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 has 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 martensitic or austenitic stainless steel and has an anti-cavitation layer (6) covering at least the sealing surface, the inner surface of the dome, and the injection orifices. The anti-cavitation layer is a chromium or nickel nitride-based coating deposited on the surface of the seat body, having a thickness between 0.5 and 50 µm and a hardness of at least 800 Hv, for a load of 0.1 kgF (0.98 N). (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, in particular for liquid alternative fuels, comprising:

[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;

[0009] in which the seat body is made of martensitic or austenitic stainless steel;

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

[0011] said anti-cavitation layer being a chromium or nickel nitride-based coating layer deposited on the surface of the seat body, having a thickness between 0.5 and 50 pm and exhibiting a hardness of at least 800 Hv, for a load of 0.1 kgF (0.98 N).

[0012] The invention thus proposes an anti-cavitation layer which is or consists of a coating layer based on chromium or nickel nitride which covers the surface of the seat body with a controlled thickness.

[0013] 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. The cavitation induced by the injection tends to remove the protective coating. passivation formed on the surface of the seat in martensitic or austenitic stainless steel, leading to the appearance of cavities which 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.

[0014] Surprisingly, the inventors found that treating the surface layer of the seat (made of martensitic or austenitic stainless steel) by forming a coating layer based on chromium or nickel nitride not only reduces corrosion but also prevents it. Indeed, the inventors observed that such a layer, by increasing the surface hardness of the material, effectively reduces the negative effect of cavitation that occurs during injection molding.

[0015] According to variants, the coating layer is advantageously formed by a plating process, preferably by electroless nickel plating ('electroless' here meaning electroless nickel plating), and the coating layer has a thickness of between approximately 10 and 50 µm, preferably between approximately 20 and 50 µm, and more preferably between approximately 20 and 30 µm. The coating layer formed by electroless nickel plating is preferably composed of 88 to 94 µm, preferably 91 to 93 µm, nickel, 6 to 12 µm, preferably 7 to 9 µm, and possibly residual elements present in trace amounts, i.e., less than approximately 0.1 µm, the mass percentage being expressed relative to the total mass of the coating layer.

[0016] When the coating layer is formed by a plating process, such as chemical nickel plating or nickel plating, said layer has a hardness of at least 800 Hv, preferably at least 1000 Hv, for a load of 0.1 kgF (0.980 N).

[0017] According to variants, the coating layer is chromium-based and is formed by a physical vapor deposition process or by chemical vapor deposition (in particular plasma-assisted (Pe-CVD)), and the coating layer has a thickness of between approximately 1 and 5 pm.

[0018] In various embodiments, when the coating layer is formed by a physical vapor deposition process or by chemical vapor deposition, the coating layer comprises an adhesion layer containing at least 90% chromium by mass of the total adhesion layer, and an outer layer of chromium nitride (in particular consisting of chromium nitride). The term chromium nitride is used here in a broad sense and covers the CrN form and / or other forms of chromium nitrides, e.g., Cr2N, or CrxN. Advantageously, the adhesion layer strengthens the adhesion of the outer chromium nitride layer to the surface of the treated injector and thus enhances the anticavitation properties of the martensitic or austenitic stainless steel.

[0019] When the coating layer is formed by a physical vapor deposition process or by chemical vapor deposition, the coating layer has a surface hardness of between 1000 and 2000 Hv for a load of 1300 to 1700 kgF (from 12.75 kN to 16.67 kN).

[0020] It will be noted that, surprisingly, compared to a conventional Kolsterisation process (in English Kolsterising®, registered trademark) generally used to reduce the risks of cavitation, the plating and / or physical vapor deposition process under the prescribed conditions also reduces the corrosion phenomena that are likely to occur due to the nature of the (new) fuels which include high levels of water and / or traces of acids, without further compromising the sensitivity to corrosion.

[0021] According to variants, the seat body can advantageously be made of hardened and tempered martensitic stainless steel.

[0022] In some variations, the seat body is made of martensitic stainless steel comprising a carbon content between 0.37 and 0.45 w.%, a chromium content between 15.0 and 16.0 w.%, a molybdenum content between 1.50 and 1.90 w.%, and a vanadium content between 0.20 and 0.40 w.%. In particular, it may be a martensitic stainless steel of type 1.4123, comprising, in addition to the elements indicated above, the following elements for which the maximum concentrations are specified: silicon 0.60 w.%; manganese 0.60 w.%; nickel 0.50 w.%; and cobalt 0.10 w.%. This type of steel is well suited for cold-forged seat manufacturing. The w.% values ​​are mass percentages of the total mass of the stainless steel composition.

[0023] In some variations, the seat body is made of martensitic stainless steel comprising a carbon content between 0.60 and 0.75 w.%, a chromium content between 16.0 and 18.0 w.%, a molybdenum content between 1.00 and 1.50 w.%, and a vanadium content between 0.20 and 0.40 w.%. In particular, it may be a modified type 440A martensitic stainless steel, comprising, in addition to the elements indicated above, the following elements for which the maximum concentrations are specified: silicon 1.00 w.%; manganese 1.0 w.%; tungsten 0.30 w.%; vanadium 0.30 w.%; and cobalt 0.30 w.%. This type of steel is well suited for machining the seat.

[0024] According to variants, the seat body is made of austenitic stainless steel comprising a carbon concentration between 0.45 and 0.55 m.%, chromium between 20 and 22 m.%, nickel between 3.5 and 5.5 m.%, manganese between 8 and 10 m.%, Nb between 1.8 and 2.5 m.% relative to the total mass of the austenitic stainless steel composition.

[0025] Preferably, the seat body, when made of martensitic steel, has a core hardness between 550 and 700 Hv, with typical values ​​between 600 and 650 Hv. Core hardness refers to the hardness of the internal part of the seat body, the Hardness depends on the chemical composition and manufacturing processes 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 30 kgF (2.94 kN).

[0026] Preferably, the seat body, when made of austenitic steel, has a core hardness between 350 and 450 Hv, with typical values ​​between 350 and 400 Hv.

[0027] In the context of the invention, the chemical nickel plating treatment, and / or the treatment by a vapor phase deposition process, can be carried out according to conventional techniques.

[0028] Advantageously, when the surface to be treated is a martensitic and / or austenitic steel, the treatment is carried out at a temperature preferably below 300 °C. When the treatment process involves temperatures between 300 °C and 500 °C, preferably between 350 and 450 °C, the surface to be treated will preferably be a martensitic stainless steel, such as type 1.4123 steel.

[0029] When the coating is applied by electroless nickel plating, specific surface preparation is carried out prior to the plating step, involving successive washing and acid treatment (or acid etching) steps to promote adhesion of the nickel deposited by the electroless nickel plating process. The nickel plating step is performed at temperatures between 80°C and 90°C, with durations depending on the target thickness. A tempering process is performed after plating (post-plating) at a temperature between 350°C and 450°C to harden the coating. The tempering temperature of the primary heat treatment must be 50°C higher than that of the post-plating tempering to avoid affecting the hardness of the metal substrate. Thus, the electroless nickel plating process is carried out at a temperature below 500°C, and preferably between 350°C and 450°C.

[0030] The physical vapor deposition process of chromium nitride is carried out in a vacuum reactor to coat essential parts of the seat, such as the sealing strip, the bag, and the injection holes. The chromium nitride deposition operation is preferably carried out at a temperature of 300 °C or lower by spraying, arc deposition, etc. When the treatment process is a vapor deposition process, the coating layer is formed at a temperature below 300 °C.

[0031] When the coating layer is based on chromium nitride and the seat body is made of austenitic or martensitic stainless steel, the coating layer is formed at a temperature less than or equal to about 300 °C.

[0032] The present injector is therefore particularly intended for the injection of alternative liquid fuels such as El00, Ml00 or e-fuel.

[0033] It will be noted that initial laboratory tests with injectors comprising a seat body with an anti-cavitation coating 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 examination of the seat revealed no obvious wear phenomena of the corrosion / cavitation type.

[0034] 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 to lift it from the seat under the effect of a magnetic field created by a solenoid.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] According to another aspect, the invention relates to a method for manufacturing a fuel injector in accordance with the present disclosure, comprising:

[0039] - the supply of a seat body made of martensitic stainless steel and / or austenitic comprising a portion of dome with injection holes, downstream of a sealing surface;

[0040] - the treatment of the seat body by plating, by physical vapor deposition or by chemical vapor deposition (in particular plasma-assisted (Pe-CVD)), in order to form an anti-cavitation layer or coating 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 layer having a maximum thickness of 50 pm and exhibiting a hardness of at least 800 Hv for a load of 0.1 kgF,

[0041] - the assembly of the seat body thus treated in the injection nozzle.

[0042] Advantageously, the surface treatment processes according to the invention make it possible to control the thickness of the anti-cavitation layer formed, particularly at the surface of the injection holes. These holes are advantageously machined to compensate for the reduction in diameter after surface treatment according to the invention. Controlling the thickness of the anti-cavitation layer makes it possible to control the flow rate of the seat and the injector. Brief description of the drawings

[0043] 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:

[0044] [Fig. 1] a longitudinal cross-sectional view through a direct injection injector fuel ;

[0045] [Fig.2] a simplified diagram of the injector seat body of the [Fig.1];

[0046] [Fig. 3] A cross-sectional view under an optical microscope of a steel seat body martensitic stainless steel according to the invention;

[0047] [Fig.4] an enlarged view of [Fig.3] a portion of the inner surface of the dome (4A), the surface of the bag (4B) and the surface of the holes (4C) of a seat body in martensitic stainless steel; and

[0048] [Fig. 5] an enlarged view of a seat body treated with martensitic stainless steel according to the invention by a plating process. Description of a preferred execution

[0049] 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-shaped 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 comprises a nozzle 4 with a seat body 3 which has 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 [Fig. 2], the seat body 3 has a cup shape, comprising a base 3.2 from which a peripheral wall 3.3 rises. The base 3.2 has a distally projecting dome 3.4 in which the injection holes 5 are formed. The region of the internal volume of the dome is typically called the bag 3.5.

[0050] 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.

[0051] 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.

[0052] 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>

[0053] In accordance with the invention, a surface hardening treatment of the plating or physical vapor deposition type was applied to the seat body 3 so as to form an anti-cavitation layer being a coating layer.

[0054] The seat body is made of martensitic or austenitic stainless steel, also referred to hereafter as the base material. It can typically be a hardened and tempered martensitic stainless steel.

[0055] The coating 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 layer is a coating layer which may comprise, depending on the nature of the deposit, a layer containing nickel, or an adhesion layer comprising at least 90% chromium and an outer layer of chromium nitride. When the coating layer is formed by chemical nickel plating, said layer has a thickness of up to 50 µm and exhibits a minimum hardness of 800 Hv for a load of 0.1 kgF (0.980 N). When the coating layer is formed by physical vapor deposition, said coating layer has a thickness (total, i.e. adhesion layer 6a and outer layer 6b) between 1 and 5 pm, and exhibits a minimum hardness of 1000 Hv for a load of 0.1 kgF (0.980 N).

[0056] This coating layer 6 (6a and 6b) 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.

[0057] For simplified processing, the entire part is treated.

[0058] Figs. 3 to 4 show cross-sectional views of a seat body according to the invention, i.e., with a dome and injection holes, treated by physical vapor deposition to form a coating layer 6 comprising an adhesion layer 6a and an outer layer 6b, with the prescribed depth and hardness. The part was treated entirely by a chemical vapor deposition process. The coating layer 6 thus formed is visible in Figures 4A, 4B, and 4C, which are microscopic images of a seat body according to the invention. The coating layer 6 comprises an adhesion layer 6a comprising at least 90% chromium (relative to the total mass of the adhesion layer) and an outer layer 6b comprising chromium nitride. The 6a adhesion layer has a thickness of 0.31 pm, the outer layer has a thickness of 1.30 pm at the surface of the sealing strip.The adhesion layer 6a has a thickness of 0.19 µm, the outer layer has a thickness of 0.63 µm at the surface of the holes, and the adhesion layer 6a has a thickness of 0.34 µm, the outer layer has a thickness of 1.48 µm at the surface of the bag.

[0059] As can be seen in [Fig. 4], the coating layer 6 (comprising an adhesion layer 6a and an outer layer 6b) is a layer of uniform thickness (the upper layer being lighter), 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. 4C). In this example, the thickness of the layer is between approximately 0.80 µm and 1.8 µm.

[0060] When the injector seat is treated by a physical vapor deposition process or by plasma-assisted chemical vapor deposition, the coating layer is formed by an adhesion layer comprising at least 90% chromium (relative to the total mass of the adhesion layer) and an outer layer based on chromium nitride. The coating layer has a total thickness of between 1 and 5 µm and a Vickers hardness of between 1000 and 2000 Hv for a load of 1300 to 1700 kgF (i.e., between 12748.64 N and 16671.3 N). The Vickers hardness obtained after treatment can also be 1000, 1100, or 1200 Hv for a load of 1300 to 1700 kgF. The adhesion layer comprising at least 90% Chromium has the advantage of improving the adhesion of the top layer of chromium nitride on the injector seat, thus improving resistance to cavitation when injecting alternative fuels such as M100 or e-fuel.

[0061] According to another embodiment, an anti-cavitation layer can be formed on the ball by a physical vapor deposition process or by plasma-assisted chemical vapor deposition, to form a diamond-like carbon (DLC) anti-cavitation layer. Generally, the DLC forms an amorphous carbon layer. The DLC layer is preferably formed on the ball.

[0062] According to another embodiment, in [Fig.5], the coating layer 6 is formed by a plating process, preferably by chemical nickel plating; it is adopted to preserve the behavior of the base material, in particular its mechanical properties.

[0063] Thus, the electroless nickel plating process is carried out at a temperature below 500°C, and preferably between 350 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.

[0064] The chemical nickel plating process involves the controlled formation of a thin layer of nickel on the surface of the seat body for a given time and temperature on the surface of the seat body.

[0065] As is known, in such thermochemical surface treatment processes, the main parameters that control the manufacturing process, and therefore the layer thickness and hardness, are temperature, pressure (species concentration), and treatment time. By opting for electroless nickel plating, the inventors have thus chosen a compromise that allows for faster processing of the parts, achieving a minimum hardness of 800 Hv at 0.1 kg·F (0.98 N), while limiting the treatment to a thickness of 50 pm. The inventors have thus established that these nickel layer parameters are sufficient to significantly limit degradation due to cavitation when operating with alternative fuels at pressures of 300 to 500 bar.

[0066] Preferably, in the case of nickel deposition by chemical nickel plating, the coating layer 6 has a hardness of at least 750 Hv at a depth of 10 pm, more preferably greater than 800 Hv at 0.1 kg.F (0.98 N).

[0067] It will be appreciated that the present invention can be advantageously implemented with known chemical nickel plating techniques, however at temperatures not exceeding 500°C, for example between 350 and 300°C. In such processes the part to be treated is immersed in a bath.

[0068] 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 according to the present invention increases surface hardness, reduces cavitation-induced cracking, 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.

[0069] 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 with an apex angle of 136°, which is pressed into the surface of the material with a specific load. The diagonal of the resulting indentation is measured, and the hardness is calculated using the applied load and the indentation area. Each measurement value is therefore given with the corresponding load.

[0070] According to the international measurement system IkgF = 9.806 N.

[0071] Preferably, Vickers hardness measurements are carried out according to ISO 6507 (ISO 6507-1:2023, ISO 6507-2:2018 and ISO 6507-3:2018) and the standard test method ASTM E384.< / invention>

Claims

Demands

1. Fuel injector for an internal combustion engine, in particular for liquid alternative fuels, comprising: 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 orifice (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 orifice(s) (5); wherein the injection orifices (5) are made in a portion of a dome (3.4), downstream of the sealing surface (3.1); wherein the seat body (3) is made of martensitic or austenitic stainless steel; characterized in that the seat body (3) has an anti-cavitation layer covering at least the sealing surface, the inner surface of the dome (3.4) and the injection holes (5); said anti-cavitation layer being a coating layer (6) based on chromium or nickel nitride deposited on the surface of the seat body (3), having a thickness between 0.5 and 50 pm and having a hardness of at least 800 Hv, for a load of 0.1 kgF (0.98 N).

2. Fuel injector according to claim 1, wherein the coating layer (6) is formed by a plating process, and the coating layer (6) has a thickness of between about 10 and 50 pm, preferably between about 20 and 50 pm, more preferably between about 20 and 30 pm; and preferably the coating layer (6) is formed by chemical nickel plating and consists of 88 to 94 m.%, preferably 91 to 93 m.% nickel and 6 to 12 m.%, preferably 7 to 9 m.% phosphorus relative to the total mass of the coating, and any residual elements present in trace amounts.

3. Fuel injector according to claim 1 or 2, wherein the coating layer (6) has a hardness of at least 800 Hv, preferably at least 1000 Hv, for a load of 0.1 kgF (0.980 N).

4. Fuel injector according to any one of claims 1 to 3, wherein the coating layer (6) is formed at a temperature below 500°C, and preferably between 350 and 450°C.

5. Fuel injector according to claim 1, wherein the coating layer (6) is chromium-based and is formed by a physical vapor deposition process or by chemical vapor deposition, preferably a plasma-assisted chemical vapor deposition process, and the coating layer (6) has a thickness of between about 1 and 5 pm.

6. Fuel injector according to claim 5, wherein the coating layer comprises an adhesion layer (6a) comprising at least 90% chromium, and an outer layer (6b) of chromium nitride.

7. Fuel injector according to claims 1, 5 or 6, wherein the coating layer (6) has a surface hardness between 1000 and 2000 Hv for a load of 1300 to 1700 kgF (12.75 kN to 16.67 kN).

8. Fuel injector according to any one of claims 1, 5 to 7, wherein the coating layer (6) is formed at a temperature less than or equal to 300 °C.

9. Fuel injector according to any one of claims 1 to 8, wherein the seat body (3) is made of austenitic stainless steel and has a core hardness between 350 and 450 Hv, in particular between 350 and 400 Hv for a load of 30 kgF (2.94 kN).

10. Fuel injector according to any one of claims 1 to 8, wherein the seat body (3) is made of martensitic stainless steel and has a core hardness between 550 and 700 Hv, in particular between 600 and 650 Hv for a load of 30 kgF (2.94 kN).

11. Fuel injector according to any one of claims 1 to 8 or 10, wherein the seat body (3) is made of martensitic stainless steel comprising a carbon concentration between 0.37 and 0.45 m.%, chromium between 15.0 and 16.0 m.%, molybdenum between 1.50 and 1.90 m.%, vanadium between 0.20 and 0.40 m.% relative to the total mass of the martensitic stainless steel composition.

12. Fuel injector according to any one of claims 1 to 810, wherein the seat body (3) is made of stainless steel martensitic comprising a carbon concentration between 0.60 and 0.75 m.%, chromium between 16.0 and 18.0 m.%, molybdenum between 1.00 and 1.50 m.%, vanadium between 0.20 and 0.40 m.% relative to the total mass of the martensitic stainless steel composition.

13. Fuel injector according to any one of claims 1 to 9, wherein the seat body (3) is made of austenitic stainless steel comprising a carbon concentration between 0.45 and 0.55 m.%, chromium between 20 and 22 m.%, nickel between 3.5 and 5.5 m.%, manganese between 8 and 10 m.%, Nb between 1.8 and 2.5 m.% relative to the total mass of the austenitic stainless steel composition.

14. A method for manufacturing a fuel injector according to any one of claims 1 to 13, comprising: supplying a seat body (3) of martensitic or austenitic stainless steel comprising a dome portion (3.4) with injection holes (5), downstream of a sealing surface (3.1); treating the seat body (3) by a plating process, by a physical vapor deposition process or by a chemical vapor deposition process to form an anticavitation layer covering at least the inner surface of the dome portion, the surface of the injection holes (5) and the sealing surface (3.1), said anticavitation layer being a coating layer (6) and having a thickness between 0.5 and 50 pm and having a hardness of at least 800 Hv for a load of 0.1 kgF (0.980 N); the assembly of the seat body (3) treated in the injection nozzle (4).

15. Use of an injector according to any one of claims 1 to 13 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.

16. 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 any one of claims 1 to 13 coupled to the fuel rail, wherein the fuel is at low boiling point, preferably an e-fuel type fuel or one consisting mainly of alcohol.

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