Gas turbine and operating method of the same

Abstract: A gas turbine in which a centrifugal compressor (3), which is driven a high pressure turbine (5), and a variable inlet guide vane (9) located at the inlet of the centrifugal compressor are provided. An axial-flow compressor is not provided between the centrifugal compressor and the variable inlet guide vane. An operating method of a gas turbine in which the output is varied by moving a variable inlet guide vane (9) while keeping the rate of rotation at a high level. It is possible to vary the output of the gas turbine in a short period of time and the durability of engine is improved.

Description: Field of the Invention The present invention relates to a gas turbine engine and to a method of operating it according to the preamble of claims 1 and 5 and as known from US-A-4.821.506. More particularly the present invention relates to a gas turbine used as a main engine and an auxiliary engine (APU) for aircraft, vehicles, industrial purposes and so forth, and a thrust gas turbine engine (turbojet, turbofan) used primarily as a main engine for aircraft. Further, the present invention relates to an operating method of the above-mentioned gas turbine. Description of the Related Art Fig. 5 is a longitudinal sectional view showing an example of a conventional gas turbine engine. Air suctioned through an air inlet port 1 is compressed by an axial-flow compressor 2 and a centrifugal compressor 3 and led to a combustor 4, where the compressed air is used for combustor of fuel. A high-pressure turbine 5 and an output turbine 6 are driven to rotate by combustion gas produced by combustion. The axial-flow compressor 2 and the centrifugal compressor 3 mentioned above are driven by the rotation of the high-pressure turbine 5. The torque of the output turbine 6 is taken out through an output shaft 7. A numeral 8 denotes a full authority digital electronic control (FADEC) device. Increase and decrease of the output is performed by regulating the supply quantity of fuel so as to vary the speed of rotation. In the above-mentioned axial-flow compressor 2, a variable inlet guide vane 9 is provided on an inlet side and a variable stationary vane 10 is provided on an outlet side, respectively, in order to prevent surging, and angles thereof are controlled by means of the FADEC device 8. Next, fig. 6 is a longitudinal sectional view showing another example of a conventional gas turbine engine. In this example, a variable turbine nozzle 11 is provided at the inlet of the output turbine 6, and output responsiveness is increased by rapidly moving the variable turbine nozzle 11 by means of the FADEC device 8. Since only the centrifugal compressor 3 is provided as the compressor, and no axial-flow compressor is provided, neither the variable inlet guide vane nor the variable stationary vane is provided. There have been such problems to be solved in above-mentioned conventional gas turbine engine as follows. In a gas turbine engine illustrated in Fig. 5, it is required to vary the engine rotation speed for regulating the output. Accordingly, the output response time is affected by the rotational moment of inertia of a rotor, and there has been a limit for reducing the speed of rotation of the engine. Namely, time is required in order to accelerate and decelerate a rotary body having large inertial mass. Since the variable inlet guide vane 9 and the variable stationary vane 10 are provided to avoid surging, the variable range is narrow and large output variation is not obtainable even if these vanes are moved. Further, there is such a problem that surging occurs when the variable inlet guide vane 9 and the variable stationary vane 10 are altered to such an extent that output can be varied. In a gas turbine engine illustrated in Fig. 6, output responsiveness is increased by moving the variable turbine nozzle 11 rapidly and fuel consumption at partial load is also improved further, but there have been problems in reliability, performance and weight because the variable mechanism has to be installed at a high temperature portion. For example, since the variable mechanism is exposed to high temperature, it is required to keep a large clearance between the vane and the wall surface taking thermal expansion into consideration. The loss caused by leakage through the clearance becomes large thus deteriorating the performance. Further, in a conventional thrust gas turbine engine, the engine rotational speed is varied buy regulating the supply quantity of fuel to alter the output thereof. When the engine rotational speed is varied in order to vary the output in a thrust gas turbine engine having no such variable mechanism, there has been a drawback that a certain period of time is required for acceleration and deceleration and high responsiveness cannot be achieved because the rotary body has a large inertial mass. Further, in some thrust gas turbine engines, a variable nozzle is provided at an inlet of the turbine and the quantity of combustion gas which flows into the turbine is regulated by opening and closing the variable nozzle to alter the engine output. In a thrust gas turbine engine including a turbine with a variable nozzle, the above-described problems are solved and fuel consumption with partial load is also improved. However, it is required to keep a large clearance between the vane and the wall surface taking thermal expansion into consideration because a variable mechanism has to be installed at a high temperature portion of the engine similarly to the engine illustrated in Fig. 6, thus causing problems in performance, reliability and weight such that leakage loss becomes large and performance deteriorates. SUMMARY OF THE INVENTION According to the present invention, there is provided a gas turbine aircraft engine comprising a high-pressure turbine, and a centrifugal compressor, characterised in that it is provided with engine power output control means comprising a variable inlet guide vane at the inlet of the centrifugal compressor in an air flow path to the latter, and engine output control means operative to adjust the engine power output primarily by adjusting the variable inlet guide vane while maintaining the turbine speed at an essentially constant high level. Further, according to the present invention, there is provided a method of operating a gas turbine aircraft engine, in which the engine comprises a centrifugal compressor and a high-pressure turbine driving the compressor and providing the engine power output, characterised in that the engine power output is controlled primarily by adjustment of a variable inlet guide vane located at an air inlet of the centrifugal compressor, while the turbine speed is maintained at an essentially constant high level. "Variable inlet guide vane" is a technical term used in fluid machinery and means a stationary vane having no moving vane in front thereof. The use of variable inlet guide vanes is known for example from US-A-4821506 and WO 89/11589. These documents disclose auxiliary gas turbines used for the supply of air under pressure, but do not suggest the use of the variable inlet guide vanes for controlling the engine power output. By means of the present invention, it is possible to reduce the flow rate of air taken into an engine so as to reduce the brake horse power of the engine even at high engine rotation by throttling the variable inlet guide vane. When the variable inlet guide vane is opened suddenly, the flow rate increases and the output also increases rapidly. Thus, the output response time of the engine is determined almost by the response time of the variable inlet guide vane. The ambient temperature being close to normal temperature, the variable inlet guide vane of the compressor can be manufactured to be thin in shape and light in weight, and it is possible not only to make the response time very short, but also to deter malfunction. In practising the present invention, the variable inlet guide vane is controlled (open and closed) in a state close to normal temperature while keeping the engine rotation at a high level so as to control (increase and decrease) the engine air flow rate and the fuel flow rate simultaneously, thus controlling the output. Thus, an engine with high responsiveness and high reliability may be realized. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal sectional view showing an embodiment in which the present invention is applied to a turboshaft engine for a helicopter; Fig. 2 is a diagram showing output response characteristics thereof; Fig. 3 is a longitudinal sectional view showing an example in which the present invention is applied to a turboprop engine for fixed wing aircraft as a second embodiment; Fig. 4 is a schematic longitudinal sectional view showing a third embodiment of the present invention; and Fig. 5 and Fig. 6 are longitudinal sectional views showing examples of a conventional gas turbine engine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a longitudinal sectional view showing an embodiment in which the present invention is applied to a turboshaft engine for a helicopter, and Fig. 2 is a diagram showing output response characteristics thereof. In Fig. 1, same symbols are assigned to those parts that are similar to conventional ones described with reference to Fig. 5 and Fig. 6, and detailed description is omitted in order to avoid prolixity. In the present embodiment, a variable inlet guide vane 9 is provided at an inlet of centrifugal compressor 3. A numeral 12 denotes an actuator for a variable inlet guide vane (VIGV). In Fig. 1, it is possible to reduce the flow rate of air taken into an engine so as to lower engine brake horsepower even at high engine rotation by throttling (making an angle larger) the variable inlet guide vane 9 (point A in Fig. 2). The air flow rate is increased by opening the variable inlet guide vane 9 suddenly from this state, and the output also increases rapidly (point B in Fig. 2). Since the engine rotation is constant at this time, the output response time of the engine is determined almost by the response of the actuator for a variable inlet guide vane (VIGV). Thus, the output response time can be made to be very short. That is, output characteristics as shown in Fig. 2 are obtained in the present embodiment. It is understood that the brake horsepower can be varied in a very short period of time according to this Figure since the brake horsepower can be throttled to 10% or less while keeping the number of rotation fixed at the rated value. Besides, the output is increased and decreased by controlling also the fuel flow rate with the FADEC 8, simultaneously with the above-mentioned control of the air flow rate. The compressor needs to operate stably in order to perform the above-mentioned operation. In a conventional axial-flow compressor equipped with a variable inlet guide vane and a variable stationary vane or in a conventional compressor in which an axial-flow compressor and a centrifugal compressor are combined with each other, stable operation when the variable inlet guide vane is closed gradually has been difficult. Such stable operation, however, is possible in a compressor composed only of a single stage or a multistage centrifugal compressor as in the present embodiment. Next, Fig. 3 is a longitudinal sectional view showing an example in which the present invention is applied to a turboprop engine for fixed wing aircraft as a second embodiment. Same symbols are assigned in this Figure to those parts that are similar to what has been described above, and detailed description thereof is omitted. A symbol 13 newly used in the present embodiment denotes a speed reducing gear box. In the present embodiment, similar operational effects as those in above-mentioned first embodiment are also obtainable. Fig. 4 is a schematic longitudinal sectional view showing a third embodiment of the present invention. In Fig. 4, air suctioned through an air suction port 21 is pressurized by a centrifugal compressor 22 and led to a combustor 23, where the pressurized air is used for combustion of fuel. The combustion gas produced by combustion is led to a turbine 24. The turbine 24 is driven to rotate by a part of energy of the combustion gas. The remaining part of the energy of the combustion gas is used for the propulsion of aircraft or the like. The above-mentioned centrifugal compressor 22 is driven by the rotation of the turbine 24. A numeral 25 denotes a full authority digital electronic control (FADEC) device. In the third embodiment, a variable inlet guide vane 26 is provided at the inlet of the centrifugal compressor 22. The variable inlet guide vane 26 is controlled by a controller (FADEC) 25 of the engine, and an angle of a variable inlet guide vane (viz. engine air flow rate) and the engine fuel flow rate are controlled at the same time. Since the variable inlet guide vane 26 and the variable mechanism of the present embodiment are arranged at the compressor inlet and operate in a state close to normal temperature, there is less fear of malfunction. According to the present invention, following effects are obtainable. 1) It is possible to obtain a wide range of output at constant engine rotation. 2) Thus, it is possible to vary the output in a short period of time. 3) Fuel consumption may be improved depending on the magnitude of the output.

Claims: A gas turbine engine, in which the engine comprises a centrifugal compressor (3), and a high-pressure turbine (5) driving the compressor and providing the engine power output characterised in that it is provided with engine power output control means comprising a variable inlet guide vane (9)at the inlet of the centrifugal compressor in an air flow path to the latter, and engine output control means (8, 12; 25, 26) operative to adjust the engine power output primarily by adjusting the variable inlet guide vane while maintaining the turbine speed at an essentially constant high level. A gas turbine plant according to claim 1 in which the gas turbine is of a brake horsepower type. A gas turbine plant as claimed in claim 1, constituting a thrust gas turbine. A gas turbine plant as claimed in claim 1, 2 or 3, in which the turbine (5) is an axial-flow turbine. A method of operating a gas turbine engine, in which the engine comprises a centrifugal compressor (3) and a high-pressure turbine (5) driving the compressor and providing the engine power output, characterised in that the engine power output is controlled primarily by adjustment of a variable inlet guide vane (9) located at an air inlet of the centrifugal compressor, while the turbine speed is maintained at an essentially constant high level. A method as claimed in the preceding claim in which the turbine is a thrust gas turbine.

Inventors: MIYAKE YOSHIAKI, MORISHITA SUSUMU, UCHIDA SEISHI, MIYAKE, YOSHIAKI, MORISHITA, SUSUMU, UCHIDA, SEISHI, Miyake, Yoshiaki, c/o Nagoya Guidance, Morishita, Susumu, c/o Nagoya Guidance, Uchida, Seishi, c/o Nagoya Guidance
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1991
Main classification: F02C9
IPC codes: F02C3, F02C9