Fuel delivery arrangement

Abstract

A fuel delivery arrangement (16) for gaseous vehicle fuel, the arrangement comprising: a fuel compressor (10); an inlet line (22) arranged to convey fuel from a reservoir (18) to the compressor (10); an outlet line (24) arranged to receive fuel discharged from the compressor (10); a bypass line (32) that extends between the inlet line (22) and the outlet line (24); a bypass valve (38) disposed on the bypass line (32), the bypass valve (38) being configured to open and close the bypass line (32) to fuel flow; and a buffer volume (20) connected to the outlet line (24), the buffer volume (20) being configured to accommodate expansion and compression of fuel to mitigate pressure variations in the outlet line (24).

Description

[0001] Fuel delivery arrangement

[0002] FIELD OF THE INVENTION

[0003] This invention relates to a fuel delivery arrangement for gaseous vehicle fuel. In particular, the invention relates to an arrangement for delivering gaseous fuel such as hydrogen to an internal combustion engine.

[0004] BACKGROUND

[0005] As automotive vehicles transition away from reliance on fossil fuels, internal combustion engines that consume gaseous fuels such as hydrogen instead of liquid fuels are gaining interest. Such engines require fuel delivery arrangements configured to handle the gaseous fuel, which systems may have similar architectures to traditional systems for liquid fuels, but with modifications to account for the different challenges that the use of gaseous fuel presents.

[0006] For example, it has been found that it is beneficial to engine performance to inject gaseous fuel at pressures greatly exceeding atmospheric pressure, for example at a pressure of approximately 300 bar. Although gaseous fuel may be held at high pressure in a vehicle fuel tank, for example at a pressure of around 700 bar when the tank is full, this pressure reduces rapidly as the tank is depleted, potentially to as low as 30 bar as the tank empties.

[0007] Accordingly, a fuel compressor is required to pressurise the fuel supplied from the fuel tank when the fuel tank pressure drops below that required by the injectors. It follows that the fuel compressor and the associated fuel delivery arrangement may need to be capable of handling a wide variation in its pressure ratio, namely the ratio of the output pressure to the input pressure, whilst delivering a demanded mass flow rate of fuel, since the input pressure varies widely while the output pressure may remain substantially constant. This is further complicated by the fact that a compressor would typically be driven by the engine and hence the compressor speed is directly related to the engine speed, whereas the required mass flow rate of fuel is dictated by the engine torque demand.

[0008] It is against this background that the invention has been devised. STATEMENTS OF INVENTION

[0009] According to an aspect of the present invention, there is provided a fuel delivery arrangement for gaseous vehicle fuel such as hydrogen. The arrangement comprises: a fuel compressor; an inlet line arranged to convey fuel from a reservoir to the compressor; an outlet line arranged to receive fuel discharged from the compressor; a bypass line that extends between the inlet line and the outlet line; and a bypass valve disposed on the bypass line. The bypass valve is configured to open and close the bypass line to fuel flow.

[0010] If the fuel delivery arrangement is used in the context of a vehicle, the reservoir may be a fuel tank of the vehicle, for example, and the arrangement may be configured to deliver fuel to an engine of the vehicle.

[0011] The bypass line may provide a flow path that bypasses one or more compression chambers of the compressor. For example, the bypass line may extend around the compressor. The bypass line and the bypass valve may enable a range of operating modes for the arrangement. For example, the bypass line may be used to bypass the compressor when fuel in the inlet line is at a sufficient pressure for the ultimate recipient of the fuel, for example a vehicle engine. The bypass line may also allow for an idling mode of operation for the compressor, by creating a fluid short circuit that connects the compressor output to its input. This can be exploited to regulate the effective output from the compressor to the outlet line, for example by switching the state of the bypass valve rapidly to control the compressor output in a manner analogous to pulse-width modulation.

[0012] The fuel delivery arrangement may comprise a buffer volume connected to the outlet line, the buffer volume being configured to accommodate expansion and compression of fuel to mitigate pressure variations in the outlet line. By absorbing fluctuations in pressure in the outlet line, the buffer volume, which may be in the form of a tank for example, may add refinement and / or compensate for any misalignment between the compressor output and the demand. The buffer volume may be configured to hold and release compressed fuel selectively. The buffer volume may be configured to hold fuel at a pressure above a threshold level and / or within a target pressure range. If the compressor is driven by a vehicle engine, the buffer volume may be configured to hold fuel at pressure when the vehicle engine is inactive.

[0013] The fuel delivery arrangement may comprise a valve such as a non-return valve disposed on the outlet line downstream of a junction between the outlet line and the bypass line.

[0014] The fuel delivery arrangement may be configured such that the compressor can be activated and deactivated selectively.

[0015] The fuel delivery arrangement may comprise a disengageable coupling through which torque is transmitted to the compressor to drive the compressor. Disengaging the coupling may deactivate the compressor. The disengageable coupling may comprise a clutch, for example.

[0016] The fuel delivery arrangement may be configured to switch the bypass valve between open and closed states while the compressor operates, to control characteristics of the fuel flowing to a fuel recipient connected to the outlet line, for example the buffer volume. The fuel delivery arrangement may be configured to vary a proportion of compression strokes of the compressor for which the bypass valve is in an open state, relative to the compression strokes for which the bypass valve is in a closed state, to control characteristics of the fuel flowing to the fuel recipient.

[0017] The fuel delivery arrangement may be configured to switch the bypass valve between open and closed states at a frequency proportionate to an operating speed of the compressor. The fuel delivery arrangement may be configured to switch the bypass valve between open and closed states in synchronisation with compression events in the compressor. In such embodiments, the fuel delivery arrangement may be configured to switch the state of the bypass valve only as compression events commence or complete.

[0018] The fuel delivery arrangement may be configured to vary the switching frequency of the bypass valve to control characteristics of the fuel flowing to a fuel recipient connected to the outlet line, for example the fuel pressure or flow rate. The fuel recipient may be an engine or a fuel injection system associated with an engine, for example. Alternatively, the fuel recipient could be a buffer volume.

[0019] The fuel delivery arrangement may comprise an electromechanical actuator for switching the bypass valve between open and closed states. Switching of the bypass valve may be controlled by a controller.

[0020] The invention also extends to a vehicle arrangement comprising the fuel delivery arrangement of the above aspect. The vehicle arrangement may comprise a reservoir such as a fuel tank connected to the inlet line of the fuel delivery arrangement. The vehicle arrangement may also include a fuel recipient to which the fuel delivery arrangement delivers fuel. The fuel recipient may be an engine or a fuel injection system associated with an engine, for example. Alternatively, the fuel recipient could be the buffer volume. The vehicle arrangement may also comprise a controller for controlling operation of the fuel delivery arrangement, for example to control operation of the bypass valve.

[0021] The invention also extends to a vehicle comprising the fuel delivery arrangement or the vehicle arrangement of the above aspects.

[0022] Another aspect of the invention provides a method of compressing gaseous vehicle fuel such as hydrogen. The method comprises: conveying fuel through an inlet line to a compressor; discharging fuel from the compressor to an outlet line connected to a fuel recipient; and operating a bypass valve to open and close a bypass line that extends between the inlet line and the outlet line, to control characteristics of the fuel flowing to the fuel recipient.

[0023] The fuel recipient may be an engine or a fuel injection system associated with an engine, for example. Alternatively, the fuel recipient could be a buffer volume.

[0024] The method may comprise switching the bypass valve between open and closed states at a frequency proportionate to an operating speed of the compressor. The method may comprise switching the state of the bypass valve in synchronisation with compression events in the compressor. The method may comprise switching the state of the bypass valve only as compression events commence or complete. The method may comprise operating the compressor simultaneously with operating the bypass valve to open and close the bypass line, to control characteristics of the fuel flowing to the fuel recipient.

[0025] The method may comprise varying a proportion of compression strokes of the compressor for which the bypass valve is in an open state, relative to the compression strokes for which the bypass valve is in a closed state, to control characteristics of the fuel flowing to the fuel recipient.

[0026] The method may comprise varying the switching frequency of the bypass valve to control characteristics of the fuel flowing to a fuel recipient connected to the outlet line.

[0027] Another aspect of the invention provides a controller configured to perform the method of the above aspect to control operation of a fuel delivery arrangement for gaseous vehicle fuel, for example the fuel delivery arrangement of the above aspect.

[0028] Another aspect of the invention provides a controller configured to control operation of a fuel delivery arrangement for gaseous vehicle fuel. The controller is configured to: operate a compressor to discharge fuel to an outlet line connected to a fuel recipient, the fuel having been conveyed to the compressor through an inlet line; and operate a bypass valve to open and close a bypass line that extends between the inlet line and the outlet line, to control characteristics of the fuel flowing to the fuel recipient. The controller may form part of the vehicle arrangement of the above aspect.

[0029] It will be appreciated that the various features of each aspect of the invention are equally applicable to, alone or in appropriate combination, the other aspects of the invention also.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and other aspects of the invention will now be described, by way of example only, with reference to Figure 1 , which is a schematic diagram of a vehicle arrangement including a fuel delivery arrangement for gaseous fuel. SPECIFIC DESCRIPTION

[0032] Figure 1 shows a gaseous fuel compressor 10 in the context of a vehicle arrangement 12 that also comprises an internal combustion engine 14. The compressor 10 forms part of a fuel delivery arrangement 16 according to an embodiment of the invention, the fuel delivery arrangement 16 being configured to deliver gaseous fuel from a fuel tank 18 to the engine 14, specifically hydrogen fuel in this embodiment.

[0033] It is noted, however, that fuel delivery arrangements according to the invention may be used in a wide range of applications and so the arrangement shown in Figure 1 is purely an example. Indeed, in some embodiments fuel delivery arrangements may find application outside the context of a vehicle, for example in fuelling stations.

[0034] In addition to the compressor 10, the fuel delivery arrangement 16 of Figure 1 also includes a control arrangement that is configured to regulate operation of the compressor 10, and a buffer volume or tank 20.

[0035] The engine 14 includes a fuel injection system that comprises a set of fuel injectors that each delivers fuel to a respective cylinder of the engine 14 in use. Although not shown in the figures, the fuel injection system may also include an accumulator, or ‘common rail’, that holds a reserve of pressurised fuel to be drawn by the injectors, as is known.

[0036] The fuel tank 18 holds fuel and so acts as a fuel reservoir within the vehicle arrangement 12. In this example, the hydrogen is held in the fuel tank 18 at 700 bar when the fuel tank 18 is full to its maximum capacity, although this pressure reduces as the fuel tank 18 is depleted in use. The fuel tank 18 is equipped with a pressure regulator, or ‘tank valve’, that reduces the pressure of fuel output by the fuel tank 18 to a level slightly above that required by the fuel injection system, for example a pressure of approximately 320 bar in this embodiment. When the pressure inside the fuel tank 18 falls below this level, the tank valve is deactivated and the fuel is output at a pressure corresponding to the pressure inside the fuel tank. It is noted that multiple fuel tanks may be used in other embodiments.

[0037] In this example, the fuel compressor 10 is generally configured as a positive displacement compressor 10 having a piston that performs compression strokes to compress fuel. The compressor 10 is configured to handle a pressure ratio that may be ten or more in this example. It is noted that other types of compressor may be used in alternative embodiments.

[0038] The fuel compressor 10 includes one or more inlets that receive gaseous fuel from an inlet line 22 extending from the fuel tank 18. Fuel is conveyed through the inlet line 22 to the compressor inlet(s) at a pressure substantially corresponding to the pressure at which fuel is output from the fuel tank 18, which is 320 bar or below in this example due to the tank valve.

[0039] The fuel compressor 10 also includes one or more outlets that discharge fuel into an outlet line 24 at or above the pressure required by the engine 14, which is approximately 300 bar in this example. A first portion of the outlet line 24 extends to the buffer tank 20, which is configured to hold pressurised fuel received from the compressor 10 until the fuel is required by the engine 14. In this respect, the buffer tank 20 is connected to the fuel injection system by a second portion of the outlet line 24.

[0040] The buffer tank 20 is therefore disposed on the outlet line 24 between the compressor outlet(s) and the fuel injection system. In broad terms, the buffer tank 20 is an additional fuel storage tank and may be generally similar to the fuel tank 18 in construction, and so offers additional fuel storage capacity within the fuel delivery arrangement 16. As shall become clearer in the description that follows, in use the buffer tank 20 receives pressurised fuel, either from the compressor 10 or directly from the fuel tank 18, thereby pressurising the buffer tank 20 so that the buffer tank 20 holds a reservoir of fuel at the pressure required by the fuel injection system at all times. Fuel is then released to the fuel injection system from the buffer tank 20 selectively when demanded. The buffer tank 20 also acts to smooth any variations in the pressure output by the compressor 10, thereby matching the characteristics of the fuel supply more closely to the demand from the engine 14, which is typically relatively steady.

[0041] It is noted that the buffer tank 20 may be omitted in other embodiments, so that fuel is delivered directly to the fuel injection system from the fuel compressor 10 or the fuel tank 18. Conversely, in other embodiments more than one buffer tank may be included, arranged in series or in parallel.

[0042] It is also noted that the buffer tank 20 is distinct from the accumulator of the fuel injection system, if present. In practical terms, typically the accumulator holds fuel at pressure only while the engine 14 operates, whereas the buffer tank 20 stores fuel at pressure even when the engine 14 is inactive. The volume of the buffer tank 20 is also typically many times greater than that of an accumulator.

[0043] A pressure regulator may be placed on an outlet of the buffer tank 20, or on the outlet line 24 downstream of the buffer tank 20, to reduce the pressure of fuel in the outlet line 24 to a level slightly above that required by the fuel injection system, for example a pressure of approximately 320 bar in this embodiment. Such a pressure regulator may be included in addition to, or as an alternative to, the tank valve.

[0044] It follows from the above that the buffer tank 20 and the engine 14 may each be considered to define fuel recipients, in that each receives compressed fuel from the fuel delivery arrangement 16. Equally, the buffer tank 20 forms part of the fuel delivery arrangement 16 that supplies compressed fuel to the engine 14.

[0045] The outlet line 24 also includes a non-return valve defining an outlet valve 26 that forms part of the control arrangement, as explained further below. The outlet valve 26 is disposed upstream of the buffer tank 20.

[0046] In this example, the fuel compressor 10 includes a drive arrangement including a driveshaft, which is driven by the engine 14. More specifically, as shown schematically in Figure 1 , a coupling 28 is provided by which the fuel compressor driveshaft is operably coupled to a crankshaft of the engine 14, such that rotation of the crankshaft as the engine 14 operates drives corresponding rotation of the driveshaft. The coupling 28 therefore transmits torque from the crankshaft to the compressor drive arrangement to provide a motive force for the compressor 10. The fuel compressor 10 of this example is sized for a direct coupling to the engine crankshaft, without a gearbox, so that the driveshaft rotates at the same rotational speed as the crankshaft.

[0047] The coupling 28 between the driveshaft and the crankshaft includes a multi-disc clutch 30 that is disposed between the engine 14 and the compressor 10, such that the engine 14 drives the fuel compressor 10 via the clutch 30. The multi-disc clutch 30 facilitates high transmission power without a significant increase in the overall size of the clutch 30, while keeping the activation force low. The clutch 30 may be similar to those known in the motorcycle industry, for example. Mechanical coupling between the clutch 30 and the compressor driveshaft, and between the crankshaft and the clutch 30, may be effected in any suitable manner to transfer torque from the crankshaft to the driveshaft.

[0048] The clutch 30 includes a servomechanism that is operable to engage and disengage selectively, for example under the control of an engine control unit (ECU) (not shown in Figure 1), namely an electronic control unit responsible for managing operation of the engine 14. The ECU may be regarded as part of the vehicle arrangement 12 in this example. In this way, the fuel compressor driveshaft can be coupled to, and decoupled from, the engine 14 at any time during operation, allowing the fuel compressor 10 to be activated and deactivated while the engine 14 operates. For example, the fuel compressor 10 may be disengaged to cease compressing fuel when the fuel pressure in the inlet line 22 is already sufficiently high forthe engine 14, in which case the fuel can be conveyed directly to the engine 14 from the fuel tank 18 without requiring any mechanical work from the fuel compressor 10.

[0049] In this respect, the fuel delivery arrangement 16 also includes a bypass line 32 that extends between a first end 34, which connects to the inlet line 22, and a second end 36, which connects to the outlet line 24 at a point between the compressor outlet(s) and the outlet valve 26. The bypass line 32 therefore creates a path that allows fuel to bypass the compressor 10, for example to enable fuel to be conveyed directly to the engine 14 from the fuel tank 18 when the fuel discharged from the fuel tank 18 and its tank valve is at a sufficient pressure for the engine 14, which in this example is 320 bar.

[0050] The bypass line 32 includes a bypass valve 38 that is operable to switch between open and closed positions, to permit or block flow through the bypass line 32, under the control of the ECU. State changes of the bypass valve 38, between open and closed positions, are driven by a solenoid actuator 40 in this embodiment. The bypass valve 38 is therefore capable of rapid, high-frequency state changes. It is noted that other actuation methods are possible for changing the state of the bypass valve 38.

[0051] Typically, the bypass valve 38 is opened while the clutch 30 switches between engaged and disengaged states, to reduce stress on the clutch 30.

[0052] When the bypass valve 38 is closed and the clutch 30 is engaged, fuel discharged by the fuel compressor 10 exerts pressure on the outlet valve 26 that generates a force sufficient to open the outlet valve 26. Once the outlet valve 26 opens, fuel flows through the outlet valve 26 and on to the buffer tank 20.

[0053] When the bypass valve 38 is open, fuel may flow in either direction through the bypass line 32. The direction of fuel flow depends in part on whether the clutch 30 is engaged.

[0054] If the clutch 30 is disengaged so that the fuel compressor 10 is inactive, fuel flows directly from the fuel tank 18 to the outlet valve 26 through the bypass line 32. Since the control arrangement is typically only configured in this way when the fuel output from the fuel tank 18 is already at the pressure required by the fuel injection system, the outlet valve 26 opens and the fuel continues to the buffer tank 20. Thus, fuel is conveyed directly from the fuel tank 18 to the buffer tank 20 in this scenario, bypassing the fuel compressor 10.

[0055] When the clutch 30 is engaged so that the fuel compressor 10 operates while the bypass valve 38 is open, the fuel output by the fuel compressor 10 takes the path of least resistance and so flows through the bypass line 32 back to the fuel compressor inlet(s), and the outlet valve 26 therefore remains closed. When the outlet valve 26 is closed, backflow from the buffer tank 20 into the bypass line 32 or towards the compressor 10 is prevented. The fuel then circulates around the bypass line 32 and the fuel compressor 10, and so between the inlet(s) and the outlet(s) of the compressor 10, remaining at a substantially constant pressure corresponding to the inlet pressure if the pressure losses are sufficiently small.

[0056] Accordingly, in this situation the bypass line 32 acts as a fluid short-circuit that effectively causes idling of the fuel compressor 10, defining an idling mode for the compressor 10 in which the fuel is held at the inlet pressure without performing significant compression work. The power consumption of the fuel compressor 10 in the idling mode is therefore minimal, as no mechanical work is performed other than to overcome friction. Conversely, a compressing mode for the compressor 10 is defined when the bypass valve 38 is closed and the clutch 30 is engaged, so that the compressor 10 performs mechanical work on the fuel.

[0057] The idling mode of the fuel compressor 10 can be exploited to regulate the pressure and flow rate of fuel output by the compressor 10 and delivered to the buffer tank 20. In this respect, the state of the bypass valve 38 can be changed at high frequency to activate compression intermittently for a desired duty cycle, so that the output pressure and flow rate that is effectively delivered is proportionate to the relative proportions of time for which the compressor 10 acts to compress fuel. For example, the bypass valve 38 may change state at up to the same frequency as the engine speed, which may be up to 3000 revolutions per minute in typical applications, corresponding to a valve switching frequency of up to 50Hz. The bypass valve 38 may even change state at a higher frequency than the engine speed, for example at double the frequency corresponding to the engine speed. More generally, the bypass valve 38 may be operated at a frequency that entails a potential change in state with every compression stroke of the compressor 10, depending on the duty cycle applied. In this respect, in this example rotation of the compressor driveshaft drives compression strokes of the piston of the compressor 10 at a frequency proportionate to the engine speed.

[0058] The bypass valve 38, the outlet valve 26 and the clutch 30 therefore define the control arrangement, which is configured to modulate the output of the fuel compressor 10 in a manner similar to pulse-width modulated (PWM) control. This enables regulation of the output pressure and flow rate delivered by the compressor 10 to the required level, against varying input pressure and independently of the engine speed.

[0059] To maintain efficient idling of the fuel compressor 10, opening and closing of the bypass valve 38 is synchronised with compression strokes performed within the compressor 10, so that the valve is either open or closed throughout each compression stroke and does not change state midway through a stroke. The frequency of state changes for the bypass valve 38 is therefore proportional to the compressor speed. The proportion of compression strokes for which the bypass valve 38 is open relative to the compression strokes for which the bypass valve 38 is closed, which may be regarded as the duty cycle applied to the bypass valve 38, then determines the rate at which fuel is delivered to the buffer tank 20 and thus contributes to holding the pressure in the buffer tank 20 within a desired range.

[0060] It is noted that the state of the bypass valve 38 is not necessarily switched at regular intervals. Instead, the switching of the bypass valve 38 is controlled in accordance with the desired duty cycle, this control being implemented by the ECU in this example. For example, the bypass valve 38 may be open for three compression strokes and then closed for a fourth compression stroke, in a repeating pattern, to provide a duty cycle of 25%, noting that compression occurs when the bypass valve 38 is closed. In other words, the compressor 10 operates in the compressing mode for 25% of the time in this scenario. While the bypass valve 38 is controlled in this manner, the state of the bypass valve 38 switches twice for every four cycles of the compressor 10 and so the switching frequency for the bypass valve 38 is proportionate to the compressor speed. In practice, the duty cycle may be varied dynamically to regulate the compressor output as may be appropriate.

[0061] In operation, the engine 14 draws fuel from the buffer tank 20 at a rate that is typically relatively steady and continuous in the short-term. Meanwhile, fuel is output from the compressor 10 intermittently in pulses corresponding to compression strokes, when the bypass valve 38 is closed, and so may not match the engine demand precisely. This could lead to pressure variation in the outlet line 24 if the compressor 10 were connected directly to the engine 14. The buffer tank 20 is of a sufficient size that expansion and compression of fuel inside the buffer tank 20, in response to the pulses and intervening gaps in the compressor output, absorbs such pressure variations and so provides a smoothing effect that refines fuel delivery. If a pressure regulator is added at, or downstream of, the outlet of the buffer tank 20, this may enable the size of the buffer tank 20 to reduce. Meanwhile, the bypass valve 38 is operated to align the averaged output of the compressor 10 with the engine demand.

[0062] As noted above, the buffer tank 20 may be omitted in other embodiments, for example if the compressor output can be controlled with sufficient accuracy. Omitting the buffer tank 20 may save space within the fuel delivery arrangement 16, for example, and may also improve storage effectiveness.

[0063] In summary, the fuel delivery arrangement 16 compensates for variation in the pressure of gaseous fuel at its source, namely the fuel tank in the above example, and thereby enables the fuel to be delivered to an internal combustion engine at the required pressure. This is achieved using a control arrangement that enables the output of a compressor of the arrangement to be regulated, or for the compressor to be bypassed entirely, according to the present operating state of the arrangement. A buffer tank may be included to add refinement and to reduce the demands placed on the compressor and the control arrangement in terms of the accuracy with which the output is regulated.

[0064] It will be appreciated that various other embodiments of the invention are also envisaged without departing from the scope of the appended claims.

[0065] For example, an actuated valve could be used for the outlet valve disposed upstream of the buffer tank on the outlet line, instead of a non-return valve as in the above example. In this case, the actuated valve could be controlled to act in a similar manner to the non-return valve of the above example, for example to open to allow flow from the compressor to the outlet line when appropriate and to close to prevent any backflow from the outlet line into the bypass line. This may entail, for example, closing the outlet valve whenever the bypass valve is open and the compressor is operating, and opening the outlet valve whenever the bypass valve is closed and the compressor is operating, or when the compressor is being bypassed. List of

[0066] 10 - fuel compressor

[0067] 12 - vehicle arrangement

[0068] 14 - engine

[0069] 16 - fuel delivery arrangement

[0070] 18 - fuel tank

[0071] 20 - buffer tank

[0072] 22 - inlet line

[0073] 24 - outline line

[0074] 26 - outlet valve

[0075] 28 - coupling

[0076] 30 - clutch

[0077] 32 - bypass line

[0078] 34 - first end of the bypass line

[0079] 36 - second end of the bypass line

[0080] 38 - bypass valve

[0081] 40 - solenoid actuator for the bypass valve

Claims

CLAIMS1. A fuel delivery arrangement (16) for gaseous vehicle fuel, the arrangement comprising: a fuel compressor (10); an inlet line (22) arranged to convey fuel from a reservoir (18) to the compressor (10); an outlet line (24) arranged to receive fuel discharged from the compressor (10); a bypass line (32) that extends between the inlet line (22) and the outlet line (24); a bypass valve (38) disposed on the bypass line (32), the bypass valve (38) being configured to open and close the bypass line (32) to fuel flow; and a buffer volume (20) connected to the outlet line (24), the buffer volume (20) being configured to accommodate expansion and compression of fuel to mitigate pressure variations in the outlet line (24).

2. The fuel delivery arrangement (16) of claim 1 , wherein the buffer volume (20) is configured to hold fuel at a pressure above a threshold level.

3. The fuel delivery arrangement (16) of claim 1 or claim 2, wherein the buffer volume (20) is configured to hold fuel within a target pressure range.

4. The fuel delivery arrangement (16) of any preceding claim, comprising a valve (26) disposed on the outlet line (24) downstream of a junction between the outlet line (24) and the bypass line (32).

5. The fuel delivery arrangement (16) of claim 4, wherein the valve (26) disposed on the outlet line (24) is a non-return valve.

6. The fuel delivery arrangement (16) of any preceding claim, wherein the compressor (10) can be activated and deactivated selectively.

7. The fuel delivery arrangement (16) of any preceding claim, comprising a disengageable coupling (28) through which torque is transmitted to the compressor (10) to drive the compressor (10).

8. The fuel delivery arrangement (16) of claim 7, wherein the disengageable coupling (28) comprises a clutch (30).

9. The fuel delivery arrangement (16) of any preceding claim, configured to switch the bypass valve (38) between open and closed states while the compressor operates (10), to control characteristics of the fuel flowing to a fuel recipient (14, 20) connected to the outlet line (24).

10. The fuel delivery arrangement (16) of claim 9, configured to vary a proportion of compression strokes of the compressor (10) for which the bypass valve (38) is in an open state, to control characteristics of the fuel flowing to the fuel recipient (14, 20).

11. The fuel delivery arrangement (16) of any preceding claim, configured to switch the bypass valve (38) between open and closed states at a frequency proportionate to an operating speed of the compressor (10).

12. The fuel delivery arrangement (16) of any preceding claim, configured to switch the bypass valve (38) between open and closed states in synchronisation with compression events in the compressor (10).

13. The fuel delivery arrangement (16) of claim 12, configured to switch the state of the bypass valve (38) only as compression events commence or complete.

14. The fuel delivery arrangement (16) of any of claims 11 to 13, configured to vary a switching frequency of the bypass valve (38) to control characteristics of the fuel flowing to a fuel recipient (14, 20) connected to the outlet line (24).

15. A vehicle arrangement (12), comprising the fuel delivery arrangement (16) of any preceding claim.

16. The vehicle arrangement of claim 15, comprising a reservoir (18), wherein the inlet line (22) is arranged to convey fuel from the reservoir (18) to the compressor (10).

17. The vehicle arrangement of claim 15 or claim 16, comprising a controller for controlling operation of the fuel delivery arrangement (16).

18. A vehicle comprising the fuel delivery arrangement (16) of any of claims 1 to 14 or the vehicle arrangement of any of claims 15 to 17.

19. A method of compressing gaseous vehicle fuel, the method comprising: conveying fuel through an inlet line (22) to a compressor (10); discharging fuel from the compressor (10) to an outlet line (24) connected to a fuel recipient (14, 20); and operating a bypass valve (38) to open and close a bypass line (32) that extends between the inlet line (22) and the outlet line (24), to control characteristics of the fuel flowing to the fuel recipient (14, 20).

20. The method of claim 19, comprising switching the bypass valve (38) between open and closed states at a frequency proportionate to an operating speed of the compressor (10).

21. The method of claim 19 or claim 20, comprising switching the bypass valve (38) between open and closed states in synchronisation with compression events in the compressor (10).

22. The method of claim 21, comprising switching the state of the bypass valve (38) only as compression events commence or complete.

23. The method of any of claims 19 to 22, comprising operating the compressor (10) simultaneously with operating the bypass valve (38) to open and close the bypass line (32).

24. The method of any of claims 19 to 23, comprising varying a proportion of compression strokes of the compressor (10) for which the bypass valve (38) is in an open state, to control characteristics of the fuel flowing to the fuel recipient (14, 20).

25. A controller configured to perform the method of any of claims 19 to 24 to control operation of a fuel delivery arrangement (16) for gaseous vehicle fuel.

Images