WO1998011388A1

WO1998011388A1 - Diagnostic methods and apparatus for laser ignition system

Info

Publication number: WO1998011388A1
Application number: PCT/US1997/016138
Authority: WO
Inventors: Dennis M. Defreitas
Original assignee: Unison Industries Limited Partnership
Priority date: 1996-09-12
Filing date: 1997-09-11
Publication date: 1998-03-19

Abstract

Diagnostic apparatus for an ignition system that uses laser energy to ignite a fuel within a combustor includes a laser energy source, a number of optical elements configured to couple laser energy from the source into a combustion zone of the combustor, a first detector that produces an output that corresponds to intensity of laser energy emitted into the combustion zone, and a control means for diagnosing operation of the ignition system based on the first detector output. The diagnostic system can also be used to produce diagnostic signals that can be used to analyze the combustion process.

Description

Title: DIAGNOSTIC METHODS AND APPARATUS

FOR LASER IGNITION SYSTEM

BACKGROUND OF THE INVENTION This invention is related to the following co-pending and/or issued United States Patent applications: Serial No. 081,732, filed June 3, 1993, now U. S. Pat. No. 5,367,869, issued November 29, 1994 entitled "Laser Ignition Methods And Apparatus For Combustors" (1930022), Serial No. 08/067,652, filed May 26, 1993, now U. S. Patent No. 5,515,681 issued May 14, 1996 entitled "Commonly Housed Electrostatic Fuel Atomizer and Igniter Apparatus For Combustors" (1930012) , and provisional application serial no. 60-020,652 filed on June 24, 1996 entitled "Ignition Methods and Apparatus Using Broadband Laser Energy" (1960030) , the entire disclosures all of which are fully incorporated herein by reference.

The invention relates generally to diagnostic techniques for ignition systems. More particularly, the invention relates to diagnostic techniques for ignition systems of the type that use laser energy for igniting fuel in a combustor. Although diagnostic techniques for conventional electrical discharge ignition systems are known, such techniques have little or no application to ignition systems that use electromagnetic energy, such as high power laser energy, to ignite fuel in a combustor or combustion chamber. In addition, known diagnostic techniques for conventional electrical ignition systems do not provide for diagnostic analysis of the ignition event within the combustor.

The objectives exist, therefore, to provide diagnostic methods and apparatus particularly suited to ignition systems that use electromagnetic energy to ignite fuel in a combustor. SUMMARY OF THE INVENTION

The present invention contemplates, in one embodiment, diagnostic apparatus for diagnosing operation of an ignition system of the type that uses laser energy to ignite a fuel within a combustor, the ignition system including a laser energy source and a first optical delivery system that includes a number of optical elements configured to deliver laser energy from said source into a combustion zone of the combustor; the diagnostics apparatus comprising: a first detector that can be optically coupled to the ignition system for detecting laser energy; and control means responsive to said first detector for diagnosing operation of the ignition system.

The present invention also contemplates diagnostic methods, including in one embodiment, a method for diagnosing operation of an ignition system that uses high power laser energy to ignite fuel within a combustor, comprising the steps of: a) producing laser ignition energy using a laser energy source,- b) transmitting the laser ignition energy through an opening into a combustor along an optical path defined by an optical delivery system disposed between said source and said opening; and c) detecting the laser energy in the ignition system and diagnosing operation of the ignition system based on said detection.

These and other aspects and advantages of the present invention will be readily understood and appreciated by those skilled in the art from the following detailed description of the preferred embodiments with the best mode contemplated for practicing the invention in view of the accompanying drawings .

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a simplified schematic diagram in partial section of a gas turbine engine combustor with the invention incorporated therewith;

Fig. 2 is a functional block diagram of a diagnostic system in accordance with the present invention;

Fig. 3 is an optical coupling arrangement shown in section;

Fig. 4 is a functional block diagram of a receiver array suitable for use with the present invention,- Fig. 5 is a table of one example of a spectral analysis that can be performed as part of the diagnostic arrangement of the present invention;

Fig. 6 illustrates a typical timing sequence involved in the diagnosis of a laser ignition system;

Fig. 7 is a functional block diagram of an alternative embodiment of the present invention;

Fig. 8 is a functional block diagram of an alternative embodiment of a receiver array that can be used with the present invention,-

Fig. 9 is a functional software module control diagram for a test firing diagnostic operation suitable for use with the present invention;

Fig. 10 is a functional software flow control diagram for a diagnostic system according to the present invention during laser operation of the ignition system; and

Fig. 11 is functional software flow control diagram for a diagnostic system according to the present invention during a combustion process. DETAILED DESCRIPTION OF THE INVENTION

With reference to Fig. 1, an embodiment of the invention is illustrated in simplified schematic form for purposes of describing the basic concepts of the invention. In this basic configuration, a laser ignition system 10 is provided for one or more combustors 12 as part of a gas turbine engine, such as may be used on an aircraft or for an industrial turbine to name just two examples. The general illustration in the various figures should not be construed in a limiting sense as to the physical location of the various elements . For example, all of the elements could be installed as part of the engine, or alternatively, for example, the laser source and related components could be located elsewhere on the aircraft or system.

It is also important to note that while the various embodiments of the invention as described herein are particularly directed to or explained in the context of use with gas turbine engines such as are commonly used for aircraft, such descriptions are intended to be exemplary in nature and should not be construed in a limiting sense. The invention is related to combustion initiation, stabilization and restart processes, rather than being limited to specific engine or combustor designs or applications. Those skilled in the art will readily appreciate that the invention can be used with different types of combustors for many types of engines and applications other than in the aerospace and airborne gas turbine applications. For example, the present invention can be applied to combustors for reciprocating and rotary engines, rocket engines, for example, liquid and solid fuel rockets, ram jet and pulse jet, to name just a few examples. A few gas turbine engine applications of interest are: jet engines including preburners, afterburners for engines, turbojets, turboprops, turbofans, large gas turbine, medium gas turbines, small gas turbines, marine gas turbines, stationary and mobile industrial gas turbines . Other combustor systems of interest are: residential and industrial furnace applications, can combustors, can annular combustors, annular combustors and dual annular combustors to name a few. As noted, the invention is also applicable to reciprocating and rotary engine applications, such as, for example, automotive applications. Thus, various embodiments are provided herein for applying the concepts and teachings of the invention to combustors that have a fixed geometry during a combustion cycle, such as a turbine can or annular combustor, and combustors that have a variable geometry during the combustion cycle. For example, a reciprocating engine cylinder in an automobile has a volume that changes with the piston stroke. These examples of combustors and engines are not intended to be an exhaustive list, of course, nor are they to limit the scope and application of the invention.

Accordingly, the term "combustor" as used herein should be construed in its broadest sense to include any structure that defines or delimits a combustion chamber or region, such as the examples identified above, wherein fuel combustion or a combustion process is initiated, sustained and/or restarted. This includes the concept of a secondary or auxiliary combustor in the form of a cavity defined by a body or wall structure, such as can be used with a flame injector or as a plasma injector, for example, for initiating combustion or a combustion process in a second or main combustor (see, for example, the above-referenced patents to DeFreitas) . The invention, it should be noted, is especially useful with flow through combustors. Flow through combustors are generally understood as combustors in which the combustion process is continuous and characterized by an uninterrupted flow through velocity which may accelerate or decelerate due to gaseous expansion or contraction but generally is not interrupted by valves, throttle plates or similar devices. Flow through combustors are further characterized by relatively high volume air flow rates through orifices without controllable throttling devices to produce a highly turbulent mixing of air and fuel for combustion. By combustion process is meant initiation of combustion by the formation of a plasma which ignites an air/fuel mixture. In the present case, a plasma is formed by laser energy, such as for example, a plasma caused by infrared laser energy of sufficient fluence to cause breakdown of air in the combustor.

As stated, the present invention relates to diagnostic techniques for ignition systems of the type that use electromagnetic energy, particularly for example laser energy, to ignite fuel in a combustor. In the illustrated embodiment of Fig. 1, the laser ignition system 10 includes a laser energy source 20 that produces a high power laser energy output that is transmitted via an optic fiber arrangement 22 to an optical igniter 24. The system further includes a diagnostics system 18 that can be incorporated as part of the ignition system 10, or as a separate interface to the ignition system, or further still as part of the engine control system. Laser energy produced by the laser source 20 is emitted by the igniter 24 in the combustor 12. This is illustrated in a simplified manner as a laser energy beam 26 that produces a laser spark/flame kernel 28 within the combustor 12. A fuel nozzle 30 produces an atomized fuel spray 32 (which may, for example, be conical in shape) that mixes with air to produce an air/fuel mixture. Combustion air is provided through a number of air inlet holes or vents (not shown) in the combustor liner 36 and/or the fuel nozzle 30. The combustible air/fuel mixture 32 is ignited typically in a primary zone 34 of the combustor 12, just downstream of the fuel nozzle 30. The laser energy 26 in this case is focussed within an optimum ignition region 33 (which for convenience of illustration and understanding is indicated by a shaded region in Fig. 1) to a very high fluence, for example 10⁹ watts/cm²-10¹³ watts/cπv 2 depending on fuel type, spray density and so forth.

Although the various exemplary embodiments described and illustrated herein relate to a basic laser ignition system of the type that uses infrared laser energy to ignite an air/fuel mixture in a gas turbine engine, this is for purposes of description and should not be construed in a limiting sense. The present invention can also be used with ignition systems that use multiple wavelength or broadband transmission of electromagnetic energy for igniting fuel, such as is disclosed in the above referenced co-pending United States provisional patent application serial no. 60-020,652. The present invention is also not limited to the exemplary configurations illustrated herein as to the optical igniter 24 and the fuel nozzle (s) . The optical igniter 24 can be separately disposed transverse the fuel spray 32 as illustrated in Fig. 1, or parallel with the fuel nozzle 30 spray axis, or can be integrally formed in the fuel nozzle, or integrated into a common housing with a fuel nozzle to provide a flame injector, the latter embodiments being fully described in the above- referenced US Patent to DeFreitas.

An electromagnetic ignition system has operational parameters that are significantly different from a conventional electrical ignition system, such as a spark plug based system. Accordingly, conventional diagnostic techniques that use current and voltage sensing of the spark discharge characteristics will not provide sufficient information about the operational performance of the electromagnetic ignition system. Conventional electrical diagnostic techniques also fail to provide real time and direct diagnostic information about the ignition process within the actual combustor, for example, the intensity and duration of the spark kernel or plasma, and the combustion process after ignition.

With reference to Fig. 2, a laser based ignition system 10 includes a laser module 40, which produces laser energy having selected wavelength and intensity characteristics. For example, the module 40 may produce infrared laser energy or ultraviolet laser energy, or other wavelengths and combinations of various wavelengths. The wavelengths and intensities (power) of the laser energy will be selected based on the specific ignition and combustion requirements for the combustor 12 that the ignition system 10 will be used with. The laser energy can be produced with any number of laser sources that are well known to those skilled in the art, and are set forth in an exemplary manner in the above-referenced disclosures . An optic fiber cable 42, having one or more optic fibers therein, is used to optically couple the laser energy from the laser module 40 to the optical igniter 24 disposed at or near an opening 44 in the inner combustor liner 36. The opening 44 may be, for example, a spark plug opening wherein the spark plug assembly has been removed. Another alternative would be to position the optical igniter 24 using a line-of-sight alignment with one of the air vent openings in the combustor. Other alternatives will be apparent to those skilled in the art, with the positioning of the optical igniter 24 being selected so as to emit the laser energy from the module 40 into the combustor 12 at the desired and preferably optimum location for ignition.

In the present embodiment, the optical igniter 24 includes an optical window 46, which in this case is realized in the form of a lens that is used to focus the laser energy from the optic fiber cable 42 into the combustor 12, as represented by the arrow 47. The output end 42b of the fiber cable 42 can be held in place with the lens 46 by a suitable ferrule, housing or other high power optical connector 48. In the case of using infrared laser energy, the lens 46 focusses the laser energy to a focal point at a desired location in the combustion chamber with a sufficiently high fluence as described hereinabove. As a result, a laser induced breakdown or laser spark 28 is created in the combustion chamber and used to ignite the combustible mixture therein. Additional details of the laser induced ignition event is described in the above-referenced disclosures.

The input end 42a of the optic fiber cable 42 is optically coupled to the laser module 40. Typically, a lens arrangement 50 (which may include one or more optical elements) is used to focus the laser energy produced by the module 40 into an optic fiber cable assembly 42. Fig. 3 illustrates one embodiment of a suitable optical coupling 52 between the lens arrangement 50 and the optic fiber cable 42. In this embodiment, the coupling 52 is a high power coupling commonly referred to as an SMA coupling (such as, for example, SMA 905 connector available from 3M Company) . The coupling 52 includes a male body 53 having a first threaded end 54 mounted to a wall 56 or other support structure of the laser module 40. The male body has a second threaded end 58, and a suitable locking device 60 such as a female hex nut which is tightened onto the male end 58'. The locking device 60 engages and secures an integral ferrule 62 that extends within the body 53 and into the laser module 40. The optic fiber 42 is disposed in the ferrule 62 and can be secured therein by any convenient technique, such as for example an adhesive epoxy. The input end 42a of the fiber optic cable 42 is disposed near or adjacent to a suitable optical window 64, such as sapphire, that also hermetically seals the body 53. A second window 65 may be used to seal the end of the ferrule 62 if required. The lens 50 is supported within the laser module 40 by any suitable mounting arrangement (not shown) so that the laser energy 66 is focussed to the input end 42a of the fiber cable 42. With reference again to Fig. 2, the laser module 40 is powered by a suitable power supply and switch arrangement 68. In the present example, system power 70 such as can be directly received from the engine alternator is input to a rectifier and filter circuit 72. The output of the rectifier circuit 72 is input to a DC to DC converter 74 which maintains a regulated DC supply for energizing the laser module 40. The output of the converter 74 is one or more DC supplies depending on the particular power requirements for the laser module 40. For example, the converter 74 may include an energy storage device such as a capacitor that will be discharged to power a flashlamp for the laser source. In other cases, for example, the output from the converter 74 may be a DC voltage that drives a laser diode array for producing laser energy. The present invention is not limited to any particular power source or laser generator.

A laser switch module 76 is used to control when electrical power is delivered to the laser generator in the laser module 40. The switch may be, for example, a solid state switch arrangement or other suitable switching device. The switch 76 is controlled by a main diagnostics processor 78, but can also be controlled, or separately controlled, by the engine ignition control system (not shown) .

The diagnostics system 18 includes a diagnostics processor 78 that can be 'realized in the form of a microprocessor, programmable logic array, discrete logic, analog logic, digital signal processor and so on to name just a few examples. The processor 78 monitors various operating parameters of the laser ignition system 10, can control ignition timing (either independently or in conjunction with the engine control system) if so desired, and also performs various diagnostic tests as will be explained in greater detail hereinafter. Control of the ignition timing can be effected, for example, by an appropriate FIRE control signal 77 to the switch 76 and an ENABLE control signal 73 to the converter 74 to control delivery of energy to the switch 76. The diagnostics processor 78 receives inputs from various monitoring points through a multiplexer and digitizer (MUX) circuit 80. The MUX 80 includes circuits that can be conventional in design for converting various analog signals to digital format suitable for processing by the diagnostics controller 78. For example, a sense circuit 82 is used to monitor the output voltage and current from the converter 74 to verify that power is being produced to energize the laser source within the laser module 40. These signals can also be used by the controller 78 to regulate the converter output. A second sense circuit 84 is used to monitor the voltage and current characteristics of the laser module 40, which information can be used to diagnose problems with the laser source, thereby providing diagnostic information as to whether the laser source is operating within prescribed limits. The current discharge pulse can also be used as a timing control to determine, for example, that the laser source flashlamp fired at the correct time. The analog signals from the sense circuits 82, 84 are digitized and input to the controller 78 via the MUX circuit 80. The actual hardware implementation of the MUX circuit will be determined by the type of controller 78 used with the present invention as well as the required signal processing for various signals received from the diagnostic elements. A watchdog timer circuit 86 can be used by the engine control system to verify that the diagnostics system is functioning properly. A non-volatile memory circuit 88 is used to store software instructions and data parameters used by the diagnostics processor 78 to diagnose failure conditions in the ignition system 10. The diagnostics arrangement of the present invention detects specific failures, and also identifies possible future failure events by identifying deteriorating system performance characteristics, and retains this information in the nonvolatile memory 88 for later use as needed. In accordance with an important aspect of the present invention, the diagnostics system 18 includes detectors or sensors for monitoring various points along the optical path of the laser energy from the laser module 40 to the combustor 12. By optical path is simply meant the various components that transmit or direct the laser energy from its source within the laser module 40 to the combustor 12. Thus, the optical path includes, for example, the laser module lens 50, the optic fiber cable 42, and the various components in the optical igniter 24.

In the embodiment of Fig. 2, the diagnostics system 18 uses a second optic fiber cable 90 to detect electromagnetic energy at the optical igniter 24. The second optic fiber cable 90 can be terminated within the igniter housing 48 in a similar manner to the first optic fiber cable 42, and disposed so as to receive a portion of laser energy reflected from a surface of the igniter lens or window 46, as represented by the directional arrow 92. The second optic fiber cable 90 can also be used to receive electromagnetic energy produced by both the plasma or laser spark 28 created by the laser energy for igniting the fuel, as well as electromagnetic energy emitted by the combustion process, as represented by the directional arrows 94.

The second optic fiber cable 90 optically couples electromagnetic energy from the optical igniter 24 to a receiver array circuit 96. The receiver array 96, in this embodiment, includes a number of detector circuits that respond to wavelength and intensity characteristics of incident electromagnetic energy. For example, a conventional photo detector, such as a photo diode or photo transistor, can be used to produce a signal that corresponds to the intensity of incident electromagnetic energy that has a wavelength or wavelengths within the spectral response of the photo detector. By using a number of different photo detectors, each having a corresponding spectral response, a diagnostic analysis of the electromagnetic energy associated with operation of the laser ignition system can be performed. With reference to Fig. 4, the receiver array 96 includes one or more detector circuits 100._^ for i=l to n where n equals the number of sensors coupled to the receiver array 96. In this embodiment, each of the detectors 100.. is realized in the form of a conventional photo detector each of which exhibits a selected wavelength response characteristic to incident electromagnetic energy thereon. Associated with each photo detector 100i is a signal conditioning circuit 102_x respectively that can be, for example, a conventional amplifier and filter if so desired. The outputs 103i of the conditioning circuits 102₁ are connected to the MUX circuit 80, which includes a multiplexer switching circuit 104 and an analog to digital converter (A/D) 106. The output 108 of the A/D converter 106 is input to the diagnostic controller 78. The controller 78 issues appropriate address and gate signals 107 for controlling the switching circuit 104, as well as timing control signals 109 to the A/D converter circuit 106. In this manner, the processor 78 receives a number of input signals that represent the electromagnetic energy detected at selectable locations along the optical path of the laser energy. The controller 78 is programmed to interpret the intensity levels of the various photo detector output signals in relation to the associated incident wavelengths to diagnose various operational characteristics of the ignition system 10. In an alternative embodiment, one or more of the signal conditioning circuits 102_x can include a threshold detector circuit (see Figs. 7 and 8 for example) for producing an output that indicates whether' electromagnetic energy within the spectral response of the associated detector 100-_^ exceeded a selected threshold intensity.

The receiver array 96 also includes signal conditioning circuits for the outputs of the converter 74 sense circuit 82 and the laser module 40 sense circuit 84. In this exemplary embodiment, the converter sense circuit includes a voltage sensor 110 and a current sensor 112 and the laser module sense circuit includes a voltage sensor 114 and a current sensor 116. The outputs of these various circuits are input to respective signal conditioning circuits 118, 120, 122 and 124, the outputs of which are input to the A/D converter 106 via the multiplexer 104. By way of example, and with reference to Fig. 2, the diagnostic system 18 can be implemented to monitor various points along the optical path of the laser energy to verify proper operation of the ignition system. The second optic fiber cable 90 receives electromagnetic energy that is reflected from the surface of the igniter lens 46. One or several of the detectors 100₁ in the receiver array 96 can be configured to be responsive to the fundamental wavelength λ₀ of the laser energy produced by the laser module 40. One such photo detector 100,_. detects the intensity at this wavelength reflected by the igniter lens 46. If sufficient intensity is detected at this point, then the diagnostic processor 78 can diagnose that the laser module 40 and all the optical components in the optical path up to the lens 46 are functioning. Another of the detectors lOO_j in the receiver array 96 can be used to detect the intensity of electromagnetic energy that is received by the second optic fiber cable 90 from within the combustor 12, using a selected wavelength response of the detector so as to determine if a spark or flame kernel was produced. Still another of the detectors 100-_^ can be used to analyze the electromagnetic energy produced by the combustion process. For example, one of the detectors in the array 96 can be used to verify that ignition actually occurred. In some cases, a plurality of the detectors 100._. may be used to monitor the spectral content and intensity of the electromagnetic radiation across a corresponding plurality of selected wavelengths, since different combustion effects exhibit different wavelength emissions . It will be noted that in Fig. 2 the optic fiber cable 90 is illustrated as having a number of optic fibers as at 126, each of which couples a portion of the electromagnetic energy received at the optical igniter 24. Each fiber or number of fibers can be terminated at a respective photo detector 100,_. in the receiver array 96. Other coupling schemes however are available and will be apparent to those skilled in the art. For example, the cable 90 could simply terminate at the receiver array 96 and a lens system or optical splitter used to direct the electromagnetic energy to the various detectors lOO_j. An important aspect of the optical coupling is that electromagnetic energy received at the optical igniter 24, both input laser energy reflected from the lens 46 and electromagnetic energy from the combustion chamber, is coupled to a series of detectors in the array 96 for diagnostic analysis by the diagnostic processor 78.

Detecting the laser energy reflected from the igniter lens 46 provides a first order verification that the optical components in the laser ignition system 10 are functioning properly. However, if insufficient reflected laser energy is detected at the optical igniter 24, this data alone does not isolate the failure. As illustrated in Fig. 2, additional detection points can be used as desired for monitoring the operation of the laser ignition system. For example, an optic fiber 128 can be used to detect laser energy reflected at the lens 50 at the output of the laser module 40. This reflected energy can be analyzed using one of the detectors 100₁ in the receiver array 96 to verify that the laser module 40 is producing laser energy with sufficient power to ignite the fuel in the combustor 12. The diagnostic processor 78 can also determine if the laser generator in the laser module 40 is deteriorating over time by comparing the output intensity of the laser generator with selectable stored historic data retained in the non-volatile memory 88, for example. Furthermore, if the laser energy detected at the lens 50 is within selected acceptable limits, but the reflected laser energy detected at the lens 46 at the optical igniter 24 is low or missing, then the diagnostic processor can determine that there is a problem in the optical path elements, such as the optic fiber cable 42. By placing optic fiber pickups on either side of the lens 50 (not shown) , the integrity of the lens can be determined. Those skilled in the art will appreciate that other points of interest along the optical path of the laser energy can be monitored, with the tradeoffs being the cost and complexity of added detectors and control software for the diagnostic system 18.

In an alternative embodiment, rather than using the optic fiber 128 to collect reflected laser energy from the lens 50, a discrete photo detector could simply be disposed within the laser module 40 in close proximity to the lens 50 to sense the reflected laser energy. The output of this photo detector could then be coupled to a signal conditioning circuit in the receiver array 96 for further analysis by the diagnostic processor 78.

Fig. 5 illustrates one example of a spectral analysis that can be performed using the diagnostic system 18 of the present invention. This is a fairly simplified table that is intended to show some of the basic features that can be implemented with the present invention, and is not intended to be an all inclusive detailed representation. In this example, a detector 100-_^ is used to detect electromagnetic energy at the source wavelength λ₀ reflected from the lens 50 in the laser module. This provides information that can be used to diagnose whether the laser module 40 is producing sufficient laser power for ignition. Another detector 100₂ also is used to detect the source wavelength λ₀, for electromagnetic energy reflected from the igniter lens 46. This provides information for diagnosing whether the laser energy produced by the laser module 40 is reaching the laser igniter 24. A third detector 100₃ is used to detect electromagnetic energy in the spectrum of .4-1.0 μM. This information can be used to diagnose whether a spark discharge occurred in the combustor (in the embodiment that uses infrared energy, for example, to create a laser spark for igniting the fuel) . A number of detectors 100₄-100₉ are used to detect electromagnetic energies within selected spectral distributions, e.g. detector 100₆ is used to detect the spectral content at λ=.7μM. These various spectral responses can be used to monitor the characteristics of the combustion process, including verifying that ignition in fact took place. The spectral analysis for the selected wavelengths can include analog intensity (e.g. amplitude) analysis, threshold intensity analysis, energy content analysis, pulse duration and pulse repetition rate analysis by appropriate selection and use of various conventional detector designs, to name a few examples of the diagnostic information available from application of the present invention.

Analysis of the electromagnetic energy received from the second optic fiber cable 90 in the embodiment of Fig. 2 can be based also on a time domain analysis. With reference to Fig. 6, at time t₀ the diagnostics processor 78 causes the laser switch 76 to close, thus energizing the laser source within the laser module 40. This produces a laser output pulse that is detected by the optic fiber 128 based on laser energy that is reflected from the laser module lens 50. The corresponding photo detector 100-_. or 100₂ and related signal processing circuits produce a signal 130 that corresponds to the laser energy pulse. The laser output pulse, and the corresponding pulse 130, may be on the order of 5-100 nanosec, for example. This laser pulse should cause a spark discharge within the combustor at time t_{l t} which spark produces electromagnetic energy that is detected by detector 100₃ which receives electromagnetic energy from the second optic fiber cable 90. The detector 100₃ produces a signal 132 that corresponds to the duration of the laser spark. The laser spark plasma may last for a time period on the order of 50 nanosec to 1 microsecond. Thus, the detector 100₃ output 132 can be used to verify a spark of sufficient intensity and duration was produced to cause ignition. Within a time t₃, ignition should occur, which event can be verified by the output 134 of one or more of the detectors 100₄.₉. The various outputs from the detectors 100i can thus be used to diagnose various aspects of the laser ignition system including laser pulse duration, intensity, plasma formation and intensity and combustion effects, to name a few examples. Note that the diagnostic processor 78 can receive intensity information from the photo detectors lOO_j in analog equivalent form (such as the output from the A/D converter) or can receive threshold detector signals that indicate whether a minimum threshold intensity was _detected, or both if so desired depending on how much data is to be acquired and processed for diagnosing the operation of the ignition system 10, the diagnostics system 18, the combustion process, or some or all of the above combinations. The timing of these events will determine the signal processing utilized, and will determine if direct memory access (DMA) channels are required for direct data storage to memory.

In accordance with another important aspect of the invention, the diagnostics system 18 includes the use of a test device 140, such as a light emitting diode, or low power red laser diode such as are used for laser surveying, targeting and pointing devices, for example. This test device 140 may be part of the laser module 40, for example, or can be separately provided within the diagnostic system 18. The test device 140 produces electromagnetic energy that is optically coupled into the same optic path used for the laser energy from the laser module 40. Preferably, the test device 140 emits safe low level electromagnetic energy into the optical path such as at the lens 50, and transmits this low level energy throughout the optical path. The diagnostic processor 78 can then use the same photo detectors 100_t, or additional photo detectors (not shown) , in the receiver array 96 to diagnose the optical continuity of the laser ignition system 10 before the more dangerous high power laser energy is emitted. Alternatively, a separate receiver array (not shown) and MUX circuit could be used during the test device operation if so needed.

The electromagnetic energy emitted from the test device 140 can be detected at the various points in the ignition system as the laser energy, with the exception that the test device 140 will not cause the production of a plasma 28 or combustion in the combustion chamber 12. In all other respects, however, the test device 140 can be used to verify the integrity and optical continuity of the various elements along the optical path of the laser energy. This operation allows a logic circuit (such as the controller 78) to prevent firing the high power laser source if the optic cable 42 or other element along the optic path of the laser energy is not properly installed. Since the controller 78 uses the same diagnostic logic circuits during the test sequence as are used during the actual ignition system operation, the test device and associated diagnostics also inherently includes the ability for the diagnostics processor to verify proper operation of the diagnostics system in the manner of a self- test . In all of the embodiments described herein, the diagnostics processor 78 can be used to produce output signals 78a to various output devices, such as, for example, computers, video displays, memory devices, LCD and LED displays, tapes, CRTs, engine control systems or aircraft maintenance computers and so on to alert personnel of the diagnostic results, particularly failures or significant changes in system performance.

In addition to the use of the test device 140 for optical integrity and continuity tests, the various optical connectors used throughout the optical path can also be equipped, if so desired, with electrical continuity circuits. A break in the electrical circuit would indicate failure of a related mechanical interconnection, such as at one of the SMA connections described herein. Fig. 7 illustrates an alternative embodiment of the present invention that utilizes a single optic fiber cable coupling between the optical igniter 24 and the laser module 40. To the extent that similar components are used as previously described with respect to the embodiment of Fig. 2, the same reference numerals are used and the description is not repeated except for clarification.

In the embodiment of Fig. 7, the laser module 40 is modified to include additional optical elements. In particular, the output laser energy 142 from the laser source 144 is focussed using a lens system 146 and directed towards the output lens 50. The laser energy is focussed by the output lens 50 into the optic fiber cable 42 as previously described hereinbefore. A hermetic window 64 can be used, and the window 64 and optic fiber cable 42 can be disposed at an output end of the laser module using a high power optical connector and ferrule (not shown in Fig. 7) such as described with reference to Fig. 3 herein.

The laser energy 150 from the lens system 146 is directed through a partially mirrored window 148 that is transparent at the fundamental wavelength of the laser source. Although in this embodiment a partially mirrored window is used, those skilled in the art will appreciate alternative embodiments can be used, such as optical splitters or simply an optical window, for example.

A portion of the source laser energy 150 is reflected by the window 148 as at 152 into an optic fiber or bundle of fibers 154 which couples the laser energy to a photo detector 100_a in the receiver array 96. The photo detector 100_a output signal is then coupled to a signal conditioning circuit 102_a as previously described herein, and may further be input to a threshold detector 156_a. The output of the threshold detector 156_a is then input directly to the diagnostic processor 78, or alternatively can be sent to the MUX circuit 80 for analysis by the diagnostic processor 78.

Most of the source laser energy 150 passes through the window 148 and out to the optic fiber cable 42 to the combustor 12. The same optic fiber cable 42 receives, from the optical igniter 24, reflected laser energy from the igniter lens 46, electromagnetic energy produced by the plasma discharge 28, and electromagnetic energy from the combustion process. This return electromagnetic energy passes back from the fiber cable 42, through the window 64 and lens 50 to the window 148 (this is represented in Fig. 7 by the double headed directional arrows 159) and is partially or fully reflected into another optic fiber or bundle 158. This output fiber 158 couples the received electromagnetic energy to another photo detector 100_b, or array of photo detectors, in the receiver array 96, with associated signal processing circuits 102_b and threshold detector circuits 156_b as desired. Thus, a single optic fiber bundle 42 provides the optical connection between the laser module 40 and the optical igniter 24, as well as transmitting the return electromagnetic energy used for diagnostic analysis. Note again that a test device 140 can be provided and optically coupled to the lens system 146 to permit diagnostic verification of the optical continuity as described hereinabove before the high power laser energy is transmitted through the ignition system 10. Fig. 8 illustrates an alternative embodiment of the receiver array 96, particularly useful with the embodiment of Fig. 7. In this embodiment, the photo detector 100_b for the return electromagnetic energy is a broadband detector that produces an output response across a wide wavelength band. The photo detector 100_b output is then input to a selectable number of narrowband wavelength detectors lβOi-160,,. These detectors can perform a spectral analysis of the return electromagnetic energy as previously described herein, with outputs sent to the respective threshold detectors 156 and the MUX circuit 80 for further processing by the diagnostic processor 78.

The laser source photo detector 100_a can also exhibit a broadband spectral response with its output coupled to a narrowband detector 160_a that is sensitive primarily at the wavelength λ₀. Again, since this circuit is primarily used to verify that adequate laser energy was produced by the laser module 40, a counter/latch 162 can be used to record the occurrence and/or duration of the output laser energy 150. Again, additional detectors lOOi and optic fiber pickups can be disposed throughout the optical path in Fig. 7 (on each side of the various lenses, for example, and the window 64) if added diagnostic failure isolation is desired. For example, various detectors (or optic fiber pick up points) D^ are illustrated in Fig. 7 (in Fig. 7, n=5) , and would be available for analysis by the diagnostic processor 78 by connecting the outputs of the detectors to the MUX 80 or other suitable input means to the processor 78. The represented positions of the detectors O_l._n in Fig. 7 are not intended to be precise, but rather to show general locations that can be used to diagnose problems along the optical path of the laser ignition system, and with the laser source 144.

With reference next to Fig. 9, an exemplary high level software module control diagram suitable for use with the diagnostics processor 78 is provided. In the exemplary software control systems described herein, it is assumed that overall system operation is controlled by an executive command module (referenced as "EXEC" in the drawings) that accesses the various software modules, in particular the diagnostics modules, as needed during operational control of the ignition system and/or the engine. Thus, a sequence that ends at EXEC indicates that control is passed back to the executive command for further operations as programmed. In Fig. 9, at block 200 the executive accesses or activates the diagnostics system 18. At block 202, the diagnostics processor 78 performs various internal tests of the processor 78. If a processor failure occurs as indicated by data at 204, the failure is logged at 206, the failure is communicated to the outside world in the desired format at 208 and the system goes into an idle mode at 210, not permitting and ignition sequence having failed to even perform a diagnostic test.

The Log Failure block 206 can be realized in a straightforward manner by electronically recording in a memory device the failure occurrence for later access. The Communication block 208 can be used to transmit controller 78 outputs to any number of devices as noted hereinabove.

If the internal tests pass at 202, the system performs diagnostic tests on the processor I/O circuits at block 212 such as the watchdog timer circuit 86, the A/D converter and multiplexer circuits 80, and the power supply 68. Another useful diagnostic test would be a test of the laser switch 76 and related timing circuits to verify proper operation before system power 70 is applied. A failure 214 at the I/O block 212 is processed in a manner similar to a failure at the internal test block 202. If the I/O test is successful, the system conducts a test firing and data acquisition sequence block 216. This block implements use of the test device 140 to transmit low power electromagnetic energy through the optical path of the laser ignition system 10, with selectable diagnostic signals produced by the diagnostics system 18. However, if the test device 140 is not used, alternatively the high power laser module 40 can be test fired (before fuel flows into the combustor) . The diagnostics processor 78 can perform numerous tests based on the acquired data including verifying the pulse duration times for the laser switch circuit 76, optical continuity tests based on detected intensities at the various selected test points based on data analysis at block 220 as described hereinbefore, electrical continuity of the optical connectors if included in the diagnostics system, and so on. A failure at 218 of the test firing control block is logged, reported and processed so as to force a system idle at 210. Associated data collected during the test firing and analyzed in the data analysis control block 220 can also be logged and reported to facilitate diagnosis of the cause of failure. This diagnostic test firing serves as a safety interlock and thereby prevents application of high power laser energy when the diagnostics system indicates optical failure or other system problems. If so desired, the executive can be assigned override authority if there is a basis for believing that the diagnostic system is not malfunctioning. A pass of the test firing sequence passes control back to the executive at 222.

With reference to Fig. 10, an exemplary software control module for the diagnostic system 18 is provided such as can be used during actual laser operation of the ignition system 10. At block 300 the laser module 40 is activated, and at block 302 the system checks the preset fire mode, which can be, for example, a test mode (no fire) , an auto fire mode, a fire on demand mode, as well as selectable shutdown modes such as auto shutdown with a single no lightoff and auto shutdown after a selected number of attempts without lightoff. When the fire command is issued at block 304, the laser module 40 emits laser energy along the optical path through to the combustion chamber, and the diagnostics processor 78 collects data (referred to as data acquisition) from the various detectors and sense circuits used in the diagnostics system 18. This data can be analyzed at various points during operation when failures are detected to further isolate the cause of the failure. At block 306 for example, the system checks if a spark plasma occurred. If not, the data analysis at block 308 may indicate that there is a failure in the optical path such as the cable 42 (by noting that laser energy was detected at the lens 50 but not at the lens 46 for example) . As another example, failure to detect a plasma may have resulted from failure to produce laser energy from the source 40 (as detected by one of the detectors 100_a, for example) . The failure is logged and communicated at blocks 310 and 312 in a manner similar to the description herein of Fig. 9, and the system idled at block 314.

If appropriate, an alternative embodiment could allow the system to retry firing the laser as at block 315 to get a spark depending on what the data analysis shows. For example, if the data analysis indicates optical continuity, then it may be that the laser energy simply failed that one time to produce a plasma, and a second or subsequent attempts can be made. Another example is that the plasma may have occurred but lightoff did not occur due to a one time timing error, or the fuel delivery was improper (failure due to non-ignition system components for example) . In other words, the diagnostic processor 78 can be programmed to identify non- critical failures that do not necessitate an ignition system shutdown, but rather permit succeeding attempts to initiate combustion. Thus the diagnostic system 18 may prevent unnecessary or false shutdowns when non-critical or intermittent failures occur that prevented ignition.

If a plasma is detected, then at block 316 the system checks if combustion (i.e. light off) occurred. If yes, the data can be stored at block 318 for future reference or for performing historical trend analysis, for example. The successful firing can be communicated at block 320 to an appropriate output device and control returned to the executive at 322.

If combustion is not detected at block 316, a "no light off" counter can be incremented at block 324, and at block 326 the system decides how to proceed based on the selected fire mode. For auto fire mode, the system communicates the no lightoff occurrence and flags the data at block 328, and then returns to block 300 to fire the laser again. In fire on demand mode as at 330, control is returned to the executive through block 320. In auto shutdown mode, the system checks at block 332 if the selected number of attempts has been performed and, if so, idles the system at block 334. Otherwise, control is returned to the executive through block 320 to attempt another light off sequence. Thus, the control system of Fig. 10 utilizes the data acquired from the various detectors of the electromagnetic energy, including the laser source, plasma and combustion electromagnetic energy, to diagnose proper operation of the laser ignition system 10. Referring to Fig. 11, the diagnostic system 18 can be used to monitor combustion as previously described herein. The control program begins at block 400, wherein it is assumed that light off has been detected in the control flow of Fig. 10. At block 402 data acquisition is performed for the various detectors used in the diagnostic system 18, particularly the detectors 100i used to analyze the electromagnetic energy emitted by the combusting fuel in the combustion chamber 12. At block 404 the data is compared with selected limits. Flame out is detected at 406, for example, when insufficient energy is detected at selected wavelengths. Such a failure is communicated at block 408, and at block 410 the system determines whether the ignition system is programmed for auto relight mode. If yes, this module sets a flame out flag 412 which indicates to the EXEC that a flame out occurred. The EXEC then schedules the laser firing control module 300 for execution. If no, the system is idled at 414, or alternatively can return control to the executive at 416 for on demand ignition mode.

If combustion characteristics are within limits at block 404, the acquired data is stored at block 418 and can be communicated as at block 420 with control then returned to the executive at 416. Monitoring the electromagnetic emissions during the combustion process can be implemented using any number of selected criteria. For example, if large amplitude (intensity) fluctuations are detected of the combustion flame brilliance, this may indicate that the combustion process is approaching a lean limit. By detecting wavelength content of the combustion flame, for example, missing wavelengths can be an indication that the fuel type was changed or that there is fuel contamination or an incorrect blend. Those skilled in the art will appreciate that the software logic described herein can be implemented using application specific integrated circuit (ASIC) technology, for example .

The invention thus provides diagnostic techniques that include the capability of diagnosing laser ignition system failures related to the laser energy source and the optical path, ignition system operating trend analysis based on data acquired from the various detectors used in the diagnostic system for monitoring combustion characteristics, and closed loop control of the laser ignition, firing and shutdown operations by monitoring the laser source, plasma characteristics and combustion process characteristics.

While the invention has been shown and described with respect to specific embodiments thereof, this is for the purpose of illustration rather than limitation, and other variations and modifications of the specific embodiments herein shown and described will be apparent to those skilled in the art within the intended spirit and scope of the invention as set forth in the appended claims .

Claims

1. An ignition system with diagnostics, the ignition system being of the type that uses laser energy to ignite a fuel within a combustor, the ignition system including a laser energy source and an optical delivery system that includes a number of optical elements configured to deliver laser energy from said source into a combustion zone of the combustor,- the diagnostics comprising: a first detector optically coupled to the ignition system for detecting laser energy; and control means responsive to said first detector for diagnosing operation of the ignition system.

2. The apparatus of claim 1 wherein said optical elements include an optical igniter disposed to emit laser energy through an opening into the combustor; said diagnostics including a first optic fiber cable for coupling laser energy at said opening to said first detector.

3. The apparatus of claim 2 wherein said laser energy source comprises a first lens, said optical elements including a second optic fiber cable that couples laser energy from said first lens to said optical igniter,- said diagnostics comprising a second detector that produces an output that corresponds to laser energy emitted into said second optic fiber cable.

4. The apparatus of claim 3 wherein said optical igniter comprises a second lens for focussing laser energy in the combustion zone of the combustor through said opening, said first optic fiber cable coupling laser energy reflected from said second lens to said first detector.

5. The apparatus of claim 1 further comprising a power source for electrically energizing said laser energy source,- wherein said control means comprises sense circuits for detecting proper operation of said power source based on current and voltage characteristics of the power source output .

6. The apparatus of claim 2 wherein said diagnostics comprises additional detectors wherein each additional detector detects electromagnetic energy within a selected wavelength band; said first optic fiber cable coupling electromagnetic energy produced by combustion of the fuel to said additional detectors.

7. The apparatus of claim 2 wherein laser energy emitted into a combustion zone of said combustor produces a plasma that ignites the fuel therein, the diagnostics comprising a second detector that detects electromagnetic energy produced by said plasma, said electromagnetic energy being coupled to said detector by said first optic fiber cable.

8. The apparatus of claim 2 wherein said first optic fiber cable couples laser energy to said optical igniter and couples laser energy from the igniter to said first detector and couples electromagnetic energy from the combustor to said first detector.

9. The apparatus of claim 8 comprising an optical splitter disposed between said laser energy source and said first optic fiber cable, said splitter causing a portion of laser energy produced by said laser energy source to be directed to said first detector.

10. The apparatus of claim 8 wherein said control means diagnoses operation of the ignition system by: 1) determining laser energy source output based on a portion of laser energy transmitted to said optical igniter,- 2) determining laser energy emitted into the combustion zone based on laser energy at said optical igniter; 3) determining plasma formation based on electromagnetic energy characteristics received from the combustor; and 4) determining combustion of the fuel based on electromagnetic energy characteristics received from the combustor.

11. The apparatus of claim 1 wherein said first detector comprises a number of devices that are individually responsive to wavelength and intensity characteristics of electromagnetic energy incident thereon, there being at least one detector at each of a selected plurality of optical connections between respective ones of said optical elements.

12. The apparatus of claim 1 wherein said optical elements include an optical igniter disposed in line with an opening to the combustor, said optical igniter comprising an optic window transparent to laser energy emitted therethrough and into the combustion zone through said opening,- said optical elements including a first optic fiber cable for coupling laser energy from said laser energy source to said optical igniter, and a second optic fiber cable for coupling to said first detector laser energy scattered by said window.

13. The apparatus of claim 12 wherein said second optic fiber cable couples electromagnetic energy from a combustion zone to said first detector.

14. The apparatus of claim 1 wherein the diagnostics comprises an electromagnetic energy test source optically coupled to said optical delivery system, said test source emitting low power electromagnetic energy to permit said control means to perform an optical continuity test of the ignition system before high power laser energy is emitted into the apparatus .

15. The apparatus of claim 14 wherein said test source comprises a light emitting diode or a low power laser diode.

16. Diagnostic apparatus for diagnosing operation of an ignition system of the type that uses laser energy to ignite a fuel within a combustor, the ignition system including a laser energy source and a first optical delivery system that includes a number of optical elements configured to deliver laser energy from said source into a combustion zone of the combustor; the diagnostics apparatus comprising: a first detector that can be optically coupled to the ignition system for detecting laser energy; and control means responsive to said first detector for diagnosing operation of the ignition system.

17. The apparatus of claim 16 comprising a second optical delivery system for coupling laser energy from different test locations in the ignition system to a number of detectors in the diagnostic apparatus,- said control means diagnosing operation of the ignition system, including operation of a laser energy source and continuity of said ignition system optical delivery system in, response to said detectors.

18. The apparatus of claim 17 wherein said control means diagnoses a combustion process in the combustor based on electromagnetic energy coupled from the combustor to a detector through said second optical delivery system.

19. The apparatus of claim 16 wherein said optical elements include an optical igniter disposed to emit laser energy through an opening into the combustor,- said diagnostics apparatus including a ^'first optic fiber cable for coupling laser energy at said opening to said first detector.

20. The apparatus of claim 19 wherein said laser energy source comprises a first lens, said optical elements including a second optic fiber cable that couples laser energy from said first lens to said optical igniter; said diagnostics apparatus comprising a second detector that produces an output that corresponds to laser energy emitted into said second optic fiber cable.

21. The apparatus of claim 20 wherein said optical igniter comprises a second lens for focussing laser energy in the combustion zone of the combustor through said opening, said first optic fiber cable coupling laser energy reflected from said second lens to said first detector.

22. The apparatus of claim 16 further comprising a power source for electrically energizing said laser energy source; wherein said control means comprises sense circuits for detecting proper operation of said power source based on current and voltage characteristics of the power source output.

23. The apparatus of claim 19 wherein said diagnostics apparatus comprises additional detectors wherein each additional detector detects electromagnetic energy within a selected wavelength band; said first optic fiber cable coupling electromagnetic energy produced by combustion of the fuel to said additional detectors .

24. The apparatus of claim 19 wherein laser energy emitted into a combustion zone of said combustor produces a plasma that ignites the fuel therein, the diagnostics comprising a second detector that detects electromagnetic energy produced by said plasma, said electromagnetic energy being coupled to said detector by said first optic fiber cable.

25. The apparatus of claim 19 wherein said first optic fiber cable couples laser energy to said optical igniter and couples laser energy from the igniter to said first detector and couples electromagnetic energy from the combustor to said first detector.

26. The apparatus of claim 19 comprising an optical splitter disposed between said laser energy source and said first optic fiber cable, said splitter causing a portion of laser energy produced by said laser energy source to be directed to said first detector.

27. The apparatus of claim 19 wherein said control means diagnoses operation of the ignition system by: 1) determining laser energy source output based on a portion of laser energy transmitted to said optical igniter,- 2) determining laser energy emitted into the combustion zone based on laser energy at said optical igniter; 3) determining plasma formation based on electromagnetic energy characteristics received from the combustor; and 4) determining combustion of the fuel based on electromagnetic energy characteristics received from the combustor.

28. The apparatus of claim 16 wherein said first detector comprises a number of devices that are individually responsive to wavelength and intensity characteristics of electromagnetic energy incident thereon, there being at least one detector at each of a selected plurality of optical connections between respective ones of said optical elements.

29. The apparatus of claim 16 wherein said optical elements include an optical igniter disposed in line with an opening to the combustor, said optical igniter comprising an optic window transparent to laser energy emitted therethrough and into the combustion zone through said opening; said optical elements including a first optic fiber cable for coupling laser energy from said laser energy source to said optical igniter, and a second optic fiber cable for coupling to said first detector laser energy scattered by said window.

30. The apparatus of claim 29 wherein said second optic fiber cable couples electromagnetic energy from a combustion zone to said first detector.

31. The apparatus of claim 16 wherein the diagnostics apparatus comprises an electromagnetic energy test source optically coupled to said optical delivery system, said test source emitting low power electromagnetic energy to permit said control means to perform an optical continuity test of the ignition system before high power laser energy is emitted into the apparatus.

32. The apparatus of claim 31 wherein said test source comprises a light emitting diode or a low power laser diode.

33. A method of diagnosing operation of an ignition system that uses high power laser energy to ignite fuel within a combustor, comprising the steps of: a) producing laser ignition energy using a laser energy source; b) transmitting the laser ignition energy through an opening into a combustor along an optical path defined by an optical delivery system disposed between said source and said opening ,- and c) detecting the laser energy in the ignition system and diagnosing operation of the ignition system based on said detection.

34. The method of claim 33 comprising the step of detecting laser energy at said opening.

35. The method of claim 34 comprising the steps of detecting laser energy from said source, and detecting electromagnetic energy produced by a combustion process in the combustor.

36. The method of claim 33 comprising the steps of producing low power electromagnetic energy and transmitting said lower power electromagnetic energy along said optical path for determining optical continuity before said laser ignition energy is transmitted along said optical path.

37. Diagnostics apparatus for an ignition system that uses laser energy to ignite a fuel within a combustor, the ignition system comprising a laser energy source that produces laser energy of sufficient energy to produce a plasma for igniting the fuel and a number of optical elements configured to couple laser energy from said source into a combustion zone of the combustor; the diagnostics apparatus comprising a first detector that produces an output that corresponds to a characteristic of electromagnetic energy incident thereon; said first detector receiving electromagnetic energy emitted by a plasma produced by the laser energy, and also receiving electromagnetic energy emitted during combustion of the fuel in the combustor; and a control means for diagnosing a combustion process based on said first detector output, said diagnosis including determining plasma formation and combustion characteristics within the combustor.

38. The apparatus of claim 37 comprising a plurality of detectors, each detector being responsive to electromagnetic energy incident thereon; said control means producing diagnostic signals representing combustion characteristics based on outputs from said detectors.

39. The apparatus of claim 37 wherein said control means detects a flame out condition and stores in memory selected output signals from said detector as a history of the combustion process.

40. The apparatus of claim 37 wherein said control means comprises means for exchanging data with a control system external the ignition system for analysis of data stored by said control means related to the combustion and ignition processes .

41. The apparatus of claim 37 wherein said control means operates executes automatic relight, fire on demand and manual override modes for controlling operation of the laser energy source for igniting the fuel based on said diagnoses.

42. The apparatus of claim 37 wherein intensity, wavelength and time domain analyses are performed by said control means based on said detector output to analyze the combustion and ignition processes in the combustor.

43. Diagnostics apparatus for an ignition system that uses high power laser energy to ignite a fuel within a combustor, the ignition system including a laser energy source and a number of optical elements forming an optical path to couple laser energy from said source into a combustion zone of the combustor; the diagnostics comprising a low power electromagnetic energy source coupled to said optical elements for transmitting low power electromagnetic energy along said optical path; a first detector that produces an output that corresponds to a measurement of electromagnetic energy transmitted along said optical path into the combustion zone; and a control means for diagnosing optical continuity of said optical path using said low power electromagnetic energy.

44. The apparatus of claim 43 wherein said first detector receives electromagnetic energy in the form of electromagnetic energy from one or more of said optical elements, and electromagnetic energy emitted from a plasma formed in the combustor by said laser energy, and electromagnetic energy emitted by a combustion process in the combustor, said control means diagnosing operation of the ignition system based on said first detector output.

45. The apparatus of claim 43 comprising means for providing and monitoring electrical continuity test circuits at optical couplings along said optical path.

46. The apparatus of claim 43 wherein said control means detects said low power electromagnetic energy at a number of test locations along said optical path, said control circuit performing a self-test of the diagnostics based on said detected energy.

47. A diagnostics apparatus for controlling an ignition system based on diagnosing a combustion process of a fuel within a combustor, the diagnostics apparatus comprising a detector that produces an output that corresponds to a characteristic of electromagnetic energy incident thereon, means for coupling electromagnetic energy produced during the combustion process from the combustor to said detector, and a control means that receives said detector output for analyzing the combustion process based on said output and controlling the ignition system in response thereto.

48. The diagnostic apparatus of claim 47 wherein said detector produces an output that corresponds to intensity and wavelength characteristics of electromagnetic energy received from the combustor during the combustion process.

49. The diagnostic apparatus of claim 48 wherein said control means detects a flame out condition based on a failure to detect electromagnetic energy over a selected bandwidth.

50. The diagnostic apparatus of claim 47 wherein said control means detects initiation of the combustion process based on detecting electromagnetic energy over a selected bandwidth.

51. The diagnostic apparatus of claim 49 wherein said control means detects a plasma that initiates a combustion process based on said detector output.

52. The diagnostic apparatus of claim 28 comprising a laser ignition system for the combustor, wherein said control means controls ignition of the combustion process, and controls ignition system operation including restart and shutdown based on said detected electromagnetic energy from the combustor.