenomena in a wide range of operating modes, and by making it possible to predict the occurrence of surge phenomena.

Claims

5 Invention formula 1. A method for protecting a gas turbine engine from surge, including air pressure sensors in the compressor, installed through two stages of the axial compressor from the combustion chamber, the number of pressure sensors must be at least three, the sensor readings are analyzed simultaneously, monitoring and controlling the speed of rotation of the compressor rotor, based on the rate of change of pressure over time, the frequency of pressure oscillations and the amplitude of oscillations, comparing the results of measurements with threshold values, a conclusion is made about the presence of surge and measures are taken to eliminate it, reducing the amount of fuel supplied to the combustion chamber, thereby reducing the rotation speed of the compressor until the amplitude and frequency of pressure oscillations according to the sensor readings decrease below the threshold values.

2. The method according to paragraph 1, characterized in that the speed of rotation of the compressor rotor increases due to its spinning by the starter until it leaves the surge zone, while the amount of fuel supplied to the combustion chamber does not increase.

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