Injector for alternative fuels

Abstract

The invention relates to a fuel injector for an internal combustion engine, in particular for liquid alternative fuels. The injector comprises an injection nozzle, the end of which has a seat body with a sealing surface and at least one injection hole. The injection holes (5) are produced in a portion of a dome, downstream of a sealing surface. The seat body is made of martensitic stainless steel and has an anti-cavitation surface layer (6) covering at least the sealing surface, the inner surface of the dome and the injection holes. The anti-cavitation surface layer is obtained via low-temperature carbonitriding and extends over 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).

Description

INJECTOR FOR ALTERNATIVE FUEL 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 (the injector is mounted in the cylinder head in an orifice that opens into the combustion chamber); and indirect injection (PFI: the injector is arranged to emit fuel into the intake manifold just before the intake valve(s)).

[0003] A fuel injector for direct gasoline injection comprises a nozzle that defines a fuel passage. The distal end of this nozzle has a seat body that defines a sealing seat located upstream of a bag-like 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 to an open position. In the closed position, the needle seals the nozzle by resting on the seat. In the open position, the needle is separated from the sealing seat, allowing fuel to flow to the injection holes that penetrate the bag wall, 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 includes a seat made of a martensitic steel-type material. With the aim of reducing the carbon footprint of industry and transportation, new fuels have emerged. Recently, fuels such as methanol and / or ethanol-based fuels (fuels derived from biomass and typically containing 10 to 100% methanol and / or ethanol by volume) have been observed to exhibit different injection behaviors, causing premature and undesired 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, particularly alternative fuels containing alcohol-like 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: an injection nozzle defining a fuel passage, the distal end of which has a seat body with a sealing surface and at least one injection orifice, the seat body cooperating with a shutter member 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 shutter member is lifted from the sealing surface to allow fuel injection through the injection orifice(s); wherein the injection orifices are made in a portion of a dome, downstream of the sealing surface; wherein the seat body is made of martensitic stainless steel;characterized in that the seat body has an anticavitation surface layer covering at least the sealing surface, the inner surface of the dome and the injection holes; said anticavitation surface layer being obtained by low temperature carbonitriding and extending to 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).

[0007] The surface anticavitation layer is thus a nitrogen- and carbon-enriched diffusion layer extending from the surface to a controlled depth. Within this diffusion layer is a saturated solid solution of carbon and nitrogen. Thanks to its low-temperature application, the diffusion layer is essentially free of carbide and nitride precipitates.

[0008] The inventors observed that the use of alternative fuels such as methanol (MeOH) and ethanol (EtOH) leads to premature wear of the injector seat. 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 and corrosion. Alternative fuels, primarily due to their lower boiling point compared to traditional fuels, increase cavitation within the injector body, particularly 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 chromium oxide-based passivation layer characteristic of stainless steels), which can even lead to cracking.

[0009] Surprisingly, the inventors found that treating the surface layer of the seat (made of martensitic stainless steel) by carbonitriding to form an anti-cavitation surface layer 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 effects of cavitation that occur during injection molding.

[0010] It should be noted that, surprisingly, compared to a conventional carbonitriding process generally used to reduce the risk of cavitation, carbonitriding under the prescribed conditions also reduces corrosion phenomena that are likely to occur due to the nature of the (new) fuels, which contain high levels of water and / or traces of acids, without further compromising susceptibility to corrosion.

[0011] The seat body can advantageously be made of hardened and tempered martensitic stainless steel.

[0012] Depending on the specific design, the seat body is made of martensitic stainless steel with 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, which, in addition to the elements listed above, contains 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 percentages by weight of the total weight of the stainless steel composition.

[0013] Depending on the specific design, the seat body is made of martensitic stainless steel with a carbon content between 0.60 and 0.75 wt%, a chromium content between 16.0 and 18.0 wt%, a molybdenum content between 1.00 and 1.50 wt%, and a vanadium content between 0.20 and 0.40 wt%. In particular, it may be a modified type 440A martensitic stainless steel, which, in addition to the elements listed above, contains the following elements for which the maximum concentrations are specified: silicon 1.00 wt%; manganese 1.0 wt%; tungsten 0.30 wt%; vanadium 0.30 wt%; and cobalt 0.30 wt%. This type of steel is well-suited for machined seat production.

[0014] 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 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 30 kgF (294.2 N).

[0015] In the context of the invention, the carbonitriding treatment can be implemented according to conventional techniques.

[0016] 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).

[0017] 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 used to create the carbonitriding atmosphere in the treatment furnace include nitrogen, ammonia, methane, acetylene, and / or other hydrocarbons. The diffusion time can typically range from 2 to 30 hours, depending on the desired layer thickness.

[0018] As explained above, gas carbonitriding is preferred for its ease of implementation while remaining effective. Alternatively, plasma carbonitriding or liquid carbonitriding (using cyanide salts, etc.) can be used.

[0019] Depending on the variant, 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).

[0020] Depending on the specific configuration, the anti-cavitation surface layer extends to a depth of up to 20 µm, or up to 15 µm, or even up to 10 µm. In particular, the anti-cavitation surface layer can be designed to have a thickness (depth) between 15 and 20 µm.

[0021] Advantageously, the anti-cavitation surface layer exhibits a hardness of at least 750 Hv at a depth of 10 pm under a load of 1 kgF (9.80 N). The hardness profile is controlled to optimize both the hardness level and cavitation resistance.

[0022] This injector is therefore particularly intended for the injection of alternative liquid fuels such as E100, M100 or e-fuel.

[0023] It is noteworthy that initial laboratory tests with injectors comprising a seat body featuring an anti-cavitation surface coating according to the invention have yielded satisfactory results. Tests were conducted with M100 fuel injected at 250 bar. After 150 hours of operation, microscopic examination of the seat revealed no obvious wear phenomena such as corrosion or cavitation.

[0024] Depending on the variant, 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.

[0025] Depending on the variant, the seat has a plurality of through-injection holes, which include an upstream part (in the direction of fuel flow), called the orifice, whose diameter is calibrated to form a jet of atomized fuel, and a downstream part of larger diameter, called the counter-orifice, which contributes to the formation of the jet.

[0026] The orifices can have a diameter between 100 and 250 µm, or between 115 and 200 µm. The counter-orifices can have a diameter between 400 and 500 µm.

[0027] The length of the orifices can be on the order of 70 to 250 pm. The thickness of the dome (3.4) in the vicinity of the orifices and counter-orifices can be on the order of 0.4 to 0.6 mm.

[0028] 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, particularly 350 bar. "Predominantly" here means comprising more than 50% alcohol, particularly more than 60%, 70%, 80%, or 90%, and up to 100%. The alcohol may, in particular, be ethanol or methanol. Specifically, the fuel may be of type E100 or M100.

[0029] E100 (EtOH) is a bioethanol-type biofuel usable for certain gasoline combustion engines and which contains 100% ethanol (pure ethanol, which can be produced, for example, from sugarcane plants). (sugar, as in Brazil). M100 (MeOH) is a biomethanol-type biofuel usable in certain gasoline combustion engines and contains 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 from water electrolysis, low-carbon or renewable electricity. They can be in liquid form (as is the case for this invention) or gaseous form.

[0030] 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.

[0031] In another aspect, the invention relates to a method for manufacturing a fuel injector according to this disclosure, comprising: - the supply of a seat body in martensitic stainless steel comprising a portion of dome with injection holes, downstream of a sealing surface; - 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); - the assembly of the treated seat body into the injection nozzle; and - in which carbonitriding is carried out by gaseous means at a temperature below 500°C. Brief description of the drawings

[0032] 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: Fig.1 a longitudinal cross-sectional view through a direct fuel injection injector: Fig.2 a simplified diagram of the injector seat body of Fig.1; Fig. 3 is a cross-sectional view under an optical microscope of a seat body according to the invention: Fig. 4 is an enlarged view of Fig. 3 of part of the dome's interior surface; and Fig.5 is an enlarged view of Fig.3 showing an injection hole. Description of a preferred execution

[0033] Fig. 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 that 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 bottom 3.2 from which a peripheral wall 3.3 rises. The background 3.2 includes a dome 3.4 distal projection in which the injection holes 5 are made. passing through the dome. The region of the interior volume of the dome is typically called bag 3.5.

[0034] The passage of fuel through the injection holes 5 is controlled by a needle-shaped shut-off device 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 symbol 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.

[0035] It should 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. Classically, 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.

[0036] The holes 5 can be, for example, 5 to 9 in number. The orifices 5.1 can have a diameter of approximately 100 µm, or more commonly between 100 and 250 µm, or even 115 and 200 µm. The counter-orifices 5.2 can have a diameter of approximately 400 to 500 µm. The length of the orifices can be approximately 70 to 250 µm. The thickness of the dome 3.4 in the section containing the orifices and counter-orifices can be approximately 0.4 to 0.6 mm. <lnvention>

[0037] 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.

[0038] The seat body is made of martensitic stainless steel, also referred to as the base material below. This is typically a hardened and tempered martensitic stainless steel.

[0039] 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).

[0040] 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-colored surface layer.

[0041] For simplified processing, the entire part is treated.

[0042] The anti-cavitation surface layer 6 is formed by a low-temperature carbonitriding process; it is adopted to preserve the behavior of the base material, in particular its mechanical properties.

[0043] 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 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 one more susceptible to corrosion. Controlling the temperature and pressure (concentration of species in the atmosphere) allows for influencing the depth of the formed layer, and therefore allows for controlling the final hardness of the base material.

[0044] The carbonitriding process involves the controlled diffusion of nitrogen and carbon for a given time and temperature onto the surface of the body. seat. This can be seen as a combined carburizing and nitriding process. It is possible to perform carburizing followed by nitriding, or vice versa, or even simultaneously. This can also be referred to as nitrocarburizing.

[0045] 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. The combined application 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 is dissolved 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.

[0046] Furthermore, it is not desirable for the anti-cavitation surface layer 6 to extend beyond 30 µm 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 leading to surface finish problems on the seat.

[0047] 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.

[0048] It will be appreciated that the present invention can be advantageously implemented with known carbonitriding techniques. These processes involve carburizing and nitriding, respectively, but 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 placed in contact with an atmosphere containing gases with nitrogen and carbon, for example, ammonia (NH3) and hydrocarbons (methane, butane, propane, etc.), possibly in the presence of argon. The diffusion of nitrogen (N) and carbon (C) atoms into the surface of the part occurs under the influence of temperature.

[0049] 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 newer 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.Carbonitriding surface treatment according to the present invention increases surface hardness, reduces cavitation-induced cracks, 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.

[0050] Figures 3 to 5 show cross-sectional views of a seat body according to the invention, i.e., with a dome and injection holes, 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 over their entire internal surface, both in the orifice area 5.1 and the counter-orifice area 5.2 (see Figure 5). In this example, the depth is approximately 15 µm.

[0051] 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.

[0052] Preferably, Vickers hardness measurements are carried out according to ISO 6507 (ISO 6507-1, 2&3:2023) and the ASTM E384 standard test method.< / lnvention>

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, in which 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 1 kgF (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.%, a chromium concentration between 15.0 and 16.0 m.%, a molybdenum concentration between 1.50 and 1.90 m.%, and a vanadium concentration 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. Fuel injector according to any one of the preceding claims, wherein injection holes (5) comprise an upstream part, referred to as orifice (5.1), the diameter of which is calibrated to form a jet of atomized fuel, and a downstream part of larger diameter, referred to as counter-orifice (5.2), which contributes to the formation of the jet.

11. Fuel injector according to the preceding claim, wherein the orifices (5.1) have a diameter between 100 and 250 pm, or between 115 and 200 pm; and / or the counter orifices (5.2) have a diameter between 400 and 500 pm.

12. Fuel injector according to the preceding claim, in which the orifices have a length of approximately 70 to 250 pm; and / or the thickness of the dome (3.4) in the vicinity of the orifices and counter-orifices is approximately 0.4 to 0.6 mm.

13. 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.

14. 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 one consisting mainly of an alcohol.

15. A method for manufacturing a fuel injector according to any one of claims 1 to 12, comprising: supplying a seat body made of martensitic stainless steel comprising 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 µm and having a hardness of at least 1000 Hv under a load of 0.1 kgF (0.98 N); assembling the seat body thus treated in the injection nozzle; and in which carbonitriding is carried out by gaseous means at a temperature below 500°C.

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