Dual-mesh glow-plug ignition module for injector-less start of micro turbojets

Abstract

TITLE: DUAL-MESH GLOW-PLUG IGNITION MODULE FOR INJECTOR-LESS START OF MICRO TURBOJETS ABSTRACT An injector-less hot-surface ignition device for micro / small turbojets comprises an igniter assembly (100) including a glow element (101), an ignition fuel supply line (102), stainless-steel mesh media (103; 201, 202), and an ignitor housing (104) forming a pre-chamber. Liquid fuel delivered via line (102) wets an outer mesh sleeve (202) and migrates by capillarity to an inner mesh sleeve (201) positioned adjacent a hottest section (203) of the glow element (101). Vaporized fuel ignites on the hot surface and issues as a pilot flame through an opening (204) oriented toward a combustor liner (402) within a combustion chamber outer casing (401). The device achieves reliable light-off at low flow and low supply pressure without a dedicated injector, reduces EMI by eliminating high-voltage exciters, and mitigates coking through controlled residence time. A start sequence includes steps (501–504): heater energization, pump initiation, capillary vaporization, and pilot flame discharge into the combustor. FIG.1 is selected. 20 Claims, 5 Drawing Sheets DATE: 22-August-2025 Keerthi J S PLACE: BANGALORE COUNSEL FOR THE APPLICANT-IN / PA-1729

Description

A) TECHNICAL FIELD

[0001] The present invention relates to ignition systems for gas-turbineengines and, more particularly, to compact, low-voltage hot-surface ignitiondevices that generate a pilot flame from liquid fuel within a pre-chambercoupled to a combustor liner. The invention is especially applicable to microand small turbojet engines, including UAV propulsion and other miniature gasturbineapplications, where injector-less, capillary-fed vaporization andreliable light-off at low fuel flows are required.B) BACKGROUND OF THE INVENTION

[0002] The subject matter disclosed herein generally pertains to ignitiontechnologies for gas-turbine engines. More particularly, the disclosureconcerns compact ignition devices intended for micro and small turbojetengines in which fuel delivery rates and available electrical power are limited,and where reliable light-off must be achieved without bulky high-voltagesystems or complex atomizing hardware.

[0003] Conventional aviation gas turbines frequently employ spark20based igniters driven by high-energy, high-voltage exciters. While effective inlarge engines, such systems can be disproportionate in size, mass, electricalload, and electromagnetic interference for micro-scale turbojets and unmannedaerial vehicle (UAV) applications. The packaging of an exciter, cabling, andshielding complicates installation in small airframes, and repetitive sparkingcan shorten electrode life and increase maintenance burden.

[0004] Torch or pre-chamber igniters are also known. Representativearrangements place an electrical heater or glow element and a dedicated fuelinjector inside a small combustion housing, producing a continuous pilot flamethat discharges into the primary combustor (e.g., U.S. Pat. No. 9,567,912; EP4 019 838 B1; EP 3 948 083 B1). Although these systems can improve lightoffrobustness, they typically rely on pressure-atomized or air-assistedinjectors, swirlers, and metering components that add cost, increase coking riskat low flow, and require fuel pressures that may be unavailable in micro-engineinstallations.

[0005] Hot-surface ignition using ceramic or metallic heaters is likewiseestablished. For example, high-temperature ceramic igniters have beenproposed for gas-turbine combustors to avoid high voltage discharge systems(e.g., U.S. Pat. No. 8,434,292). These devices can deliver reliable local heatinput but still require a suitable means of presenting liquid fuel in a controlledmanner to the hot surface, particularly during transient start conditions and atvery low fuel delivery rates.

[0006] Prior disclosures also describe the use of porous or capillarymedia in conjunction with a glow element to vaporize liquid fuel within acontained volume, thereby generating ignition products (e.g., U.S. Pat. No.3,232,055). Such arrangements evidence the general concept of positioning afuel-retentive body adjacent a heated element within an igniter housing.However, these teachings do not address the specific challenges of microturbojet integration, including through-liner packaging, pilot-flame dischargegeometry, and sustained operation at extremely low fuel flow rates typical ofminiature engines.

[0007] Separately, fuel vaporizer tubes and related combustor hardwarehave long been used to promote fuel evaporation and mixing within gas-turbinecombustors (e.g., U.S. Pat. No. 3,531,937; U.S. RE30,925). While thesecomponents handle liquid-fuel thermal conditioning, they are not, in and ofthemselves, ignition devices and generally depend on upstream atomization orhigher bulk flow to function effectively. Their adaptation to micro-scaleengines remains constrained by size, thermal inertia, and start-sequence controlrequirements.

[0008] In the micro- and miniature-turbojet field, various ignitionsolutions have been explored. Some model-scale engines describe glow-plugignition and micro-combustor arrangements (e.g., U.S. Pat. No. 5,782,079),and certain disclosures for micro turbojets combine a heating plug with anozzle within a small ignition chamber (e.g., CN 109441643 B). These systemsnevertheless tend to employ separate injectors or nozzles that can clog orpoorly atomize at low pressure, and they may demand tighter fuel-systemtolerances than are practical in small UAV platforms.

[0009] Mechanical integration of heaters or glow elements withcombustor liners has also been addressed (e.g., U.S. Pat. No. 11,392,112; U.S.Pat. No. 11,692,489), illustrating mounting interfaces that seal or bridge linerapertures. Such teachings are pertinent to serviceability and robustness but donot, by themselves, provide a passive, injector-less fuel metering andvaporization path suitable for consistent pilot flame generation at micro-enginestart conditions.

[0010] The foregoing approaches exhibit limitations when applied tosmall turbojets operating with fuel delivery on the order of tens of millilitersper minute and with minimal pump head. At these scales, injector-basedsystems can suffer from inadequate atomization, wall wetting, or carbondeposition; high-voltage spark systems can be electrically and mechanicallyburdensome; and unmetered fuel presentation to a hot surface can lead toinconsistent ignition or thermal runaway within a compact housing.

[0011] Accordingly, there is a need for an ignition device that (i)eliminates reliance on high-voltage exciters, (ii) avoids separate atomizinginjectors and associated swirl hardware, (iii) passively meters and transportsliquid fuel to a hot surface via capillary action over a controlled path length,and (iv) produces a stable pilot flame that discharges into the combustor linerwith repeatable geometry, all within a compact assembly amenable to linermountedinstallation and field service.

[0012] There is a further need for such a device to operate over a widerange of ambient conditions (including cold-soak starts and varying fuelviscosities), to be tolerant of low fuel pressures and low flow ratescharacteristic of micro-scale systems, and to mitigate coking by controllinglocal heat flux and residence time within the ignition housing. Desirably, thedevice should also minimize electromagnetic emissions, reduce part count, andimprove ignition reliability relative to systems requiring external injectors orexciters.

[0013] The present disclosure addresses these needs by providing anignition architecture that utilizes a low-voltage hot-surface element within acompact housing and a defined, capillarity-based fuel conveyance andvaporization path to form a pilot flame for ignition of the main combustor. Thisbackground description is provided to place the invention in technical context.It is not an admission that any document cited herein is prior art under anyparticular statute or jurisdiction, nor that any feature described in thebackground is essential to the claimed invention.

[0014] The above-mentioned shortcomings, disadvantages and problemsare addressed herein, which will be understood by reading the followingspecification.C) OBJECTS OF THE INVENTION

[0015] The primary object of the present invention is to provide acompact, low-voltage hot-surface ignition device that reliably produces a pilotflame for initiating combustion in micro and small turbojet engines.

[0016] The other object of the present invention is to provide an injectorlessignition architecture that transports liquid fuel by capillary action througha defined path to a heated element, according to the embodiment of the presentinvention.

[0017] Another object of the present invention is to provide a dual-layerstainless-steel mesh wick surrounding a glow element to enable controlled fuelwetting, vaporization, and pilot-flame formation at very low fuel flow rates,according to the embodiment of the present invention.

[0018] Another object of the present invention is to reduce or eliminatethe need for high-voltage exciters and associated electromagnetic interference,weight, and packaging constraints in small airframes, according to theembodiment of the present invention.

[0019] Another object of the present invention is to achieve consistentlight-off at low supply pressures and across a broad range of ambienttemperatures and fuel viscosities, including cold-soak conditions, according tothe embodiment of the present invention.

[0020] Another object of the present invention is to minimize carbondeposition and coking within the ignition housing by regulating local heat flux,residence time, and fuel presentation to the hot surface, according to theembodiment of the present invention.

[0021] Another object of the present invention is to provide a linermounted ignition housing with a dedicated discharge port that projects a stablepilot flame into the main combustor with repeatable geometry, according to theembodiment of the present invention.

[0022] Another object of the present invention is to simplify fuel-systemrequirements for micro turbojets by avoiding precision atomizers, swirlers, andpressurized injectors within the ignition device, according to the embodimentof the present invention.

[0023] Another object of the present invention is to enable rapid, fieldserviceableinstallation and replacement through an interface that seals andmechanically integrates with a combustor liner, according to the embodimentof the present invention.

[0024] Another object of the present invention is to provide improvedignition reliability and reduced part count relative to torch-igniter systemsemploying separate injectors, according to the embodiment of the presentinvention.

[0025] Another object of the present invention is to offer compatibilitywith common turbine fuels (including kerosene and Jet-A) at micro-engineflow rates on the order of tens of milliliters per minute, according to theembodiment of the present invention.

[0026] Another object of the present invention is to deliver a compactassembly with reduced mass and volume suitable for unmanned aerial vehiclepropulsion and other miniature gas-turbine applications, according to theembodiment of the present invention.

[0027] Another object of the present invention is to enhancemanufacturability by utilizing commercially available glow elements andmetal meshes with specified pore characteristics, according to the embodimentof the present invention.

[0028] Another object of the present invention is to improve startsequencerobustness when integrated with simple low-voltage power suppliesand low-pressure fuel pumps, according to the embodiment of the presentinvention.

[0029] Another object of the present invention is to provide thermalmanagement features within the ignition housing that sustain hot-surfacetemperatures adequate for vaporization while protecting adjacent structures,according to the embodiment of the present invention.

[0030] Another object of the present invention is to enable retrofit ofexisting micro and small turbojet platforms by providing a drop-in ignitionmodule with minimal changes to the fuel and electrical subsystems, accordingto the embodiment of the present invention.

[0031] These and other objects and advantages of the present inventionwill become readily apparent from the following detailed description taken inconjunction with the accompanying drawings.D) SUMMARY OF THE INVENTION

[0032] The embodiments of the present invention disclose a compact,injector-less hot-surface ignition device for micro and small turbojet enginesthat generates a pilot flame within a pre-chamber and discharges it into acombustor liner.

[0033] According to the embodiment, the device comprises a lowvoltageglow element disposed within a metal housing, a first stainless-steelmesh sleeve surrounding the glow element, and a second stainless-steel meshsleeve concentrically surrounding the first sleeve to define a capillary fuel pathfrom an inlet to a glow-heated surface.

[0034] According to the embodiment, the housing provides at least onemetered air inlet and a discharge outlet oriented to project the pilot flame intothe combustor primary zone, and further includes a liner-mounting interfaceconfigured to seal and mechanically integrate the device with a combustor wallfor installation and service.

[0035] In one embodiment, the disclosed invention describes a dualmeshwick architecture having specified porosity (e.g., about 50-75 μmnominal pore) arranged to passively meter and vaporize liquid turbine fuels atlow flow and low supply pressure without a dedicated atomizing injector.

[0036] The device thereby achieves reliable light-off with reducedelectromagnetic emissions, reduced part count, and mitigated coking byregulating local heat flux and residence time within the pre-chamber whilemaintaining a stable pilot-flame geometry at the outlet.

[0037] Additionally, the disclosure provides methods of operationincluding wetting the outer mesh with liquid fuel, transferring the fuel bycapillary action to the inner mesh, vaporizing the fuel on the glow-heatedsurface, and directing the resulting ignition products through the outlet to ignitethe main combustor.

[0038] In one embodiment, the disclosed ignition device incorporatesthermal shielding, electrical connectors, and replaceable mesh cartridges orsleeves to facilitate field service, as well as optional sensors or control logicconfigured to regulate glow-element power during start sequences.

[0039] The embodiments further contemplate material and geometricvariations including alternative mesh weaves, sintered metallic felts, singlemeshconfigurations, graded-porosity stacks, and alternative housinggeometries adapted to different combustor liners while remaining injector-lessand capillary-fed.

[0040] In another embodiment, the invention is provided as a retrofitignition module for existing micro turbojet platforms, delivered as a linermounted assembly with a defined electrical interface and a low-pressure fuelconnection suitable for unmanned aerial vehicle propulsion and otherminiature gas-turbine applications.

[0041] These and other aspects of the embodiments herein will be betterappreciated and understood when considered in conjunction with the followingdescription and the accompanying drawings. It should be understood,however, that the following descriptions, while indicating preferredembodiments and numerous specific details thereof, are given by way ofillustration and not of limitation. Many changes and modifications may bemade within the scope of the embodiments herein without departing from thespirit thereof, and the embodiments herein include all such modifications.E) BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The other objects, features and advantages will occur to thoseskilled in the art from the following description of the preferred embodimentand the accompanying drawings in which:

[0043] FIG. 1 illustrates the overall compact igniter assembly accordingto an embodiment of the present invention.

[0044] FIG. 2 illustrates a sectional view of the compact igniterassembly showing the dual-layer mesh wick, glow element, capillary fuel path,metered air inlets, and pilot-flame discharge outlet, according to anembodiment of the present invention.

[0045] FIG. 3 illustrates the liner-mounted installation of the compactignition device and the orientation of the pilot flame into the combustorprimary zone, according to an embodiment of the present invention.

[0046] FIG. 4 illustrates the electrical and thermal arrangement of theignition housing, including power interfacing and thermal shielding featuresthat sustain hot-surface temperatures while protecting adjacent structures,according to an embodiment of the present invention.

[0047] FIG. 5 illustrates a schematic of system-level flow diagramillustrating start-sequence of an injector-less ignition architecture thattransports liquid fuel by capillary action through a defined path to a heatedelement for ignition according to an embodiment of the present invention.

[0048] Although specific features of the present invention are shown insome drawings and not in others. This is done for convenience only as eachfeature may be combined with any or all of the other features in accordancewith the present invention.F) DETAILED DESCRIPTION OF THE INVENTION

[0049] In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which the specificembodiments that may be practiced is shown by way of illustration. Theseembodiments are described in sufficient detail to enable those skilled in the artto practice the embodiments and it is to be understood that the logical,mechanical and other changes may be made without departing from the scopeof the embodiments. The following detailed description is therefore not to betaken in a limiting sense.

[0050] The present disclosure relates to a compact ignition apparatusconfigured to generate a pilot flame within a pre-chamber and to deliver saidpilot flame into a gas-turbine combustor for light-off of the main combustionzone. With reference to FIG. 1, an igniter assembly 100 includes a glowelement 101, an ignition fuel supply line 102, at least one stainless steel mesh103 disposed proximate to the glow element 101, and an ignitor housing 104that encloses the foregoing components and interfaces mechanically with acombustor structure.

[0051] The ignitor housing 104 is configured to define an internalignition volume (pre-chamber) that receives liquid fuel and air and, uponheating by the glow element 101, produces a localized pilot flame whichdischarges toward the primary combustion region of the turbine engine. Incertain embodiments, the ignitor housing 104 provides one or more meteredair inlets sized to regulate oxidizer admission during start, and an outletaperture oriented to direct the pilot products into the combustor.

[0052] In the embodiment illustrated in FIG. 1, the ignition fuel supplyline 102 is fluidly coupled to the ignitor housing 104 so as to convey liquidfuel into the internal ignition volume where the stainless-steel mesh 103 ispositioned to receive, retain, and distribute the incoming fuel by capillaryaction. The arrangement enables injector-less fuel presentation to the hotsurface of the glow element 101, thereby simplifying the fuel system whileenabling controlled vaporization at low flow rates.

[0053] FIG. 2 illustrates a sectional configuration the compact igniterassembly in which a dual-layer mesh wick surrounds the glow element 101.An inner stainless-steel mesh sleeve 201 (first mesh) and an outer stainlesssteelmesh sleeve 202 (second mesh) are arranged concentrically to define acapillary fuel path from the ignition fuel supply line 102 to the hottest regionof the glow element 101. In representative embodiments, each mesh exhibits anominal pore size of about 50-75 μm, selected to balance capillary transportwith vapor release.

[0054] The glow element 101 includes a hottest section 203 which, whenenergized at low voltage, attains a temperature sufficient to vaporize fuel thathas migrated through the outer mesh 202 into the inner mesh 201. An openingfor the flame 204 is disposed so that the resulting ignition products and pilotflame discharge from the pre-chamber with a defined geometry. The concentricrelationship between the meshes 201 and 202 provides progressive wetting andcontrolled fuel residence time adjacent to the hottest section 203.

[0055] In operation, fuel entering via the ignition fuel supply line 102initially wets the outer mesh 202, which acts as a reservoir and coarsedistributor. Capillary forces then convey fuel into the inner mesh 201, wherethe proximity to the hottest section 203 of the glow element 101 promotesdroplet disintegration and rapid phase change. Vaporized fuel mixes withadmitted air within the pre-chamber and is ignited on or near the heatedsurface, producing a stable pilot flame that exits the opening 204.

[0056] The dual-mesh arrangement of FIG. 2 provides enhancedrepeatability of light-off by establishing a defined capillary pathway and heatflux environment. The outer mesh 202 cushions transient variations inincoming flow, while the inner mesh 201 meters delivery to the glow-heatedregion, thereby mitigating wall wetting and coking. The absence of a dedicatedatomizing injector reduces part count and susceptibility to low-pressuremaldistribution.

[0057] With reference to FIG. 3 (liner-mounted installation), the igniterassembly 100 is positioned such that the opening 204 is oriented toward thecombustor primary zone. The ignitor housing 104 may be configured to seatagainst or through a combustor wall to establish a sealed interface, therebycontaining pilot combustion within the pre-chamber until discharge. Theorientation of the outlet relative to the main airflow is selected to promoteflame propagation into the combustor dome region.

[0058] Further, as depicted schematically in FIG. 4, the igniter assembly100 is mechanically integrated with a combustion chamber outer casing 401and a combustor liner 402. The ignitor housing 104 passes through or mountsto the combustor liner 402 in a manner that accommodates thermal growthwhile maintaining sealing at operating temperatures. Electrical leads to theglow element 101 are routed to minimize thermal exposure and to preservedielectric integrity adjacent to the combustor hardware.

[0059] The interface between the igniter assembly 100 and thecombustor liner 402 may include gaskets, bushings, or other sealing featuresformed from high-temperature materials to prevent hot-gas leakage to theannulus between the liner 402 and outer casing 401. The ignitor housing 104may incorporate thermal shielding to reduce conductive and radiative heattransfer to surrounding engine structures.

[0060] The stainless-steel mesh 103 of FIG. 1 is, in embodiments,implemented by the concentric mesh sleeves 201 and 202 of FIG. 2. The meshweave, wire diameter, and sintering state may be selected to achieve targetcapillary characteristics and mechanical durability. The meshes 201, 202 aresupported within the ignitor housing 104 such that intimate contact with theglow element 101 is maintained where desired while permitting removal andreplacement for service.

[0061] The glow element 101 is a low-voltage hot-surface heater (forexample, a metallic or ceramic glow plug) configured to produce sufficientsurface temperature at the hottest section 203 to ignite vaporized turbine fuels.Electrical power delivery may be controlled to achieve staged heating duringstart and to avoid overheating during soak conditions. The arrangement iscompatible with compact power supplies commonly available in smallairframes.

[0062] The ignition fuel supply line 102 is arranged to introduce liquidfuel proximate to the outer mesh 202 so as to promote even wetting without jetimpingement on the hottest section 203. Check valves, filters, or flowrestrictors may be incorporated upstream of the supply line 102 to preventbackflow and to stabilize delivery during transient pump operation.

[0063] According to certain embodiments, the ignitor housing 104includes at least one metered air inlet sized to admit a controlled amount of airinto the pre-chamber. The metering may be achieved by calibrated orifices orpassages formed in the housing 104. The air inlets are positioned to encouragemixing with vaporized fuel while avoiding direct cooling of the hottest section203 that would otherwise inhibit ignition.

[0064] The opening for the flame 204 is dimensioned to establish apressure drop that, in cooperation with the air inlets, sustains a stable pilotflame and directed discharge into the combustor. The geometry of the opening204 may be selected to shape the pilot plume such that it intersects the localmain airflow and fuel spray (if present) within the combustor primary zone toachieve reliable light-off.

[0065] With reference to the method sequence of FIG. 5, ignition isinitiated at step 501 by energizing the glow element 101 and preparing the fuelsystem. At step 502, a pump starts fuel supply through an ignition manifoldand into the ignition fuel supply line 102, delivering fuel to the ignitor housing104. At step 503, fuel enters the stainless-steel mesh system (outer mesh 202,inner mesh 201) and disintegrates into droplets and vaporizes adjacent to thehottest section 203. At step 504, the vaporized fuel ignites at the glow plug tipand the flame plunges through the opening 204 into the combustion chamber,thereby igniting the main combustor.

[0066] The foregoing architecture facilitates reliable starts under lowfuel supply pressure and across a wide range of ambient conditions by relyingon capillary transport through meshes 201, 202 rather than pressure-atomizinginjectors. The design minimizes electromagnetic emissions by eliminatinghigh-voltage exciter hardware and reduces overall component count. The linermountedconfiguration relative to the combustor liner 402 and outer casing 401further enables straightforward installation and field service.

[0067] Variations and modifications are contemplated without departingfrom the scope of the disclosure. By way of non-limiting examples, the meshsystem may comprise a single sleeve (201 or 202) with graded porosity; theignitor housing 104 may adopt alternative geometries to accommodatedifferent combustor liners 402; and the fuel entry into the supply line 102 maybe oriented or baffled to tailor wetting dynamics. Unless expressly statedotherwise, the terms "comprise," "include," and variations thereof are intendedto be non-limiting, and features described in connection with one embodimentmay be combined with features of another embodiment as appropriate.G) ADVANTAGES OF THE INVENTION

[0068] The disclosed ignition module provides multiple technicaladvantages in micro and small gas-turbine applications. By presenting liquidfuel solely via capillary transport through a dual, concentric mesh wick-outersleeve (202) feeding inner sleeve (201) adjacent the hottest section (203) of theglow element (101)-the device eliminates atomizing injectors and swirlerswithin the ignitor housing (104), thereby reducing part count, cloggingsusceptibility, and maintenance while enabling reliable light-off at low flowand low supply pressure. Low-voltage operation of the glow element (101)obviates high-voltage exciters, lowering electromagnetic interference, wiringcomplexity, mass, and packaging burden. Progressive capillary meteringstabilizes wetting dynamics, mitigates wall wetting and coking, and yields arepeatable pilot-flame geometry at the opening (204) with calibrated airadmission. The architecture accommodates common turbine fuels and remainstolerant to viscosity variation, including cold-soak starts.

[0069] Further advantages arise from compact, liner-mountedintegration whereby the assembly (100) interfaces with the combustor liner(402) inside the outer casing (401), simplifying installation in constrainednacelles and minimizing intrusion into the core flow. Field serviceability isenhanced through a removable mesh cartridge and replaceable housing (104),reducing downtime and lifecycle cost. Optional sensing and control permitdeterministic start sequencing (501-504) and post-transfer power reduction toavoid overheating, improving robustness across engine and ambientconditions. The injector-less, low-power design supports straightforwardretrofit of existing platforms, decreases shielding and harness requirements,and scales efficiently across diverse micro-turbojet configurations.

Claims

1. An ignition module for initiating combustion in a micro turbojet engine, comprising: a glow element (101); an ignitor housing (104) defining a pre-chamber and having an outlet opening (204) oriented toward a combustor liner (402); an ignition fuel supply line (102) fluidly coupled to the pre-chamber; and a dual-layer capillary wick including an outer stainless-steel mesh sleeve (202) and an inner stainless-steel mesh sleeve (201) disposed concentrically about at least a portion of the glow element (101), each sleeve having a pore size of 50-75 gm; wherein fuel delivered via the ignition fuel supply line (102) wets the outer mesh sleeve (202) and is transported solely by capillary action into the inner mesh sleeve (201) adjacent a hottest section (203) of the glow element (101) to vaporize the fuel and form a pilot flame that issues through the outlet opening (204); and wherein no atomizing injector is disposed between the ignition fuel supply line (102) and the inner mesh sleeve (201).

2. The ignition module as claimed in claim 1, wherein the ignitor housing (104) includes at least one calibrated air inlet dimensioned to admit oxidizer to the pre-chamber while maintaining a stable pilot flame at the outlet opening (204).

3. The ignition module as claimed in any preceding claim, wherein the outlet opening (204) is oriented to project the pilot flame into a primary combustion zone downstream of the combustor liner (402) so as to intersect a local main airflow for flame propagation.

4. The ignition module as claimed in any preceding claim, wherein the glow element (101) is configured for low-voltage operation in a range of 6-12 volts.

5. The ignition module as claimed in any preceding claim, wherein the ignition fuel supply line (102) is configured to deliver turbine fuel at a flow rate of 10-60 millilitres per minute at a supply pressure not greater than 0.5 bar gauge.

6. The ignition module as claimed in any preceding claim, wherein at least one of the mesh sleeves (201, 202) is a woven stainless-steel mesh selected from plain-Dutch and Hollander weaves and optionally sintered to enhance mechanical stability.

7. The ignition module as claimed in any preceding claim, wherein the dual-layer mesh (201, 202) is housed as a removable cartridge within the ignitor housing (104) to facilitate field replacement.

8. The ignition module as claimed in any preceding claim, further comprising a thermal shield associated with the ignitor housing (104) to reduce conductive and radiative heat transfer to adjacent engine structures including a combustion chamber outer casing (401).

9. The ignition module as claimed in any preceding claim, wherein the ignitor housing (104) includes a liner-mounting interface configured to seal against the combustor liner (402) and accommodate differential thermal growth relative to the combustion chamber outer casing (401).

10. The ignition module as claimed in any preceding claim, further comprising an electrical connector and strain-relieved leads arranged external to a compressor or combustor pressure case for supplying power to the glow element (101).

11. The ignition module as claimed in any preceding claim, wherein the inner mesh sleeve (201) is positioned in direct thermal communication with the hottest section (203) of the glow element (101) to promote droplet disintegration and rapid phase change.

12. The ignition module as claimed in any preceding claim, wherein the calibrated air inlet(s) and the outlet opening (204) are jointly dimensioned to establish a pressure drop that sustains pre-chamber combustion while directing a coherent pilot plume into the combustor.

13. The ignition module as claimed in any preceding claim, further comprising at least one sensor selected from temperature, voltage, current or optical flame sensors and a controller configured to regulate power to the glow element (101) during an ignition sequence.

14. A method of igniting a micro turbojet combustor using the ignition module as claimed in claim 1, comprising: energizing the glow element (101) within the ignitor housing (104) so as to heat the hottest section (203); starting a pump to deliver liquid fuel through an ignition manifold and the ignition fuel supply line (102) to the pre-chamber; wetting the outer mesh sleeve (202) with the fuel and transporting the fuel by capillary action into the inner mesh sleeve (201) adjacent the hottest section (203) to vaporize the fuel; and forming a pilot flame and discharging the pilot flame through the outlet opening (204) into the combustor downstream of the combustor liner (402).

15. The method as claimed in claim 14, wherein power to the glow element (101) is regulated according to a closed-loop control algorithm responsive to at least one of temperature, voltage or current feedback to achieve a target hot-surface temperature.

16. The method as claimed in claim 14 or claim 15, wherein the fuel comprises kerosene, Jet-A or a functional equivalent suitable for turbine operation.

17. The method as claimed in any of claims 14 to 16, wherein the ignition sequence is executed following a cold-soak condition with elevated fuel viscosity and maintains stable pilot formation at the outlet opening (204).

18. The method as claimed in any of claims 14 to 17, wherein fuel delivery into the ignitor housing (104) is ramped at a rate of 0.1-1.0 millilitres per second to minimize wall wetting and coking.

19. The method as claimed in any of claims 14 to 18, wherein oxidizer admission to the pre-chamber through the calibrated air inlet(s) is metered to establish an equivalence ratio between 0.4 and 1.0 during pilot formation.

20. The method as claimed in any of claims 14 to 19, wherein upon detection of stable pilot transfer to the main combustor the controller reduces or terminates power to the glow element (101) to prevent overheating.