Fuel injector nozzle and method of making same

Abstract

A fuel injector and a nozzle for a fuel injector are provided. The nozzle is made of a hardened nozzle body blank. The hardened nozzle body blank is machined to leave a hard wear layer on the exterior surface of the nozzle body blank. The nozzle includes at least one orifice formed through a hard wear layer on an exterior surface of the nozzle body blank.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of the filing date of U.S. Provisional Application Serial No. 63 / 595,462, filed on November 2, 2023, which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to a fuel injection system for an internal combustion engine, and more particularly to a fuel injector nozzle and method of making the same. Background Art

[0004] Some fuel injectors include one or more orifices extending through a nozzle of the fuel injector. The orifices are subject to high mechanical loads and stresses during the fuel injection process. As a result, cavitation and erosion of material along the orifices can change the spray pattern and the amount of fuel passing through the orifices. Therefore, fuel injector nozzles are replaced at appropriate intervals. Although various attempts have been made to improve the durability of nozzle orifices, further improvements are still needed, such as those disclosed herein.

[0005] Disclosure of Illustrative Embodiments

[0006] In order to clearly, concisely and accurately describe the illustrative embodiments of the present disclosure, the manner and process of making and using the present disclosure and to enable the practice, making and using of the present disclosure, reference will now be made to certain exemplary embodiments, including the exemplary embodiments illustrated in the figures, and the present disclosure will be described using reference terms. It should be understood, however, that no limitation is thereby imposed on the scope of the present invention and that the present invention includes and protects such changes, modifications and other applications of the exemplary embodiments as will occur to those skilled in the art. Summary of the invention

[0007] The present disclosure includes a unique nozzle for a fuel injector and a fuel injection system for an internal combustion engine. The nozzle includes at least one spray hole for spraying fuel from the fuel injector. The spray hole extends from the inner surface of the nozzle to an outlet at the outer surface of the nozzle. The outer surface includes a hard wear-resistant material layer through which at least one spray hole is formed to improve the wear resistance at the outlet of the at least one spray hole, thereby improving the performance and life of the fuel injector.

[0008] In an embodiment, a nozzle for a fuel injector is provided. The nozzle includes an elongated body extending along a longitudinal axis from a first end of the elongated body to an opposite second end of the elongated body. The elongated body includes a longitudinally extending fuel passage extending from the first end of the elongated body to the second end of the elongated body. The outer surface at the second end of the elongated body includes a hard wear-resistant layer. At least one spray hole at the second end of the elongated body is formed through the hard wear-resistant layer, which is formed on the outer surface of the elongated body. At least one spray hole extends from the outer surface to the inner surface.

[0009] A method for producing a fuel injector nozzle is disclosed, comprising: hardening a nozzle body blank to include a hardened core and a hardened surface that is harder than the hardened core; machining the hardened surface of the nozzle body blank to maintain a hard wear layer on an outer surface of the nozzle body blank; and forming at least one spray hole through the hard wear layer on the outer surface of the nozzle body blank.

[0010] The present disclosure is neither intended to identify the key or essential features of the claimed subject matter nor to be used as an aid in limiting the scope of the claimed subject matter. Additional embodiments, forms, objects, features, advantages, aspects and benefits will become apparent from the following description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The description herein refers to the accompanying drawings, wherein like reference numerals refer to like parts throughout the several views, and in which:

[0012] Figure 1 is a schematic cross-sectional view of a fuel injector according to an embodiment of the present disclosure.

[0013] Figure 2 The present invention is a method for producing Figure 1 A schematic cross-sectional illustration of certain aspects of a fuel injector nozzle.

[0014] Figure 3 The present invention is a method for producing Figure 1 A cross-sectional view of certain additional aspects of a nozzle of a fuel injector.

[0015] Figure 4 The present invention is shown in the embodiment of the present invention. Figure 1 A cross-sectional view of the material layers produced during the nozzle construction of a fuel injector.

[0016] Figure 5 is a flow chart of a process for making a nozzle for a fuel injector according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0017] refer to Figures 1 to 4 , a nozzle 30 of a fuel injector 20 is shown. The nozzle 20 includes an elongated body 32 extending along a longitudinal axis 34 from a first end 42 of the elongated body 32 to an opposite second end 44 of the elongated body 32. The elongated body 32 includes an inner surface 50 defining a longitudinally extending fuel passage 36 extending from the first end 42 of the elongated body 32 to the second end 44 of the elongated body 32. The outer surface 52 at the second end 44 of the elongated body 32 includes a hard wear layer 70. At least one spray hole 38 at the second end 44 of the elongated body 32 is formed through the hard wear layer 70 formed on the outer surface 52 of the elongated body 32, and the at least one spray hole extends from the outer surface to the inner surface.

[0018] Further references Figure 5 , discloses a method 500 for producing a fuel injector nozzle 30. The method 500 includes: an operation or step 502 for hardening a nozzle body blank 32' to include a hardened core 74, and hardening the nozzle body blank 32' to include a hardened surface that is harder than the hardened core 74; an operation or step 504 for machining the hardened surface of the nozzle body blank 32' to maintain a hard wear layer 70 on the outer surface 52 of the nozzle body blank 32'; and an operation or step 506 for forming at least one spray hole 38 through the hard wear layer 70 on the outer surface 52 of the nozzle body blank 32'.

[0019] refer to Figure 1 , the fuel injector system 10 includes an accumulator 12 connected to a fuel injector 20 via a connection component 14. The accumulator 12 may be, for example, part of a high pressure common rail fuel injector system. The connection component 14 may include, for example, valves, throttles, control chambers, pipes, and other components that may be typically provided to connect the fuel injector 20 to the accumulator 12.

[0020] The fuel injector 20 includes a nozzle 30 that houses a needle valve 22. The nozzle 30 includes an elongated body 32 extending along a central longitudinal axis 34. The body 32 includes a fuel passage 36 in which the needle valve 22 is received. The needle valve 22 is elongated and extends between a proximal end 24 and a distal end 26 of the needle valve 22. The needle valve 22 moves longitudinally up and down in the fuel passage 36 to selectively start and stop fuel injection from the fuel passage 36 through one or more spray holes 38 of the nozzle 30.

[0021] Although only two orifices 38 are shown, embodiments having only one orifice or having three or more orifices are contemplated. In addition, the orifices 38 may be arranged in any pattern on the nozzle 30. In the illustrated embodiment, the orifices 38 are circular and include a uniform diameter from the inlet to the outlet. However, non-circular orifices and orifices having a non-uniform or varying size along the axial length of the orifice are also contemplated.

[0022] The nozzle 30 includes a first end 42 oriented proximally and an opposite second end 44 oriented distally. The second end 44 includes a dome 58 having a convex outer surface 52. The dome 58 extends about the longitudinal axis 34, and the orifice 38 is formed through the dome 58 from the outer surface 52 to the inner surface 50.

[0023] Fuel passage 36 forms pocket 46 in nozzle seat 48 at second end 44 of body 32. Distal end 26 of needle valve 22 moves in and out of engagement with inner surface 50 at nozzle seat 48 to selectively close and open orifice 38 for injecting fuel from pocket 46.

[0024] For example, during a fuel injection event, the closing force is removed from the needle valve 22 to allow the needle valve 22 to lift from the inner surface 50 of the nozzle seat 48 so that fuel is injected from the bladder 46 into the engine cylinder (not shown) through the spray hole 38. A needle valve spring 28 surrounding a portion of the needle valve 22 may be disposed in the fuel passage 36 to assist in controlling the longitudinal movement of the needle valve 22.

[0025] Now refer to Figures 2 to 4 Further details of the nozzle 30 including the dome 58 and the orifice 38 are discussed, it being understood that such details may also apply to any other orifice provided with the nozzle 30. Figure 2 , the nozzle body blank 32' is shown before the nozzle orifice 38 is formed. The nozzle body blank 32' is core hardened to a first hardness and then case hardened to a second hardness before the nozzle orifice 38 is formed. As a result, a hard wear layer 70 is formed on the outer surface 52 (including on the dome 58 at the distal end 44 of the nozzle body blank 32'). In addition, a hard wear layer 70 may also be formed on the inner surface 50.

[0026] In an embodiment, the first hardness is 40HRC to 45HRC (Rockwell hardness), and the second hardness is 60HRC to 65HRC.Other embodiments contemplate other hardness values ​​and / or measurements, as long as the hard wear layer is harder than the core.

[0027] In an embodiment, the size of the nozzle body blank 32' is designed so that even after the nozzle body blank 32' is finally machined, the hard wear layer 70 remains on the dome 58 and maintains a desired minimum thickness between the inner surface 50 and the outer surface 52 at the location where the nozzle hole 38 will be formed. In an embodiment, the desired minimum thickness is at least 100 microns to provide the desired wear resistance to the fuel spray at the outlet of the nozzle hole 38. In an embodiment, the desired minimum thickness is about 100 microns to 140 microns to provide the desired wear resistance at the outlet of the nozzle hole 38.

[0028] exist Figure 3 , the spray hole 38 is formed from the outer surface 52 of the dome 50 through the hard wear layer 70 to the inner surface 50 of the nozzle seat 48. For example, the spray hole 38 is formed to include an outlet 62 that opens through the hard wear layer 70 on the outer surface 52 of the nozzle body 32 at the dome 58. The spray hole 38 is formed through the dome 58 to include an inlet 60 that opens through the hard wear layer 70 on the inner surface 50 of the nozzle body 32 at the bladder 46.

[0029] The spray hole 38 includes a hole-defining surface 64 that passes through the dome 50, extends around the spray hole 38, and the hole-defining surface 64 extends from the inlet 60 to the outlet 62. The hole-defining surface 64 can be configured to define a conical spray hole 38 from the inlet 60 to the outlet 62. The hole-defining surface 64 can also or alternatively include, for example, longitudinal and / or spiral grooves, stepped configurations with different diameters, swirl-inducing configurations, varying cross-sectional sizes and / or shapes, cylindrical shapes, etc. Each of the spray holes 38 can have the same shape and / or configuration, or different shapes and / or configurations.

[0030] In an embodiment, the inner surface 50 and / or the outer surface 52 include a hard wear resistant material layer 70 that is produced after two-step hardening of the nozzle body blank 32' before the nozzle hole 38 is formed. In an embodiment, the first step involves hardening the core of the nozzle body blank 32' to a first hardness using a first heat treatment, and the second step involves hardening the surface (including the outer surface 52 of the dome 58 of the nozzle body blank 32') to a second hardness greater than the first hardness using a second heat treatment. The hard wear resistant layer 70 is a layer of material that remains on the surface or outer portion 52 of the dome 58 after final machining and after subjecting the hardened nozzle body blank 32' to a grinding, polishing and etching state before the nozzle hole 38 is formed.

[0031] Various techniques are contemplated for forming the orifice 38 through the hard wear layer 70, such as electrospark machining, electrochemical machining, laser drilling, micro-drilling, etc. In an embodiment, the hard wear layer 70 has a thickness of at least 100 microns extending from the outlet 62 along the hole-defining surface 64 after final machining to provide the orifice 38 with desired durability at or near the outlet 62. In an embodiment, the hard wear layer 70 has a thickness of about 100 microns to 140 microns extending from the outlet 62 along the hole-defining surface 64 after final machining to provide desired durability at the orifice outlet 62.

[0032] refer to Figure 4 , the core 74 is the original core material of the nozzle body blank 32' after core hardening in the first heat treatment of the nozzle body blank 32'. The core material of the nozzle body blank 32' can be any material suitable for use in a fuel injector nozzle, including, for example, any suitable metal and / or metal alloy. In an embodiment, the hardening of the nozzle body blank 32' can produce a diffusion layer 72 between the hard wear layer 70 and the core 74 of the nozzle body blank 32'.

[0033] In an embodiment, the hardening of the core 74 of the nozzle body blank 32' is accomplished using a heat dissipation process, and the hard wear layer 70 is also accomplished using a heat dissipation process. The heat dissipation process is designed to produce a uniform compound layer that includes the hard wear layer 70 and may include a porous layer covering the hard wear layer 70. In an embodiment, before the nozzle hole 38 is formed through the dome 58, the porous layer is removed from above the hard wear layer 70 on the outer surface 52 while maintaining the hard wear layer 70 with a desired minimum thickness. In an embodiment, the heat dissipation process is a gas nitriding process.

[0034] In an embodiment, the hole defining surface 64 includes a hardened surface profile that varies along the length of the orifice 38. For example, the hole defining surface 64 includes a first hardness extending from the outer surface 52 toward the inner surface 50 by a distance corresponding to the thickness of the hard wear layer 70, and a second hardness extending along the core 74 to the hard wear layer on the inner surface 50, the second hardness being less than the first hardness. The hard wear layer on the inner surface 50 can have a hardness greater than the hardness of the core 74.

[0035] In an embodiment, the pores in the porous layer covering the hard wear layer 70 formed by the surface hardening nitriding process are removed by a machining process before forming the spray hole 38. The machining process is controlled to keep the desired minimum thickness of the hard wear layer 70 while removing the porous layer. In an embodiment, the hardening and machining processes are controlled so that the thickness of the hard wear layer 70 after removing the porous layer is about 100 microns to 140 microns. In an embodiment, the nitriding process is designed to provide a hard wear layer 70 with a thickness of at least 100 microns after completing the abrasive flow machining process. In an embodiment, the hard wear layer 70 lacks surface pores after machining.

[0036] Since the nozzle hole 38 is formed through the hard wear layer 70 produced before the nozzle hole 38 is formed, the outlet 62 of the nozzle hole 38 and the outlets of other nozzle holes formed through the hard wear layer 70 are provided with enhanced mechanical and chemical properties. For example, the outlet 62 of the nozzle hole 38 has improved wear and corrosion performance characteristics compared to a nozzle having a nozzle hole formed through an external surface lacking a hard wear surface 70. The nitriding process of the present disclosure forms an extremely hard outer "shell" layer with compressive residual stress on the nozzle body blank 32', thereby making the outlet 62 of the nozzle hole 38 extremely strong against wear and fatigue.

[0037] Figure 5 , a method 500 for making a fuel injector nozzle according to the present disclosure is shown. The method 500 includes an operation 502 to core harden a nozzle body blank 32'. The nozzle body blank 32' can be machined from a solid soft blank of core material that will eventually form the nozzle 30. The nozzle body blank 32' can be machined to form the external shape and internal shape of the nozzle 30, such as the fuel passage 36, before core hardening. However, the spray holes 38 are not formed before the nozzle body blank 32' is hardened.

[0038] The core hardening treatment of the nozzle body blank 32' can be, for example, a heat dissipation process, such as a gas nitriding process, to increase the surface hardness to a specific hardness to facilitate subsequent machining. This first hardening treatment is followed by a second hardening treatment to form a hard wear-resistant layer 70 on the exposed surface of the core-hardened nozzle body blank 32' (including the outer surface 52 of the dome 58). The second hardening treatment can also be, for example, a heat dissipation process, such as a gas nitriding process. Other embodiments contemplate any suitable heat treatment process to harden the core 74 and / or the exterior of the dome 58.

[0039] The surface hardening of the nozzle body blank 32' forms a hard wear layer 70 along the inner surface 50 and / or the outer surface 52 (including the dome 58). The outer surface 52 of the nozzle body blank 32' at the dome 58 is surface hardened to a second hardness that is greater than the hardness of the hardened core 74. In an embodiment, the core 74 is hardened to 40HRC to 45HRC (Rockwell hardness), and the hard wear layer 70 is hardened to a hardness of 60HRC to 65HRC.

[0040] The method 500 continues to operation 504 to maintain the hard wear layer 70 on the exterior surface 52 of the dome 58 while machining the nozzle body blank 32'. In an embodiment, the exterior of the nozzle body blank 32' is machined after hardfacing to the final dimensions of the nozzle 30 while maintaining the hard wear layer 70 on the exterior surface 52 of the dome 50 at a desired minimum thickness.

[0041] The method 500 continues to operation 506 to form the orifice 38 through the hard wear layer 70 on the dome 58 in the hardfaced nozzle body blank 32'. The orifice location may be laser marked, and the orifice 38 may be formed from the outer surface 52 of the dome 50, through the outer hard wear layer 70, the core 74, and then through the inner hard wear layer.

[0042] As discussed above, the nozzle holes 38 may be formed in the core-hardened and case-hardened nozzle body blank 32' using any suitable hole forming device and / or technique. The outlet 62 of the nozzle hole 38 extends through the hard wear layer 70 on the exterior surface 52 of the dome 58. After the nozzle hole 38 is formed, no further machining or material removal of the exterior surface 52 of the dome 58 is required or performed. The hard wear layer 70 extends along the outlet end of the nozzle hole 38 and extends outwardly from the outlet 62 of the nozzle hole 38 along the exterior surface 52 of the dome 58.

[0043] Additional written descriptions of several aspects of the present disclosure will now be provided. According to one aspect, a nozzle for a fuel injector is provided. The nozzle includes an elongated body extending along a longitudinal axis. The body extends along the longitudinal axis from a first end of the elongated body to an opposite second end of the elongated body. The elongated body includes an inner surface defining a longitudinally extending fuel passage and an outer surface located at the second end of the elongated body. The fuel passage extends from the first end of the elongated body to the second end of the elongated body, and at least one spray hole is formed at the second end of the elongated body. The outer surface includes a hard wear-resistant layer formed thereon. At least one spray hole is formed through the hard wear-resistant layer formed on the outer surface of the elongated body to extend from the outer surface to the inner surface.

[0044] In an embodiment, the inner surface includes a hard wear layer at the second end of the elongated body, and at least one orifice is formed through the hard wear layer formed on the outer surface and the inner surface.

[0045] In an embodiment, the at least one orifice comprises a plurality of orifices, and each of the plurality of orifices forms a hard wear resistant layer through an outer surface of the elongated body.

[0046] In an embodiment, the second end of the elongated body includes a dome, and the hard wear resistant layer is formed on a convex outer surface of the dome.

[0047] In an embodiment, the core of the elongated body is hardened to a first hardness and the exterior of the elongated body is hardened to a second hardness greater than the first hardness to form a hard wear layer prior to forming the at least one orifice.

[0048] In an embodiment, at least one of the nozzle orifices includes a hole-defining surface extending from an outlet at an exterior surface of the elongated body to an inlet on an interior surface of the elongated body. The hard wear-resistant layer extends along the hole-defining surface from the outlet toward the inlet, so that the hole-defining surface includes a first hardness along the hard wear-resistant layer and a second hardness along the core of the nozzle body, the second hardness being less than the first hardness.

[0049] In another embodiment, the hard wear-resistant layer extends outwardly from the outlet of at least one spray hole along the outer surface of the elongated body. The hard wear-resistant layer extends outwardly from the inlet of at least one spray hole along the inner surface of the elongated body.

[0050] In embodiments, the hard wear resistant layer comprises a thickness of at least 100 microns.

[0051] In embodiments, the hard wear resistant layer comprises a thickness of at least 100 microns to 140 microns.

[0052] According to another aspect of the present disclosure, a method for producing a fuel injection nozzle is provided, the method comprising: hardening a nozzle body blank to include a hardened core and a hardened surface harder than the hardened core; machining the hardened surface of the nozzle body blank to maintain a hard wear layer on an outer surface of the nozzle body blank; and forming at least one spray hole through the hard wear layer on the outer surface of the nozzle body blank.

[0053] In an embodiment, machining of the hardened surface is controlled such that a minimum thickness is maintained for the hard wear resistant layer on the exterior surface after machining is completed.

[0054] In an embodiment, the mechanical processing of the hardened surface is controlled so that after the mechanical processing is completed, the minimum thickness of the hard wear layer on the outer surface is at least 100 microns. In an embodiment, the mechanical processing of the hardened surface is controlled so that after the mechanical processing is completed, the minimum thickness of the hard wear layer on the outer surface is about 100 microns to 140 microns.

[0055] In an embodiment, the inner surface of the hardened surface includes a hard wear resistant layer. The inner surface defines a fuel passage. The method also includes forming at least one spray hole from the outer surface through the inner surface.

[0056] In embodiments, the method includes forming a dome including at least a portion of the exterior surface on a nozzle body blank, and forming at least one orifice through the dome.

[0057] In an embodiment, hardening the nozzle body blank includes hardening a core of the nozzle body blank to a first hardness, and hardening a surface of the nozzle body blank to a second hardness greater than the first hardness.

[0058] In another embodiment, hardening the core to a first hardness includes hardening the core to about 40HRC to 45HRC, and hardening the surface to a second hardness includes hardening the surface to about 60HRC to 65HRC. In another embodiment, the core is hardened in a core hardening heat treatment process, and the surface is hardened in a surface hardening heat treatment process, which is performed after the core hardening heat treatment process and before forming at least one nozzle hole.

[0059] In an embodiment, hardening the nozzle body blank includes subjecting the nozzle body blank to two separate heat dissipation processes to first harden the core of the nozzle body blank and then case harden the exterior surface of the nozzle body blank. In another embodiment, the heat dissipation process is a gas nitriding process.

[0060] Although the illustrative embodiments of the present disclosure have been described in detail and in the drawings and the foregoing description, this is to be considered illustrative rather than restrictive in nature, and it is to be understood that only certain exemplary embodiments have been shown and described, and all changes and modifications that fall within the spirit of the claimed invention are expected to be protected. It should be understood that although the use of words (such as, preferably, preferred, preferred, or more preferred) utilized in the above description indicates that the features described so may be more desirable, it is not necessary and embodiments without such words are envisioned to be within the scope of the present invention, which scope is defined by the appended claims. When reading the claims, it is intended that when words such as "one", "a", "at least one", or "at least one portion" are used, it is not intended to limit the claim to only one article, unless there is an explicit statement to the contrary in the claim. When the language "at least a portion" and / or "a portion" is used, the article may include a portion and / or the entire article unless there is an explicit statement to the contrary.

Claims

1. A nozzle for a fuel injector, the nozzle comprising: an elongated body extending along a longitudinal axis, the body extending along the longitudinal axis from a first end of the elongated body to an opposite second end of the elongated body, the elongated body comprising: an inner surface defining a longitudinally extending fuel passage extending from the first end of the elongated body to the second end of the elongated body; an exterior surface at the second end of the elongated body, the exterior surface including a hard wear resistant layer formed thereon; and At least one spray hole located at the second end of the elongated body is formed through the hard wear-resistant layer formed on the outer surface of the elongated body to extend from the outer surface to the inner surface.

2. The nozzle of claim 1, wherein the inner surface includes a hard wear layer at the second end of the elongated body, and the at least one spray hole is formed through the hard wear layer formed on the outer surface and the inner surface.

3. The nozzle of claim 1, wherein the at least one orifice comprises a plurality of orifices, and each of the plurality of orifices forms through the hard wear resistant layer on the exterior surface of the elongated body.

4. The nozzle of claim 1 wherein the second end of the elongated body includes a dome and the hard wear resistant layer is formed on a convex outer surface of the dome.

5. The nozzle of claim 1, wherein a core of the elongated body is hardened to a first hardness and an exterior of the elongated body is hardened to a second hardness greater than the first hardness to form the hard wear layer prior to forming the at least one orifice.

6. The nozzle of claim 1 , wherein the at least one spray hole comprises a hole defining surface extending from an outlet at the outer surface of the elongated body to an inlet on the inner surface of the elongated body, and the hard wear resistant layer extends along the hole defining surface from the outlet toward the inlet, so that the hole defining surface comprises a first hardness along the hard wear resistant layer and a second hardness along the core of the nozzle body, the second hardness being less than the first hardness.

7. The nozzle of claim 6, wherein: The hard wear-resistant layer extends outwardly from the outlet of the at least one spray hole along the outer surface of the elongated body; and The hard wear resistant layer extends outwardly from the inlet of the at least one spray hole along the inner surface of the elongated body.

8. The nozzle of claim 1, wherein the hard wear resistant layer comprises a thickness of at least 100 microns.

9. The nozzle of claim 1, wherein the hard wear resistant layer comprises a thickness of about 100 microns to 140 microns.

10. A method for producing a fuel injection nozzle, the method comprising: hardening the nozzle body blank to include a hardened core and a hardened surface harder than the hardened core; machining the hardened surface of the nozzle body blank to maintain a hard wear resistant layer on an exterior surface of the nozzle body blank; as well as At least one spray hole is formed through the hard wear resistant layer on the exterior surface of the nozzle body blank.

11. The method of claim 10, wherein machining the hardened surface is controlled such that a minimum thickness is maintained for the hard wear resistant layer on the exterior surface after the machining is completed.

12. The method of claim 10, wherein machining the hardened surface is controlled such that a minimum thickness of at least 100 microns is maintained for the hard wear resistant layer on the exterior surface after machining is completed.

13. The method of claim 10, wherein machining the hardened surface is controlled such that a minimum thickness of about 100 microns to 140 microns is maintained for the hard wear resistant layer on the exterior surface after the machining is completed.

14. The method of claim 10, wherein an inner surface of the hardfacing includes a hard wear layer, the inner surface defining a fuel passage, and further comprising: The at least one spray hole is formed from the outer surface through the inner surface.

15. The method of claim 10, further comprising forming a dome on the nozzle body blank that includes at least a portion of the exterior surface, and forming the at least one orifice includes forming the at least one orifice through the dome.

16. The method of claim 10, wherein hardening the nozzle body blank comprises: hardening the core of the nozzle body blank to a first hardness; as well as The surface of the nozzle body blank is hardened to a second hardness greater than the first hardness.

17. The method of claim 16, wherein hardening the core to the first hardness comprises hardening the core to approximately 40 HRC to 45 HRC and hardening the surface to the second hardness comprises hardening the surface to approximately 60 HRC to 65 HRC.

18. The method of claim 16, wherein the core is hardened in a core hardening heat treatment process and the surface is hardened in a surface hardening heat treatment process, the surface hardening heat treatment process being performed after the core hardening heat treatment process and before forming the at least one nozzle hole.

19. The method of claim 10, wherein hardening the nozzle body blank comprises subjecting the nozzle body blank to two separate heat dissipation processes to first harden the core of the nozzle body blank and then case harden the exterior surface of the nozzle body blank.

20. The method of claim 19, wherein the heat dissipation process is a gas nitriding process.

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