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 (6) is made of martensitic stainless steel and has an anti-cavitation surface coating (6) covering at least the sealing surface, the inner surface of the dome, and the injection orifices. The anti-cavitation surface coating is obtained by low-temperature carbonitriding and extends to a maximum depth of 30 µm, and has a hardness of at least 1000 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 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;

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

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

[0011] said anti-cavitation surface layer being obtained by low temperature carbonitriding and extending over a maximum depth of 30 pm, and having a minimum surface hardness of 1000 Hv for a load of 0.1 kgF (0.98 N).

[0012] The anti-cavitation surface layer is thus a diffusion layer enriched in nitrogen and carbon, which extends from the surface to a controlled depth.

[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.Injection-induced cavitation tends to remove the passivation layer formed on the surface of the martensitic stainless steel seat, leading to the appearance of cavities that are susceptible to corrosion (particularly following the local disappearance of the natural oxide-based passivation layer). of chromium 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 stainless steel) by forming an anti-cavitation surface layer through carbonitriding not only reduces corrosion but also prevents it. Indeed, the inventors observed that such a layer, enriched with nitrogen and carbon, increases the surface hardness of the material and effectively reduces the negative effect of cavitation that occurs during injection molding.

[0015] It will be noted that, surprisingly, compared to a conventional Kolsterisation process generally used to reduce the risks of cavitation, carbonitriding 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.

[0016] The seat body can advantageously be made of hardened and tempered martensitic stainless steel.

[0017] In some variations, the seat body is made of martensitic stainless steel comprising a carbon content between 0.37 and 0.45 wt.%, a chromium content between 15.0 and 16.0 wt.%, a molybdenum content between 1.50 and 1.90 wt.%, and a vanadium content between 0.20 and 0.40 wt.%. 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 wt.%; manganese 0.60 wt.%; nickel 0.50 wt.%; and cobalt 0.10 wt.%. This type of steel is well suited for cold-forged seat manufacturing. The wt.% values ​​are weight percentages of the total weight of the stainless steel composition.

[0018] 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.

[0019] Preferably, the seat body has a core hardness between 550 and 700 Hv, with typical values ​​between 600 and 650 H. Core hardness refers to the hardness of the internal part of the seat body, the hardness of which depends on the chemical composition and manufacturing treatments of the steel. It is preferably measured at depths of at least 0.400 mm, preferably at least 0.750 mm from the surface. This hardness is preferably measured for a load of 30 kgF (294.2 N).

[0020] In the context of the invention, the carbonitriding treatment can be carried out according to conventional techniques.

[0021] Advantageously, a low-temperature gaseous carbonitriding process is used. This is generally simple to implement, more environmentally friendly, and the parts produced are clean (not contaminated by the manufacturing process).

[0022] Low-temperature gas carbonitriding is carried out at a temperature of approximately 300 to 500 °C, preferably between 400 and 450 °C or 450 to 500 °C. Typically, the gases that can be used to create the carbonitriding atmosphere in the treatment furnace include nitrogen, ammonia, methane, acetylene, and / or other hydrocarbons. The diffusion time can typically be on the order of 2 to 30 hours, depending on the thickness of the layer to be produced.

[0023] As explained above, gas carbonitriding is preferred for its ease of implementation, while remaining effective. Alternatively, carbonitriding can be carried out using plasma or liquid carbonitriding (with cyanide-type salts, etc.).

[0024] According to variants, the anti-cavitation surface layer has a surface hardness between 1000 Hv and 1200 Hv, preferably between 1000 and 1100 Hv, for a load of 0.1 kgF (0.98 N).

[0025] Depending on variations, the anti-cavitation surface layer extends to a depth of up to 20 pm, or up to 15 pm, or even up to 10 pm. In particular, the anti-cavitation surface layer can be designed to have a thickness (depth) between 15 and 20 pm.

[0026] Advantageously, the anti-cavitation surface layer has a hardness of at least 750 Hv at a depth of 10 pm for a load of 1 kgf (9.80 N). The hardness profile is controlled here to optimize the level of hardness and resistance to cavitation.

[0027] The present injector is therefore particularly intended for the injection of alternative liquid fuels such as El00, Ml00 or e-fuel.

[0028] It will be noted that initial laboratory tests with injectors comprising a seat body having an anti-cavitation surface 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 observation of the seat did not reveal any obvious wear phenomena of the corrosion / cavitation type.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] According to another aspect, the invention relates to a method for manufacturing a fuel injector in accordance with the present disclosure, comprising:

[0034] the supply of a seat body made of martensitic stainless steel comprising a portion of dome with injection holes, downstream of a sealing surface;

[0035] the treatment of the seat body by carbonitriding in order to form an anti-cavitation surface 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 surface layer extending to a maximum depth of 30 pm and having a hardness of at least 1000 Hv for a load of 0.1 kgF (0.98 N);

[0036] the assembly of the seat body thus treated in the injection nozzle; and

[0037] in which carbonitriding is carried out by gaseous means at a temperature below 500°C. Brief description of the drawings

[0038] 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:

[0039] [Fig. 1] A longitudinal cross-sectional view through a direct fuel injection injector:

[0040] [Fig.2] a simplified diagram of the injector seat body of the [Fig.1];

[0041] [Fig.3] a cross-sectional view under an optical microscope of a seat body according the invention:

[0042] [Fig.4] an enlarged view of [Fig.3] of part of the inner surface of the dome; And

[0043] [Fig.5] an enlarged view of [Fig.3] showing an injection hole. Description of a preferred execution

[0044] 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. .

[0045] 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 the action of a generated magnetic field by a solenoid 12, when it is powered. Conventionally, 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.

[0046] 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.

[0047] 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>

[0048] In accordance with the invention, a carbonitriding type surface hardening treatment was applied to the seat body 3 so as to form an anti-cavitation surface layer.

[0049] The seat body is made of martensitic stainless steel, also referred to hereafter as the base material. This is typically a hardened and tempered martensitic stainless steel.

[0050] The anti-cavitation surface 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 surface layer is a nitrogen and carbon enriched diffusion layer, which extends from the surface to a depth of up to 30 pm, and which has a minimum hardness of 1000 Hv for a load of 0.1 kgF (0.98 N).

[0051] This anti-cavitation surface 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.

[0052] For simplified processing, the entire part is treated.

[0053] The anti-cavitation surface layer 6 is formed by a process of Low temperature carbonitriding; it is adopted to preserve the behavior of the base material, in particular its mechanical properties.

[0054] Thus, the low-temperature carbonitriding process is carried out at a temperature below 500°C, for example from 350 to 500°C and preferably between 400 and 450°C, to avoid a phase transition or the precipitation of undesirable compounds which These factors could have a negative effect, such as the formation of a more ductile (soft) material or one more susceptible to corrosion. Controlling temperature and pressure (concentration of species in the atmosphere) allows us to influence the depth of the formed layer, and therefore to control the final hardness of the base material.

[0055] The carbonitriding process involves the controlled diffusion of nitrogen and carbon over a given time and temperature onto the surface of the seat body. This can be viewed as a combined carburizing and nitriding process. It is possible to carry out carburizing followed by nitriding, or vice versa, or even simultaneously.

[0056] As is known, in such surface thermochemical treatment processes, the main parameters controlling the manufacturing process, and therefore the layer depth and hardness, are temperature, pressure (species concentration), and treatment time. It is worth noting that the simultaneous performance of carburizing and nitriding provides a synergistic effect. On the one hand, carburizing, as such, is a rapid process but tends to weaken the material in terms of corrosion. Nitriding, on the other hand, is comparatively longer (with very long treatment times for the automotive industry), but generates less deformation and less degradation of corrosion resistance (when nitrogen passes into solid solution in the matrix without forming nitrides).By opting for carbonitriding, the inventors have chosen a compromise that allows for faster processing of parts, achieving a minimum hardness of 1000 Hv at 1 kg·F, while limiting the treatment to 30 µm. The inventors have thus established that these carbonitrid layer parameters are sufficient to significantly limit cavitation-related damage when operating with alternative fuels at pressures of 300 to 500 bar.

[0057] 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.

[0058] Preferably, the anti-cavitation surface layer 6 has a hardness of at least 750 Hv at a depth of 10 pm, more preferably between 750 and 800 Hv.

[0059] It will be appreciated that the present invention can be advantageously implemented with known carbonitriding techniques, respectively carburizing and nitriding, however at temperatures not exceeding 500°C, for example between 450 and 500°C. As is known, in such processes the part to be treated is brought into contact with an atmosphere comprising gases containing nitrogen and carbon, by Examples include ammonia (NH3) and hydrocarbons (methane, butane, propane, etc.), possibly in the presence of argon. The diffusion of nitrogen (N) and carbon (C) atoms in the surface of the part occurs under the effect of temperature.

[0060] 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 carbonitriding 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.

[0061] Figs. 3 to 5 show cross-sectional views of a seat body according to the invention, That is, with a dome and injection holes, and treated to form an anti-cavitation surface layer 6 with the prescribed depth and hardness. The part was entirely gaseous treated. The seat body is embedded in a resin that appears black. As can be seen, the anti-cavitation surface layer 6 is a layer of uniform thickness (lighter surface layer), also in the region of the holes 5, which are coated on their entire internal surface, both in the orifice 5.1 and counter-orifice 5.2 (see [Fig. 5]). In this example, the depth is approximately 15 µm.

[0062] 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.

[0063] Preferably, Vickers hardness measurements are carried out according to ISO 6507 (ISO 6507-1, 2&3:2023) and the standard test method ASTM E384.< / 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 orifice (5), the seat body cooperating with a sealing member (8) movable axially between a closed position in which it rests on the sealing surface to prevent fuel injection, and an open position in which the sealing member is lifted from the sealing surface to permit fuel injection through the injection orifice(s); 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 stainless steel; characterized in that the seat body (3) has an anti-cavitation surface layer (6) covering at least the sealing surface, the inner surface of the dome and the injection holes; said anti-cavitation surface layer being obtained by low temperature carbonitriding and extending over a maximum depth of 30 pm, and having a hardness of at least 1000 Hv, for a load of 0.1 kgF (0.98 N).

2. Fuel injector according to claim 1, wherein the anti-cavitation surface layer extends to a depth of up to 20 pm, or up to 15 pm, or even up to 10 pm.

3. Fuel injector according to claim 1 or 2, wherein the anti-cavitation surface layer has at a depth of 10 pm a hardness of at least 750 Hv for IkgF (9.80 N).

4. Fuel injector according to claim 1, 2 or 3, wherein the seat body has a core hardness between 550 and 700 Hv, in particular between 600 and 650 Hv.

5. Fuel injector according to claim 4, wherein the core hardness is measured for a load of 30 kgF (294.2 N).

6. Fuel injector according to any one of the preceding claims, wherein the seat body is made of martensitic stainless steel comprising a carbon concentration between 0.37 and 0.45 m.%, in chromium between 15.0 and 16.0 m.%, in molybdenum between 1.50 and 1.90 m.%, in vanadium between 0.20 and 0.40 m.%.

7. Fuel injector according to any one of claims 1 to 5, wherein the seat body is made of martensitic stainless steel comprising a carbon concentration between 0.60 and 0.75 m.%, a chromium concentration between 16.0 and 18.0 m.%, a molybdenum concentration between 1.00 and 1.50 m.%, and a vanadium concentration between 0.20 and 0.40 m.%.

8. Fuel injector according to claim 6 or 7, wherein the seat body is made of hardened and tempered martensitic stainless steel.

9. Fuel injector according to any one of the preceding claims, wherein the carbonitriding process is a gaseous carbonitriding process at a temperature below 500°C.

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 fuel injector according to any one of the preceding claims coupled to the fuel rail, wherein the fuel is low boiling point, preferably an e-fuel type fuel or predominantly comprising an alcohol.

12. A method for manufacturing a fuel injector according to any one of claims 1 to 9, comprising: supplying a seat body made of martensitic stainless steel including a dome portion with injection holes, downstream of a sealing surface; treating the seat body by carbonitriding to form an anti-cavitation surface layer covering at least the inner surface of the dome portion, the surface of the injection holes and the sealing surface, said anti-cavitation surface layer extending to a maximum depth of 30 pm and exhibiting a hardness of at least 1000 Hv under a load of 0.1 kgF (0.98 N); the assembly of the treated seat body in the injection nozzle; and in which carbonitriding is carried out by gaseous means at a temperature below 500°C.

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