Porous, flame-quenching linings in flame paths of motor enclosures to reduce peak explosion pressure and prevent flame transmission

Abstract

An electrical machine includes an enclosure that features a plurality of assembly joints. An ignition source ignites a reactant mixture distributed within the enclosure to cause a flame to propagate from inside the enclosure to outside the enclosure through one or more flame paths. The one or more flame paths are formed along the plurality of assembly joints, where one or more porous linings are positioned along the one or more flame paths, and where the one or more porous linings within the one or more flame paths cool down and reduce a flow rate of the flame as the flame propagates through the one or more flame paths.

Description

773011 (P240379 W001)POROUS, FLAME-QUENCHING LININGS IN FLAME PATHS OF MOTOR ENCLOSURES TO REDUCE PEAK EXPLOSION PRESSURE AND PREVENT FLAME TRANSMISSIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims priority from copending Italian Patent Application No. 102024000019951, filed September 6, 2024, which is incorporated by reference in its entirety for all purposes.FIELD

[0002] The present disclosure relates to electrical machines. In particular, the present disclosure relates to electric machines that are designed to operate in an explosive atmosphere.BACKGROUND

[0003] Electric machines (such as electric motors) that are designed to be operated in explosive atmospheres (e.g., oil & gas, chemicals, dust) are required to pass explosion proof certification tests (e.g., Ex d type certification according to the IEC 60079-1 standard, as listed in Atmospheres, E. (2007) Part 1: Equipment Protection by Flameproof Enclosures “d”. IS / IEC, 60079-1. Ex ‘d’ type certification stands for flameproof enclosure certification. To comply with this certification, electric machine enclosures are designed to withstand explosion pressure and flame paths are designed along the assembly joint of two components, such as enclosure and endshield, to achieve non-transmission of flame to the outer environment. Hence, flameproof enclosures of electric machines are able to withstand explosion pressure and prevent flame transmission to the ambient surrounding of the electric machines, in case of an ignition inside the enclosure. To pass the certification tests, to be certified as flameproof enclosures, enclosures of the electric machines are required to withstand three to five times the maximum reference pressure without suffering any damage. This results in a heavier enclosure design to withstand the high explosion pressure. Assembly joints along two components of flameproof enclosures (for example assembly joints between enclosure body and cover flanges) are designed to include long and narrow gaps or openings, known as flame paths.

[0004] The flame paths, or flameproof joints, of the flameproof enclosures - which are designed in the assembly joints of the electric machine enclosure - serve two purposes: (i) to relieve the pressure and lower peak explosion pressure caused by the ignition of explosive773011 (P240379 W001) gases within the electric machine enclosure; and (ii) to cool / slow down the burnt gases, caused by the combustion occurring within the electric machine enclosure, before releasing the burnt gases outside the electric machine enclosure, so that ignition does not propagate to the outside environment. The specifications for openings of flame paths are very stringent and are required to be narrow enough to allow the hot burnt gases to cool and slow down sufficiently before exiting.

[0005] To meet the requirements of the certification tests, parts such as cover end-shields, shaft and inner bearing covers have tight dimensional tolerances and are expensive to manufacture. Frequently, part-to-part variability do not conform causing quality issues among assembled units. It often may take multiple iterations in assembly process of electric machines before the required specifications are met.SUMMARY

[0006] A first aspect of the present disclosure relates to an electrical machine, featuring: an enclosure, comprising: a plurality of assembly joints; an ignition source, that ignites a reactant mixture contained in the enclosure to cause a flame, that propagates from inside the enclosure to outside the enclosure through one or more flame paths; and the one or more flame paths, wherein the one or more flame paths are formed along the plurality of assembly joints, wherein one or more porous linings are positioned along the one or more flame paths, and wherein the one or more porous linings within the one or more flame paths cool down and reduce a flow rate of the flame as the flame propagates through the one or more flame paths.

[0007] According to an implementation of the first aspect, a porous medium of the one or more porous linings comprises at least one of ceramic foam, metal foam, metal wire mesh, and metal wool.

[0008] According to an implementation of the first aspect, the porous medium comprises open pores with interconnected passageways.

[0009] According to an implementation of the first aspect, the one or more porous linings are cut from pre-manufactured material of the porous medium and adhered to channels of the one or more flame paths.

[0010] According to an implementation of the first aspect, the one or more porous linings are sputtered on a surface of the one or more flame paths.

[0011] According to an implementation of the first aspect, a first assembly joint of the assembly joints is present between a stator frame of the electrical machine and a drive-end773011 (P240379 W001) cover of the electrical machine, and wherein a first flame path of the one or more flame paths is formed along the first assembly joint.

[0012] According to an implementation of the first aspect, a second assembly joint of the assembly joints is present between a drive-end endshield bore of the electrical machine and a shaft of the electrical machine, and wherein a second flame path of the one or more flame paths is formed along the second assembly joint.

[0013] According to an implementation of the first aspect, a third assembly joint of the assembly joints is present between a stator frame non-drive-end bore of the electrical machine and a shaft of the electrical machine, and wherein a third flame path of the one or more flame paths is formed along the third assembly joint.

[0014] According to an implementation of the first aspect, a fourth assembly joint of the assembly joints is present between a terminal box of the electrical machine and a terminal box cover of the electrical machine, and wherein a fourth flame path of the one or more flame paths is formed along the fourth assembly joint.

[0015] According to an implementation of the first aspect, a fifth assembly joint of the assembly joints is present between a terminal box of the electrical machine and an intermediate plate of the electrical machine, and wherein a fifth flame path of the one or more flame paths is formed along the fifth assembly joint.

[0016] According to an implementation of the first aspect, the porous medium is thermally cycled to achieve a predetermined percentage of porosity.

[0017] According to an implementation of the first aspect, the porous medium is pressure treated to achieve a predetermined percentage of porosity.

[0018] According to an implementation of the first aspect, the porous medium is annealed to achieve a predetermined percentage of porosity.

[0019] A second aspect of the present disclosure provides an ignition, using an ignition source, of a reactant mixture distributed within an enclosure of an electrical machine, to cause a flame to propagate from inside the enclosure to outside the enclosure through one or more flame paths, wherein the one or more flame paths are formed along a plurality of assembly joints of the electric machine, wherein one or more porous linings are positioned along the one or more flame paths, and wherein the one or more porous linings within the one or more flame paths cool down and reduce a flow rate of the flame as the flame propagates through the one or more flame paths.773011 (P240379 W001)

[0020] According to an implementation of the second aspect, a porous medium of the one or more porous linings comprises at least one of ceramic foam, metal foam, metal wire mesh, and metal wool.

[0021] According to an implementation of the second aspect, the porous medium comprises open pores with interconnected passageways.

[0022] According to an implementation of the second aspect, the one or more porous linings are cut from pre-manufactured material of the porous medium and adhered to channels of the one or more flame paths.

[0023] According to an implementation of the second aspect, the one or more porous linings are sputtered on a surface of the one or more flame paths.

[0024] According to an implementation of the second aspect, a first assembly joint of the assembly joints is present between a stator frame of the electrical machine and a drive-end cover of the electrical machine, and wherein a first flame path of the one or more flame paths is formed along the first assembly joint.

[0025] A third aspect of the present disclosure provides an open rotor comprising: a plurality of assembly joints; an ignition source that ignites a reactant mixture distributed within the enclosure to cause a flame to propagate from inside the enclosure to outside the enclosure through one or more flame paths; and the one or more flame paths, wherein the one or more flame paths are formed along the plurality of assembly joints, wherein one or more porous linings are positioned along the one or more flame paths, and wherein the one or more porous linings within the one or more flame paths cool down and reduce a flow rate of the flame as the flame propagates through the one or more flame paths.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Subject matter of the present disclosure will be described in even greater detail below based on the exemplary figures. All features described and / or illustrated herein can be used alone or combined in different combinations. The features and advantages of various embodiments will become apparent by reading the following detailed description with reference to the attached drawings, which illustrate the following:

[0027] FIG. 1 illustrates a simplified diagram of an electrical machine that highlights locations of flame paths, according to one or more examples of the present disclosure; and773011 (P240379 W001)

[0028] FIG. 2 illustrates a simplified diagram of a porous lining installed along a flamepath of an assembly joint of end-shield and stator frame, according to one or more examples of the present disclosure.DETAILED DESCRIPTION

[0029] Examples of the present application will now be described more fully hereinafter with reference to the accompanying FIGs., in which some, but not all, examples of the application are shown. Indeed, the application may be exemplified in different forms and should not be construed as limited to the examples set forth herein; rather, these examples are provided so that the application will satisfy applicable legal requirements. Where possible, any terms expressed in the singular form herein are meant to also include the plural form and vice versa, unless explicitly stated otherwise. Also, as used herein, the term “a” and / or “an” shall mean “one or more” even though the phrase “one or more” is also used herein. Furthermore, when it is said herein that something is “based on” something else, it may be based on one or more other things as well. In other words, unless expressly indicated otherwise, as used herein “based on” means “based at least in part on” or “based at least partially on”.

[0030] For electric machines (e.g., electric motors) to operate in explosive atmosphere (e.g., oil & gas, chemicals, dust), electric machines are required to pass explosion proof certification tests (e.g., Ex d type certification according to the IEC 60079-1 standard). In some embodiments, the certification tests may involve measuring a maximum explosion pressure (e.g., reference pressure) inside of a flameproof enclosure (e.g., enclosure) of the electric machine in an event of an ignition of the flame within the flameproof enclosure of the electric machine. To pass the certification tests, flameproof enclosures of the electric machines may be required to withstand five times the maximum explosion pressure without suffering any damage.

[0031] In some embodiments, the internal geometry of electric machines may feature multiple compartments interconnected with long and narrow passages (e.g. drive-ends & nondrive-ends connected via air gap between rotor and stator) which can lead to higher peak explosion pressure in a secondary compartment due to a pre-compression effect known as ‘pressure piling’.

[0032] In some embodiments, a primary compartment is a compartment in the flameproof enclosure where flammable gases may be ignited. A second compartment may be a different compartment in the flameproof enclosure of the electric machine. For example, in case ignition773011 (P240379 W001) starts in a drive-end (DE) of a motor, the DE volume may be considered as the primary compartment. A narrow air gap may connect the DE and non-drive-end (NDE) volume. Flames from the ignition may propagate from drive -end volume to the non-drive-end volume and the hence non-drive-end may be considered as the secondary compartment. Pressure piling effect may be expected in secondary compartment (e.g., the non-drive-end volume) leading to high peak explosion pressure in secondary compartment.

[0033] The flameproof enclosures of electric machines may be designed to be heavy to withstand the high explosion pressure caused by an ignition of a flame within the enclosure of the electric machine. The flameproof enclosures of electric machines may also be configured to sufficiently cool and / or slow down the hot burnt gases, caused by an internal ignition, before they exit the enclosure so that in an event of internal ignition, the heat of the gas and / or any spark or flame, does not propagate outside the enclosures of the electric machines.

[0034] Different components of an enclosure of an electric machine are connected using assembly joints (e.g., flameproof joints). In some cases, assembly joints may be mating surface of two components forming joint. For example, there are assembly joints that connect a stator frame and an endshield of the electric machine, and a shaft and bore of the electric machine. In flameproof enclosures, the assembly joints include long and narrow openings that are known as flame paths. In case of an ignition of an explosive gas within the enclosure of the electric machine, the flame paths are designed to serve two purposes: (i) to dissipate pressure and lower peak explosion pressure; and (ii) to cool / slow down burnt gases before the burnt gases are release outside the enclosure of the electric motor. The standards requirements for the openings of flame paths are very stringent and may be required to be narrow enough to allow hot burnt gases to cool and slow down sufficiently before releasing the gases.

[0035] To meet the standards requirements, parts such as cover end-shields, shaft and inner bearing covers have small dimensional tolerances and are expensive to manufacture. In some embodiments, part-to-part variability may not conform causing non-uniformity among assembled units. Multiple iterations of the assembly process of electric machines may be performed before the required specifications of the openings of the flame paths are met.

[0036] The present disclosure discusses the use of a porous lining within flame paths of assembly joints of enclosures of electric machines. Flame paths reduce the peak explosion pressure within the enclosure (by venting) of the electric machine and prevent -transmission of a flame (by cooling and slowing down the flame) ignited within the enclosure of the electric machine, to the outside surrounding. Porous linings installed on walls of flame path openings contributes to further reduction of peak explosion pressure and promotes non-transmission of773011 (P240379 W001) flame to outside the enclosure of the electric machine. Porous media used in the porous lining has a high surface area to volume ratio and consists of narrow interconnected passageways where a flame ignited within the enclosure of the electric machine can be quenched and slowed down as it passes through the interconnected passageways.

[0037] In some embodiments, porous linings allow flame paths to be increased to the maximum allowed gap size as specified in the IEC standard. Non-transmission of the flame is achieved with a bigger gap size because porous media are more efficient in cooling and slowing down the flame. Additionally, and / or alternatively, bigger gap size allows for more venting and hence reduce explosion pressure.

[0038] Porous lining in flame path openings further enhances the non-transmission effects of the flame path openings by significantly slowing down and extinguishing the hot burnt gases, caused by the flame ignited within the enclosure of the electric machine, before they exit the enclosure of the electric machine. As the hot burnt gases flow through the long and narrow flame path openings, the metal walls of the openings extract heat energy from hot burnt gases which leads to local quenching of the combustion products, such as burnt gases and active radicals. In addition, a no-slip boundary condition at the wall of the flame path or assembly joint acts to slow down the hot burnt gases. For example, a no-slip boundary condition is created when velocity of gases at a stationary wall of the flame path or flame proof joint of the electric machine is zero. In some embodiments, the porous lining present at the wall of the flame path or flame proof joint provides more surface area than plain unlined wall of flame path. The porous lining absorbs more heat from the combustion gases (more surface area) and hence further slows down and quenches the flame before the flame exits the enclosure of the electric machine.

[0039] FIG. 1 illustrates a simplified diagram of an electrical machine that highlights locations of flame paths, according to one or more examples of the present disclosure. FIG. 1 depicts an electrical machine 102. In some embodiments, electrical machine 102 may be an electric motor. The electric machine 102 includes a rotor and a stator frame. In some embodiments, the electric machine 102 may include a stator frame, drive-end endshield, nondrive-end endshield, shaft, drive-end endshield bore, non-drive-end endshield bore, inner bearing cover, terminal box cover, and terminal box frame, shaft.

[0040] The enclosure of the electric motor 102 includes a plurality of assembly joints that connect the various components of the electric motor 102 to each other. The assembly joints include long and narrow openings that are known as flame paths. In some embodiments, assembly joints between two components of an electric motor enclosure may include an773011 (P240379 W001) assembly joint between a stator frame and end-shield of the electrical machine and / or a gap between inner diameter of end-shield and shaft of the of the electrical machine. In some cases, flame paths (e.g., flameproof joints) are gaps on assembly joints of two components.

[0041] The flame paths are designed to serve two purposes in case of an ignition within an enclosure of the electric motor 102: (i) to dissipate pressure and lower peak explosion pressure within the enclosure; and (ii) to cool / slow down burnt gases before burnt gases are released outside the enclosure of the electric motor 102.

[0042] Some exemplary flame paths 104, 106, and 108 are shown as part of the electric machine 102 in FIG. 1. Flame path 104 is part of an assembly joint between the stator frame and a drive-end (DE) cover. In some embodiments, the flame path 104 may be included in a cylindrical part of a spigot joint. Flame path 106 is part of an assembly joint between the DE endshield bore of the electric motor 102 and a shaft of the electric motor 102. In some embodiments, the flame path 106 may be included in a cylindrical joint for shaft glands with rolling element bearing. Flame path 108 is part of an assembly joint between the stator frame NDE bore and shaft of the electric motor 102. In some embodiments, the flame path 108 may be included in a cylindrical joint for shaft glands with rolling element bearing. Flame path 110 is part of an assembly joint between a terminal box of the electric motor 102 and a terminal box cover of the electric motor 102. In some embodiments, the flame path 110 may also be part of an assembly joint between the terminal box of the electric motor 102 and an intermediate plate of the electric motor 102.

[0043] In order for the electric machine 102 to pass the certification requirements for various standards, such as the Ex d type certification according to the IEC 60079-1 standard, the openings of the flame paths 104, 106, 108, and 110 are strictly regulated. For example, the openings of the flame paths 104, 106, 108, and 110, are very stringent and may be required to be narrow enough to allow hot burnt gases to cool and slow down sufficiently before releasing the gases. The use of porous linings (discussed in more detail with respect to FIG. 2) allow for tolerances and flexibilities in the dimensions of the openings of the flame paths that make it easier to manufacture assembly joints.

[0044] Additionally and / or alternatively, there may be a flame path in the NDE side. For example, the flame path may be located between the stator frame of the electrical machine 102 and an NDE cover.

[0045] FIG. 2 illustrates a simplified diagram of a porous lining installed along a flamepath of an assembly joint of end-shield and stator frame, according to one or more examples of the present disclosure. FIG. 2 shows an exemplary exploded view of a flame path that is part773011 (P240379 W001) of the assembly joint between the stator frame 204 and a DE endshield cover 202. In some embodiments, when the stator frame 204 and the DE endshield cover 202 are assembled, there is small gap (approximately 0.1 to 0.4 millimeter) between the internal surfaces of the two elements. This gap may be known as a flame path. The internal surfaces of the gap created by DE endshield cover 202 and the stator frame 204 are lined with flame quenching porous coating 206. The flame quenching porous coating 206 on the surfaces of the DE end-shield cover 202 and stator frame 204 in allow a larger toleration in variation of a size of an opening of a flame path of the assembly joint. For example, the flame quenching porous coating 206 allow a size of the opening of the corresponding flame path to be increased (to the maximum limit specified in the IEC standard) and achieve the non-transmission of flame from within an enclosure of the electric motor 102 to outside the electric motor 102. This leads to increased safety since hot gases are more likely to be cooled and slowed down before they exit to the explosive atmosphere.

[0046] In some embodiments, the application of flame quenching porous coating 206 allows the maximum safe opening size to be increased (bigger gap size with coating can produce same flame quenching effect as smaller gaps size without coating) hence can reduce the peak explosion pressure (more venting with bigger gap sizes).

[0047] In some embodiments, the porous materials used to line channels of the flame paths of the assembly joints are metal foam (e.g., nickel, stainless steel etc.), ceramic foam, metal wool (such as stainless steel wool), and aluminum silicate wool. The porous materials used in the porous linings of the flame paths may contain open pores with porosity of at least 25%. Linings with materials having a higher porosity of 85-90% and high specific surface area can be effective in decreasing the speed of a flame as it travels through the flame paths and exits through openings of the flame path. Linings with materials having a higher porosity of 85-90% and high specific surface area also reduces turbulence at the openings of the flame path, hence preventing re-ignition of a flame ignited within the enclosure of the electric motor 102. In some embodiments, the porous material used in the flame quenching porous coating 206 may be pressure treated, or annealed, or thermally cycled to achieve the required percentage of porosity.

[0048] In some embodiments, the thickness of the flame quenching porous coating 206 may range from three (3) millimeter (mm) to fifteen (15) mm depending on a size of the motor and flame path of the assembly joint.773011 (P240379 W001)

[0049] In some embodiments, porous material may be sputtered onto surface to form the flame quenching porous coating 206 or may be cut from pre-manufactured material and adhered to the surfaces of the flame paths 104, 106, 108, and 110.

[0050] In some cases, the flame quenching porous coating 206 may increase safety of the electric motor 102 by lowering peak explosion pressure in case of an ignition of a flame within an enclosure of the motor 102 during operation of the electric motor 102 in an explosive environment. Therefore, the electric motor 102 may be able to pass the IEC 60076- 1 certification test since the enclosure of the electric motor 102 may be able to withstand the resulting lower peak explosion from an ignition within the enclosure of the electric machine 102.

[0051] In some embodiments, as the peak explosion pressure is lowered by installation of the flame quenching porous coating 206, the materials needed for thickness and design of the enclosure of the electric motor 102 may be reduced, which reduces a housing size of the electric motor 102, thereby reducing the resources needed to manufacture the electric motor 102.

[0052] In some embodiments, the flame quenching porous coating 206 may be used along a cable entry passage for a stator winding to the terminal box of the electric motor 102.

[0053] While subject matter of the present disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Any statement made herein characterizing the invention is also to be considered illustrative or exemplary and not restrictive as the invention is defined by the claims. It will be understood that changes and modifications may be made, by those of ordinary skill in the art, within the scope of the following claims, which may include any combination of features from different embodiments described above.

[0054] The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and / or C” or “at least one of A, B or C” should be interpreted773011 (P240379 W001) as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.

Claims

773011 (P240379 W001)CLAIMSWhat is claimed is:

1. An electrical machine, comprising: an enclosure comprising: a plurality of assembly joints; an ignition source that ignites a reactant mixture distributed within the enclosure to cause a flame to propagate from inside the enclosure to outside the enclosure through one or more flame paths; and the one or more flame paths, wherein the one or more flame paths are formed along the plurality of assembly joints, wherein one or more porous linings are positioned along the one or more flame paths, and wherein the one or more porous linings within the one or more flame paths cool down and reduce a flow rate of the flame as the flame propagates through the one or more flame paths.

2. The electrical machine of claim 1, wherein a porous medium of the one or more porous linings comprises at least one of ceramic foam, metal foam, metal wire mesh, and metal wool.

3. The electrical machine of claim 2, wherein the porous medium comprises open pores with interconnected passageways.

4. The electrical machine of claim 2, wherein the one or more porous linings are cut from pre -manufactured material of the porous medium and adhered to channels of the one or more flame paths.

5. The electrical machine of claim 1, wherein the one or more porous linings are sputtered on a surface of the one or more flame paths.

6. The electrical machine of claim 1 , wherein a first assembly j oint of the assembly joints is present between a stator frame of the electrical machine and a drive-end cover of the electrical machine, and wherein a first flame path of the one or more flame paths is formed along the first assembly joint.

7. The electrical machine of claim 6, wherein a second assembly joint of the assembly joints is present between a drive-end endshield bore of the electrical machine and a773011 (P240379 W001) shaft of the electrical machine, and wherein a second flame path of the one or more flame paths is formed along the second assembly joint.

8. The electrical machine of claim 7, wherein a third assembly joint of the assembly joints is present between a stator frame non-drive-end bore of the electrical machine and a shaft of the electrical machine, and wherein a third flame path of the one or more flame paths is formed along the third assembly joint.

9. The electrical machine of claim 8, wherein a fourth assembly joint of the assembly joints is present between a terminal box of the electrical machine and a terminal box cover of the electrical machine, and wherein a fourth flame path of the one or more flame paths is formed along the fourth assembly joint.

10. The electrical machine of claim 9, wherein a fifth assembly j oint of the assembly joints is present between a terminal box of the electrical machine and an intermediate plate of the electrical machine, and wherein a fifth flame path of the one or more flame paths is formed along the fifth assembly joint.

11. The electrical machine of claim 2, wherein the porous medium is thermally cycled to achieve a predetermined percentage of porosity.

12. The electrical machine of claim 2, wherein the porous medium is pressure treated to achieve a predetermined percentage of porosity.

13. The electrical machine of claim 2, wherein the porous medium is annealed to achieve a predetermined percentage of porosity.

14. A method, comprising: igniting, using an ignition source, a reactant mixture distributed within an enclosure of an electrical machine, to cause a flame to propagate from inside the enclosure to outside the enclosure through one or more flame paths, wherein the one or more flame paths are formed along a plurality of assembly joints of the electric machine, wherein one or more porous linings are positioned along the one or more flame paths, and wherein the one or more porous linings within the one or more flame paths cool down and reduce a flow rate of the flame as the flame propagates through the one or more flame paths.773011 (P240379 W001)15. The method of claim 14, wherein a porous medium of the one or more porous linings comprises at least one of ceramic foam, metal foam, metal wire mesh, and metal wool.

16. The method of claim 15, wherein the porous medium comprises open pores with interconnected passageways.

17. The method of claim 15, wherein the one or more porous linings are cut from pre-manufactured material of the porous medium and adhered to channels of the one or more flame paths.

18. The method of claim 14, wherein the one or more porous linings are sputtered on a surface of the one or more flame paths.

19. The method of claim 14, wherein a first assembly joint ofthe assembly joints is present between a stator frame of the electrical machine and a drive-end cover of the electrical machine, and wherein a first flame path of the one or more flame paths is formed along the first assembly joint.

20. An open rotor comprising: a plurality of assembly joints; an ignition source that ignites a reactant mixture distributed within the enclosure to cause a flame to propagate from inside the enclosure to outside the enclosure through one or more flame paths; and the one or more flame paths, wherein the one or more flame paths are formed along the plurality of assembly joints, wherein one or more porous linings are positioned along the one or more flame paths, and wherein the one or more porous linings within the one or more flame paths cool down and reduce a flow rate of the flame as the flame propagates through the one or more flame paths.

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