Patent Publication Number: US-2020284200-A1

Title: Aircraft engine reignition

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 USC 119(e) of Provisional Patent Application bearing Ser. No. 62/813,331 file on Mar. 4, 2019, the contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The application relates generally to engine operation, and more particularly to techniques for reigniting engines. 
     BACKGROUND OF THE ART 
     An engine flameout refers to unintended shutdown of an engine due to the extinction of flames in the combustion chamber. In some cases, inclement weather conditions may be responsible for an engine flameout, for example due to ingested ice or water during a rain storm and/or a hail storm. Other causes of engine flameout are also known to exist. 
     When an engine flameout event occurs during aircraft flight, or in other sensitive circumstances, proper and timely reignition of the engine can be crucial. Traditional approaches require a pilot or other operator to manually command reignition of the engine. In the case of engine flameout during aircraft flight, the pilot may need to concurrently stabilize the aircraft, making manually commanding reignition of the engine a complex operation. In other cases, the pilot may be absent from the cockpit for a period of time (e.g. the aircraft is on autopilot), and thus the engine may be left non-operational for an extended duration. 
     As such, there is room for improvement. 
     SUMMARY 
     In accordance with a broad aspect, there is provided a method for reigniting an engine of an aircraft. An engine flameout event is detected during flight. Responsive to detecting the engine flameout event, an engine speed and a commanded engine operating state are monitored. The engine speed is compared to a predetermined threshold. A determination is made regarding whether the commanded engine operating state corresponds to an engine on state. When the commanded engine operating state corresponds to the engine on state, and when the engine speed is below the predetermined threshold, a predetermined ignition sequence for the engine is initiated. 
     In accordance with another broad aspect, there is provided a system for reigniting an engine of an aircraft. The system comprises a processing unit and a non-transitory computer-readable medium coupled to the processing unit and comprising computer-readable program instructions. The computer-readable program instructions are executable by the processing unit for: detecting an engine flameout event during flight; responsive to detecting the engine flameout event, monitoring an engine speed and a commanded engine operating state; comparing the engine speed to a predetermined threshold; determining whether the commanded engine operating state corresponds to an engine on state; and while the engine commanded engine operating state to an the engine on state, and when the engine speed is below the predetermined threshold, initiating a predetermined ignition sequence for the engine. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1  is a schematic cross-sectional view of an example engine, in accordance with one or more illustrative embodiments; 
         FIG. 2  is a block diagram of an example system for reigniting an engine of an aircraft, in accordance with one or more illustrative embodiments; 
         FIG. 3  is a flowchart of an example method for reigniting an engine of an aircraft, in accordance with one or more illustrative embodiments; and 
         FIG. 4  is block diagram of an example computing device for implementing the method of  FIG. 3 , in accordance with one or more illustrative embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , there is illustrated a gas turbine engine  100 . Note that while engine  100  is a turbofan engine, the methods and systems described herein may be applicable to turboprop, turboshaft, and other types of gas turbine engines, or combustion engines generally. In addition, the engine  100  may be an auxiliary power unit (APU), an auxiliary power supply (APS), a hybrid engine, or any other suitable type of engine. In addition, although the foregoing discussion relates to a singular engine  100 , it should be understood that the techniques described herein can be applied substantially concurrently to multiple engines. 
     The engine  100  generally comprises in serial flow communication: a fan  120  through which ambient air is propelled, a compressor section  140  for pressurizing the air, a combustor  160  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section  180  for extracting energy from the combustion gases. Axis  110  defines an axial direction of the engine  100 . In some embodiments, a low pressure spool is composed of a low pressure shaft and a low pressure turbine. The low pressure shaft drives the propeller  120 . A high pressure spool is composed of a high pressure turbine attached to a high pressure shaft, which is connected to the compressor section  140 . It should be noted that other configurations for the engine  100  are also considered. 
     Control of the operation of the engine  100  can be effected by one or more control systems, for example an engine controller  210 . The engine controller  210  can modulate a fuel flow rate provided to the engine  100 , the position and/or orientation of variable geometry mechanisms within the engine  100 , a bleed level of the engine  100 , and the like. 
     In the course of normal operation, it can occur that the engine  100  experiences a flameout event: that is to say, that an unintended shutdown of the engine  100  can occur due to the extinction of flames in the combustor  160 . The flameout event can occur despite various countermeasures taken to prevent or reduce the risk of the flameout event occurring. In response to the flameout event occurring, it may be desirable for a controller of the engine  100  to initiate a procedure for reignition of the engine  100  without operator input, for instance to reduce the number of tasks required of the operator of the engine  100 . As used herein, the terms “reignite”, “reigniting”, or “reignition” refer to procedures for starting an engine from a low speed and/or substantially stopped condition, and to procedures for renewing the flames in the combustor  160  of the engine  100  while the engine  100  is still at a high speed condition; that is to say, when one or more elements of the engine  100  are rotating at a high speed. 
     With reference to  FIG. 2 , there is shown a system  200  for reigniting an engine of an aircraft, for example the engine  100 . The system  200  is composed of the engine controller  210 , an ignition system  220 , and optionally a high-speed reignition system  222 . The system  200  is communicatively coupled to the engine  100  for obtaining information about the operating conditions of the engine  100 , for instance from one or more sensors incorporated within the engine  100 , or coupled thereto. Additionally, the ignition system  220  and the high-speed reignition system  222  are coupled to the engine  100  for respectively causing ignition and high speed reignition of the engine  100 . For example, the ignition system  220  is used to ignite the engine  100  when the engine is off or at a low speed condition. In instances in which the engine  100  is part of an aircraft, the ignition system  220  is used by the engine controller  210  to cause ignition of the engine  100 , for instance when the aircraft is on the ground, or at low speed during flight. The high-speed reignition system  222  can be used by the engine controller  210  to reignite the engine when the engine is flamed out and remains at a high speed condition, for instance during flight, when the aircraft is already airborne and travelling at some speed. 
     The system  200  is also communicatively coupled to operator input  230 , which can include buttons, switches, dials, or other discrete-type input mechanisms, touchscreens or other electronic input devices, and the like. For example, the engine controller  210  can be communicatively coupled to the operator input  230  for obtaining various commands from an operator of the engine  100 . For example, the operator input  230  includes an activation switch for the engine  100  which sets a commanded operating state for the engine  100 . The commanded operating state can be an “off” state, an “on” state, a “start” state, and the like, each associated with respective positions for the activation switch. The “off” position is used to command the engine  100  to shut down when in operation, and to remain shut down. The “on” position is used to command the engine  100  to remain in operation. The “start” position, which can be a momentary switch position, is used to command the engine to begin operation when in a shutdown state; that is to say, to cause the engine  100  to transition from the “off” state to the “on” state. It should be noted that other embodiments are considered: the operator input  230  can include other types of devices for commanding the engine  100  to operate in one or more states. Additionally, other states for the engine  100  are also considered: for instance, a separate “shut down” state can be used to cause the engine  100  to transition from the “on” state to the “off” state, and the like. 
     The engine controller  210  can be any suitable type of engine controller, including a full-authority digital engine controller (FADEC) or similar device. In some embodiments, the engine controller  210  is used in the context of an aircraft. The engine controller is configured for controlling operation of more than one engine  100  substantially concurrently. The engine controller  210  is also configured for logging various information about aircraft usage and operating conditions, including engine speed, engine operating state, and the like, and to log the occurrence of certain events, for example engine flameout events. To this end, the engine controller  210  can be provided with, or be coupled to, a variety of sensors to allow the engine controller  210  to monitor operating conditions of the engine. 
     In operation, the engine controller  210  can monitor the operating state of the engine  100  and compare with the commanded operating state for the engine  100 , as provided via the operator input  230 . In the event of an engine flameout event, the engine controller  210  is configured for initiating a procedure to attempt to reignite the engine  100 , if the commanded operating state remains unchanged. Put differently, following an engine flameout event, the engine controller  210  verifies whether an operator has requested a change in the operating state of the engine  100 , via the operator input  230 . If the commanded operating state is still the “on” state, the engine controller  210  attempts to reignite the engine  100 ; that is to say, the engine controller  210  attempts reignition without any specific input from the operator of the engine  100 . 
     The detection of a flameout event within the engine  100  can be done in any suitable fashion. In some embodiments, the engine controller  210  can determine the occurrence of a flameout event due to a drop in speed or power of the engine  100 , which was not commanded by an operator via the operator input  230 . In other embodiments, the engine controller  210  can determine the occurrence of a flameout event due to a change in temperature within the engine  100 , or within a particular portion thereof. Other approaches for detecting the flameout event are considered. 
     Following detection of a flameout event, the engine controller  210  is configured for attempting to reignite the engine  100  using the ignition system  220  or, optionally, the high-speed reignition system  222 , depending on the operating conditions of the engine  100 . In some embodiments, the engine controller  210  determines, based on a speed of the engine  100 , whether reignition of the engine should be performed by the ignition system  220  or by the high-speed reignition system  222 . The speed of the engine can be determined in any suitable fashion, using any suitable sensors and/or algorithms. For example, when the speed of the engine  100  is above a first threshold, the engine controller  210  commands the high-speed reignition system  222  to attempt to reignite the engine  100 . When the speed of the engine  100  is below a second threshold, the engine controller  210  instead commands the ignition system  220  to reignite the engine  100 . The ignition system  220  can perform a predetermined ignition sequence for the engine  100 , which may also be used when cold starting the engine  100  on the ground, or the like. When the speed of the engine is between the first and second thresholds, the engine controller  210  can be configured to not attempt reignition, unless manually commanded by an operator. 
     The particular speed thresholds used by the engine controller  210  when deciding whether to reignite the engine  100  can vary based on implementation, engine type, engine operating conditions, safety standards, and the like. For example, the first threshold can be set at 85% of a maximum speed for the engine  100 , at 50% of a maximum speed for the engine  100 , or at any other suitable fraction of the maximum speed for the engine  100 . The second threshold can be set at 25% of the maximum speed for the engine  100 , 15% of the maximum speed for the engine  100 , or any other suitable fraction of the maximum speed for the engine  100 . In instances where the engine  100  operates in the context of an aircraft, the maximum speed for the engine  100  can be a cruising speed, a maximum takeoff speed, or any other suitable speed. Other thresholds can be set based on other values, depending on the operating context of the engine  100 . 
     In addition, it should be understood that other factors may be used by the engine controller  210  when determining whether to use the high-speed reignition system  222  or the ignition system  220 . For instance, the altitude of the aircraft, the air pressure in the vicinity of the engine  100 , the operating temperature of the engine, and the like, can factor into the decision of the engine controller  210 . Other factors can also be considered. 
     In some embodiments, the engine controller  210  substantially continuously monitors the commanded operating state for the engine  100  following the occurrence of the flameout event. If, at any point, the commanded operating state is changed, the engine controller  210  cancels the reigniting procedures initiated by the engine controller  210 , and waits for the operator of the engine  100  to manually request reignition of the engine  100 , for example by setting the commanded operating state to “start”. Alternatively, if the commanded operating state is changed, the engine controller  210  can delay the reigniting procedure initiated by the engine controller  210  until the commanded operating state is changed once again. For example, if the commanded operating state is returned to the “on” position, the engine controller  210  can resume the reignition procedure. In some other embodiments, the engine controller  210  substantially continuously monitors the speed of the engine  100 : if the speed of the engine  100  is suitable for attempting a reignition procedure, the engine controller  210  then determines whether the commanded operating state is the “on” state, and if so, attempts reignition, as appropriate. Other embodiments are also considered. 
     In some embodiments, prior to attempting reignition of the engine  100 , the engine controller  210  can command a fuel purge of the engine  100 . The fuel purge can be performed in any suitable way, for instance by dry motoring the engine  100 . For example, once the engine controller  210  has determined that the speed of the engine  100  is below the second threshold, and that the commanded operating state for the engine  100  is set to “on” (for instance as set by the operator input  230 ), the engine controller  210  can command dry motoring of the engine  100  for a predetermined period of time. Other steps can also be taken prior to reigniting the engine  100 . 
     In some embodiments, the engine controller  210  is configured for determining whether the reignition attempt was successfully executed. Techniques similar to those used for detecting the flameout event can be used to determine whether the engine  100  was successfully reignited. When the engine  100  was not successfully reignited, the engine controller  210  can produce an alert, for example for an operator of the engine  100 . The alert can be a visual alert, an audible alert, or the like. In addition, the engine controller  210  can attempt to reignite the engine  100  substantially continuously, if a previous attempt has failed. Once the engine  100  is successfully reignited, the engine controller  210  can return to normal operation, and can optionally inform the operator that the engine  100  is once again operational. 
     In one example, the engine controller  210  detects an engine flameout event, then determines the commanded engine operating state and the engine speed. The operator input  230  still indicates a commanded operating state of “on”, and the engine speed is above the first threshold. The engine controller  210  then attempts to reignite the engine  100  via the high-speed reignition system  222 . When the engine controller  210  detects that the high-speed reignition system  222  failed to reignite the engine  100 , the engine controller once again determines the commanded engine operating state and the engine speed. At this second time, the engine controller  210  determines that the engine speed is now below the second threshold, and that commanded engine operating state is unchanged. The engine controller  210  then commands the ignition system  220  to attempt reignition of the engine  100 . After determining that the engine  100  was successfully reignited, the engine controller  210  can return to normal operation. 
     With reference to  FIG. 3 , there is shown a method  300  for reigniting an engine of an aircraft, for example the engine  100 . As will be described, certain optional steps of the method  300  can also serve for reigniting the engine  100 . It should also be noted that although the foregoing discussion is focused on embodiments in which the engine  100  is used in the context of an aircraft, other implementations are also considered. In some embodiments, the method  300  forms part of one or more procedures initiated by a controller of the engine  100 , for instance the engine controller  210 , for reigniting the engine  100  without any specific operator input. 
     At step  302 , the operation of the engine  100  is monitored, for example by the engine controller  210 , to detect the occurrence of flameout events, such as flameout events during flight. At decision step  304 , when a flameout event is detected by the engine controller  210 , the method  300  moves to step  306 . As long as no flameout event is detected, the method returns to step  302 . 
     At step  306 , the speed of the engine  100  and the commanded operating state for the engine  100  are monitored, for example by the engine controller  210 . The engine controller  210  is configured for interfacing with any suitable type and number of sensors, systems, and the like, for adequately monitoring the speed and commanded operating state of the engine  100 . 
     At decision step  308 , a determination is made regarding whether the commanded operating state for the engine  100  is set to the on state. For example, the engine controller  210  detects the commanded operating state from an operator input, for instance the operator input  230 . Optionally, if the commanded operating state is set to off, or any other state different from the on state, the method  300  proceeds to step  320 , where the reignition procedure initiated by the engine controller  210  is halted. Optionally still, the method  300  can return to step  306 , and continue to monitor the speed and commanded operating state. When the commanded operating state is set to the on state, the method  300  proceeds optionally to decision step  310 , or to decision step  314 . 
     At optional decision step  310 , a determination is made regarding whether the engine speed is above a first threshold. The first threshold can be a fraction of a maximum operating speed of the engine  100 , for example 85% of the maximum speed, 50% of the maximum speed, or any other suitable value. When the engine speed is above the first threshold, the method  300  moves to optional step  312 . When the engine speed is not above the first threshold, the method  300  moves to decision step  314 . The comparison between the engine speed and the first threshold can be performed in any suitable way, using any suitable calculations or algorithms. 
     At step  312 , a predetermined reigniting sequence for the engine  100  is initiated, for example by the engine controller  210 . The reigniting sequence can be implemented by any suitable device or system, including the high speed reignition system  222 . In this fashion, an attempt at reigniting the engine is performed when the commanded operating state is the on state, and when the engine speed is above the first predetermined threshold. Optionally, after step  312 , the method  300  can move to decision step  318 . 
     At decision step  314 , a determination is made regarding whether the engine speed is below a second threshold, which is distinct from the first threshold. The second threshold can be a fraction of a maximum operating speed of the engine  100 , for example 25% of the maximum speed, 15% of the maximum speed, or any other suitable value. When the engine speed is below the second threshold, the method  300  moves to step  316 . When the engine speed is not below the second threshold, the method  300  can return to some previous step, for instance step  306 , and continue to monitor the speed and commanded operating state of the engine  100 . The comparison between the engine speed and the second threshold can be performed in any suitable way, using any suitable calculations or algorithms. 
     At step  316 , a predetermined ignition sequence for the engine  100  is initiated, for example by the engine controller  210 . The ignition sequence can be implemented by any suitable device or system, including the ignition system  220 . In this fashion, an attempt at reigniting the engine is performed when the commanded operating state is the on state, and when the engine speed is below the second predetermined threshold. In some embodiments, the ignition sequence implemented by the ignition system  220  is the same ignition sequence as would be used to start the engine  100  from a shutdown state, for instance a cold start ignition sequence. In other embodiments, the ignition sequence may be a different ignition sequence. Optionally, after step  316 , the method  300  can move to decision step  318 . 
     At decision step  318 , optionally a determination is made regarding whether an engine reignition is detected. For example, the engine controller  210  is configured for monitoring the operating conditions of the engine  100  to detect a reignition of the engine  100 , following steps  312  or  316 , respectively. If the engine  100  was successfully reignited, the method  300  can optionally move to step  320 . If the engine  100  was not successfully reignited, the method  300  can return to some previous step, for instance step  306 , to reattempt reigniting the engine  100 . Optionally still, if the engine  100  was not successfully reignited, an alert can be produced for the operator of the engine  100 , for instance by the engine controller  210 . 
     At step  320 , following successful reignition of the engine  100 , or following a determination that the commanded operating state has changed, or is no longer set to the “on” state, the reignition procedure initiated by the engine controller  210  can be deactivated. In some embodiments, once the controller-initiated procedure is deactivated, the engine controller  210  requires a manual input from an operator to reignite the engine. 
     In some embodiments, a fuel purge of the engine  100  is performed as part of either or both of the predetermined reigniting sequence at high speed and the predetermined ignition sequence. Other variations are also considered, as appropriate. 
     With reference to  FIG. 4 , the method of  FIG. 3  may be implemented by a computing device  410  as an embodiment of the engine controller  210 . The computing device  410  comprises a processing unit  412  and a memory  414  which has stored therein computer-executable instructions  416 . The processing unit  412  may comprise any suitable devices configured to implement the functionality of the engine controller  210  such that instructions  416 , when executed by the computing device  410  or other programmable apparatus, may cause the functions/acts/steps performed by the engine controller  210  as part of the method  300  and as described herein to be executed. The processing unit  412  may comprise, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, a central processing unit (CPU), an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, other suitably programmed or programmable logic circuits, custom-designed analog and/or digital circuits, or any combination thereof. 
     The memory  414  may comprise any suitable known or other machine-readable storage medium. The memory  414  may comprise non-transitory computer readable storage medium; for example; but not limited to; an electronic, magnetic, optical; electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. The memory  414  may include a suitable combination of any type of computer memory that is located either internally or externally to device; for example random-access memory (RAM); read-only memory (ROM); compact disc read-only memory (CDROM); electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like. Memory  414  may comprise any storage means (e.g., devices) suitable for retrievably storing machine-readable instructions  416  executable by processing unit  412 . 
     It should be noted that the computing device  410  may be implemented as part of a FADEC or other similar device, including electronic engine control (EEC), engine control unit (EUC), engine electronic control system (EEGS), and the like. In addition, it should be noted that the techniques described herein can be performed by the engine controller  210  substantially in real-time. 
     The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the present disclosure. Still other modifications which fall within the scope of the present disclosure will be apparent to those skilled in the art, in light of a review of this disclosure. 
     Various aspects of the systems and methods described herein may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. Although particular embodiments have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects. The scope of the following claims should not be limited by the embodiments set forth in the examples, but should be given the broadest reasonable interpretation consistent with the description as a whole.