Abstract:
A gas turbine engine system includes an air inlet, an inlet particle separator located at the air inlet and having a blower selectively driven by a variable output motor, and a controller for dynamically controlling the variable output motor that selectively drives the blower of the inlet particle separator.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to particle separators and debris control systems for use with gas turbine engines. 
         [0002]    Rotorcraft (e.g., helicopters) that use gas turbine engines can operate at a variety of altitudes, and can generally operate at relatively lower altitudes than most fixed-wing aircraft. Low-altitude operation poses operational difficulties for gas turbine engines not always presented at higher altitudes. For instance, landing and taking-off from unpaved areas can “kick up” large amounts of dust and debris. As such, gas turbine engines of rotorcraft operating at low altitudes are often exposed to ambient air that contains a significant amount of debris, typically consisting of large amounts of small, airborne particles or dust. Debris ingested by gas turbine engines is problematic, and can cause erosion and other damage to components of the engine. Such damage can cause engine performance to deteriorate, and can make engine repairs necessary. For example. gas turbine engines contain airfoils having thin edges and tips that are highly sensitive to erosion, and any erosion damage to those areas can significantly impair the efficiency and effectiveness of the airfoil. 
         [0003]    Inlet particle separator (IPS) systems are known that provide fine object filtering of ambient air that enters gas turbine engines. The IPS system typically includes a specially designed duct or a ramp-like structure hereinafter referred to as a “ramp” that propels particles radially outward while allowing only relatively clean air to pass through a more radially inward passageway to the interior of the engine. These known IPS systems can include blowers to help move ambient air along the “ramp” to a collector and then expel particles from the engine. Those blowers are mechanically powered by a fixed-gear connection to a gas turbine engine spool. A problem with these systems is that the mechanical power diverted to the IPS system produces a parasitic power loss that negatively impacts fuel burn efficiency of the engine. This is at least partially due to the fact that fixed gearing powers the blower at a constant speed (that is, a speed that is a constant proportion of engine operational speed) whenever the engine is operating, without the capability to turn the blower off while the gas turbine engine is still operating. This is inefficient because in certain situations, such as when the gas turbine engine is operating at relatively high altitudes, the amount of debris in ambient air is generally relatively low. In those situations where the amount of debris is low, operation the IPS system blower provides little or no practical benefit, yet still produces a parasitic power loss. Moreover, the amount of debris in ambient air is dynamically variable across engine operation cycles, but known engine systems do not provide a means to adaptively match debris control system operation to actual ambient air conditions in real time. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    A gas turbine engine system includes an air inlet, an inlet particle separator located at the air inlet and having a blower selectively driven by a variable output motor, and a controller for dynamically controlling the variable output motor that selectively drives the blower of the inlet particle separator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is an exploded schematic view of a gas turbine engine having a debris control system according to the present invention. 
           [0006]      FIG. 2  is a schematic view of the debris control system. 
           [0007]      FIG. 3  is a block diagram of a control algorithm for the debris control system. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    In general, the present invention provides a debris control system having a blower that can be powered at selected speed and power settings as a function of the distribution of debris present in ambient air entering a gas turbine engine. The blower can thus be turned “on” or “off” on demand, and, when turned on, operated at speed and power settings that are dynamically matched to desired particle separation performance characteristics in real time. This provides efficient operation of the debris control system with reduced power consumption. As used herein, the term “debris” refers generally to any kind of airborne particulate or foreign object matter present in ambient air that can enter a gas turbine engine. 
         [0009]      FIG. 1  is an exploded schematic view of a gas turbine engine  10  having a debris control system  12  that includes an inlet debris monitoring system (IDMS)  14 , a blower  16 , a particle separator “ramp”  18 , an exhaust debris monitoring system (EDMS)  20 , and a control system  22 . As shown in  FIG. 1 , ambient air  24  containing a relatively large amount of particulate debris enters an inlet of the engine  10 , and exhaust gas  26  containing a relatively small amount of particulate debris exits the engine  10 . The presence of particulate debris in the ambient air  24  is common when the engine  10  is installed in an aircraft or rotorcraft operating at relatively low altitudes, and the amount of particulate debris present in the ambient air  24  generally decreases when the engine  10  is operating at higher altitudes. It should be recognized that the actual amount of particulate debris present in the ambient air  24  and the exhaust gas  26  will vary according to operating conditions. 
         [0010]    The engine  10  is a conventional gas turbine engine suitable for use with an aircraft or rotorcraft. The engine  10  depicted in  FIG. 1  is shown by way of example and not limitation. It should be understood that the present invention can be utilized with a gas turbine engine of nearly any configuration. 
         [0011]    The IDMS  14  is positioned where the ambient air  24  enters the engine  10 , and generates a current that is disturbed as debris passes the IDMS  14 . The IDMS can also be present at the point where the sand has been separated from the ambient air  24 , i.e. downstream of the blower  16 . The magnitude of the disturbance of the current is proportional to the size of the passing debris particles, and the disturbance of the current also indicates the amount of particles in the ambient air  24 . The IDMS  14  can include a pair of electrostatic ring sensors available from Smiths Aerospace, London, UK. In  FIG. 1 , two pairs of electrostatic ring sensors are shown. In alternative embodiments, other types of IDMS sensors can be used and different numbers of sensors can be employed as desired. It should be understood that two pairs of electrostatic ring sensors are not required, and embodiments of the present invention can utilize fewer sensors for the IDMS  14  in order to reduce cost and complexity of the system. 
         [0012]    The EDMS  20  is an electrostatic sensor positioned where the exhaust gas  26  leaves the engine  10 . The EDMS  20  can include an electrostatic sensor that operates like the IDMS sensor discussed above. However, because there is generally less debris present in the exhaust gas  26  than in the ambient air  24 , the EDMS  20  can utilize a relatively small sensor positioned along a periphery of the combustion flowpath rather than a larger ring-shaped sensor that surrounds the flowpath. 
         [0013]    The particle separator “ramp”  18  can be a specially designed duct or ramp-like structure having a known configuration with a generally frustoconical shape. The ambient air  24  entering the engine  10  passes along the ramp  18 , which directs debris radially outward to a collection assembly  28  that then expels the debris from the engine  10 , while “clean” gas from the ambient air  24  can pass to a combustion flowpath of the engine  10 . In this sense, the ramp  18  provides a path along which debris can develop momentum in a direction that is different from the combustion flowpath, in order to separate the particulate debris from the gas in the ambient air  24 . Typically, the “clean” gas then enters a compressor section of the engine  10 . 
         [0014]    The blower  16  is positioned adjacent to the ramp  18 , and can selectively generate a fluid flow to propel debris from the ramp  18  to the collection assembly  28 . The blower  16  can include impeller structures of a known type. As explained in greater detail below, the blower  16  is dynamically powered and can be activated or deactivated independently of the turbine cycle of the engine  10 . Moreover, the blower  16  can operate at any selected speed. Operation of the blower  16  is governed by the control system  22 . 
         [0015]      FIG. 2  is a cross-sectional schematic view of the debris control system  12 . During engine operation, ambient air  24  enters an engine inlet cowl  10 A and passes the IDMS  14 . Debris  24 A is then directed radially outward along the ramp (or inlet particle separator)  18  to the collection assembly  28  (not shown), while relatively clean air  24 B is directed to a combustion flowpath  10 B. Alternatively, the IDMS  14  can be positioned in the flowpath of the relatively clean air  24 B downstream from the ramp  18 . The blower  16  is positioned adjacent to the ramp  18 , and is powered by a dynamically adjustable motor  30 , such as an electric motor. A motor control unit  32  controls operation of the electric motor  30 , and is in turn governed by the control system  22 . An electrical power supply  34  provides electrical power to the electric motor  30  and the motor control unit  32 . The electrical power supply  34  can be an aircraft engine-powered generator, an engine starter unit, batteries, or other electrical energy source. 
         [0016]    During engine operation, the IDMS  14  sends an inlet debris distribution signal to the control system  22 , which can be integrated into an electronic engine controller or can be stand-alone control circuitry. The EDMS  20  also sends an exhaust debris distribution signal to the control system  22 . The inlet and exhaust debris distribution signals provide the control system  22  with information regarding the particle size and particle count of debris relative to the IDMS  14  and the EDMS  20 . As a function of the debris distribution signals, the control system  22  sends an actuator command to the motor control unit  32 , which in turn commands appropriate operation of the electric motor  30  and the blower  16 . In this way, the debris control system  12  can adaptively match blower  16  operation to actual conditions of the ambient air  24  in real time. The electric motor  30  can be powered on when needed, at a dynamically selected speed and power, and powered off when operation of the blower  16  would provide little or no debris control benefit. 
         [0017]      FIG. 3  is a block diagram of an exemplary control algorithm for the debris control system  12 . IDMS debris distribution signals  14 A and EDMS debris distribution signals  14 B are sent to selection and transformation logic  36  of the control system  22 . In addition, threshold setting logic  40  of the control system  22  sends a threshold signal to the comparator  38 . The selection and transformation logic  36  identifies relevant data from the debris distribution signals  14 A and  14 B, reduces electrical noise, and sends a filtered feedback signal to a comparator  38  of the control system  22 . The selection and transformation logic  36  is capable of generating a feedback signal appropriate for the position of the IDMS  14  and EDMS  20  in a given embodiment. For example, if the IDMS  14  is positioned before the ramp  18 , the selection and transformation logic  36  will generate a feedback signal that estimates the amount of debris (e.g., sand) in the cleaned air  24 B based on the IDMS debris distribution signal  14 A, the speed of the blower  16  and an estimate of flow of the ambient air  24 . If the IDMS  14  is positioned after the ramp  18 , then the selection and transformation logic  36  will produce a filtered version of the feedback signal that can be compared directly with the threshold signal. It is anticipated that the IDMS  14  can have different configurations within the engine  10  because in certain installations, it may not be possible to attach the IDMS  14  to a duct behind the ramp  18 . The threshold signal can be fixedly established as a function of desired debris distribution parameters for a given engine and operating conditions, or can be dynamically adjusted based on user (e.g., pilot) input or control system  22  calculation based on additional data. The comparator  38  performs a comparison between the selected feedback signal and the threshold signal and produces an error signal output sent to stabilizing control logic  42  of the control system  22 . The stabilizing control logic  42  generates an actuator command as a function of the error signal, and sends the actuator command to the motor control unit  32 . 
         [0018]    The control algorithm shown in  FIG. 3  allows the actuator command sent to the motor control unit  32  to operate the electric motor  30  at selected speed and power settings as a function of the distribution of debris in the ambient air  24 . When little or no debris is present in the ambient air  24 , such as when the engine  10  is operating at high altitudes, the electric motor  30  can be turned off. Under other operational conditions, such as when the engine  10  is operating at low altitudes where significant amounts of debris are present in the ambient air  24 , the electric motor  30  can be operated at speed and power settings that are dynamically matched to desired particle separation performance characteristics in real time. The present invention thus allows the electric motor  30  and the blower  16  to be powered only as much as necessary to achieve desired particle separation and debris control. This adaptive, on-demand blower operational scheme reduces or eliminates parasitic power loss for the engine  10  due to particle separation, which in turn improves fuel burn efficiency. 
         [0019]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention. For instance, the particular configurations of the blower and ducting of the debris control system of the present invention can vary as desired for particular applications.