Plasma Ignition and Combustion Assist System for Gas Turbine Engines

Abstract

An ignition and combustion support system and method comprising a plasma igniter and an electronic driver unit for use in gas turbine engines operating under low air density, reduced voltage conditions, and overall pressure ratios of 3:1 to 7:1. The plasma igniter has an internal chamber housing a centrally located and electrically insulated electrode attached to an electrical lead, a driver unit, and an AC or DC power source. The electrode features a corner located near an exit end of the igniter, and the plasma arc ignites the fuel-air mixture to create a flame that extends into a primary combustion zone of a combustor of the gas turbine. The driver unit is comprised of low-cost microsecond voltage wave periods or energy-efficient nanosecond pulses. The method employs the plasma igniter and electronic driver unit described herein separately or together with other components.

Description

Cross - Reference to Related Applications

[0001]

[0001] This application claims the benefit and priority of U.S. Provisional Application No. 63 / 153,022, filed on February 24, 2021, which was filed under all applicable provisions of Title 35 of the United States Code, including but not limited to Sections 120, 121, and 365(c), and is hereby incorporated by reference in its entirety into this application.

Technical Field

[0002]

[0006] The present invention relates to an ignition system for a turbine engine. More specifically, the present invention is a plasma ignition system having an electronic driver unit and one or more igniter components for use in various gas turbine engine applications, particularly in small turbojets and small high - speed turbogenerators having a relatively low pressure ratio of 3:1 to 7:1 overall.

Background Art

[0003]

[0007] All combustion engines have an air - fuel mixture that is ignited inside a combustor, and the hot air generated within the combustor is then used to rotate blades such as those in a turbine, piston, etc. Current ignition systems, such as spark igniters, rely on stoichiometry, gas pressure, the timing of the generated spark, and the applied voltage, which are multiple factors for combustion to occur. To create a sufficiently large spark, everything must be carefully calculated and calibrated to maximize performance and reliability.

[0004]

[0008] One problem with current ignition systems is that they are generally not suitable for small, lightweight engines, defined as engines having a diameter of less than 16 inches and a weight of less than 25 lbm, such as those used in lightweight drones, small missiles, air jamming devices, etc., because the cost, size (exciter electronics larger than 3-inch cube), and weight (heavier than 1.0 lbm) of current ignition systems make them inappropriate. For smaller applications such as drones, ideally, lighter and lower power components are required, and thus, a simple, lightweight ignition system with re-ignition / restart capabilities and flexibility according to the needs of a particular application is preferred.

[0005]

[0009] The need for improved operability of combustion systems (stability over a wider range of fuel / air mixtures at higher flame stretch rates and shorter residence times), and the limitations of prior art ignition systems, have led to strong interest in research using plasma igniters and appropriate applications of this technology, including use in internal combustion engines and dual fuel engines. The performance of current ignition systems is insufficient for small gas turbines, such as those used in drones and those operating under low pressure ratios and low combustor inlet temperatures. The cost and limited performance of conventional spark ignition systems and pyrotechnic flare igniters have led to a need for better systems to achieve ignition-off, including re-ignition using low-cost components.

[0006]

[0010] What is needed is a plasma ignition and combustion assist system comprising a plasma igniter and an electronic drive unit that can be used in a small gas turbine engine, and a method of using a plasma igniter system having a function to select between a more energy-efficient application and a more cost-effective application. Also needed is a plasma igniter that generates a continuous electric arc. Also needed is an ignition system that can operate at a lower voltage level than a conventional spark system but can deliver a higher energy output to a combustor. Also needed is a plasma igniter that extends a plasma arc into a primary combustion area of a combustor to improve fuel combustion efficiency. Also needed is an ignition system having multiple re-ignition capabilities.

Summary of the Invention

[0007]

[0011] A plasma ignition and combustion assist system and method using a plasma igniter and an electronic driver unit with a gas turbine engine operating under low temperature, low pressure ratio, and other conditions inappropriate for a conventional spark system. The plasma igniter and the electronic driver unit are lightweight and suitable for use in drones and other applications requiring multiple re-ignition capabilities, as well as in low-cost and high-efficiency options. The plasma igniter and the electronic driver unit in the method can be used together with or separately from other igniters and driver units.

[0008]

[0012] In a first aspect of the plasma ignition system, the plasma igniter is composed of a substantially cylindrical igniter body having a lead end and an outlet end and an inner wall defining a chamber between the ends. An electrode having a proximal end and at least one of a conical distal end and a cylindrical distal end is housed centrally inside the chamber so as to be electrically insulated from the inner wall, forming a substantially annular air gap in the chamber around the electrode. The igniter body is electrically grounded to the combustor or directly grounded to the igniter driver electronics via an insulating wire. The diameter of the electrode is about 0.125 to 2.0 inches. The electrode distal end is arranged towards the outlet end of the igniter body, At most 0.15 inches of the coil At least one corner having a fillet radius is further formed. In some embodiments, the corner is configured as a protrusion. The arc gap from the corner to the inner wall of the igniter body is in the range from the minimum or shortest distance from the corner to the inner wall to the minimum or shortest distance measured to the inner wall at the outlet end. In some embodiments, the arc gap is about 0.125 inches to about 0.75 inches, and in other embodiments, the arc gap is about 0.04 inches to 0.5 inches. The electrical lead connects the electrode to the driver unit and the power supply. The air supply through hole in the igniter body allows air to flow into the air gap and exit from the outlet end, pushing the plasma arc generated in the arc gap into the primary combustion region of the combustor of the gas turbine engine. In some embodiments, the air supply through hole is sized and shaped to assist an air injection velocity in the range of about 50 - 300 ft / sec.

[0009]

[0013] In another aspect of the plasma igniter, at least one of a fuel supply port, which can be a simple orifice, and a fuel atomizing injector integrated with the fuel supply port and the igniter body is included. In some embodiments, the fuel supply port is sized and shaped to control at least one of a fuel velocity of an amount of fuel entering an arc gap in the range of about 5 - 300 ft / sec and an inlet pressure in the range of 2.5 psia - 100 psia. In other embodiments, the amount of fuel entering the annular arc gap enters as fuel droplets having an average diameter greater than 80 microns.

[0010]

[0014] In yet another aspect of the plasma igniter, an air supply through - hole is disposed between the insulator and the outlet end of the igniter body, whereby an air flow entering the air gap through the air supply through - hole pushes the arc generated within the igniter body into the primary combustion region of the combustor.

[0011]

[0015] In yet another aspect of the plasma igniter, the igniter body is selected from a group of igniter bodies including an igniter body of an extended length and a truncated igniter body.

[0012]

[0016] In another aspect of the plasma igniter system, the driver unit includes an input power controller, a voltage oscillator that operates with the input power controller, a transformer that operates with the voltage oscillator and the input power controller, an on - off switch that operates with the input power controller, and a power supply that provides at least one of an AC input and a DC input to the driver unit. The driver unit supplies voltage and current outputs to the electrodes and is grounded to the engine or the combustor. The input power is regulated, filtered, and modulated by the input power controller. The voltage oscillator creates an electrical output waveform at a desired frequency and level. The transformer converts the electrical output waveform generated by the voltage oscillator and generates a voltage level and a rate of voltage change sufficient to create an electrical arc. connected and a voltage oscillator, a transformer that operates with the voltage oscillator and the input power controller, connected and an on - off switch that operates with the input power controller, a power supply that provides at least one of an AC input and a DC input to the driver unit. connected The driver unit supplies voltage and current outputs to the electrodes and is grounded to the engine or the combustor. The input power is regulated, filtered, and modulated by the input power controller. The voltage oscillator creates an electrical output waveform at a desired frequency and level. The transformer converts the electrical output waveform generated by the voltage oscillator and generates a voltage level and a rate of voltage change sufficient to create an electrical arc.

[0013]

[0017] In yet another aspect of the driver unit, the voltage and current supplied to the electrodes are transient, and the voltage wave period is measured at least in one of the nanosecond pulses and microsecond pulses of the repetition period.

[0014]

[0018] In yet another aspect of the driver unit, the oscillating voltage output level at the electrodes ranges from about 250 Vrms to 7000 Vrms.

[0015]

[0019] In yet another aspect of the driver unit, a DC power supply having a voltage level of 10 Vdc to 120 Vdc supplies current to a circuit that generates a variable or constant frequency voltage wave of about 10 kHz to 10000 kHz.

[0016]

[0020] In yet another aspect of the driver unit, the input power controller is at least one of a passive circuit having a single state for input and output, and a voltage and current regulation system.

[0017]

[0021] In yet another aspect of the driver unit, a voltage level increase of 100 to 1000 times the input voltage through a voltage transformer is generated by either an induction electric coil or a set of energy storage capacitors to achieve an oscillating voltage increase.

[0018]

[0022] In a method of using a plasma igniter and a plasma igniter system having an electronic driver unit, the method includes determining at least one of a desired size and weight of the plasma igniter based on engine size, space availability, or kinetic applications; determining a desired operating life of the igniter electrodes; determining a desired power efficiency of the plasma igniter system; maintaining power compatibility of the plasma igniter system with the engine's power source; determining an engine pressure ratio; and determining whether the plasma igniter and driver unit are operable only at the first ignition and start of the engine or at multiple times after the first ignition and start of the engine.

[0019]

[0023] In another aspect of the method, the step of determining the engine pressure ratio includes identifying an engine having a low pressure ratio of 3:1 to 7:1, a small volumetric flow rate of less than 15 m 3 / sec and operating at a temperature of less than 400 degrees Fahrenheit, and after the step of determining the engine pressure ratio, selecting an electronic driver unit having a voltage output suitable for at least one of the respective pressure ratios and volumetric flow rates.

[0020]

[0024] In yet another aspect of the method, the step of selecting the electronic driver unit further includes sizing an arc gap according to increased voltage requirements.

[0021]

[0025] In an even further aspect of the method, the method is used with a turbojet having a thrust in the range of about 15 to 600 lbf.

[0022]

[0026] In yet another aspect of the method, the method is used with a turbogenerator having a power output of 5 to 100 kW.

[0023]

[0027] In yet another aspect of the method, the method further comprises operating the plasma igniter to sustain combustion or increase combustion efficiency when the mixing and reaction times are short, or when the fuel-air mixture in the combustor combustion zone is outside the range of conventional lean-rich flammability limits, and the step is performed after a step of determining whether the plasma ignition system is operable only at the first ignition and start-up of the engine or at multiple points in time after the first ignition and start-up.

[0024]

[0028] The features and advantages of the present invention will become apparent from consideration of the following detailed description presented in connection with the accompanying drawings.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

DETAILED DESCRIPTION OF THE INVENTION

[0026]

[0043] A plasma ignition and combustion assist system for use in a gas turbine engine is composed of a plasma igniter 100 in two embodiments shown in FIGS. 1 - 10 and an electronic driver unit or drive unit or driver unit 50 in two embodiments shown in FIGS. 11 - 13.

[0027]

[0044] The plasma igniter 100 is composed of an igniter body 10 defined by an outer wall 10c and a pair of opposing open ends. The igniter body 10 is grounded to either the engine of the gas turbine engine or the combustor 40. The igniter body 10 has an inner wall 28 that defines a generally cylindrical inner chamber, and the inner chamber has a lead end 10b surrounded by a holding cap 12 disposed on the lead end 10b and an opposing outlet end 10a. The holding cap 12 is formed with a hole sized and shaped to receive an electrical lead 20.

[0028]

[0045] The generally cylindrical electrode 24 having a proximal end 24b and a distal end 24a is connected at the proximal end 24b by a solder or brazed or crimped joint 22 to the electrode end 20b of the electrical lead 20, and the joined electrode - electrical lead is disposed inside the chamber through a hole in the retaining cap 12. It should be noted that the crimped joint 22 includes any other suitable connection, and the use of the term "crimped joint" is not meant to be limiting. The electrode 24 and the electrical lead 20 are disposed centrally within the chamber and are electrically insulated from the inner wall 28 of the igniter body 10 by a certain amount of potting or solder amount typically sandwiched between the lead wire retainer or retainer 18 and the crimped joint 22. The position of the electrical lead 20 is fixed by the retainer 18 around the perimeter of the electrical lead 20 and is attached inside the retaining cap 12 at one end. Thus, a generally annular air gap 30 is created between the inner wall 28 and the electrode 24 disposed centrally within the chamber. One or more through - holes or air supply holes 32 are formed in the igniter body wall leading from the outside of the igniter body 10 into the air gap 30. A certain amount of air generated by an air compressor is supplied into the air gap 30 through the air supply holes 32. In some embodiments, alternative or additional fuel supply ports 34 are also formed within the igniter body 10 and lead into the air gap 30. The air supply holes 32 and the fuel supply ports 34 are typically formed near the proximal end 24b of the electrode 24, but in fact, they may be disposed anywhere between the outlet end 10a of the igniter body 10 and the insulator 16 inside the chamber. The fuel supply port 34 may be configured as a simple orifice or may include a fuel atomizing injector integral with the igniter body 10 along with the port 34. When the fuel supply port 34 is present, a fuel supply line 36 for supplying fuel into the air gap 30 is fixed to the fuel supply port 34. The power end 20a of the electrical lead is attached to the High voltage output 62 for supplying power to the igniter 100.

[0029]

[0046] FIG. 1 shows an embodiment 100a of the truncated body of an igniter 100 in which the distal end 24a extends into the primary combustion region 42 of the combustor 40 beyond the outlet end 10a. The distal end 24a has a generally conical shape with the tip or apex 24c disposed beyond the outlet end 10a of the igniter body 10. At the base of the distal end 24a, a corner 24d having a radius of At most 0.15 inches is further formed, and a smaller radius is preferred. By including the corner 24d, the distance between the electrode 24 and the inner wall 28 is reduced, thus causing a narrowing of the air gap 30 at the outlet end 10a. The corner 24d may actually have a uniform size and shape around the circumference of the distal end 24a as shown in FIG. 1, or may be formed as a regular series of protrusions around the circumference of the base of the distal end 24a as shown in FIGS. 6-8.

[0030]

[0047] The arc gap 26, shown as a wavy line in the figure, is typically the shortest distance measured from the electrode 24 to the inner wall 28, as most clearly shown in FIG. 1 using the truncated body igniter 100a, and can actually be the same measurement as the air gap 30. The formation of the plasma arc can occur anywhere along the length from the electrode 24 to the inner wall 28, but by including the corner 24d, the distance of the air gap 30 is shortened, and the formation of the plasma arc at the shortest distance of the air gap 30 to the inner wall 28 at the corner 24d is promoted. Thus, in the drawings, the arc gap 26, shown as a wavy line in the figure, also substantially indicates the plasma arc. This is effective for the ignition of the discharge and to ensure that the discharge is placed proximal to at least one of the flame retention or combustor recirculation zone 44. In all the figures, the arc gap 26 is shown as originating from the corner 24d to the inner wall 28 at the exit end 10a of the igniter body 10, and in FIG. 2, this distance is not the shortest distance between the corner 24d and the inner wall 28. FIG. 2 shows the location of the arc gap 26 when there is an air flow within the air gap 30, and the air flow extends the distance of the arc gap 26 to the inner wall 28 at the exit end 10a, and thus effectively moves the plasma arc formation towards the exit end 10a. When air is not actively supplied through the air gap 30, the arc gap 26 in FIG. 2 can actually be the shortest distance from the corner 24d to the inner wall 28 as shown in FIG. 1. Thus, the distance of the arc gap 26 can vary depending on whether there is an air flow within the air gap 30 and whether it exits the exit end 10a. The inventors note that in other embodiments, instead of configuring the corner 24d as a protrusion to promote arc discharge at the location of the corner 24d, the inner wall 28 can instead be designed to have a flange or other protrusion that constricts the exit end 10a of the igniter body 10, having the same end result of promoting plasma arc formation at the constriction point of the igniter body 10.The presence of the corner portion 24d on the electrode 24 at the outlet end 10a and the air flow towards the outlet end 10a optimize the plasma arc formation at the outlet end 10a such that the resulting flame 70 is positioned in the primary combustion region 42 of the combustor 40. When the electrode 24 receives current from the driver unit 50, the current jumps across the space between the electrode 24 and the inner wall 28 in the arc gap 26, and if there is an air flow in the air gap 30, the flame 70 extends outwardly from the arc gap 26 across the outlet end 10a and into the primary combustion region 42.

[0031]

[0048] The truncated body igniter 100a also 34 and the fuel line 36 may have or may not be supplied with fuel. In embodiments having the fuel port 34 and the fuel line 36 the fuel - air mixture from the fuel port 34 and the air supply hole 32 enters the air gap 30 around the electrode 24 and swirls through the air gap 30. The plasma arc formed in the arc gap 26 ignites the fuel, creates the flame 70, and the moving air pushes the arc and the flame 70 caused by the combustion of the fuel through the outlet end 10a of the igniter 100a and into the combustor 40. The igniter body 10 and the centrally disposed electrode 24 are heated by the passage of current through both components, and this heating facilitates the process of evaporation and dispersion of the fuel injected into the air gap 30.

[0032]

[0049] On the outer wall 10c of the truncated body igniter 100a, a wide - body mounting base 10e is further formed, which has a larger diameter compared to the outer wall 10c and is sized and shaped to enable the easier fixing of the igniter body 10 to the combustor 40.

[0033]

[0050] FIG. 2 shows an embodiment of an extended igniter body 100b in which the distal end 24a and the apex 24c of the electrode 24 do not extend beyond the outlet end 10a of the igniter body 10. In FIG. 2, the corner 24d is at the base of the conical distal end 24a, but the corner 24d is formed without any protrusions, and the cylindrical electrode 24 tapers towards the apex 24c at the corner 24d instead. The air gap 30 has a uniform distance from the inner wall 28 to the body of the electrode 24. The arc gap 26 is shown from the corner 24d to the inner wall 28 at the outlet end 10a of the igniter body 10, and is a longer distance compared to the arc gap 26 in the embodiment of the frustum body igniter 100a of FIG. 1. As described above, when the igniter 100b is in use, the air injected into the air gap 30 through the air supply hole 32 flows out from the outlet end 10a of the igniter body 10 and extends the plasma arc to the distance of the arc gap 26, and thus to what is shown in FIG. 2 in the state of the arc gap 26 and the plasma arc indicated by the wavy line.

[0034]

[0051] Compared to the frustum body igniter 100a, typically, the extended body igniter 100b includes a fuel port 34 and a fuel line 36 together with the air supply hole 32.

[0035]

[0052] The plasma igniters 100 and the embodiments 100a, 100b of the plasma igniter 100 are supplied with voltage and current by an electronic driver unit 50, which is shown in FIGS. 12 and 13 as a schematic diagram of two exemplary embodiments of the driver unit 50 and its component blocks. The driver unit 50 supplies power to the plasma igniters 100, 100a, 100b. The driver unit 50 assists in generating a sufficiently high electric field so that an electric arc is generated between the electrode 24 and the inner wall 28 of the igniter torch body 10. The arc gap 26 and the geometry of the electrodes are design parameters that affect the required voltage level. The larger the arc gap 26, the higher the voltage requirement. As shown in FIG. 11, since the frequency of the voltage wave and the resulting arc are effectively continuous, the timing for triggering the plasma arc is not an important requirement in these systems. The time of the wave, measured as 1 / frequency, is shorter than the residence time of an effective combustor and is typically 0.5 to 30 msec. The power and voltage depend on the ignition energy required for the combustor 40. Typical levels are in the range of 100 to 500 watts (RMS power input to the system). The energy delivered in the arc gap 26 is typically 5 to 10 times lower than the power input. However, the inventors note that these parameters can vary without limitation, and those skilled in the art will recognize that variations in these parameters outside of these typical levels do not negate the novelty or usefulness of the present invention.

[0036]

[0053] FIG. 12 shows a first embodiment of the driver unit 50 in the state of a schematic diagram of the plasma ignition driver unit 50 by component blocks. Input power 54can be either AC or DC. Since most aircraft systems use 28Vdc power, this is the preferred power input. The voltage output 62 depends on the output frequency of the driver unit 50, which can range from 5kHz to 100MHz. The voltage output level ranges from 250Vrms to 7000Vrms. The peak voltage level can be significantly high. As shown in FIG. 12, the driver unit 50 has an input power 54 controller 56 for adjusting, filtering, and modulating the input power, and a voltage oscillator 64 for creating a voltage waveform of the correct frequency and level using a transformer to generate the high voltage required for arc discharge in the igniter 100. The driver unit 50 also has a triggering input 52 configured as the simplest form of an on / off signal, and connections to a safety fuse and EMI shield to reduce electromagnetic noise from the driver unit 50.

[0037]

[0054] FIG. 13 shows a second embodiment of the driver unit 50. In this system, a simple zero voltage switching unit 58 is used together with a step-up transformer or flyback transformer 60. This circuit is common and is used in applications where different DC voltage levels are required. The transformer 60 steps up the primary side voltage to a higher voltage required for plasma generation. This step-up ratio can be customized to optimize engine operating parameters and is controlled by the ratio of the primary winding to the secondary winding of the transformer, magnetic flux coupling, and induction effects. The circuit can be tuned to a specific frequency, and usually, a higher frequency is preferred for plasma ignition systems. Due to the simplicity and availability of low-cost components in the driver unit 50, this is a desirable means for plasma igniter power input. The input power controller 56 can be a complex voltage and current regulation system or a simple passive circuit that is a single state for input and output.

[0038]

[0055] The driver unit 50 supplies voltage and current to the plasma igniters 100, 100a, 100b such that there is a transient rate of voltage rise sufficient to create an electrical arc from the corner 24d of the electrode 24 to the inner wall 28 of the grounded igniter body 10. The two types of driver units 50 used in this system include a low-cost AC driver unit 50 having a microsecond voltage wave period and a high-cost and energy-efficient nanosecond pulsed driver unit 50. Any of the driver units 50 shown in FIGS. 12 and 13 can be configured to be low-cost (microsecond voltage wave) or have good energy efficiency (nanosecond pulse), but the high-cost and energy-efficient driver unit 50 requires relatively more expensive electronics with faster switching capabilities and may or may not require a physically larger unit. Thus, any of the igniters 100a, 100b can be driven by any of the electronic driver units 50. A single engine can have multiple igniters 100 and driver units 50, with at least one igniter 100 and one driver unit 50 per engine. The type of driver unit 50 used depends on the desired cost and use of the system. The AC driver unit 50 is low-cost and is more suitable for engine ignition where startup requires only a short period, typically less than 1 minute. The nanosecond pulsed driver unit 50 is more power-efficient. Any of the driver units 50 can be used for ignition, restart, and combustion sustainment, for improving efficiency, and for conditions where the mixing and reaction times are short or where the fuel-air mixture in the combustor combustion zone is outside the range of conventional lean-rich flammability limits. These systems, unlike the pyrotechnic or flare devices used in conventional military unmanned systems, allow for multiple engine starts and are desirable when it is desired to balance the cost of the system with improvements in the engine's operating range and fuel efficiency over a period exceeding 5 minutes.

[0039]

[0056] In short, both the low-cost and high-cost (good energy efficiency) designs are DC power supplies. The circuit that drives arc formation is the difference between these driver units. In the low-cost design, the arc is generated by an AC voltage switching circuit with a simple step-up transformer. In the high-cost design, voltage boosting is performed using high-frequency switching components with different voltage amplifiers (solid-state devices). The high-cost design is used for the implementation of higher efficiency and better arc characteristics, such as faster and easier arc discharge with more active ion generation.

[0040]

[0057] In the case of the driver unit 50 having a DC power supply with a voltage level of 10Vdc to 120Vdc, the driver unit 50 supplies current to a circuit that generates a variable or constant frequency voltage wave of about 10kHz to 10000kHz. The input power controller 56 can be configured as a passive circuit having a single state for input and output, or as a voltage and current regulation system. In the case of the driver unit 50 of FIG. 12, a voltage level increase of 100 to 1000 times the input voltage via the voltage transformer 64 is generated by an inductive coil or alternatively by a set of energy storage capacitors to achieve an oscillating voltage increase.

[0041]

[0058] The plasma ignition and combustion assist system is applicable to a wide range of gas turbines. The full range includes both land-based power systems and aircraft engines. The system described herein is expected to be less costly than conventional spark ignition systems. In 2021, the low-cost system is less than about $500, and the high-cost system is over $2,500. In comparison, the cost of a conventional spark ignition system in 2021 is $4,000 - $7,000. The plasma igniters 100, 100a, 100b, and driver unit 50 of the plasma assist system described herein generate continuous or pulsed arcs without the need for expensive and complex triggering electronics, and the voltage required to sustain the plasma arc is several times lower than that of a spark ignition system, thereby reducing the need for complex insulation leads and connectors.

[0042]

[0059] Plasma assisted ignition is most applicable to small or compact gas turbines that must operate with short combustor dwell times. These engines are characterized by a low pressure ratio with a low combustor inlet pressure (pressure levels less than about 125 psia), and a temperature less than 400°F, and an overall dwell time (volume / volume flow rate) of less than about 15 msec. Larger engines with higher pressure ratios having an overall pressure ratio greater than 7:1 may benefit from the plasma igniters 100 and driver unit 50 described herein, but typically have a single spark system with a higher voltage. The plasma assist system based on the plasma igniters 100 and driver unit 50 described herein can primarily benefit large-scale land-based power systems by operating continuously during operation, thereby improving lean stability and enabling stable operation under conditions consistent with lower nitrogen oxide (NOx) and carbon monoxide (CO) emissions.

[0043]

[0060] Typical engines for which the plasma ignition and combustion assist system is useful include the following. [1] Small turbojets with a thrust range of 15 lbf to 600 lbf. These are generally used in flight systems (such as small missiles, surveillance aircraft / drones, airborne jamming devices, and commercial drones). These engines use a variety of heavy distillate fuels, including Jet-A, Diesel, and JP-10. Current engine models suitable for use with a plasma assist system include the ATI070, as well as all derivatives of the B300STG turbojet and the ATI200, a 200 lbf thrust turbojet. In these engines, the plasma ignition and combustion assist system is used for ignition and for extending the engine start / operation envelope at low engine speeds and / or output levels at high altitudes. The plasma ignition and combustion assist system enables multiple starts and / or restarts during flight. And [2] Small high-speed turbogenerators with a power output range of 5 to 100 kW. These generators are most commonly airborne power generation systems used in small unmanned civilian and military aircraft where high output / weight is required. Other suitable applications for the plasma ignition and combustion assist system include those where high output is required in a small lightweight package, including small ground power units. Current engine models suitable for use with a plasma assist system include the ATI010e, which are derivatives of the B140TG and SP10e, both 10 kWe turbogenerators, the ATI35e, which is a derivative of the B300STG 35 kWe turbogenerator, and the SP75e, a 75 kWe turbogenerator. In these engines, the plasma ignition and combustion assist system is used for ignition and starting. The systems within this application enable multiple starts and / or restarts during flight.

[0044]

[0061] Engines suitable for use with a plasma ignition and combustion assist system have a relatively low overall pressure ratio of 3:1 to 7:1, and plasma arc discharge in air is relatively easy due to the low air density and the reduction in voltage required for electrical arc generation.

[0045]

[0062] It should be understood that the above configuration is merely an example of the application of the principles of the present invention. Without departing from the scope of the present invention, numerous modifications and alternative configurations can be devised by those skilled in the art.

Description of Reference Numerals

[0046]

[0042] The following is a list of reference labels used in the drawings to label the components of different embodiments of the present invention, and the names of the components shown. 100 Plasma igniter 100a Truncated body igniter 100b Extended body igniter 10 Igniter body 10a Outlet end 10b Lead end 10c Outer wall 12 Holding cap 10e Mounting base 16 Insulator 18 Lead wire holder 20 Electrical lead 20a Power end of the electrical lead 20b Electrode end of the electrical lead 22 Crimped or brazed joint or solder 24 Electrode 24a Distal end of the electrode 24b Proximal end of the electrode 24c Tip or apex of the electrode 24d Corner 26 Arc gap 28 Inner wall of the chamber of the igniter body 30 Air gap 32 Air supply hole 34 Fuel supply hole 36 Fuel supply line 40 Combustor 42 Primary combustion region of the combustor 44 Combustor recirculation zone 50 Electronic drive unit or electronic driver unit or driver unit or drive unit or driver or unit 52 On / Off trigger 54 Input power (AC or DC) 56 Input power controller 58 Zero voltage switching block 60 Flyback transformer 62 High voltage output 64 Voltage oscillator and transformer block 70 Flame

Claims

1. A plasma igniter for use with an electronic driver unit and a combustor of a gas turbine engine, the plasma igniter being disposed inside the combustor, the combustor having a primary combustion region, the plasma igniter comprising an igniter body, an electrode, an arc gap, a substantially annular air gap, an electrical lead, and an air supply through hole, the igniter body having a lead end and an opposite outlet end, and an inner wall defining a chamber between the lead end and the outlet end, the outlet end of the igniter body being an open end of the chamber disposed near the primary combustion region of the combustor, the igniter body being either electrically grounded to the combustor or directly grounded to the electronic driver unit by an insulating wire, the electrode having a proximal end and at least one of a conical distal end and a cylindrical distal end received inside the chamber at the center of the igniter body and electrically insulated from the inner wall of the igniter body, the distal end being further configured as a terminal disposed toward the outlet end of the igniter body, at least one corner portion having a corner radius of up to 0.15 inches being further formed at the distal end, the arc gap having a predetermined distance measured from the corner portion to the inner wall of the igniter body, the arc gap being a distance selected from a group of distances including a minimum distance from the corner portion of the electrode to the inner wall of the igniter body and a minimum distance from the corner portion to the inner wall at the outlet end of the igniter body, the air gap being between the electrode and the inner wall, the electrical lead having an electrode end and a power end, the electrode end being fixed inside the electrode at the proximal end, the power end being connected to the electronic driver unit, whereby current is supplied by the electronic driver unit to the electrical lead and the electrode, A plasma igniter, wherein the air supply through-hole is formed in the air gap through the igniter body, so that air flows into the air supply through-hole, into the arc gap, and out of the outlet end of the igniter body.

2. The plasma igniter according to claim 1, further comprising a fuel supply port formed in the igniter body, the fuel supply port further comprising an inlet attached to a fuel supply line and an opposite outlet terminating within the air gap, wherein fuel enters the air gap through the fuel supply line and the fuel supply port.

3. Further comprising at least one protrusion on the distal end, wherein the corner is the outermost surface of the protrusion, The plasma igniter according to claim 1, wherein a maximum circumferential measurement of the distal end of the electrode includes the protrusion.

4. The plasma igniter according to claim 2, wherein the air supply through-hole is disposed between an insulator and the outlet end of the igniter body, so that an air flow entering the air gap through the air supply through-hole pushes an arc generated within the igniter body into the primary combustion region of the combustor.

5. The plasma igniter according to claim 1, wherein the igniter body is electrically grounded to the combustor, the combustor is grounded to the gas turbine engine, and the gas turbine engine is grounded to the electronic driver unit.

6. The plasma igniter according to claim 1, wherein the arc gap is from about 0.125 inches to about 0.75 inches.

7. The arc gap is from about 0.04 inches to 0.5 inches, The plasma igniter according to claim 1, wherein a diameter of the electrode is from about 0.125 inches to 2.0 inches.

8. The plasma igniter according to claim 1, wherein the igniter body is at least substantially a cylindrical metal body.

9. The plasma igniter according to claim 2, wherein the igniter body and the electrode are heated by the current, whereby heating promotes evaporation and dispersion of fuel injected into the air gap.

10. The fuel supply port of the plasma igniter according to claim 2 is sized and shaped to control at least one of a fuel velocity in the range of about 5 to 300 ft / sec and an inlet pressure in the range of 2.5 psia to 100 psia of fuel entering the arc gap.

11. The plasma igniter according to claim 9, wherein fuel entering the annular arc gap enters as fuel droplets having an average diameter greater than 80 microns.

12. The plasma igniter according to claim 1, wherein the air supply through-hole is sized and shaped to assist an air injection velocity in the range of about 50 to 300 ft / sec.

13. The plasma igniter according to claim 1, wherein the igniter body is selected from a group of igniter bodies including an igniter body of an extended length and a truncated igniter body.

14. An ignition system for a gas turbine engine comprising an electronic driver unit and an igniter, wherein the electronic driver unit is for use with the igniter having an igniter body with an inner wall, the inner wall accommodating an electrode centrally disposed in a spaced-apart relationship with the inner wall, and the electronic driver unit being in electrical communication with the electrode, the electronic driver unit being, an input power controller, a voltage oscillator in communication with the input power controller, a transformer in communication with the voltage oscillator and the input power controller, An on-off switch communicating with the input power controller, A power supply providing at least one of an AC input and a DC input to the electronic driver unit and comprising The electronic driver unit supplies voltage and current outputs to the electrode, The electronic driver unit is grounded to a gas turbine engine or a combustor, The input power is adjusted, filtered, and modulated by the input power controller, The voltage oscillator creates an electrical output waveform at a desired frequency and level, The transformer converts the electrical output waveform generated by the voltage oscillator and generates a voltage level and rate of voltage change sufficient to create an electric arc, The igniter is a plasma igniter driven by the electronic driver unit, The plasma igniter is an electrode having a lead end and an opposite conical distal end, the opposite conical distal end having a vertex at the tip of the conical distal end and a corner formed at the base of the conical distal end, the corner having a corner radius of up to 0.15 inches, An igniter body having an inner wall defining a chamber having an outlet end and a lead end, the chamber centrally accommodating the electrode in a spaced relationship with the inner wall such that the corner is disposed at the outlet end, and an air gap being formed between the electrode and the inner wall, An arc gap having at least one of the minimum distance from the corner to the inner wall and the minimum distance from the corner to the inner wall at the outlet end, An electrical lead attached to the lead end of the electrode, the electronic driver unit supplying power to the electrical lead and the electrode, An air supply through-hole formed in the igniter body and in the air gap, wherein an air flow flowing into the air gap through the air supply through-hole flows into the arc gap and flows out from the outlet end of the igniter body, the air supply through-hole A spark ignition system comprising **Claim 15** The voltage and current supplied to the electrode are transient, The spark ignition system according to claim 14, wherein a voltage wave period is measured in at least one of a nanosecond pulse and a microsecond pulse of a repetition period. **Claim 16** The spark ignition system according to claim 14, wherein the oscillating voltage output level at the electrode is in the range of about 250 Vrms to 7000 Vrms. **Claim 17** A DC power supply having a voltage level of 10 Vdc to 120 Vdc to the electronic driver unit supplies current to a circuit that generates a variable or constant frequency voltage wave of about 10 kHz to 10000 kHz. The spark ignition system according to claim 14. **Claim 18** The spark ignition system according to claim 14, wherein the input power controller is at least one of a passive circuit having a single state for input and output and a voltage and current regulation system. **Claim 19** A voltage level increase of 100 to 1000 times the input voltage through a voltage transformer is generated by either an induction coil or a set of energy storage capacitors to achieve an oscillating voltage increase. The spark ignition system according to claim 14. **Claim 20** A method of using a plasma igniter together with an electronic driver unit, Determining at least one of a desired size and weight of the plasma igniter based on the size, space availability, or dynamic application of the gas turbine engine; Determining a desired operating life of the igniter electrode; Determining a desired power efficiency of a plasma igniter system; Maintaining power compatibility with a power source of the gas turbine engine of the plasma igniter system; Determining an engine pressure ratio, and the step of determining the engine pressure ratio includes identifying a gas turbine engine having a low pressure ratio of 3:1 to 7:1, a small volumetric flow rate of less than 15 m ３ / sec, and operating at a temperature of less than 400 degrees Fahrenheit; after the step of determining the engine pressure ratio, further comprising selecting an electronic driver unit having a voltage output suitable for at least one of the respective pressure ratios and the volumetric flow rate; determining whether the plasma igniter and the electronic driver unit are operable only at the first ignition and start of the gas turbine engine or at multiple times after the first ignition and start of the gas turbine engine; operating the plasma igniter to sustain combustion or increase combustion efficiency when the mixing and reaction times are short or when the fuel-air mixture in the combustor combustion zone is outside the range of conventional lean-rich flammability limits, the step of operating the plasma igniter being performed after the step of determining whether the plasma ignition system is operable only at the first ignition and start of the gas turbine engine or at multiple times after the first ignition and start.

21. The method of claim 20, wherein the step of selecting an electronic driver unit further includes sizing an arc gap according to increased voltage requirements.

22. The method of claim 20 for use with a turbojet having a thrust in the range of about 15 to 600 lbf.

23. The method according to claim 20, for use with a turbogenerator having an electric power output of 5 to 100 kW.

24. The method according to claim 20, for use with an electronic driver unit, wherein the electronic driver unit comprises an input power controller, a voltage oscillator in communication with the input power controller, a transformer in communication with the voltage oscillator and the input power controller, an on - off switch in communication with the input power controller, and a power source for providing at least one of an AC input and a DC input to the electronic driver unit and the electronic driver unit supplies voltage and current outputs to the electrode, the electronic driver unit is grounded to the gas turbine engine or to the combustor, the input power is adjusted, filtered, and modulated by the input power controller, the voltage oscillator creates an electrical output waveform at a desired frequency and level, the transformer converts the electrical output waveform generated by the voltage oscillator and generates a voltage level and a voltage rate of change such that an electric arc is generated within the arc gap.

25. The method according to claim 20, for use with a plasma igniter, wherein the plasma igniter comprises an igniter body, an electrode, an arc gap, a substantially annular air gap, an electrical lead, and an air supply through - hole, the igniter body has a lead end and an opposite outlet end and has an inner wall defining a chamber between the lead end and the outlet end, the outlet end of the igniter body is the open end of the chamber disposed near the primary combustion region of the combustor, and the igniter body is electrically grounded to the combustor. The electrode has a proximal end and at least one of a conical distal end and a cylindrical distal end that is received in the center of the interior of the chamber and electrically insulated from the inner wall of the igniter body. The distal end is further configured as a terminal disposed toward the outlet end of the igniter body. At least one corner is further formed at the distal end, having a corner radius of up to 0.15 inches. The arc gap is a predetermined size measured from the corner to the inner wall of the igniter body. The arc gap is a distance selected from the group of distances including the minimum distance from the corner of the electrode to the inner wall of the igniter body and the minimum distance from the corner to the inner wall at the outlet end of the igniter body. The air gap is between the electrode and the inner wall. The electrical lead has an electrode end and a power end. The electrode end is fixed inside the electrode at the proximal end, and the power end is connected to the electronic driver unit, whereby current is supplied by the electronic driver unit to the electrical lead and the electrode. The air supply through hole is formed through the igniter body and into the air gap, whereby air flows into the air supply through hole, into the arc gap, and out of the outlet end of the igniter body.

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