INJECTOR FOR ALTERNATIVE FUEL

Abstract

The invention relates to a fuel injector for an internal combustion engine, particularly for liquid alternative fuels. The injector comprises an injection nozzle whose tip includes a seat body with a sealing surface and at least one injection orifice. The injection orifices (5) are formed in a portion of a dome, downstream of a sealing surface. The seat body is made of high-temperature austenitic stainless steel and has an anti-cavitation diffusion layer covering at least the sealing surface, the inner surface of the dome, and the injection orifices. The anti-cavitation diffusion layer is obtained by a diffusion surface treatment and extends to a maximum depth of 30 µm, having a hardness of at least 750 Hv, for a load of 0.1 kgF. (Fig. 1)

Description

Title of the invention: INJECTOR FOR ALTERNATIVE FUELS technical field

[0001] The present invention relates to fuel injection in internal combustion engines, and more particularly to fuel injectors intended for the direct injection of liquid alternative fuels, for example of type E100, M100 or e-fuel. State of the art

[0002] Fuel injectors, or simply injectors, are used in internal combustion engines to introduce controlled amounts of fuel into a cylinder / combustion chamber. Typically, two configurations are used: direct injection (injector mounted in the cylinder head in an orifice that opens into the combustion chamber); indirect injection (PFI: the injector is arranged to emit fuel into the intake duct just before the intake valve(s)).

[0003] A fuel injector for direct gasoline injection comprises a nozzle portion defining a fuel passage, the distal end of which has a seat body defining a sealing seat located upstream of a bag portion equipped with a plurality of injection holes. A sealing element in the form of a needle or ball can be moved axially from a closed position to an open position. In the closed position, the needle closes the nozzle by resting on the seat. In the open position, the needle is separated from the sealing seat and allows fuel to pass through the injection holes, which penetrate the wall of the bag, thus enabling the injection / atomization of fuel into the combustion chamber. The injector is directly controlled by an electromechanical actuator, for example, a solenoid.

[0004] Conventionally, such an injector for direct gasoline injection comprises a seat made of a martensitic steel-type material. With the aim of reducing the carbon footprint of industry and the transportation sector, new fuels have recently emerged, such as methanol- and / or ethanol-based fuels (fuels derived from biomass and typically containing 10 to 100% methanol and / or ethanol by volume). It has been observed that these alternative fuels exhibit different injection behaviors, causing premature and undesirable wear of the injector, particularly at the seat. Technical problem

[0005] There is therefore a need to develop injectors that are resistant to a wide variety of fuels, more particularly to alternative fuels including alcohol-type compounds. General description of the invention

[0006] With this objective in mind, the present invention relates to a fuel injector for an internal combustion engine comprising, in particular for liquid alternative fuels:

[0007] an injection nozzle defining a fuel passage whose distal end comprises a seat body with a sealing surface and at least one injection hole, the seat body cooperating with a shuttering member that is axially movable between a closed position in which it rests on the sealing surface to prevent fuel injection, and an open position in which the shuttering member is lifted from the sealing surface to allow fuel injection through the injection hole(s);

[0008] in which the injection holes are made in a portion of the dome, downstream of the sealing surface; characterized in that

[0009] the seat body is made of high temperature austenitic stainless steel, which is an austenitic stainless steel comprising 0.5 to 0.6 m.% Carbon, less than 0.5 m.% Silicon, less than 10.0 m.% Manganese, 15 to 25 m.% Chromium, 1.0 to 6.0 m.% Ni, less than 3.0 m.% Niobium, less than 2.0 m.% Tungsten, less than 1.0 m.% Nitrogen, and the balance of Iron (i.e. up to 100 m.%);

[0010] the seat body has an anti-cavitation diffusion layer covering at least the sealing surface, the inner surface of the dome and the injection holes;

[0011] said anti-cavitation diffusion layer being obtained by a surface treatment by diffusion and extending over a maximum depth of 30 pm, and having a hardness of at least 800 Hv on the surface, for a load of 0.05 kgF (0.49 N).

[0012] The invention thus proposes an anti-cavitation surface layer which is a diffusion layer obtained by a diffusion treatment on the surface of the seat body, making it possible to enrich the surface of the seat body with carbon or with carbon and nitrogen depending on the diffusion process used. The diffusion layer extends from the surface of the seat body to a controlled depth.

[0013] It will be appreciated that the seat body is made of high-temperature austenitic stainless steel. High-temperature austenitic stainless steel, as defined in the invention, represents an austenitic stainless steel that provides resistance to comparatively higher temperatures than conventional austenitic stainless steel, notably through the addition of nitrogen and nickel.

[0014] The seat body is advantageously made of high-temperature austenitic stainless steel of the CrMnNi type. In particular, the austenitic stainless steel comprises or is composed of 0.5 to 0.6 m% Carbon, less than 0.5 m% Silicon, less than 10.0 m% Manganese, 15 to 25 m% Chromium, 1.0 to 6.0 m% Ni, less than 3.0 m% Niobium, less than 2.0 m% Tungsten, less than 1.0 m% Nitrogen, and Iron (to reach m.100%). The mass percentages m.% are expressed relative to the total mass of the austenitic stainless steel composition. The compositions may include other residual elements present as impurities at levels generally less than 0.1 m.%.

[0015] Depending on variants, the seat body is made of austenitic stainless steel of type VA61, VA66, or VA63.

[0016] The inventors observed that the use of alternative fuels such as methanol (MeOH) and ethanol (EtOH) leads to premature wear of the injector seat. In particular, they found that this premature wear is induced by the physicochemical properties of these alternative fuels, which, at the injector's operating pressure, increase cavitation erosion and corrosion. Alternative fuels, primarily due to their lower boiling point compared to traditional fuels, increase cavitation within the injector body, especially when the needle / ball contacts the injector seat.Injection-induced cavitation tends to remove the passivation layer formed on the surface of the austenitic stainless steel seat, leading to the appearance of cavities that are susceptible to corrosion (particularly following the local disappearance of the natural chromium oxide-based passivation layer characteristic of stainless steels), which can even lead to cracking.

[0017] Surprisingly, the inventors found that treating the surface layer of the seat (made of high-temperature austenitic stainless steel) by forming an anti-cavitation diffusion layer, also called a surface layer, not only reduces corrosion but also prevents it. Indeed, the inventors observed that such a diffusion layer enriched with carbon and / or nitrogen increases the surface hardness of the austenitic stainless steel seat body (generally to at least 800 Hv for a 0.05 kgf load) and thus effectively reduces the negative effect of cavitation that occurs during the injection of alternative fuels.

[0018] It should be noted that, generally, injector seat bodies are made of martensitic stainless steel, austenitic stainless steel having higher ductility and lower mechanical strength than stainless steels martensitic. For this reason, and particularly with regard to reduced hardness, austenitic steels were not typically used in this type of application.

[0019] The present invention thus overcomes a technical prejudice held by those skilled in the art. In particular, the inventors have found that a high-temperature austenitic stainless steel as described makes it possible to manufacture a seat body that exhibits suitable mechanical properties and resistance to corrosion and cavitation in the context of alternative fuel injection. Initial tests have demonstrated that such a high-temperature austenitic stainless steel exhibits improved performance compared to conventional martensitic stainless steels.

[0020] Preferably, the seat body has a core hardness between 350 and 450 Hv. Core hardness refers to the hardness of the internal part of the seat body, the hardness of which depends on the chemical composition and processing of the steel. It is preferably measured at depths of at least 0.400 mm, and preferably at least 0.750 mm from the surface. This hardness is preferably measured under a load of 10 kgf (98, IN).

[0021] According to variants, the diffusion surface treatment is a thermochemical surface treatment by carbon diffusion, conventionally called Kolsterizing (in English, Kolsterising, registered trademark). Preferably, the treatment is carried out at a temperature between 300°C and 550°C, preferably below 500°C, and more preferably below 450°C.

[0022] The high-temperature austenitic stainless steel seat body treated by a carbon diffusion surface treatment includes a diffusion layer extending from the surface of the seat body to a depth of up to 30 pm, or up to 25 pm, or up to 20 pm, or even up to 15 pm.

[0023] Preferably, the seat body treated by a carbon diffusion surface treatment has an anti-cavitation diffusion layer having a surface hardness of between 800 and 1200 Hv for a load of 0.05kgF (0.49 N).

[0024] Preferably, after treatment, the anti-cavitation diffusion layer has a hardness of at least 400 Hv at a depth of 5 pm for a load of 1 kgF (9.81 N). After treatment, the anti-cavitation diffusion layer has a hardness between 350 and 450 Hv at a depth of 30 pm for a load of 10 kgF (98.1 N).

[0025] Advantageously, carbon diffusion is a process for diffusing carbon beneath the surface of the treated stainless steel part and is carried out at low temperature. Advantageously, carbon diffusion does not form chromium carbide precipitates that could embrittle the stainless steel. Furthermore, this treatment increases abrasion resistance without altering the corrosion resistance of austenitic stainless steel.

[0026] In various embodiments, the diffusion surface treatment is a thermochemical nitrocarburizing diffusion process characterized by a nitrogen- and carbon-enriched diffusion layer extending from the surface to a controlled depth. This can be described as a double hardening layer, more precisely obtained by nitrogen diffusion for surface hardening and by carbon diffusion to facilitate the hardness transition to the ductile core. This treatment is carried out on the surface of the high-temperature austenitic steel seat body. The anticavitation diffusion layer can be obtained by a nitrocarburizing process at a temperature below 550°C, preferably between 300 and 500°C, and extends to a depth of up to 30 µm, or up to 25 µm, or up to 20 µm, or even up to 15 µm.

[0027] Preferably, the anti-cavitation diffusion layer has a hardness of at least 750 Hv for 0.1 kgF (0.98 N) at a depth of 2 pm, or alternatively, the anti-cavitation diffusion layer has a hardness of at least 400 Hv for 1 kgF (9.81 N) at a depth of 10 pm. Advantageously, the seat body has a surface hardness of up to 1200 Hv after nitrocarburizing treatment. The hardness profile can be controlled to optimize the level of hardness for cavitation resistance, in particular by adjusting the amounts of nitrogen and carbon supplied to the surface and the depth gradient.

[0028] The present injector is therefore particularly intended for the injection of alternative liquid fuels, such as E100, M100 or e-fuel.

[0029] It will be noted that initial laboratory tests with injectors comprising a seat body having an anti-cavitation diffusion layer according to the invention have yielded satisfactory results. Tests were carried out with M100 fuel injected at 250 bar. After 150 hours of operation, microscopic observation of the seat did not reveal any obvious wear phenomena of the corrosion / cavitation type.

[0030] According to variants, the obturator is a needle, in particular with a ball welded to the end, and an armature surrounds the needle and cooperates with it for the lifting of the seat under the effect of a magnetic field created by a solenoid.

[0031] According to another aspect, the invention relates to the use of the present injector for injecting e-fuel or biomass-derived biofuels, predominantly composed of alcohol, into a cylinder of an internal combustion engine at pressures of 250 to 500 bar, in particular 350 bar. "Predominantly" here means comprising more than 50% alcohol, in particular more than 60%, 70%, 80%, or 90%, and up to 100%. The alcohol may, in particular, be ethanol or methanol. In particular, the fuel may be of the ElO0 or MlO0 type.

[0032] E100 (EtOH) is a bioethanol-type biofuel usable for certain gasoline combustion engines and containing 100% ethanol (pure ethanol, which can be produced, for example, from sugarcane plants, as in Brazil). M100 (MeOH) is a biomethanol-type biofuel usable for certain gasoline combustion engines and containing 100% methanol (pure methanol, which is present, for example, on the automotive market in China). In the context of the invention, e-fuels are synthetic fuels or electrofuels that can be produced from carbon dioxide, nitrogen dioxide (synthesis of e-ammonia), "green" hydrogen produced by water electrolysis, low-carbon or renewable electricity. They can be in liquid form (as is the case for this invention) or gaseous form.

[0033] According to another aspect, the invention relates to an internal combustion engine comprising a fuel supply system including a liquid fuel tank, a fuel rail connected to the liquid fuel tank via at least one high-pressure pump for supplying the fuel rail at a pressure of at least 100 bar, and at least one fuel injector according to the invention coupled to the fuel rail, in which the fuel is low boiling point, preferably an e-fuel type fuel or one consisting mainly of an alcohol.

[0034] According to another aspect, the invention relates to a method for manufacturing a fuel injector in accordance with the present disclosure, comprising:

[0035] the supply of a high-temperature austenitic stainless steel seat body comprising a dome portion with injection holes, downstream of a sealing surface;

[0036] the treatment of the seat body by diffusion surface treatment in order to form an anti-cavitation diffusion layer covering at least the inner surface of the portion of the dome, the surface of the injection holes and the sealing surface, said anti-cavitation diffusion layer extending over a maximum depth of 30 pm and having a hardness of at least 750 Hv for a load of 0.1 kgF;

[0037] the assembly of the seat body thus treated in the injection nozzle; and

[0038] wherein the seat body is made of austenitic stainless steel comprising 0.5 to 0.6 m.% Carbon, less than 0.5 m.% Silicon, less than 10.0 m.% Manganese, 15 to 25 m.% Chromium, 1.0 to 6.0 m.% Ni, less than 3.0 m.% Niobium, less than 2.0 m.% Tungsten, less than 1.0 m.% Nitrogen, and Iron; and

[0039] the surface treatment is carried out by a carbon or carbon and nitrogen diffusion treatment process at a temperature below 550°C. Brief description of the drawings

[0040] Other features and characteristics of the invention will become apparent from the detailed description of some advantageous embodiments presented below by way of illustration, with reference to the accompanying drawings. These show:

[0041] [Fig-1] a longitudinal cross-sectional view through a direct fuel injection injector;

[0042] [Fig.2] a simplified diagram of the injector seat body of the [Fig.1];

[0043] [Fig.3] a cross-sectional view under an optical microscope of a seat body according the invention:

[0044] [Fig.4] an enlarged view of [Fig.3] of part of the inner surface of the dome; And

[0045] [Fig.5] an enlarged view of [Fig.3] showing an injection hole. Description of a preferred execution

[0046] Figure 1 shows a cross-sectional view of a fuel injector 1, or simply injector. The injector 1 has a conventional design for direct gasoline injection and will therefore be described briefly. It comprises a generally tubular housing 2 extending along a longitudinal direction A and defining an internal passage 7 for the liquid fuel extending from an inlet portion on a proximal side 2.1 and an outlet portion on a distal side 2.2. The outlet portion includes a nozzle 4 with a seat body 3 having an annular sealing surface 3.1 and a plurality of injection holes 5. The seat body 3 is an added component fixed to the tubular portion of the nozzle by press fitting and welding. As can be seen more clearly in Figure 2, the seat body 3 has a cup shape, comprising a bottom 3.2 from which a peripheral wall 3.3 rises. The background 3.2 includes a dome 3.4 in distal projection in which the injection holes are made 5. The region of the internal volume of the dome is typically called bag 3.5. .

[0047] The passage of fuel through the injection holes 5 is controlled by a needle-shaped shut-off member 8 arranged in the passage 7. The needle 8, which includes a ball 9 welded to its distal end, is movable between a closed position, as shown in [Fig. 1], and an open position (not shown). In the closed position, the ball 9 rests on the annular sealing surface 3.1 of the seat body 3 and prevents fuel from passing into the bag 3.5 and the injection holes 5. The reference numeral 10 indicates an armature surrounding the needle 8, which allows the needle to be lifted from its seat by a magnetic field generated by a solenoid 12 when it is energized. Classically, the armature moves in the proximal direction under the effect of the magnetic field and moves the needle by cooperating with an annular radial collar of the needle 8. The needle 8 is returned to the closed position by a spring 13.A second spring 14 returns the armature to its rest (distal) position.

[0048] It will be noted that the sealing surface 3.1 typically surrounds the dome 3.4 and is therefore upstream of the injection holes 5. The injection holes 5 pass completely through the dome 3.4, at respective predetermined angles with respect to the axis A. Conventionally, the injection holes 5 comprise a first part, called orifice 5.1, whose diameter is calibrated to form a jet of atomized fuel, and a second part of larger diameter, called counter-orifice 5.2, which contributes to the formation of the jet.

[0049] The holes 5 can be, for example, from 5 to 9 in number. The orifices 5.1 can have a diameter of around 100 pm; the counter-orifices 5.2 can have a diameter of around 400 to 500 pm. <invention>

[0050] In accordance with the invention, a surface hardening treatment by diffusion of the Kolsterization type (carbon diffusion) was applied to the seat body 3 so as to form an anti-cavitation diffusion layer.

[0051] Figs. 3 to 5 show cross-sectional views of a seat body according to the invention, i.e., with a dome and injection holes, and treated to form an anti-cavitation diffusion layer 6 with the prescribed depth and hardness. As can be seen, the anti-cavitation diffusion layer 6 is a layer of uniform thickness (lighter surface layer), also in the region of the holes 5, which are coated over their entire internal surface, both in the orifice part 5.1 and the counter-orifice part 5.2 (see [Fig. 5]). In this example, the depth is between 22 and 24 µm.

[0052] The seat body is made of high-temperature austenitic stainless steel developed for valve applications, the main components of which are iron, chromium, manganese, and nickel. The austenitic structure is achieved primarily through the addition of nitrogen and nickel, balanced by the high chromium content, despite an average carbon percentage of approximately 0.5% (standard austenitic steels have carbon percentages below 0.10%). This austenitic stainless steel is also referred to as the base material hereafter. The seat body material comprises 0.52 m% Carbon, 0.20 m% Silicon, 9.0 m% Manganese, 21.0 m% Chromium, 4.0 m% Ni, 2.0 m% Niobium, 1.0 m% Tungsten, 0.50 m% Nitrogen, and Iron to make up to 100 m% (balance).High-temperature austenitic stainless steels alloyed with chromium, nickel, and manganese are particularly advantageous due to their excellent corrosion resistance, even in aggressive environments such as high temperatures, high pressures, or in the presence of corrosive gases or elements. Here, an austenitic stainless steel composition is used with niobium (Nb) and tungsten (W), the presence of which improves the mechanical properties of the stainless steel at high temperatures. high temperatures but also improve the stability of the austenitic structure at high temperatures.

[0053] The anti-cavitation diffusion layer is formed so as to cover at least the inner surface of the dome 3.4, the surface of the injection holes 5, and the annular sealing surface 3.1. The anti-cavitation diffusion layer is a carbon-enriched diffusion layer, which extends from the surface to a depth of up to 24 pm ([Fig.4] and 5), and which has a surface hardness of 1098 Hv for a load of 0.05 kgF.

[0054] This anti-cavitation diffusion layer 6 is visible in Figures 3 to 5, which are microscopic images of a seat body according to the invention. It is the grey-coloured surface layer.

[0055] For simplified processing, the entire part is treated.

[0056] The anti-cavitation diffusion layer 6 is formed by a Kolsterization process at low temperature, i.e. at a temperature below 550°C; it is adopted to preserve the behavior of the base material, in particular its mechanical properties.

[0057] Thus, the low-temperature Kolsterization process is carried out at a temperature below 550°C, for example, from 300 to 500°C and preferably between 400 and 450°C, to avoid phase transitions or the precipitation of undesirable compounds that could have a negative effect, such as the formation of a more ductile (soft) material or a material more susceptible to corrosion. Controlling the temperature and pressure (concentration of species in the atmosphere) allows the depth of the formed layer to be influenced, and therefore allows the final hardness of the base material to be controlled.

[0058] The Kolsterization process involves the controlled diffusion of carbon onto the surface of the seat body. This process results in a diffusion layer beneath the surface of the seat body that exhibits a hardness gradient with increasing depth, thus enhancing the wear resistance of the seat body. The surface carbon content increases by approximately 1 µm.% in the diffusion layer, i.e., on the surface of the part, following Kolsterization.

[0059] As is known, in such surface thermochemical treatment processes, the main parameters that control the process, and therefore the layer depth and hardness, are temperature, pressure (species concentration), and treatment time. By opting for Kolsterization, the inventors have thus chosen a compromise that allows for faster treatment of the parts, achieving a hardness of 750 Hv at 0.1 kg·F, while limiting the treatment to a depth of 30 µm. The inventors have thus established that these parameters of the diffusion layer based carbon is sufficient to significantly limit cavitation-related degradation when operating with alternative fuels at pressures of 300 to 500 bar.

[0060] Furthermore, it is not desirable for the anti-cavitation surface layer 6 to extend beyond 30 pm in the dome and hole region, so as not to weaken them. Indeed, excessive hardening depth in this region would cause embrittlement, potentially accelerating fatigue phenomena due to fuel cyclic pressures and causing surface finish problems on the seat.

[0061] The anti-cavitation diffusion layer 6 exhibits a hardness of 605 Hv at a depth of 10 pm for a load of 0.01 kgF, 413 Hv at a depth of 50 pm for a load of 0.5 kgF, and a core hardness of 381 Hv for a load of 10 kgF (98, IN). In comparison, the high-temperature austenitic stainless steel seat body before treatment exhibits a hardness of 541 Hv at a depth of 10 pm for a load of 0.01 kgF, 358 Hv at a depth of 50 pm for a load of 0.5 kgF, and a core hardness of 323 Hv for a load of 10 kgF (98, IN). The hardness of the seat body is therefore improved after carbon diffusion treatment.

[0062] It will be appreciated that the present invention can be advantageously implemented with known Kolsterization techniques, however, at temperatures not exceeding 550°C, for example between 300 and 500°C.

[0063] Furthermore, the inventors observed that increasing the surface hardness of the injector nozzle body not only reduces the risk of cavitation, and therefore cavitation-related cracking, but also reduces the risk of corrosion. Indeed, liquid fuels such as methanol and ethanol (or a mixture thereof) have lower boiling points compared to conventionally used fuels. Moreover, these new fuels have higher water content, increased acidity, and weaker lubricating properties, consequently leading to a greater risk of corrosion and premature wear due to friction.The surface treatment by Kolsterization according to the present invention increases surface hardness, reduces cracking caused by cavitation, and also reduces the risk of removing the passivation layer during cavitation phenomena, thus reducing the risk of erosion and corrosion and increasing wear resistance.

[0064] In the context of the invention, hardness is indicated according to the Vickers scale. As is known, this measurement method uses a diamond indenter in the shape of a square-based pyramid that is pressed into the surface of the material with a specific load. The diagonal of the indentation left is measured, and the hardness is calculated in using the applied load and the surface area of ​​the indentation. Each measurement value is therefore given with the corresponding load.

[0065] Vickers hardness measurements are typically carried out according to ISO 6507 (ISO 6507-1:2023, ISO 6507-2:2018 and ISO 6507-3:2018) and the ASTM E384 standard test method.< / invention>

Claims

Demands

1. Fuel injector for an internal combustion engine comprising, in particular for liquid alternative fuels: an injection nozzle (4) defining a fuel passage (7) the distal end of which has a seat body (3) with a sealing surface (3.1) and at least one injection hole (5), the seat body (3) cooperating with a sealing member (8) movable axially between a closed position in which it rests on the sealing surface (3.1) to prevent fuel injection, and an open position in which the sealing member is lifted from the sealing surface (3.1) to permit fuel injection through the injection hole(s) (5); wherein the injection holes (5) are made in a portion of a dome (3.4), downstream of the sealing surface (3.1); characterized in that the seat body (3) is made of austenitic stainless steel comprising 0.5 to 0.6m.% Carbon, less than 0.5m% Silicon, less than 10.0m% Manganese, 15 to 25m% Chromium, 1.0 to 6.0m% Ni, less than 3.0m% Niobium, less than 2.0m% Tungsten, and less than 1.0m% Nitrogen, and Iron; the seat body (3) has an anti-cavitation diffusion layer (6) covering at least the sealing surface (3.1), the inner surface of the dome and the injection holes (5); said anti-cavitation diffusion layer (6) being obtained by a diffusion surface treatment and extending to a maximum depth of 30 pm, and having a hardness of at least 750 Hv, for a load of 0.1 kgF (0.98 N).

2. Fuel injector according to claim 1, wherein the anti-cavitation diffusion layer (6) is obtained by a carbon diffusion process at a temperature between 300°C and 550°C, preferably below 500°C, and extends over a depth of up to 30 pm, or up to 25 pm, or up to 20 pm, or even up to 15 pm.

3. Fuel injector according to claim 1 or 2, wherein the anti-cavitation diffusion layer (6) has a surface hardness of between 800 and 1200 Hv for a load of 0.05kgF (0.49 N).

4. Fuel injector according to any one of the preceding claims, wherein the anti-cavitation diffusion layer (6) has, at a depth of 5 pm, a hardness of at least 400 Hv for a load of IkgF (9.81 N).

5. Fuel injector according to any one of the preceding claims, wherein the anti-cavitation diffusion layer (6) has a hardness of between 350 and 450 Hv at a depth of 30 pm, for a load of 10 kgF (98.1 N).

6. Fuel injector according to claim 1, wherein the anti-cavitation diffusion layer (6) is obtained by a nitrocarburizing process at a temperature below 550°C, preferably at a temperature between 300 and 500°C, and extends over a depth of up to 30 pm, or up to 25 pm, or up to 20 pm, or even up to 15 pm.

7. Fuel injector according to claim 1 or 6, wherein the anti-cavitation diffusion layer (6) has at a depth of 10 pm a hardness of at least 400 Hv for IkgF (9.81 N).

8. Fuel injector according to any one of the preceding claims, wherein the seat body (3) has a core hardness of between 350 and 450 Hv, the core hardness being measured for a load of 10 kgF (9.80 N).

9. Fuel injector according to any one of the preceding claims, wherein the seat body (3) of high-temperature austenitic stainless steel is made of 0.52 m% Carbon, 0.20 m% Silicon, 9.0 m% Manganese, 21.0 m% Chromium, 4.0 m% Ni, 2.0 m% Niobium, 1.0 m% Tungsten, 0.50 m% Nitrogen, and Iron up to 100 m% by total weight of the high-temperature austenitic stainless steel composition.

10. Use of an injector according to any one of the preceding claims for the injection of liquid fuel of the e-fuel type or comprising predominantly an alcohol into a cylinder of an internal combustion engine, at pressures of 250 to 500 bar, in particular 350 bar.

11. Internal combustion engine comprising a fuel supply system including a liquid fuel tank, a fuel rail connected to the liquid fuel tank via at least one high-pressure pump for supplying the fuel rail at a pressure of at least 100 bar, and at least one

12. fuel injector according to any one of claims 1 to 9 coupled to the fuel rail, wherein the fuel is a low boiling point fuel, preferably an e-fuel type fuel or one consisting mainly of an alcohol. A method for manufacturing a fuel injector according to any one of claims 1 to 9, comprising: the supply of a seat body (3) made of high temperature austenitic stainless steel comprising a portion of dome (3.4) with injection holes (5), downstream of a sealing surface (3.1); the treatment of the seat body (3) by diffusion surface treatment to form an anti-cavitation diffusion layer (6) covering at least the inner surface of the portion of the dome (3.4), the surface of the injection holes (5) and the sealing surface (3.1); said anti-cavitation diffusion layer (6) extending to a maximum depth of 30 pm and having a hardness of at least 750 Hv for a load of 0.1 kgF; the assembly of the seat body (3) thus treated in the injection nozzle (4); and in which the seat body is made of austenitic stainless steel comprising 0.5 to 0.6 m.% Carbon, less than 0.5 m.% Silicon, less than 10.0 m.% Manganese, 15 to 25 m.% Chromium, 1.0 to 6.0 m.% Ni, less than 3.0 m.% Niobium, less than 2.0 m.% Tungsten, less than 1.0 m.% Nitrogen, and Iron; The surface treatment is carried out by a carbon diffusion treatment process or a carbon and nitrogen treatment process at a temperature below 550°C.