Transient plasma ignition in gas turbine engines

Abstract

A system and method for improving the ignitability of fuel-air mixtures in gas turbine engines at high altitude and other difficult to ignite conditions. In the preferred embodiment, an advanced ignition system that is capable of applying high voltage, nanosecond duration pulses (< 100 ns) across an exciter to generate non-equilibrated discharges has been shown to improve ignitability as well as operate at lower temperatures and higher altitudes as compared to traditional ignition sources.

Description

TRANSIENT PLASMA IGNITION IN GAS TURBINE ENGINESCROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent application claims priority of U.S. Patent Application No. 63 / 736,984, filed on December 20, 2024, the entire disclosure of which is hereby incorporated by reference herein for all purposes.COPYRIGHT NOTICE

[0002] A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.TECHNICAL FIELD

[0003] This description relates to systems and methods that produce and / or employ high voltage, high power nanosecond pulses to generate non-equilibrated transient plasmas discharges in a combustion chamber of a gas turbine engines for igniting fuel-air mixtures in the gas turbine engines.BACKGROUND

[0004] Gas turbine engines used on aircraft typically employ an ignition system to light and re-light the fuel in the main combustion chamber, at which point the flame is self sustaining. Challenges in ignition include variations in environmental conditions (e.g., temperature, humidity, altitude, for instance variations between relatively warm versus relatively cold temperatures, relatively dry versus relatively wet environments, relatively low versus relatively high altitudes), variation in fuel quality, and variations in structure for instance due to wear and tear on turbine engine components. Relighting the engine at high altitudes is typically more difficult than at low altitudes because cold conditions inhibit effective fuel vaporization.SUMMARY

[0005] Transient Plasma Systems, Inc. (TPS) has demonstrated the ability to improve gas turbine ignition compared to existing capacitive discharge ignition using a system that generates high-power nanosecond duration pulses to generate non-equilibrated, transient plasma discharges.

[0006] Non-equilibrated transient plasmas containing high energy electrons can be used in place of a thermally equilibrated electrical arc to ignite fuel-air mixtures. Depending on operating conditions, the combustion process may be enhanced when the fuel-air mixture is ignited by a non-equilibrated transient plasma compared to when the mixture is ignited by a thermally equilibrated arc or spark. Experiments in a variety of engines have shown that these improvements in the combustion process include higher peak cylinder pressure, increased indicated mean effective pressure, reduced ignition delay, and the ability to reliably ignite leaner mixtures. Recent work has shown that these performance improvements may be enhanced in some operating conditions by applying more than one transient plasma discharge event before and / or during a single combustion event. To accomplish this, a power source is required to produce one or more transient plasma discharge(s) at a given rate. This disclosure describes electrical circuitry designed to produce one or more electrical pulses, each pulse generally having a duration between 1 nanosecond and 100 nanoseconds, as well as methods for integrating this circuitry with an engine. This disclosure also describes generation of nanosecond sparks, which may not be low temperature. This disclosure further describes circuitry that results in improved rise time and pulse duration as compared to the conventional systems, leading to enhanced results in gas turbine engines.

[0007] Briefly and in general terms, the present disclosure is directed to an advanced ignition system for gas turbine engines, for instance gas turbine engines employed in aircraft. The advanced ignition system includes one or more exciters (e.g., circuitry) that produce high voltage electrical pulses with a duration of nanoseconds that drive one or more igniters to create a non-equilibrated transient discharge inside a combustion chamber of a gas turbine engine. The advanced ignition system can optionally include one or more igniters, positioned in the combustion chamber of the gas turbine engine and electrically coupled to the exciter(s), the igniter(s) operable to create a non-equilibrated transient discharge inside the combustion chamber of a gas turbine engine. The advanced ignition system can optionally include cables suitable to couple the high frequency pulsesof the exciter(s) to the igniter(s). The advanced ignition system can optionally include one or more power sources (e.g., DC-DC power converter, DC bus).

[0008] The advanced ignition system can optionally include, or be operationally positioned with respect to, a torch ignitor in the combustion chamber of the gas turbine engine. A torch ignitor can, for example, be used in lieu of spark ignitors to provide an ignition source for combustors located in the combustion chamber of gas turbine engines. Torch ignitors provide a flame to the combustion chamber of a gas turbine engine as an ignition source rather than the electric current provided by spark ignitors. A torch ignitors typically remains active while the gas turbine is operating.

[0009] In some implementations, the ignition system is directly powered by an available DC power source, and, depending on the application, this power source is typically a fixed voltage from 0 VDC to 600 VDC inclusive.

[0010] The ignition system can, for example, include a DC-DC power converter, a rapid capacitor charger, and a pulse forming circuit (e.g., exciter) that generates high voltage nanosecond duration pulses. Such can, for example, employ an architecture similar to that described in International (PCT) patent application US2022 / 038047 published as WO2023 / 014522, although changes can be made to provide suitable DC voltages for the specific application to gas turbine engines. Alternatively, the ignition system can obtain power from a DC power bus, for instance an existing or legacy DC power bus of an aircraft.

[0011] As used herein and in the claims, term legacy refers to structures that were already part of a vehicle, gas turbine engine or other apparatus prior to installation of the ignition system or components thereof. Notably, the ignition system or components thereof can come in the form of a retrofit kit. A retrofit kit can include one or more exciter drive circuits operable to produce a plurality of high voltage electrical pulses with a duration of nanoseconds, where high voltage is equal to or greater than 1 kV and nanosecond is equal to or less than 100 ns. Such may advantageously be employed with one or more legacy ignitors operable to create the non-equilibrated transient discharge inside the combustion chamber of the gas turbine engine. Such may advantageously be employed with one or more legacy cables that electrically couple the exciter drive circuit(s) with the ignitor(s). Alternatively, a retrofit kit can include one or more ignitors operable to create the non-equilibrated transient discharge inside the combustion chamberof the gas turbine engine. Alternatively, a retrofit kit can include one or more cables that electrically couple the exciter drive circuit(s) with the ignitor(s).

[0012] The igniter can, for example, comprise a high voltage center electrode, surrounded by a dielectric and then a grounded shell. In some implementations, the ignition system includes one or more standard gas turbine igniters. In other implementations, the ignition system employes one or more custom electrodes similar in at least some respects to spark plugs for automobile engines. An exciter can, for example, take the form described in U.S. patent 11,929,595 although other forms of exciters can be employed.

[0013] The foregoing summary does not encompass the claimed subject matter in its entirety, nor are the embodiments intended to be limiting. Rather, the embodiments are provided as mere examples.

[0014] Other features of the disclosed embodiments and implementations will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the disclosed embodiments and implementations.

[0015] While generally described in terms of gas turbine engines of aircraft, the teachings herein and the claims are not limited to aircraft unless specifically recited as such.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. l is a schematic diagram of a gas turbine engine and an ignition system for the gas turbine engine, according to at least one illustrated implementation.

[0017] FIG. 2 is a graph that shows airspeed versus altitude to demonstrate the envelope over which relight using conventional ignition can occur.

[0018] FIG. 3 is a schematic diagram showing dimensions of a high voltage nanosecond pulsed ignition system that demonstrates improved performance, and a block diagram of subsystems of an ignition architecture of the high voltage nanosecond pulsed ignition system.

[0019] FIG. 4 is a schematic diagram of an exciter drive circuit that drivers the igniter, according to at least one implementation.

[0020] FIG. 5 is a schematic diagram of an exciter circuit that may be used to driver the igniter, according to another implementation.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] This disclosure describes an advanced ignition system that can, for example, be used for lighting a gas turbine engine that extends the relight envelope and improves performance beyond what is possible with a traditional capacitive discharge ignition system. In at least one implementation, a system generates high voltage (> 1 kV) pulses with nanosecond duration (< 100 ns) across an igniter. The electric field across the anode and cathode of the igniter creates a sufficiently high reduced electric field to initiate an electrical discharge. The risetime and duration of the pulse are sufficiently short that the discharge is characterized by electrical streamers propagating across the igniter gap, producing either a non-equilibrated transient plasma or a nanosecond spark, depending on the conditions within the combustion chamber.

[0022] FIG. 1 shows a gas turbine engine and an ignition system for the gas turbine engine, according to at least one illustrated implementation. The gas turbine engine can take any of a large variety of forms, for example a gas turbine engine of an aircraft. An aircraft can have one or more gas turbine engines, and one or more ignition system. The ignition system includes at least a first exciter drive circuit, and may include two or even more exciter drive circuits (e.g. , a second exciter drive circuit, a third exciter drive circuit). The exciter drive circuit(s) is operable to produce a plurality of high voltage electrical pulses with a duration of nanoseconds, where high voltage is considered equal to or greater than 1 kV and nanosecond is considered equal to or less than 100 ns.

[0023] The ignition system optionally includes a first ignitor, and may include two or even more ignitors (e.g., a second ignitor, a third ignitor). Alternatively, the ignitor(s) can be part of an existing apparatus (e.g., part of an existing or legacy gas turbine engine), and can even advantageously take the form of existing or legacy ignitors already installed in the gas turbine engine(s). The ignitor(s) is located at least partially inside the combustion chamber of the gas turbine engine and is operable to create the non-equilibrated transient discharge inside the combustion chamber of the gas turbine engine when driven by an exciter drive circuit.

[0024] The ignition system optionally includes a first cable, and may include two or even more cables (e.g., a second cable, a third cable). Alternatively, the cable(s) can be part of an existing apparatus (e.g., part of an existing or legacy gas turbine engine), and can even advantageously take the form of existing or legacy cables already installed in thegas turbine engine(s). The cable(s) electrically couples the exciter drive circuit(s) with the ignitor(s).

[0025] FIG. 1 summarizes the results of the testing Applicant conducted in 2024 using a gas turbine engine and Applicant’s high voltage nanosecond ignition system with an ignitor installed in the combustion chamber. The advantages provided by the Applicant’s transient plasma ignition system include the ability to re-light the gas turbine engine at higher altitudes and under other more strenuous conditions, such as flooded start event, a flame out, and faster ignition in many conditions. One or more sensors can, for example, detect one or more of a flooded start event, a flame out event, or an event or a signal or command to start-up the gas turbine engine and / or or a signal or command indicating a need to reignite the gas turbine engine. Thus, the ignition system can for example, be responsive to detection of an occurrence of a flame out condition in the gas turbine engine, or a flooded start condition, or a signal or command indicating a need to reignite the gas turbine engine.

[0026] FIG. 2 shows a graph of airspeed versus altitude to demonstrate an envelope over which relight using conventional ignition can occur. To extend the ignition envelope shown in Fig. 2, the ignition system described here produces high voltage, nanosecond duration pulses (< 100 ns) repetitively for as long as necessary to achieve ignition. Data has shown that higher repetition rate results in better performance, with effective repetition rates being greater than 10 kHz. The ignition system described herein was tested and demonstrated the ability to extend this envelope. Thus, an advanced ignition system that is capable of applying high voltage, nanosecond duration pulses (< 100 ns) across an exciter to generate non-equilibrated discharges has been shown to improve ignitability as well as operate at lower temperatures and higher altitudes as compared to traditional ignition sources.

[0027] FIG. 3 shows dimensions of Applicant’s high voltage nanosecond pulsed ignition system that demonstrates improved performance. The block diagram of typical subsystems of the ignition architecture is also shown. Such subsystems can include, for example, a DC-DC power converter, a rapid charger (e.g., rapid capacitor charger), and a pulse former (e.g., exciter drive circuit). The DC-DC power converter can receive an input DC voltage and produce a DC supply voltage, and optionally charging a rapid capacitor charger. The pulse former outputs drive pulses (e.g., a plurality of high voltageelectrical pulses with a duration of nanoseconds, where high voltage is equal to or greater than 1 kV and nanosecond is equal to or less than 100 ns).

[0028] Experiments have shown that the ignition system should apply multiple pulses up until the time ignition occurs, which may require 0-30 seconds . The long duration of operation sets the thermal design requirements for the electronics, packaging, and heatsinking.

[0029] Experiments have shown that the minimum viable requirements are an average power of operation of 125 Watts, a pulse voltage of 5 kV, a pulse repetition rate of 300 kHz to deliver 1500 pulses per burst, and burst repetition rate of 300 Hz (the rate that the bursts at 300 kHz repeat). Ranges from 500 V- 10 kV, 10 kHz - 1 MHz, and pulses per burst 1 - 3,000 are also possible.

[0030] FIG. 4 shows an exciter circuit that drivers the igniter, according to at least one implementation. In this depiction there are four repeating circuits composed of a capacitor, MOSFET, transmission line, magnetic core, and passive or active reset circuit. Each transmission line is wound around its own magnetic core to make a common mode choke. A separate winding is would around each core to connect the reset circuit. Reset can be achieved in a number of ways, either actively or passively. The outputs of each transmission line are connected as shown in Fig. 4 to create a transmission line transformer in which the cores present high impedance looking back from the load, preventing current from a neighboring stage from flowing back toward the input. The voltage of each stage adds in series to achieve multiplication gain. This topology was chosen to keep cost of the exciter in check and also provide a high bandwidth circuit capable of generating nanosecond duration pulses.

[0031] The circuit illustrated in FIG 4 is designed to generate high voltage (0-4 kV) for the circuit shown here, nanosecond duration (5-100 ns) pulses repetitively at a repetition rate from 0 - 1 MHz. The voltage can be increased by adding additional power stages like the four repeating stages shown in the figure. Four stages is shown for the preferred embodiment because testing has shown that four stages is enough to generate a reactive plasma that extends ignition capability beyond what is possible with conventional ignition exciters and igniters.

[0032] In this circuit capacitors C1-C4 are charged by the DC / DC converter to the set voltage point. During charging the MOSFETs Q1-Q4 are off. When the exciter receives a trigger signal, MOSFETs Q1-Q4 are driven on to their conducting state, dischargingenergy from capacitors C1-C4 into transmission lines T1-T4. The MOSFETs are on for a period of time that is proportional to the pulse duration. Upon reaching the desired pulse on-time, the MOSFETs turn off generating the falling edge of the pulse. These approximately square wave pulses travel along the transmission lines, which are wound on magnetic cores to create common mode chokes. Each core also has an additional winding that connects to the a core reset circuit to prevent core saturation. The outputs of each transmission line are connected as shown in FIG. 4 to create a transmission line transformer, where the high impedance of the common mode chokes prevent currents from flowing from a neighboring stage back toward the input of the circuit. Instead, the currents from each stage flow through the load, and the voltage of each stage is added in series, creating voltage multiplication.

[0033] The output of the exciter is connected to the igniter. When possible, it is advisable to connect using short interconnect. If a longer cable is employed it may be desirable to approximately impedance match the exciter to the cable impedance.

[0034] FIG. 5 shows an exciter circuit that may be used to driver the igniter, according to at least another implementation. Applicant has performed experiments with an exciter built from this schematic to demonstrate the efficacy of nanosecond duration high voltage pulses in gas turbine engines. The pulse is formed by D3, which is a drift-step-recovery- diode that is initially forward biased by a sinusoidal current when Q2 switches. This sinusoidal current reverses direction after the first half-cycle, flowing in the reverse direction through the diode until the charge stored in its junction is removed and the diode quickly becomes reverse biased, blocking current flow through the diode. The circuit is tuned so that ideally all of the energy switched into the LC tank circuit is stored in L2 at the moment that the diode becomes reverse biased. In this way, D3 works as an opening switch, switching inductively stored energy into the igniter. This circuit is typically designed to produce pulses with durations from 2-30 ns. For the gas turbine experiments, voltage between 500 V - 10 kV were considered; however, this circuit is capable of producing higher voltages by using appropriately rated arrays of DSRD diodes to make up D3.

[0035] Legacy ignitors can include ignitors commercially available from Champion Aerospace, e.g., for instance as part numbers CH31900-6, CH31965, CH31843 (T3),CH31905, CH31772A, CH31904-2, FHE256-10A, FHE256-10B, CH34661, CH31858-2,CH31926, FHE146-7A, CH34158, CH34419, or various others such as those listed in theChampion Aerospace AV22 catalog, see www. championaerospace. com / products / igniters#catalog. Legacy cables can include ignition leads commercially available from Champion Aerospace, e.g., for instance as part numbers CH53552-1, CH53552-2, CH53552-3, CH53569-1, CH53569-2, CH53440, CH53440-1, CH53566-1, CH53566-3, CH53515-1, CH53515-2, CH53515-3, CH53515- 4, or various others such as those listed in the Champion Aerospace AV22 catalog, see www.championaerospace.com / products / ignition-leads#catalog.

[0036] The ignition system can, for example, be communicatively coupled to a full authority digital engine or electronics control (FADEC) system of the aircraft. The ignition system can, for example, include a relay that couples the ignition system or a component thereof to be controlled by the FADEC and operable to selectively provide power to a first ignitor located at least partially in a combustion chamber of the gas turbine engine.

[0037] The ignition system can include or be coupled to a diagnostic system that monitors a system operation and health of one or more components of the ignition system. The diagnostic system can, for example, checks= a functionality of one or more components of the ignition system. The diagnostic system can, for example, verify an operational condition of the first igniter by checking for an abnormal open circuit condition or an abnormal short circuit condition.

[0038] The teachings of U.S. patent 7,767,433: U.S. patent 7,901,929; U.S. patent 7,901,930; U.S. patent 9,377,002; U.S. patent 9,617,965; U.S. patent 10,587,188; U.S. patent 10,631,395; U.S. patent 10,072,629; U.S. patent 11,478,746; U.S. patent 11,929,595; U.S. patent application publication 2014 / 0109886; U.S. patent application publication 2020 / 035949; U.S. patent application publication 2020 / 0025393; U.S. patent application publication 2022 / 0285922; U.S. patent application publication 2022 / 0337036;International (PCT) patent application PCT / US2009 / 045073 published as W02010 / 011408; International (PCT) patent application PCT / US2019 / 014237 published as WO2019 / 143992; International (PCT) patent application PCT / US2019 / 014339 published as WO2019 / 144037; International (PCT) patent application PCT / US2022 / 018312 published as WO2022 / 187226; International (PCT) patent application US2022 / 024815 published as WO2022 / 225784; International (PCT) patent application US2022 / 038047 published as WO2023 / 014522; and U.S. patent application publication 2023 / 0032942, are each incorporated by reference herein in their entireties.

Claims

CLAIMS1. An ignition system operable to create a non-equilibrated transient discharge inside a combustion chamber of a gas turbine engine, the ignition system comprising: at least a first exciter drive circuit operable to produce a plurality of high voltage electrical pulses with a duration of nanoseconds, where high voltage is equal to or greater than 1 kV and nanosecond is equal to or less than 100 ns.

2. The ignition system of claim 1, further comprising: at least a first ignitor located at least partially inside the combustion chamber of the gas turbine engine and operable to create the non-equilibrated transient discharge inside the combustion chamber of the gas turbine engine; and at least a first cable that electrically couples the first exciter drive circuit with the first ignitor.

3. The ignition system of claim 2, wherein the first cable and the first ignitor are connected to the first exciter drive circuit and are a legacy cable and legacy igniter that were installed in the gas turbine engine prior to an installation of the first exciter drive circuit and the first exciter drive circuit is a retrofit to a legacy gas turbine engine apparatus.

4. The ignition system of claim 1, further comprising: a DC-DC power converter; a rapid capacitor charger electrically coupled to the DC-DC power converter, and wherein the rapid capacitor charger is electrically coupled provide power to the first exciter drive circuit.

5. The ignition system according to any one of claims 1 through 4, further comprising: a diagnostic system that monitors a system operation and health of one or more components of the ignition system.

6. The ignition system according to claim 5 wherein the diagnostic system checks a functionality of one or more components of the ignition system.

7. The ignition system according to claim 5 wherein the diagnostic system verifies an operational condition of the first igniter by checking for an abnormal open circuit condition or an abnormal short circuit condition.

8. The ignition system of claim 1, wherein the first exciter drive circuit is installed on an aircraft and the gas turbine engine is part of the aircraft.

9. The ignition system of claim 8, wherein the ignition system is communicatively coupled to a full authority digital engine or electronics control (FADEC) system of the aircraft.

10. The ignition system of claim 9, further comprising: a relay coupled to be controlled by the FADEC and operable to selectively provide power to a first ignitor located at least partially in a combustion chamber of the gas turbine engine.

11. The ignition system of claim 8, wherein the ignition system is responsive to detection of an occurrence of a flame out condition in the gas turbine engine.

12. The ignition system of claim 8, wherein the ignition system is responsive to detection of an occurrence of an engine start-up signal.

13. The ignition system of claim 8, wherein the ignition system is responsive to detection of an occurrence of a flooded start event.

14. The ignition system of claim 1, further comprising: at least a second exciter drive circuit operable to produce a plurality of high voltage electrical pulses with a duration of nanoseconds, where high voltage is equal to or greater than 1 kV and nanosecond is equal to or less than 100 ns;at least a second ignitor located at least partially inside the combustion chamber of the gas turbine engine and operable to create the non-equilibrated transient discharge inside the combustion chamber of the gas turbine engine; and at least a second cable that electrically couples the second exciter drive circuit with the second ignitor.

15. A method for improving ignition and relight in a gas turbine engine using an advanced ignition system, comprising: producing, by at least a first exciter drive circuit, a plurality of high voltage electrical pulses with a duration of nanoseconds, where high voltage is greater than 1 kV and nanosecond is less than 100 ns; electrically coupling, via a cable, the plurality of high voltage electrical pulses with the duration of nanoseconds to an ignitor located in a combustion chamber of a gas turbine engine; and generating, by the ignitor, a plurality of non-equilibrated discharges in the combustion chamber of the gas turbine engine.

16. The method of claim 15 wherein the producing the plurality of high voltage electrical pulses with the duration of nanoseconds is in response to the gas turbine engine being in an ON state.

17. The method of claim 15 wherein the producing the plurality of high voltage electrical pulses with the duration of nanoseconds is in response to the gas turbine engine an engine start signal.

18. The method of claim 15 wherein the producing the plurality of high voltage electrical pulses with the duration of nanoseconds is in response to a detection of an occurrence of a flame out condition.

19. The method of claim 15, further comprising: producing a DC supply voltage via a DC-DC power converter; charging a rapid capacitor charger electrically coupled to the DC-DC power converter;supplying power from the rapid capacitor charger to the first exciter drive circuit.

20. The method according to any one of claims 15 through 19, further comprising: monitoring, by a diagnostic system, an ignition system operation and health of one or more components of the ignition system.

21. The method according to claim 20 wherein monitoring the ignition system operation and health of one or more components of the ignition system includes checking a functionality of one or more components of the ignition system.

22. The method according to claim 20 wherein monitoring the ignition system operation and health of one or more components of the ignition system includes verifying an operational condition of at least a first igniter by checking for an abnormal open circuit condition or an abnormal short circuit condition.

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