WO2024231336A1

WO2024231336A1 - A combustion engine, a fuel system for the combustion engine, and a method of supplying fuel to the combustion engine

Info

Publication number: WO2024231336A1
Application number: PCT/EP2024/062435
Authority: WO
Inventors: Jeppe Kiilerich ØSTERLUND; Lasse Ankjær BODILSEN; Mads Niebuhr JØRGENSEN; Poul Erik BRAMSEN
Original assignee: Eltronic Fueltech AS
Current assignee: Eltronic Fueltech AS
Priority date: 2023-05-08
Filing date: 2024-05-06
Publication date: 2024-11-14
Anticipated expiration: 2025-11-08

Abstract

A combustion engine (2) with a fuel system comprising a valve (9) defining a variable flow of the liquid fuel at a process pressure in a recirculation fuel-path (7). The flow depends on an opening degree controlled by movement of a valve element (25). To make autonomous adjustment particularly in case of peak pressures, the valve comprises a force balance structure moves the valve element (25) based on a force balance between a process force created by the process pressure and a control force. An electronic control structure (10) is configured to control the opening degree by amending the control force based on an electrical signal representing the process pressure.

Description

A COMBUSTION ENGINE, A FUEL SYSTEM FOR THE COMBUSTION ENGINE, AND A METHOD OF SUPPLYING FUEL TO THE COMBUSTION ENGINE

INTRODUCTION

The invention relates to a combustion engine and a fuel system for a combustion engine operated with liquid fuel. Particularly, the invention relates to a system of the kind forming a fuel-path in a downstream direction from a fuel storage to the combustion engine and having a fuel pump creating a flow of the fuel which is received by a booster pump before injection into a combustion chamber. A recirculation fuel-path extends from a return-point downstream of the fuel pump to a recipient, e.g., constituted by the fuel storage. The recirculation fuel-path ensures a backflow of excessive fuel, i.e., an amount of fuel delivered by the fuel pump and exceeding what is consumed by the engine. The invention particularly relates to the high-pressure engine type sometimes referred to as a diesel engine irrespective that it may run on other kinds of fuel. In this type of engine, fuel is injected into the combustion chamber at a very large pressure provided by a booster pump. Often, this type of engines is self-igniting meaning that ignition is caused by the high temperature derived from the high-pressure.

BACKGROUND

Engines are made for different fuel systems including gas phase and liquid phase fuel such as diesel, natural gas, petroleum gas, methanol, ethanol, and ammonia. Existing fuel systems for high-pressure engines comprises a supply pump for delivering fuel from a tank to a booster pump. The pressure of the supply pump is moderate, and the booster pump raises the pressure and delivers the fuel to fuel injectors upstream of a combustion chamber in the engine at a much larger pressure.

In large engines, e.g. engines of power plants and large ships, the fuel system with the supply pump is normally completely separated from the injection structure. The injection structure including the booster pump and the injection valves by which the fuel is injected into the cylinders are part of the engine itself. Whereas the engine is made by an engine maker, the fuel supply system is a separate system which is often manufactured by a different company.

The fuel is typically delivered either at a fixed pressure or at a variable pressure which changes e.g., as a function of airflow in an air manifold, or alternatively based on speed or torque. In modern engines the flow of fuel is controlled by a computer processing unit (CPU) based on various sensors, e.g., including air-flow, temperature, and NOX sensors.

In large engines, and for the booster pump to work efficiently, it is typically required to deliver fuel at a relatively constant pressure to the booster pump. The fuel supply systems are therefore normally designed to deliver a relatively fixed pressure which is low compared to the injection pressure. Typical ranges could be 50-80 bar pressure from the fuel system and several hundred bar after the booster pump. In small engines where the fuel supply system forms an integrated part of the engine, the fuel may be supplied at a pressure which varies with the flow into the combustion chamber. This is, however, not desired in large engines where a fixed pressure before the booster pump is desired.

When operating conditions change, the consumed amount of fuel also changes. The recirculation fuel-path is normally capable of absorbing variations by returning the excessive fuel to the storage.

Different approaches are applied for controlling the pressure in the fuel-path. One solution is to provide a pressure-controlled valve in the recirculation fuel-path. The pressure-controlled valve may be mechanical or electrical, and under normal operating conditions, it ensures a correct pressure in the fuel-path by opening and closing a flow back to the tank depending on a pressure in the fuel-path or a pressure in the recirculation fuel-path.

In certain situations, e.g., in high load conditions and with rapidly changing loads, a peakpressure may exceed a target operating pressure for the engine, and in extreme cases, the peak-pressure may damage parts of the engine or fuel system. For that reason, existing fuel systems often include a separate safety valve. The safety valve opens at a threshold pressure and prevents damage. Most often, however, the safety valve is designed for rapid pressure release, and therefore, the engine may not function when the safety valve opens. Typically, the engine will either stop or continue to operate at reduced torque. Moreover, the safety valve is configured for rapid pressure relief and not for obtaining a precise pressure, and the pressure obtainable with such valves is typically un-precise - i.e., the error between the desired process pressure and the obtained process pressure is large. In the following, this error is referred to as the process pressure error (PPE).

In a dual fuel engine, e.g., switchable between diesel as a primary fuel and ammonia as a secondary fuel, an alarm in the secondary fuel system may require an almost instant emergency stopping of the secondary fuel supply. Typically, within one revolution, the engine will switch to the primary fuel. This means that the fuel path is abruptly blocked, which may cause an extreme version of the pressure peak event with pressure surge travelling backwards in the system. Regarding rapid pressure surges which may occur in a dual fuel system, the safety relief valves may not react quickly enough since the ripple travels at the speed of sound in the fluid.

In high-pressure engines, rapid pressure surges may become particularly problematic since the booster pump is typically a positive displacement pump.

In high-pressure engines with a positive displacement booster pump, the fuel supply system may typically include a centrifugal pump. Such a pump allows pressure pulsations and surges to propagate backwards through the pump and therefore prevents or reduces the risk of hazard or damage. Even though the centrifugal pump thereby protects against excessive pressures in the supply system, the centrifugal pump also has a disadvantage. Particularly, it is more difficult to predict and control the flow and pressure provided by the centrifugal pump and the pressure before the booster pump may therefore vary undesirably.

Centrifugal pumps perform well at low discharge pressures but may not scale competitively compared to positive displacement type pumps. Hence supplying fuel to the booster pump at an increased pressure may call for the use of a positive displacement type fuel pump.

Centrifugal pumps remain competitive for low to moderate pressure applications. As the requirement for the pressure on the fuel pump discharge side increases, so increase the competitiveness of positive displacement type pumps compared to centrifugal types.

However, positive displacement type pumps prevent or restrict backflow of fuel, and pressure ripples travelling backwards in the system may therefore become damaging. Moreover, in high-pressure engines, using a booster pump for injecting fuel into the cylinder, the pressure between fuel supply system and fuel booster pump may experience pressure variations introduced as a function of the individual piston movements of the booster pump and supply pump.

SUMMARY

It is an object of embodiments of the disclosure to provide a high-pressure type combustion engine, a fuel system for such an engine, and a method of supplying fuel to an engine which allow improved pressure conditions. It is particularly an object to allow continuous control while releasing peak-pressures and therefore allow good performance even when reducing excessive pressures. For this and other reasons, in a first aspect, is disclosed a high-pressure type combustion engine comprising a fuel supply system and a fuel injection system, wherein the fuel supply system is configured to supply fuel at a target pressure to the fuel injection system. It is desired to maintain the target pressure as a stabile pressure.

The fuel injection system comprises a booster pump configured as a positive displacement pump for elevating the target pressure before injection into a combustion chamber of the combustion engine. The fuel system comprises:

- a fuel-path forming a downstream direction from a fuel storage to a fuel outlet connected to the fuel injection system;

- a fuel pump configured as a positive displacement pump to provide a flow of liquid fuel at a process pressure in the fuel-path;

- a recirculation fuel-path extending from a return-point in the fuel-path, e.g. to the fuel storage, the return-point being downstream of the fuel pump;

- a valve defining a variable flow of the liquid fuel in the recirculation fuel-path depending on an opening degree controlled by movement of a valve element;

- a force balance structure comprising a pressure responsive member and being configured to move the valve element based on a force balance between a process force and a control force, where: o the process force results from the process pressure acting on the valve member; and o the control force results from a control force acting on the valve member through a pressure responsive member, and

- an electronic control structure configured to control the opening degree by amending the control force based on an electrical signal defining the process pressure.

Since the fuel pump is a positive displacement pump, it may, unlike centrifugal pumps, work well even with a low flow rate across the pump, and it may provide a high-pressure in a single stage. Furthermore, it may be less affected by the pressure against which it operates. In certain situations, it is therefore superior for regulating flow and pressure in the fuel supply system.

The positive displacement pump of the fuel system provides a predictable flow and pressure in the fuel system and therefore increases the ability to keep the pressure before the booster pump constant. Moreover, the positive displacement pump may typically be smaller than a centrifugal pump having several stages for creating a high differential pressure.

Since the fuel of the fuel supply system flows between two positive displacement pumps, i.e. between the fuel pump and the booster pump, the fuel flows between two pumps both having inability to be affected by the pressure. Moreover, both displacement pumps create a pulsating pressure. Accordingly, pressure peaks develop already due to the structure of the pump, and they may not have a chance to propagate through either side of the fuel supply system. The pressure variations will be experienced as pulsations travelling backwards in the supply line and they may reach the fuel system. Here, the force balance structure of the control valve may reduce or completely absorb these pulsations by allowing fuel to bypass the fuel pump and propagate further backwards in the system to the recipient. If the fuel system were provided with a centrifugal fuel pump, the backwards flow and absorption of pulsation could occur partly through the centrifugal fuel pump. However, when the fuel pump is a positive displacement type pump, the backwards flow would be excluded through the pump, and the force balance structure is the only way of absorbing the pulses unless dedicated absorption measures are deployed, such as pulsation dampeners.

In addition, the aforementioned shift between different types of fuel may create even larger pressure surges, and pressure ripples capable of destroying the fuel line may arise.

For that purpose, the force balance structure may smoothen the ripples. In combination, the specific pump of the fuel system and the specific valve including the force balance structure enables a more precise and constant pressure before the booster pump without increasing the risk of destroying the fuel system.

In normal operation, the electronic control structure may control the opening degree by reading an electronic pressure signal, converting the electronic pressure signal into an amendment of the control force, and by precise amendment of the control force. This may provide efficient and precise pressure adjustment at pressures within a normal pressure range. Even though this provides precise adjustment, it may not be the fastest way of adjusting the pressure.

The purpose the pressure responsive member is to allow an autonomous adjustment of the valve and its degree of opening. This allows a certain amount of fuel to be returned to the fuel storage. The pressure responsive member is therefore preferably an autonomous responsive member configured to react on pressure peaks without the need for electrical control signals. Examples include pressure responsive members being elastically deformable such as springs and viscous or pneumatic bellows.

In case of peak-pressures, the force balance structure may further control the opening degree and provide a swift reaction directly based on the process force resulting from the process pressure acting on the pressure responsive member. Due to the pressure responsive member, this force balance can be changed by the peak-pressures, and the pressure may, without time consuming signal translation between pressure signals and electrical signals, directly amend the control force by the impact of the pressure on the pressure responsive member. This may be a much faster, however less precise way of amending the control force since it does not require calculation of an electrical response to an observed pressure by execution of a transfer function in the electronic control structure. Moreover, the control and the relief of pressure are based on movement of one single valve element which potentially further reduces the reaction time and increases simplicity, durability, and reliability compared with use of a pressure relief valve being separate from the control valve.

Accordingly, the engine can maintain a precise process pressure and perform well while reducing peak-pressures very swiftly and thereby allow safe and continuous operation.

The combustion engine may e.g., be a piston engine with a piston movable in a cylinder. As opposed e.g., to jet engines, such piston engines may cause rapid pressure variations which can be partly or fully absorbed by the valve and force balance structure.

The pressure responsive member may be a movable wall, e.g., a membrane or diaphragm separating two spaces with different pressures. By movement of the diaphragm, the diaphragm can absorb pressure in one of the two spaces. The pressure responsive member could also be a piston movable in a cylinder and separating two spaces in the cylinder and thereby absorb pressure in one of the two spaces.

The control force may be independent on pressures downstream the booster pump. The adjustment of the control force by the electronic control structure could be based on electronic processing of inputs from electrical sensors and with no direct interaction with or contribution from any process force, pressure, temperature, flow or the like.

The force balance structure may act directly on the valve element with no signal conversion. The control force may result from a control pressure acting on one side of the pressure responsive member, and a reference pressure acting on an opposite side of the pressure responsive member. In this case, the pressure responsive member could be a diaphragm or a piston movable in a cylinder etc. The reference pressure could e.g., be atmospheric pressure, herein referred to as PA, or it could be the process pressure, herein referred to as Pp, or it could be any fraction of the process pressure.

When the force balance is a pressure balance between pressure on opposite sides of the pressure responsive member, the control becomes simple and potentially more robust and faster since no conversion of the pressure into an electrical signal is needed. I.e., the force balance which moves the valve element is derived with no electrical signal conversion directly based on the pressures. The opening degree of the valve element may be controlled simultaneously by the electronic control structure and the force balance structure, i.e., the force balance is established simultaneously with the electronic control structure controlling the opening degree. This provides the ability to provide a fast reaction to pressure peaks and still continuously applying the control signal from the electronic control structure. The latter may be more precise and better to remove the error, and the combination may therefore provide a precise and fast control.

The electronic control structure may be constituted by a CPU with memory and computer executable code for enabling various functions. Software program instructions and data may be stored on a non-transitory, computer-readable storage medium, and when the instructions are executed by the CPU the functions associated with those instructions are carried out.

When the pressure responsive member is a diaphragm or piston with a control pressure applied on one side, the electronic control structure may comprise an electronic valve structure configured to control the control pressure and thereby amend the force balance by amending the control pressure.

The control pressure may e.g., be a relatively low pressure, e.g., between 1 and 10 bar taken from a regular compressor tank. The valve may be defined with a pressure intensifier such that the relatively low control pressure can control a higher process pressure. The electronic valve may open and close a passage between this regular compressor tank and the pressure responsive member.

The pressure responsive member may alternatively or additionally include a spring structure providing the control force. In this case, the process force, i.e., the force resulting from the process pressure acting on the valve member, acts against the force from the spring structure. In case of pressure bursts, the spring structure will allow the valve member to move when the process force exceeds the control force.

The electronic control structure may comprise a power operated actuator for moving the spring structure and changing the pre-tensioning of the spring structure based on the electrical signal defining the process pressure. The electronic control structure thereby controls the opening degree by amending the control force.

The force balance structure may also comprise a combination with a spring structure and a diaphragm or a combination with a spring structure and a piston. The pressure signal may depend on the process pressure, i.e. , a transfer function may provide the translation from an error between an actual process pressure and a desired process pressure.

The fuel system may further comprise an expansion tank configured to reduce excessive pressure in the fuel-path, excessive pressure being a pressure above an upper threshold. The expansion tank may be a traditional expansion tank e.g., having an encapsulated compressible member, e.g., a balloon structure with a pressure defining the capability to reduce the excessive pressure. The expansion tank may increase the stability and safety further.

Normally, the fuel pump in similar fuel systems is a centrifugal pump. Such a pump is simple and cheap and offers the advantage that it may absorb excessive pressures by backflow through the pump. Since the valve and force balance structure of the present disclosure are configured to absorb rapid pressure variations, the fuel pump may particularly be a positive displacement pump configured to deliver an approximated steady flow at a specific speed of the pump. Particularly, the pump's pumping action may be cyclic and driven by pistons in a cylinder. This structure does not allow a back flow but offers a higher pressure and a more precise pressure, and it could be allowed in view of the valve structure included in the fuel system.

The positive displacement pump may be configured to provide a variable flow of the liquid fuel based on a pump control signal, and it may be controlled by the electronic control structure.

When the valve autonomously adapts to the actual pressure situation and automatically allows excessive fuel back to fuel storage, the problem of excessive fuel is potentially just moved backwards in the system. For the solution to become more useful, a feature may be implemented for absorbing the pulsations further back, e.g., in the fuel storage. In one embodiment, the system comprises a two-phase tank in which a gas phase will effectively absorb pressure pulsations and excessive fuel. This two-phase tank may constitute the recipient. Alternatively, the recipient may be constituted e.g., by the fuel storage.

It may not be practical to have a two-phase tank between the fuel pump and the fuel outlet to the engine since it potentially increases the risk of sending gas phase fuel to the engine. Accordingly, the two-phase tank is preferably before the fuel pump.

The valve may comprise a position sensor which determines the position of the valve element. The position sensor could be an analogue sensor, e.g., providing a variable resistance or capacitance when the valve element moves. The position sensor may be used for controlling the position of the valve, e.g., by controlling the speed of the fuel pump, and thereby obtaining a desirable average position of the valve element.

In a second aspect, the disclosure provides a fuel system for a combustion engine, particularly a high-pressure engine, e.g., a 2 or 4 stroke engine, e.g. of the self-igniting kind such as a diesel engine.

In a third aspect, the disclosure provides a method of supplying fuel to a combustion engine according to the second aspect. The method comprises:

- establishing a flow of fuel at a process pressure in the fuel-path;

- consuming a part of the fuel in the combustion engine while recirculating a remaining part of the fuel in the recirculation fuel-path;

- establishing a force balance by creating a control force which counteracts a process force defined by the process pressure until a desired process pressure is achieved.

The force balance may be established while the combustion engine is running.

LIST OF DRAWINGS

Fig. 1 illustrates diagrammatically a fuel system;

Figs. 2 and 3 illustrate a valve for a fuel system;

Figs. 4 and 5 illustrate details of the valves;

Figs. 6a, 6b, and 7 illustrate control loops;

Figs. 8 and 9 illustrate pressure diagrams, and

Fig. 10 illustrates an embodiment of the valve.

DETAILED DESCRIPTION

Fig. 1 illustrates schematically, an example of a combustion engine with a fuel system 1. The illustrated fuel system comprises a fuel-path 3 forming a downstream direction indicated by the arrow 4. The fuel-path extends from a fuel storage 5 to the combustion engine 2. A fuel pump 6 raises the pressure Poi, which is the pressure in the supply storage 5, to a process pressure, P_p, at which pressure the liquid fuel is delivered to the injection part of the combustion engine, marked with an E. In the injection part of the combustion engine, the fuel pressure is boosted to a higher booster pressure PB. The booster pressure is typically obtained by a high-pressure fuel injector pump forming an internal component of the combustion engine, herein we refer to the injector pump as a booster pump.

The recirculation fuel-path 7 extends from the return-point 8 downstream of the fuel pump 6 in the fuel-path 3. The recirculation fuel-path 7 extends to the fuel storage 5. Sometimes, an additional return path is provided from each injector nozzle of the combustion engine 2 back to the supply storage 5.

A valve 9 is inserted in the recirculation fuel-path. The valve defines a variable flow of the liquid fuel, and the variable flow is controlled by varying an opening degree of a valve element by moving the valve element relative to the valve body. The valve 9 and components thereof are illustrated in further details in Figs. 2-5. The option of adding a manually adjustable valve 20 in parallel with the valve 9 may for some cases be beneficial e.g. if it is desired to secure a minimum flow area in the recirculation fuel-path.

The fuel system further comprises an electronic control structure 10, 10' configured to control the opening degree by amending the control force based on a pressure signal. When the control force changes, it changes the balance between the control force and the process force and the flow conditions through the valve changes.

The fuel system may further comprise the illustrated safety valve 11 and the illustrated accumulator 12 functioning as an expansion tank.

The pressure sensor 13 is an electronic sensor communicating the process pressure with the electronic control structure.

In operation, the electronic control structure 10 receives a signal from the sensor 13. In this case, the pressure signal on which the control force is based, is the process pressure. The control loop of the electronic control structure is illustrated in Figs. 6 and 7 and will be explained later. In summary, the electronic control structure determines the control force based on the process pressure. For this example, the set-point signal to 10 is transmitted from a common controller 10'. In terms of hardware, 10 may be integrated in 10' or be a separate controller.

The fuel system further comprises a fuel pump controller 17 configured to receive a pump control signal and to control the fuel pump 6 based thereon. The flow meter 18 determines a flow of the liquid fuel in the fuel-path 3, and the return valve 19 allows the liquid fuel to be returned to the suction side of the pump. Particularly the return valve may be adjusted to a pressure herein referred to as "overpressure valve opening pressure". At this pressure, the return valve works as a fuse which sends flow of liquid fuel back to the suction side of the pump. This is optional, and it could be considered as a last chance of avoiding excessive pressure, and as a chance of avoiding release of the liquid fuel to the atmosphere e.g. through a traditional over pressure release valve.

In the following, different embodiments are described. A first embodiment is referred to as a pneumatic pressure control force balance structure, and a second embodiment is referred to as a mechanical pressure control force balance structure. Further embodiments are also explained.

In one embodiment, referred to as a pneumatic force balance structure embodiment, the force balance structure comprises a pressurised chamber, and the pressure responsive member is constituted by a wall part of the chamber. The control force results from a control pressure, Pc, acting on one side of the pressure responsive member, and atmospheric pressure, Pa, which acts on an opposite side of the pressure responsive member. The pressurised chamber may form an integrated part of the valve. Fig. 2 illustrates an example of such a valve.

Due to the valve, and particularly due to the pressure responsive member, the valve may autonomously adjust its degree of opening with which it can allow a greater or lesser degree of fuel to return backwards in the system. In this way, the pressure problem may ultimately be moved backwards in the fuel system. For absorbing the pulsations, the valve may be complemented with a pressure absorbing feature, e.g., a two-phase tank arranged as the recipient of the fuel.

Fig. 2 illustrates the valve 9. The valve comprises a valve housing 21, a process media inlet side 22 extending from an inlet to the valve seat. The process media outlet side 23 extends from the valve seat to the outlet for delivering the liquid fuel. The valve seat defines sealing surfaces 24 between the valve element 25 and the valve housing 21. The valve element 25 can thereby open and close the passage between the inlet side and the outlet side, and therefore provide a variable flow of the liquid fuel in the recirculation fuel-path depending on an opening degree of the valve element.

In the following, the inlet side of the valve element refers to the surface of the valve element being exposed towards the inlet side 22 and the outlet side of the valve element refers to the surface of the valve element being exposed towards the outlet side 23. The valve element 25 is moved by forces resulting from pressure on the inlet side of the valve element and pressure on the outlet side of the valve element 25, and forces acting on the valve element via the stem 26.

The stem extends through the bonnet 27 and which is therefore guided by the bonnet. The stem extends through a sealing interface 28 of the bonnet 27 and is attached to a stem plate 29 in the lower space 30 above the bonnet 27. The stem plate 29 can interact with and be moved by a pressure responsive member 31.

The bonnet 27 is connected to ambient space via the breathing port 43, such that the pressure in the bonnet 27 and thus the lower space 30 equals the ambient pressure which is typically the atmospheric pressure.

The bonnet 27 defines in combination with the sealing interface 28, a barrier between two different atmospheres, one being the fuel containing atmosphere of the fuel system and the other being the atmosphere of ambient space.

In this embodiment, the pressure responsive member 31 is an elastically deformable diaphragm which is movable inside the dome 32 depending on a pressure difference on opposite sides of the diaphragm.

The valve comprises a pneumatic inlet 33 and a pneumatic outlet 34 connected to a control valve for injection of air into the upper space 35.

In operation, the pressure in the inlet side is typically higher than in the outlet side, i.e. , normally, the difference corresponds to the pressure which is provided by the fuel pump 6 subtracted the pressure loss in the flow path. Due to the higher pressure in the inlet side, the pressure balance on the valve member, c.f. also fig. 4 results in an upwards pressure, herein referred to as FP resulting from the pressure of the process media. This pressure acts to open the valve and increase the flow.

The electronic control structure controls an electromagnetic valve at each of the pneumatic inlet 33 and the pneumatic outlet 34 and thereby controls the pressure in the upper space 35 above the pressure responsive member 31. Based on a pressure difference between the pressure in the upper space 35 and the pressure in the lower space 30, the pressure responsive member deflects and creates a force herein referred to as Fp_n resulting from the pneumatic state. This force potentially presses the stem plate and thus the valve element 25 downwards. In that case, the force acts to close the valve and thereby reduce the flow of the liquid fuel from the process media inlet to the process media outlet. The balance between Fp and Fp_n results in the actual position of the valve element and thus the flow conditions in the recirculation fuel-path and thus controls the process pressure Pp.

In summary, the force balance structure of the valve in Fig. 2 is constituted by a pressurised chamber withing the dome 32, i.e., the chamber defining the lower and upper spaces 30, 35. This chamber is split into two parts by the diaphragm constituting in this embodiment, the pressure responsive member 31. The control force results from Fp and Fp_n, i.e., resulting from the control pressure, Pc, in the pressurised chamber and acting on the inner surface 36, the atmospheric pressure PA acting on an opposite, outer surface 37 of the pressure responsive member 31, and the process pressure, Pp acting on the inlet side and outlet side of the valve member.

In the disclosed valve, the opening degree of the valve element is controlled simultaneously by the electronic control structure regulating the pressure in the upper space 35 and by the force balance structure.

The pressure responsive member 31 is directly attached to the stem plate 29 and it thereby acts directly on the valve element in both directions. Alternatively, the pressure responsive member 31 is separate from the stem plate 29 such that it can abut and press the valve element 25 downwards but not pull the valve element in the opposite direction. In this case, only the process pressure, Pp acting on the inlet side and outlet side of the valve member can lift the valve member. This embodiment may work but can be undesired if there is a risk of the pressure at the inlet side being lower than the pressure at the outlet side. In that case, the valve becomes stuck in a closed position.

Since the movement occurs based on a pressure difference between the lower and upper spaces 30, 35, no signal conversion is needed, i.e., the process pressure directly influences the valve position, and the system becomes capable of reacting extremely fast to pressure peaks and ripples.

The electronic control structure comprises an electronic valve structure configured to control the control pressure. The electronic valve structure could be a 3/2 way valve selectively connecting the pressurised chamber with a pressure source and with ambient space. When connecting the pressurised chamber with the pressure source, the control pressure Pc increases, and when connecting the pressurised chamber with the ambient space, the control pressure Pc decreases. The pressure source could be output from a compressor or a compression tank.

Fig. 3 illustrates an embodiment referred to as spring force balance structure embodiment. In this embodiment, a valve like the valve illustrated in Fig. 2, however not completely identical. In the valve of Fig. 3, elements having the same function as counterpart elements of the valve in Fig. 2 are presented with the same numbers.

The valve in Fig. 3 comprises a spring structure, in this case illustrated with a coiled spring

39, and a spring button 40. Above the spring button 40, and attached to the spring button

40, the valve comprises an actuator stem 41 extending upwards into an actuator illustrated by the box 42. This could e.g., be a linear actuator.

In operation, the actuator 42 is controlled by the electronic control structure and will normally operate to lower and raise the valve element 25 to define a desired pressure in the recirculation fuel-path. However, the process pressure, Pp, found in the flow path between the inlet and the outlet acts on the valve element 25 and provides an upwards force to lift the valve element 25 against the force from the spring structure 39.

In case of excessive pressures or pressure ripples, the force from the process pressure, Pp, may exceed the pressure of the spring structure and thus enable an upwards movement of the valve element 25 and thus reduce the pressure in the recirculation fuel-path and thus in the fuel-path by letting more fuel flow to the fuel storage.

Fig. 4 illustrates schematically the functioning of the valve in Fig. 2 and illustrates the control force resulting from the balance between Fp and Fp_n, i.e. , resulting from the control pressure, Pc, in the pressurised chamber and acting on the inner surface 36, the atmospheric pressure PAacting on an opposite, outer surface 37 of the pressure responsive member 31, and the process pressure, Pp acting on the inlet side and outlet side of the valve member. Interaction between valve element 25 and the outer surface 37 could be without a fixed connection. In that case, the pressure responsive member 31 only contacts the valve element 25 when the outer surface 37 is urged downwards and presses against the valve element. Alternatively, the responsive member and the valve element could be fixedly connected, e.g., by bolting or riveting the illustrated diaphragm to the valve element.

Fig. 5 illustrates schematically the functioning of the valve in Fig. 3 where the valve element 25 is moved by the deformation of the spring structure 39 or by the actuator 42 via the actuator stem 41.

Fig. 6a illustrates the control loop for the electronic control structure operating the valve illustrated in Figs. 2 or 3. In this control loop, Pm refers to the supply pressure which is the desired pressure in the fuel-path for correct operation of the engine. The sensor 13 is indicated as MPS (media process sensor) and sends an observed process pressure, Pp which is subtracted from P_m. The resulting error is used in the controller, C, which based thereon calculates a control setting X_p. The control setting is converted to a control activity Y_m by the valve actuator, VA. Y_m, in this connection, is process pressure PP, and the electronic control structure calculates a change in position of the membrane or spring structure which is carried out by the valve actuator, VA. Valve actuator, VA, is where the actuator changes its position with X__p from an initial position, i.e., the pressure error e_m becomes a position error x_p which then provides the desired movement which could be movement and thus pre-stressing of the spring structure in Fig. 3 or change of pressure in the valve in Fig. 2, i.e., if the valve is according to Fig. 2, the control setting would be a desired pneumatic pressure in the upper space 35, and the control activity would be insertion of air into or release of air from the upper space 35. If the valve is according to Fig. 3, the control activity would be movement of the actuator stem 41 by use of the actuator 42.

It may be desirable if the valve moves back and forth relative to a position which provides the ability to react in both directions, i.e. both to increase the flow towards the recipient and to reduce the flow towards the recipient. Herein we refer to the term average valve position to describe the position in which the valve is located when the process pressure, Pp, is suitable. Whenever the process pressure, Pp, deviates from the desired pressure, the valve compensates by movement away from the average position. Since the flow through the valve is counteracted by the fuel pump, there is a relationship between the average position of the valve and the speed of the pump.

Fig. 6b describes a control loop for positioning the valve in a desired average position by controlling the speed of the fuel pump.

In Fig. 6b, the Actual valve position, Avp, is subtracted from the Target valve position, Tvp, and the valve position error, Ep is input for the controller C. Based thereon, the controller provides a pump speed setting, Ps, which defines a new pump speed P-RPM. This new pump speed provides a change in flow which will affect the flow balance and therefore cause a change in the average valve position.

Fig. 7 illustrates a more advanced control loop where the valve actuator is constituted by a closed loop pneumatic control system, i.e., the inner loop comprising pneumatic pressure sensor PPS measuring pneumatic pressure Mp.

In this inner loop, the pneumatic pressure in upper chamber 35 (Fig. 2) is measured by the PPS sensor and the reading is subtracted from the control setting XP determined by the outer loop. If the pressure responsive member is constituted by spring structure (Fig. 3), then the PPS could be a pre-tension sensor configured to determine a pre-tensioning of the spring.

The resulting error, i.e. Xp minus M_p the pressure measured by PPS, in this case an error of the pneumatic pressure, PP in the upper space 35 is used by the inner controller to provide a control setting for the solenoid valve control, SVC, controlling injection of air into and release of air from the upper space 35. The actual process media pressure PP is measured by the PMP sensor, PMP, and Pp is returned in the outer loop and subtracted from the desired media pressure Pm. The error, e_m, is used as input in the controller, C to calculate XP.

Fig. 8 illustrates how the force balance structure supports and protects against excessive pressure by preventing the pressure peaks. This is caused by the pressure responsive member. The centre line 81 illustrates a target pressure, i.e., the desired process pressure of the liquid fuel.

The electronic control structure strives to maintain the process pressure close to this target operating pressure. During system operation, the force balance structure helps reduce peak pressures effectively reducing the amplitude of the pressure fluctuations. The force balance structure thereby maintains a relatively constant pressure and facilitates a continuous engine operation with no excessive pressure peaks. The components of the fuel system are protected, and a long lifetime and safe operation can be expected.

In extreme situations, e.g., when shifting from secondary to primary fuel type, the pressure may exceed the upper limit of the operative pressure range. In this situation, the safety valve opens. However, since the force balance structure also counteracts the extreme pressure, the opening of the safety valve can be very short, and when the safety valve opens and closes, the force balance structure supports a fast re-establishing of a pressure balance with a process pressure within the operative pressure range.

The electronic control structure may control a pneumatic pressure in the upper space, or a pre-tensioning of the spring etc, depending on the type of pressure responsive member being used. The electronic control structure may be implemented in a CPU with memory and computer executable code for enabling various functions which will be described in further details below. The illustrated fuel system may e.g., comprise a dedicated controller specifically made for carrying out the process of amending the control force. The controller could, alternatively, be constituted at least partly by a standard computer system, e.g., a PLC or simply a PC with suitable control output. The controller comprises a data interface for communication of data externally, e.g., for exporting results and for importing pressure readings, and desired process pressures from an engine controller.

The electronic control structure may be a distributed controller comprising more than one CPU arranged in connection with specific components and interconnected e.g., by a data bus structure. In one example, the electronic control structure comprises a CPU arranged to control the fuel pump, another CPU arranged to control the control force, e.g., by amending a pressure in the upper space 35 or by pre-tensioning of the spring 39. The controller may particularly be configured to provide different control actions depending on obtained process pressure in the liquid fuel.

Fig. 9 Illustrates pressure definitions used as references in the system. Line 91 illustrates a "Target operating pressure", which is the desired pressure.

The lines 92, 93 indicates an "Acceptable off-set" where line 92 is a lower acceptable offset and 93 is an upper acceptable offset.

By crossing these lines, the operating system will report either a warning or an error, as liquid fuel is delivered at a pressure which is outside the range that we consider acceptable. The consequence of this may vary, examples are that a warning is issued in the system or that the system is stopped.

The line 94 indicates an "Overpressure valve opening", which is a pressure where a special fuse is connected and sends flow of liquid fuel back to the suction side of the pump, this is optional, and it could be considered as a last chance of avoiding excessive pressure.

The line 95 indicates "Safety valve opening" is the limit at which media is sent out of the system to protect the system from mechanical breakage. In this case, the fuel is released into the environment, e.g., into a collection drum.

Fig. 10 illustrates an embodiment of the valve corresponding to the valve illustrated in Fig. 2 but where the pressure responsive member 31 is not directly attached to the stem plate 29. In operation, the pressure responsive member 31 can only press the valve element 25 downwards but not lift the valve element. While this may be advantageous for the sake of reducing wear on the pressure responsive member 31, it will only work if the process pressures in all valve operating states are capable of creating a load on the valve element which will try to open the valve, i.e. when the load influences the pressure absorbing member. Alternatives to the above discussed pneumatic pressure control balance structure and spring structure-based force balance structures exist.

In one example the force balance structure may include permanent magnet(s) on the valve element and a magnet field which balances movement of the valve element against the process pressure. This can then be overridden by influencing the field strength via an electromagnet. In another example, movement of the valve element may be influenced by a piezo structure controlled by a CPU to counteract the process pressure on the valve element.

The following definitions apply herein: High-pressure type An engine operating like a diesel engine by combustion of combustion engine diesel or other fuels. The engine may or may not have spark plugs or similar ignition aid, as long as the general principle is according to the principle of a diesel engine, i.e., that the engine includes a pre-pump for establishing a target pressure and a booster pump for raising the target pressure to a relatively large pressure, typically a pressure ensuring or aiding the ignition of the fuel.

Positive displacement A pump where fluid is positively displaced from a fixed volume pump container, e.g., a rotary displacement pump or a reciprocating displacement pump.

Process pressure (PP) : Pressure of the liquid fuel downstream of the pump, e.g. at the fuel outlet, i.e. at the interface to the engine. I.e. the actually obtained pressure

Desired process Set value for the engine, e.g. a desired pressure of 85 bar at pressure, (Pm) the interface to the engine. The pressure is typically a recommended setting for correct operation of the engine

Process pressure error Difference between desired and obtained process pressure

(PPE)

Peak-pressure A local minimum or maximum pressure of the process pressure, e.g. a pressure exceeding a certain threshold in a short period of time.

Control force A force acting on one side of the pressure responsive member and derived from a control pressure or from other pressure means such as a spring etc.

Process force A force derived by the process pressure and acting on the valve member

Average valve position A desirable position of the valve when the process pressure is correct. Recipient A location to which the excessive amount of fuel is returned. This could be the fuel storage or another location capable of receiving the fuel.

List of numbered features

1 Fuel system

2 Engine

3 Fuel-path

4 Downstream direction

5 Fuel Storage

6 Fuel pump

7 Recirculation fuel-path

8 Return-point

9 Valve

10, 10' Electronic control structure

11 Safety valve

12 Accumulator

13 Pressure sensor

14 Actuator mechanism on the valve 9

15 Power supply for electronic control structure

16 Isolation valve

17 Fuel pump controller

18 Flow meter

19 return valve

20 manually adjustable valve

21 Valve housing

22 Inlet side of valve housing

23 Outlet side of valve housing

24 Sealing surfaces of valve seat

25 Valve element

26 Stem

27 Bonnet

28 Sealing interface

29 Stem plate

30 Lower space

31 Pressure responsive member

32 Dome

33 Pneumatic inlet

34 Pneumatic outlet 35 Upper space

36 Inner surface of diaphragm

37 Outer surface of diaphragm

38 Lower surface of stem plate 39 Coiled spring

40 Spring button

41 Actuator stem

42 Actuator

Claims

1. A high-pressure type combustion engine comprising a fuel supply system (1) and a fuel injection system, wherein the fuel supply system is configured to supply fuel at a target process pressure to the fuel injection system, and wherein the fuel injection system comprises a booster pump configured as a positive displacement pump for elevating the target pressure before reaching injectors for injection into a combustion chamber of the combustion engine (2), the fuel supply system comprising :

- a fuel-path (3) forming a downstream direction from a fuel storage (5) to the injection system;

- a fuel pump (6) configured as a positive displacement pump to provide a flow of liquid fuel at the target process pressure in the fuel-path;

- a recirculation fuel-path (7) extending from a return-point (8) in the fuel-path (3) to a recipient (5), the return-point (8) being downstream of the fuel pump (6);

- a valve (9) defining a variable flow of the liquid fuel in the recirculation fuel-path (7) depending on an opening degree controlled by movement of a valve element (25);

- a force balance structure comprising a pressure responsive member and being configured to move the valve element (25) based on a force balance between a process force and a control force, where: o the process force results from the process pressure acting on the valve member; and o the control force results from a control force acting on the valve member through a pressure responsive member, and

- an electronic control structure (10) configured to control the opening degree by amending the control force based on an electrical signal representing the process pressure.

2. The combustion engine according to claim 1, wherein the control force is independent on pressures downstream the booster pump.

3. The combustion engine according to claim 2, wherein the process pressure in the fuel-path is influenced by operation of the booster pump when the fuel flows in the fuel-path.

4. The combustion engine according to claim 3, wherein the influence is cyclic.

5. The combustion engine according to any of the preceding claims, wherein the control force is a result of a control pressure acting on one side of the pressure responsive member and a reference pressure acting on an opposite side of the pressure responsive member.

6. The combustion engine according to claim 5, wherein the electronic control structure comprises an electronic valve structure configured to control the control pressure.

7. The combustion engine according to any of the preceding claims, wherein the pressure responsive member is a spring structure providing the control force depending on a degree of pre-tensioning.

8. The combustion engine according to claim 7, wherein the electronic control structure comprises an actuator for pre-tensioning the spring structure based on the pressure signal.

9. The combustion engine according to any of the preceding claims, wherein the control force is adjusted simultaneously by the electronic control structure and the force balance structure.

10. The combustion engine according to any of the preceding claims, wherein the electronic control structure is configured to move the valve element based on a difference between a desired process pressure (Pm) and a measured process pressure (Pp) at the fuel outlet.

11. The combustion engine according to any of the preceding claims, further comprising an expansion tank configured to reduce excessive pressure in the fuel-path, excessive pressure being a pressure above an upper threshold.

12. The combustion engine according to any of the preceding claims, wherein the fuel pump is a positive displacement pump.

13. The combustion engine according to claim 12, wherein the positive displacement pump is configured to provide a variable flow of the liquid fuel based on a pump control signal.

14. The combustion engine according to any of the preceding claims, further comprising a pressure limiter configured to activate at a pressure above an upper excessive pressure, and configured to reduce a pressure in the fuel-path downstream of the pump or in the recirculation fuel-path when activated.

15. The combustion engine according to any of the preceding claims, comprising a two-phase tank including a gas phase, the two-phase tank being arranged for receiving liquid fuel from recirculation fuel-path.

16. The combustion engine according to any of the preceding claims, wherein the valve comprises a position sensor which determines the opening degree of the valve element.

17. The combustion engine according to any of the preceding claims, comprising an overpressure release valve configured to release fuel from the recirculation fuel-path or from the fuel-path to an injection point between the fuel storage and the fuel pump.

18. The combustion engine according to claim 17, wherein the overpressure release valve is controlled by the electronic control structure, and wherein the electronic control structure is configured to execute an Overpressure valve opening command to the overpressure release valve when a threshold overpressure is reached in the fuel-path.

19. The combustion engine according to claim 17, wherein the overpressure release valve is controlled by a mechanical element which is compliant when a threshold overpressure is reached in the fuel-path.

20. The combustion engine according to any of the preceding claims comprising a fuel pump controller (17) configured to control the fuel pump based on a desired average position of the valve element (25).

21. The combustion engine according to any of the preceding claims, forming a piston engine with a piston movable in a cylinder.

22. The combustion engine according to claim 21, comprising an injector structure for injection of fuel into the cylinder, and a booster pump between the fuel outlet and the injector structure, the booster pump being a piston pump.

23. A fuel system for a combustion engine according to any of the preceding claims comprising:

- a fuel-path (3) forming a downstream direction from a fuel storage (5) to a fuel outlet for connection of the fuel system to the combustion engine;

- a fuel pump (6) configured as a positive displacement pump to provide a flow of liquid fuel at a target process pressure in the fuel-path;

- a force balance structure comprising a pressure responsive member and being configured to move the valve element (25) based on a force balance between a process force and a control force, where: o the process force results from the process pressure acting on the valve member; and o the control force results from a control force acting on the valve member through a pressure responsive member, and - an electronic control structure (10) configured to control the opening degree by amending the control force based on an electrical signal representing the process pressure.

24. A method of supplying fuel to a combustion engine according to any of claims 1-22, the method comprising : - establishing a flow of fuel at a process pressure in the fuel-path;

25. The method according to claim 24, wherein the force balance is established while the combustion engine is running.