High-pressure fuel supply system for direct injection of liquid fuel into a dual-fuel internal combustion engine

Abstract

This high-pressure fuel supply system (33) for the direct injection of liquid fuel into a dual-fuel internal combustion engine of a motor vehicle configured to burn liquid and gaseous fuel comprises a high-pressure pump (34) intended to be supplied with fuel by a low-pressure circuit (53) and supplying injectors (48), and is characterized in that it comprises, downstream of the injectors (48), at least one return circuit (52) to the low-pressure circuit (53). Figure for the abbreviation: Fig 3

Description

Title of the invention: High-pressure fuel supply system for the direct injection of liquid fuel into a dual-fuel internal combustion engine technical field

[0001] The present invention relates to the field of internal combustion engines, and more particularly to engines comprising a dual fuel system of which at least one liquid fuel supply system includes a high-pressure pump and injectors.

[0002] More particularly, the invention relates to the cooling of a high-pressure pump and injectors. Previous techniques

[0003] In an internal combustion engine, gas-based fueling, for example with liquefied petroleum gas, acronym "LPG", or with compressed natural gas, acronym "CNG", makes it possible to reduce greenhouse gas emissions, in particular carbon dioxide, as well as pollutant emissions compared to fueling by injection of a liquid fuel, for example pure gasoline, or a mixture of gasoline and ethanol, or even pure ethanol.

[0004] However, gaseous fuel presents certain technical problems, such as the need to be heated to start the engine, and logistical problems since only a few supply points are available to users. Therefore, it is necessary to maintain a liquid-based fuel, generally gasoline-based, to ensure engine starting and the vehicle's range as required by users.

[0005] Gas combustion uses controlled ignition, so in a dual carburetion, gas carburetion will preferably be associated with gasoline-based carburetion.

[0006] A dual-fuel gas and gasoline, or more generally liquid, engine is required to comply with the same regulatory standards as a single-fuel engine.

[0007] Direct gasoline injection technology, abbreviated as "DGI," allows fuel to be injected directly into the engine cylinders. Direct injection reduces fuel consumption and carbon dioxide emissions, as well as pollutant emissions.

[0008] Gas-powered carburetion is therefore generally associated with direct gasoline injection carburetion.

[0009] In an IDE-type fuel injection system, fuel (gasoline and / or ethanol) is injected directly into the combustion chamber at high pressure to ensure proper fuel atomization in the engine cylinders while maintaining the ability to introduce a sufficient quantity of fuel into the cylinders between each combustion. An IDE-type fuel injection system therefore comprises direct injectors, one per engine cylinder, and a high-pressure liquid fuel pump.

[0010] The high-pressure pump of an IDE-type fuel system is generally driven by a component of the internal combustion engine, for example a camshaft with an intermediate tappet. The high-pressure pump is thus fixed to the engine and heats up during its operation.

[0011] The fuel inside the high-pressure pump is susceptible to cavitation, as hydrodynamic conditions conducive to its formation can arise during the suction phase of the high-pressure pump, particularly due to pressure drops. Cavitation can cause significant damage to the high-pressure pump. Therefore, it is necessary to prevent cavitation by maintaining a sufficiently low temperature inside the high-pressure pump.

[0012] Furthermore, each direct injector is located near an engine cylinder and has one end in contact with the combustion gases. Its temperature must therefore also be kept sufficiently low to prevent any damage.

[0013] Classically, on a single-carburetor IDE type engine, the circulation of fuel in the carburetion system is sufficient to cool it, the flow consumed by the engine being high enough to maintain the temperature sufficiently low in the high-pressure pump and in the direct injectors.

[0014] However, on a dual-fuel engine, for example with gas and IDE-type fuel systems, there is not enough fuel flow through the IDE-type fuel system when the engine is running in gas-fuel mode to ensure cooling of the IDE-type fuel system. The IDE-type fuel system therefore requires a dedicated cooling system.

[0015] An existing solution consists of inserting a coolant chamber around the high-pressure pump onto the engine.

[0016] Reference can be made in this regard to document DE 10 2013 206 433 - Al which describes cooling systems external to the high-pressure pump.

[0017] However, such a solution imposes additional volume on the engine in a particularly constrained environment between the various engine components and the empty area of ​​mechanical components inside the vehicle to guarantee the safety of the pedestrians in the event of a collision with the vehicle. Furthermore, this solution does not allow for the cooling of the injectors.

[0018] Another existing solution consists of injecting, during the gas-fueling phases, the necessary and sufficient quantity of gasoline to cool the IDE-type fuel system. The fuel burned in the combustion chamber during each cycle is then a mixture of gas and gasoline.

[0019] Such a method is described in the applicant's patent application FR2009671. According to this method, a first injector is adapted for the indirect injection of a gaseous fuel such as LPG, and a second injector is adapted for the direct injection of a liquid fuel such as gasoline. The drawback of this solution is that it leads to increased gasoline consumption when the engine is running on gas and the temperature of the IDE-type fuel system is too high.

[0020] US patent 20090320774 discloses a method for controlling an internal combustion engine that can operate with liquid or gaseous fuel, which provides that, when the engine is running on gas, a thermally charged component of the engine, for example the injector nozzle, is cooled with liquid fuel. This method has the disadvantage of increasing gasoline consumption.

[0021] The applicant's French patent application FR 2109201 discloses a high-pressure pump comprising a low-pressure liquid fuel outlet connected to the low-pressure chamber and configured to create a continuous flow of liquid fuel through the inlet valve and the low-pressure chamber during engine operation with gaseous fuel. This continuous flow cools the high-pressure pump but not the fuel injectors.

[0022] An existing solution (“The new Audi 2.01 g-tron - another step for the sustainable mobility of the future” - AUDI, Internationales Wiener Motorensymposium 2017) involves cooling the high-pressure pump by means of a spacer containing a coolant chamber between the engine and the base of the high-pressure pump. With or without the spacer, this solution has several drawbacks. Raising the high-pressure pump relative to its original position on the engine, on which the dual carburetor is installed, is contrary to regulations, as this results in a mechanical component entering the safety zone reserved for pedestrian protection in the event of a collision.This solution also requires the installation of a coolant supply circuit, fed from a cold section of the engine's cooling system located away from the high-pressure pump, and which runs through the engine compartment, whose architecture is already very constrained. Finally, this solution does not cool the injectors.

[0023] In view of the above, the object of the invention is to propose a high-pressure supply system for a fuel injection system for a dual-carburetion engine which does not increase gasoline consumption, which cools both the high-pressure pump and the injectors, and which increases the volume used by the high-pressure pump as little as possible. Description of the invention

[0024] The invention relates to a high-pressure fuel supply system for the direct injection of liquid fuel into a dual-fuel internal combustion engine of a motor vehicle configured to burn a liquid fuel and a gaseous fuel.

[0025] The fuel supply system includes a high-pressure pump intended to be supplied with fuel by a low-pressure circuit and supplying injectors. It is characterized in that it includes, downstream of the injectors, at least one return circuit to the low-pressure circuit.

[0026] For example, the high-pressure pump includes a pump body comprising a low-pressure fuel inlet opening into a fuel inlet duct, a high-pressure fuel outlet, and a compression chamber connecting the fuel inlet duct to the high-pressure fuel outlet.

[0027] Advantageously, the high-pressure pump is configured to create a continuous flow of liquid fuel through the pump body during engine operation with gaseous fuel.

[0028] Advantageously, each injector is equipped with a valve to control the passage of liquid fuel from the injector into the return circuit located downstream of it.

[0029] According to one characteristic, the valve is mechanical.

[0030] Advantageously, the valve is set at a value sufficiently higher than the nominal operating pressure of the direct injection system for gasoline and / or ethanol.

[0031] According to another feature, the valve is electrically controlled.

[0032] Advantageously, the valve is piloted in the open position during the gaseous fuel supply phase of the engine and piloted in the closed position during the liquid fuel supply phase of the engine.

[0033] The invention further relates to a dual-fuel internal combustion engine of a motor vehicle configured to burn a liquid fuel and a gaseous fuel characterized in that it comprises a high-pressure fuel supply system as described above.

[0034] The invention also relates to a motor vehicle characterized in that it comprises an internal combustion engine as described above. Brief description of the drawings

[0035] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0036] [Fig.l] illustrates, in a very schematic way, an example of the general structure of a dual-fuel internal combustion engine;

[0037] [Fig.2] represents, in a very schematic way, an example of an open circuit for a direct gasoline injection system of a dual-fuel internal combustion engine according to the prior art;

[0038] [Fig.3] represents, in a very schematic way, an example of a closed circuit with a return circuit controlled by a mechanical valve according to an embodiment of the invention;

[0039] [Fig.4] represents, in a very schematic way, an example of a closed circuit with a return circuit controlled by a valve piloted in the open position according to another embodiment of the invention; and

[0040] [Fig.5] represents, in a very schematic way, an example of a closed circuit with a return circuit controlled by a valve piloted in the closed position according to the same embodiment of the invention as that represented in [Fig.4]. Detailed description of at least one embodiment

[0041] In [Fig.1], the general structure of a dual-fuel internal combustion engine 1, in particular of the spark-ignition type operating on gasoline and / or ethanol, and gas, of a motor vehicle, has been schematically represented.

[0042] This architecture is given by way of example and does not limit the invention to the single configuration of the architecture presented.

[0043] In the illustrated example, the internal combustion engine 1 comprises, but is not limited to, three inline cylinders 2, a fresh air intake manifold 3, an exhaust manifold 4 and a turbocharger system 5.

[0044] The cylinders 2 are supplied with air via the intake manifold 3, or intake distributor, itself supplied by a pipe 6 equipped with an air filter 7 and the compressor 5b of the turbocharger 5 of the engine 1.

[0045] The turbocharger 5 essentially comprises a turbine 5a driven by the exhaust gases and a compressor 5b mounted on the same axis or shaft as the turbine 5a and ensuring compression of the air distributed by the air filter 7, in order to increase the quantity (mass flow) of air admitted into the cylinders 2 of the engine 1. The turbine 5a may be of the "variable geometry" type, that is to say that the turbine wheel is equipped with variable inclination vanes in order to modulate the amount of energy taken from the exhaust gases, and thus the boost pressure.

[0046] As regards the exhaust manifold 4, it recovers the exhaust gases from combustion and expels them to the outside, by via a gas exhaust duct 8 opening onto the turbine 5a of the turbocharger 5 and by an exhaust line 9 mounted downstream of said turbine 5a.

[0047] By way of non-limiting example, the engine 1 includes a combustion gas aftertreatment system 10. The aftertreatment system 10 will not be described further.

[0048] The engine 1 is associated with a liquid fuel direct injection carburetion system comprising, for example, fuel injectors (not referenced) injecting a liquid fuel, such as pure gasoline, or a mixture of gasoline and ethanol, directly into each cylinder 2 from a liquid fuel tank 11.

[0049] The engine 1 is associated with a second fuel system (not shown) by injecting gas into the cylinders 2 from a gaseous fuel tank 12.

[0050] By "gas" we mean liquefied petroleum gas, abbreviated "LPG", or compressed natural gas, abbreviated "CNG".

[0051] The direct injection fuel system for liquid fuel (gasoline and / or ethanol) includes a high-pressure pump (not shown in [Fig. 1]) configured to ensure proper atomization of the liquid fuel into the cylinders 2 of the engine 1 while maintaining the ability to introduce a sufficient quantity of liquid fuel into the cylinders 2 between each combustion. This high-pressure pump is driven by a component of the internal combustion engine, specifically a camshaft and an intermediate tappet. The pump is therefore mounted on the cylinder head or some other part of the engine.

[0052] A known example of a high-pressure pump is illustrated in [Fig.2].

[0053] The high-pressure pump 13 comprises a pump body 14 substantially cy lindrique comprising a low pressure fuel inlet 15 opening into a fuel inlet duct 16, a high pressure fuel outlet 17 and a compression chamber 18 connecting the fuel inlet duct 16 to the high pressure fuel outlet 17.

[0054] The pump 13 further includes a low-pressure chamber 19 connected to the fuel inlet duct 16 and a plunger 20 that moves in translation within the pump body 14.

[0055] The pump 13 includes a cap 21, fixed relative to the body, in which the plunger rod 20 slides.

[0056] The low-pressure chamber 19 is located axially below the plunger piston 20.

[0057] As illustrated, the pump 13 includes an inlet valve 22 of the communication chamber pressure 18, a valve 23 outlet of the compression chamber 18 and a valve 24 discharge of the high pressure circuit.

[0058] In normal operation of the direct injection system of gasoline and / or ethanol, the plunger 20 is driven by a cam (not shown) and via a tappet (not shown), generally at a rate of one pumping cycle per combustion cycle of the engine.

[0059] Fuel is pushed into the high-pressure pump 13 at a supply pressure of approximately 3 to 6 bars by a low-pressure pump (not shown) through the fuel inlet 15.

[0060] During the fuel intake phase in the compression chamber 18 by the plunger 20, the unpiloted inlet valve 22 is open and fuel flows from the fuel inlet 15 and the low-pressure chamber 19 while the plunger 20 descends from its top dead center to its bottom dead center. The outlet valves 23 and relief valves 24 are held closed by the force of their respective springs (not referenced).

[0061] During the phase of controlling the quantity of fuel pumped, i.e. when the plunger 20 begins to rise from its bottom dead center, a volume of fuel is expelled from the compression chamber 18 through the open inlet valve 22 to the inlet 15 and the low pressure chamber 19. The outlet valves 23 and discharge valves 24 are kept closed by the force of their respective springs (not referenced) and by the fuel pressure present at the outlet 17.

[0062] When the volume remaining in the compression chamber 18 corresponds to the quantity to be pumped, the inlet valve 22 is piloted in the closed position.

[0063] During the fuel compression phase in the compression chamber 18 and in the outlet 17, the fuel is expelled from the compression chamber 18 by the outlet valve 23 while the plunger 20 continues its ascent to its top dead center.

[0064] Compressed fuel flows through the high-pressure pipe 25, located upstream of a high-pressure rail 26. The rail 26 provides a fuel reservoir and distributes the fuel to the inlet of each injector 27 via their respective cups 28. When the injectors 27 are electrically activated, the needles 29, which are guided within the bodies of the injectors 27, rise, allowing fuel to flow into the injectors 27 and thus cool the body 30, the needle 29, the ball 31, and the nozzle 32 of each injector 27. Each injector 27 corresponds to a cylinder 2 of the engine 1.

[0065] When the engine is running on an alternative fuel, i.e. without using the direct gasoline injection system, the plunger 20 is always driven by the cam which is not disengageable.

[0066] Due to the fuel being forced through the inlet valve 22 by the movements of the plunger 20, and the lack of fuel renewal in the high-pressure pump Due to pressure 13 and the ambient temperature of said pump, the fuel temperature in the high-pressure pump 13 increases and reaches cavitation conditions. Therefore, it is necessary to cool the high-pressure pump during these engine operating phases when the gasoline direct injection system is not in use.

[0067] Figure 3 illustrates a high-pressure circuit 33 for a direct gasoline injection system of an internal combustion engine according to an embodiment of the invention.

[0068] The pump 34 comprises a substantially cylindrical pump body 35 comprising a low-pressure fuel inlet 36 opening into a fuel inlet 37, a high-pressure fuel outlet 38 and a compression chamber 39 connecting the fuel inlet 37 to the high-pressure fuel outlet 38.

[0069] The pump 34 further includes a low-pressure chamber 40 connected to the fuel inlet duct 37 and a plunger 41 that moves in translation within the pump body 35.

[0070] The pump 34 includes a cap 42, fixed relative to the body, in which the plunger rod 4L slides

[0071] The low-pressure chamber 40 is located axially below the plunger piston 4L

[0072] As illustrated, the pump 34 includes an inlet valve 43 of the com chamber pressure 39, an outlet valve 44 from the compression chamber 39 and a discharge valve 45 from the high pressure circuit connecting the high pressure chamber 39 and the fuel outlet 38.

[0073] The normal operation of the direct gasoline injection system is identical to that of the prior art described with reference to [Fig.2] and will not be described further here.

[0074] When the engine is running on an alternative fuel, i.e. without using the direct gasoline injection system, the plunger 41 is always driven by the cam which is not disengageable and the low pressure pump (not shown) is configured to deliver the liquid fuel (gasoline) to the high pressure pump 34 through the inlet 36.

[0075] Closing the inlet valve 43 allows the fuel to be pressurized in the compression chamber 39.

[0076] The compressed fuel passes through the high-pressure pipe 46, located upstream of a high-pressure rail 47. The rail 47 allows a fuel reserve to be built up and the fuel to be distributed to the inlet of each injector 48 via their respective cups 49.

[0077] Since the injectors are continuously closed when the engine is running on gas, a A mechanical valve 50 integrated into the body 51 of each injector 48 allows the fuel to be evacuated to the corresponding return circuit 52, connected downstream to the low pressure circuit 53 which supplies the pump 34. Each injector 48 is therefore equipped with a valve 50 and connected to a corresponding return circuit 52.

[0078] The high-pressure circuit 33, which is then a closed circuit 33, is supplied by a low-pressure circuit 53 and includes in the upstream to downstream direction a high-pressure pump 34, a high-pressure pipe 46, a high-pressure rail 47, injectors 48 equipped with a valve 50 per injector and return circuits 52 connected downstream to the low-pressure circuit 53.

[0079] The closed circuit 33 allows fuel to be renewed in the high-pressure pump 34 and in the injectors 48. The fuel renewal helps to lower the temperature of the high-pressure pump 34 and to cool the body 51 of the injectors 48.

[0080] In order to optimize the cooling of the lower part of the injector, in particular the ball 54 and the nose 55, the valve 50 is placed as close as possible to the nose depending on the practical possibilities of integrating the return circuits 52 into the cylinder head.

[0081] In order to ensure that, during normal operation of the gasoline and / or ethanol direct injection system, all of the compressed fuel sent by the pump 34 to the injectors 48 is injected into the engine cylinders, the mechanical valves 50 are set to a value sufficiently higher than the nominal operating pressure of the gasoline and / or ethanol direct injection system. This set value may, for example, be 380 bar in the case of a nominal average pressure of the direct injection system of 350 bar, with pressure variations of plus or minus 20 bar.

[0082] During the operating phases of the gas engine, the pump 34 must generate a pressure greater than the setting of the valves 50, in order to overcome the resistance of the mechanical valves 50 and send the fuel into the return circuits 52. This energy expenditure can prove troublesome in the overall energy expenditure balance.

[0083] An optimized variant presented below consists of replacing the mechanical valves 50 with electrically controlled valves, controllable to any position between a fully open position represented in [Fig.4] and a fully closed position represented in [Fig.5].

[0084] The embodiment of [Fig.4], in which the same elements bear the same references, differs from the embodiment of [Fig.3] only in that the valve integrated into the body of each injector is an electrically controlled valve 56 and shown here in the fully open position.

[0085] Figure 5 shows the same embodiment as that illustrated in Figure 4, with the difference that the valves 56 are shown here in the com- position Completely closed.

[0086] Thanks to the pilot valves 56 shown in figures 4 and 5, the fuel is directed either to the return circuits 52, when fueling is done with gas and with the valves 56 in the open position, or to the injector nozzle 55, when fueling is done with gasoline and / or ethanol and with the valves 56 in the closed position.

[0087] In the embodiment with pilot valves 56, the valves 56 do not block the passage of fuel to the return circuits 52 when the carburetion is carried out with gas and they are in the open position, which makes it possible to reduce the overall energy consumption of the system.

Claims

Demands

1. High-pressure fuel supply system (33) for the direct injection of liquid fuel into a dual-fuel internal combustion engine (1) of a motor vehicle configured to burn liquid fuel and gaseous fuel, comprising a high-pressure pump (34) intended to be supplied with fuel by a low-pressure circuit (53) and supplying injectors (48), characterized in that it comprises downstream of the injectors (48) at least one return circuit (52) to the low-pressure circuit (53), each injector (48) being provided with a valve (50, 56) enabling control of the passage of liquid fuel from the injector into the return circuit (52) located downstream of it.

2. High-pressure fuel supply system (33) according to claim 1, wherein the high-pressure pump (34) comprises a pump body (35) including a low-pressure fuel inlet (36) opening into a fuel inlet duct (37), a high-pressure fuel outlet (38) and a compression chamber (39) connecting the fuel inlet duct (37) to the high-pressure fuel outlet (38).

3. High-pressure fuel supply system (33) according to claim 2, wherein the high-pressure pump (34) is configured to create a continuous flow of liquid fuel through the pump body (35) during the operation of the engine (1) with gaseous fuel.

4. High pressure supply system (33) according to any one of claims 1 to 3, wherein the valve (50) is mechanical.

5. High-pressure fuel system (33) according to claim 4, wherein the valve (50) is set at a value sufficiently higher than the nominal operating pressure of the direct injection system of gasoline and / or ethanol.

6. High pressure supply system (33) according to any one of claims 1 to 3, wherein the valve (56) is electrically controlled.

7. High-pressure fuel supply system (33) according to claim 6, wherein the valve (56) is piloted in the open position during the gaseous fuel supply phase of the engine and piloted in the closed position during the liquid fuel supply phase of the engine.

8. Dual-fuel internal combustion engine (1) of a vehicle with-

9. A motor vehicle configured to burn liquid fuel and gaseous fuel, characterized in that it comprises a high-pressure fuel supply system (33) according to any one of claims 1 to 7. A motor vehicle characterized in that it comprises an internal combustion engine (1) according to claim 8.

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