WO2015181320A1

WO2015181320A1 - Direct injection engine preventing malfunction due to the presence of lpg bubbles in its fuel supply system

Info

Publication number: WO2015181320A1
Application number: PCT/EP2015/061895
Authority: WO
Inventors: Javier ARÍZTEGUI CORTIJO; Guillermo GUILLERMO WOLFF ELÓSEGUI; Jaime GUTIÉRREZ SERNA; Alois Fürhapter
Original assignee: AVL List GmbH; Repsol SA
Current assignee: AVL List GmbH; Repsol SA
Priority date: 2014-05-28
Filing date: 2015-05-28
Publication date: 2015-12-03
Anticipated expiration: 2016-11-28

Abstract

The invention relates to a direct injection engine (100) which comprises a fuel supply system having: - a low-pressure circuit comprising a low pressure fuel supply line (10) connecting a low pressure pump (11) submerged in fuel tank (12) to a low pressure chamber (97) which is part of a pump (9); and, - a high-pressure circuit comprising a high pressure fuel supply line (15) connecting a high pressure chamber (91) of the pump (9) to a high pressure rail (7); the high and low pressure chambers being connected by a flow control valve (96, 93); wherein the direct injection engine (100) comprises: - means for balancing pressure between the high-pressure circuit and the low-pressure circuit; - means for eliminating any remaining LPG in gas phase in the low- or high- pressure circuits; the direct injection engine further comprising control means (13) for operating the means for balancing pressure between the high-pressure circuit and the low-pressure circuit and the means for eliminating any remaining LPG in gas phase in the low- or high- pressure circuits at least before the engine is started or during start of the engine.

Description

Direct injection engine preventing malfunction due to the presence of LPG bubbles in its fuel supply system

TECHNICAL FIELD

The present invention relates to the field of direct injection engines, and specifically, of direct injection engines using liquefied petroleum gases (also known as LPG, AutoGas, propane, butane).

STATE OF THE ART

It is a fact that vehicles equipped with direct injection engines operated on LPG produce fewer harmful emissions, and can offer some savings on fuel costs, compared with gasoline or diesel. Direct injection engines using liquefied petroleum gas or LPG are therefore advantageous in this sense.

When LPG is used in liquid phase, bubbles of fuel are usually formed in the fuel supply system to the engine. If those bubbles are not removed, they can cause performance problems in the engine ranging from combustion irregularities, which may in turn derive in breaching the emission limits, to a stop of the engine making it impossible to restart it.

In fact, when LPG is used in direct injection engines, it should be injected directly in liquid phase into the combustion chamber. This is so because, in order to introduce fuel inside the combustion chamber, it is necessary to overcome the pressure created by the piston during the compression stroke. Strictly speaking, for modern spark ignition engines, this would require pressures in excess of 15 to 20 bar, depending on the compression ratio. In fact, modern injection systems for spark ignition engines work at pressures of up to 250 bar in order to improve atomisation of the fuel and consequently mixture formation. In any case, at pressures above 15 bar and at ambient temperatures around 20 °C, LPG is in liquid phase and consequently it is injected in the engine in liquid phase. However, since LPG is a very volatile fuel, a modest increase of temperature might cause the formation of bubbles of LPG in gas phase within the liquid LPG. The temperature at which this process starts depends on pressure and LPG composition. For example, for pure propane at 20 bar, boiling starts at around 60 °C.

If the LPG direct injection engine is running at high or full load and for some reason the engine is stopped (for instance, to fill up the fuel tank), the fact is that the engine is at about 100°C and the exhaust system is at temperatures in the range 500-1000°C, depending on the past working conditions and on the point considered within the system. With the stop of the engine, air flow through the engine compartment stops. Consequently, the hotter parts of the engine and exhaust system transfer heat to the colder parts. With the stop of the engine, LPG flow through the injection system also stops. The amount of LPG trapped within the injection system gets hotter and starts evaporating forming bubbles. If this process continues, the accumulation of bubbles creates obstructions in the piping and in the components of the injection system, preventing the passage of fuel to the combustion chamber, thereby provoking the engine to stop and/or not to restart. This process is known as vapour lock. Due to the higher volatility of LPG compared to gasoline, the risk of vapour lock appearance is much higher when using LPG.

DESCRIPTION OF THE INVENTION

In order to avoid the problems indicated in the previous section with LPG bubbles in the fuel supply system of direct injection engines operated on LPG, the present invention relates to a direct injection engine which eliminates or prevents the formation of LPG bubbles in its fuel supply system.

A first aspect of the present invention refers to a direct injection engine which comprises a fuel supply system having:

a low-pressure circuit comprising a low pressure fuel supply line connecting a low pressure pump submerged in fuel tank to a low pressure chamber which is part of a pump; and,

a high-pressure circuit comprising a high pressure fuel supply line connecting a high pressure chamber of the pump to a high pressure rail;

the high and low pressure chambers being connected by a flow control valve;

wherein the direct injection engine comprises:

- means for balancing pressure between the high-pressure circuit and the low-pressure circuit;

means for eliminating any remaining LPG in gas phase in the low- or high- pressure circuits;

the direct injection engine further comprising control means for operating the means for balancing pressure between the high-pressure circuit and the low-pressure circuit and the means for eliminating any remaining LPG in gas phase in the low- or high- pressure circuits at least before the engine is started or during start of the engine.

The direct injection engine as defined above prevents the formation of or eliminates fuel bubbles in its fuel supply system.

In a preferred embodiment the means for balancing pressure between the high-pressure circuit and the low-pressure circuit comprises means for pressurizing the low pressure circuit to 45 bar absolute pressure.

Preferably, the means for pressurizing the low pressure circuit to 45 bar absolute pressure include a low pressure pump which is able to provide a pressure of at least 45 bar in the low pressure fuel supply line. Or it is also possible to provide an additional pump in series with the low pressure pump, this additional pump being able to raise the pressure provided by the low pressure pump to at least 45 bar in the low pressure fuel supply line.

In this preferred embodiment the control means are preferably configured to keep the low pressure circuit at 45 bar absolute pressure not only before the engine is started or during start of the engine, but also during a few seconds after the direct injection engine is started.

In another preferred embodiment of the invention, the means for balancing pressure between the high-pressure circuit and the low-pressure circuit comprises providing a return path for releasing pressure from the high-pressure circuit to the low-pressure circuit.

In a preferred embodiment the flow control valve is designed to operate against a counter-pressure of at least 45 bar. The control means are configured to operate the flow control valve before the direct injection engine is started or during start of the engine. This return path can be a return path provided between the high pressure chamber and the low pressure chamber by means of an operated valve. Or the return path can be a return path provided between the high pressure chamber and the tank by means of an operated valve.

In this case the control means are configured to operate the flow control valve and/or either operated valve not only before the direct injection engine is started or during start of the engine but also during the first strokes of the pump.

In still a preferred embodiment of the invention, the means for balancing pressure between the high-pressure circuit and the low-pressure circuit comprises providing a return path from the high pressure rail to the tank by means of an operated valve. In this case the control means are preferably configured to activate the operated valve not only before the engine is started or during start of the engine, but also during the first strokes of the pump.

The means for eliminating any remaining LPG in gas phase in the low-pressure circuit preferably comprise providing an outlet in the low pressure chamber, the outlet being connected to the tank by means of a return path. This outlet is preferably located in an uppermost part of the low pressure chamber.

The means for eliminating any remaining LPG in gas phase in the low-pressure circuit may further comprise:

a low pressure pump being able to provide sufficient flow so as to make LPG bubbles flow to the tank (which is preferably a flow of at least 0.4 dm³/h for each kW of engine power and more preferably of at least 0.6 dm³/h for each kW of engine power), the low pressure pump working against sufficient counter-pressure above the pressure inside the tank so as to provoke the collapse of LPG bubbles (which is a counter-pressure of at least 4 bar and preferably 8 bar above the pressure inside the tank); and

a restriction in the return path for guaranteeing that the pressure in the low pressure line is at least 8 bar above the pressure of the tank.

In this case the control means are configured to activate the low pressure pump to its maximum flow and to active the restriction before the direct injection engine is started or during start of the direct injection engine. In a preferred embodiment of the invention, the low pressure fuel supply line is connected to the low pressure chamber through an inlet which is located in front of the flow control valve.

In a further preferred embodiment, the direct injection engine further comprises a shell surrounding the high pressure rail inside of which a cooling agent can circulate.

The different aspects and embodiments of the invention defined in the foregoing can be combined with one another, as long as they are compatible with each other.

Additional advantages and features of the invention will become apparent from the detailed description that follows and will be particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate an embodiment of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be carried out. The drawings comprise the following figures:

Figure 1 schematically shows a LPG direct injection engine according to a first preferred embodiment of the invention.

Figure 2 schematically shows a first preferred embodiment of a high pressure injection pump according to the invention. Figure 3 schematically shows a LPG direct injection engine according to a second preferred embodiment of the invention.

Figure 4 schematically shows a LPG direct injection engine according to a third preferred embodiment of the invention. Figure 5 schematically shows a second preferred embodiment of the high pressure injection pump according to the invention. Figure 6 schematically shows a third preferred embodiment of the high pressure injection pump.

Figure 7 schematically shows a LPG direct injection engine according to a fourth preferred embodiment of the invention. DESCRIPTION OF A PREFERRED EMBODIMENT

The following description is not to be taken in a limiting sense but is given solely for the purpose of describing the broad principles of the invention. Embodiments of the invention will be now described by way of example, with reference to the above-mentioned drawings showing elements and results according to the invention.

The invention proposes a direct injection engine in which engine malfunction is avoided by eliminating or preventing the formation of liquefied petroleum gas (LPG) bubbles in its the fuel supply system, when the direct injection engine is run on LPG. Figure 1 schematically shows an LPG direct injection engine 100 which comprises:

a combustion chamber 1 having a spark plug 2;

a piston 3;

an intake valve 4 or valves for letting air come inside the combustion chamber;

an exhaust valve 5 or valves for letting exhaust gases go out of the combustion chamber; - one or more injectors 6 for injecting fuel into the combustion chamber;

a high pressure pump 9 for feeding pressurized liquefied petroleum gas to the injectors; and

an electronic control unit 13, ECU, for controlling the operation of the direct injection engine.

During operation of the engine, the intake valve(s) 4 is opened and air is inducted inside the cylinder by means of the downward motion of the piston. During the intake and/or the compression stroke, LPG is injected directly inside the combustion chamber through the injector 6, mixing with the air present therein. Around top dead centre (TDC), the spark plug 2 releases a spark which ignites the mixture of air and LPG. The pressure increase caused by the combustion pushes the piston 3, which generates mechanical power. Finally, the exhaust valve(s) 5 is opened and the combustion gases are expelled to the exhaust system.

As also shown in Figure 1 , the direct injection engine 100 comprises a fuel supply system having: a low pressure fuel supply line 10 with a low pressure pump 1 1 submerged in a tank 12 where the fuel is; and,

a high pressure fuel supply line 15 including a high pressure pump 9 with a flow control valve (solenoid 96 + check valve 93, see Fig. 2), a high pressure rail 7 with a pressure sensor 8 at one end, and high pressure direct injection injectors 6.

In Figure 2 the details of a high pressure pump 9 according to a first preferred embodiment are depicted. These high-pressure pumps usually comprise:

• a high pressure chamber 91 ;

· a low pressure chamber 97 filled with LPG from the tank 12 through inlet 101 ;

• a plunger 92 which moves in and out of the high pressure chamber 91 ;

• a first check valve 93 on the intake side to avoid back flow to the low pressure chamber 97;

• a second check valve 94 to avoid back flow from the high pressure rail 7 to the high pressure chamber 91 ;

· a safety valve 95 to avoid over pressure in the high pressure chamber 91 ;

• a solenoid 96 which together with the first check valve 93 form a flow control valve, located in the passage from the low pressure chamber 97 to the high pressure chamber 91 .

The control of the pressure delivered by the high pressure pump 9 is based on the actual pressure in the rail 7 read by the pressure sensor 8. During operation of the engine, LPG flows into the rail 7 coming from the high pressure pump 9 and flows out of the rail through the injectors 6. The plunger 92 moves in and out of the high pressure chamber 91 , typically actuated by a cam. During the outward stroke, LPG flows from the low pressure chamber 97 to the high pressure chamber 91 through the first check valve 93 filling it with fuel. During the inward stroke, fuel is forced through the second check valve 94 to the high pressure rail 7, while the first check valve 93 prevents flow of LPG to the low pressure chamber 97.

Additionally, and according to the first preferred embodiment of the invention, the low pressure chamber 97 includes an outlet 201 in its uppermost part connected via a low pressure return line 200 to the tank 12, thereby providing a "return path" such that any LPG bubbles formed in the low pressure circuit naturally flow into the return line by buoyancy (Archimedes' principle).

In a second preferred embodiment of the invention, the low pressure pump 1 1 in the tank 12 is able to provide a flow of at least 0.4 dm³/h for each kW of the engine, or preferably of at least 0.6 dm³/h for each kW of the engine, against a counter-pressure of at least 4 bar, or preferably 8 bar, above the pressure inside the tank 12. This embodiment has a double objective: on the one hand, such a high flow is able to make LPG bubbles rapidly flow to the tank 12; on the other hand, the increase of pressure in 8 bar might provoke the collapse of LPG bubbles depending on the temperature. As shown in Figure 3, in this preferred embodiment a low pressure control system is also provided, for guaranteeing that the pressure in the low pressure line 10 is at least 8 bar above the tank pressure, so that LPG is provided at a pressure of at least 15 bar with respect to ambient pressure in the low pressure fuel supply line 10 (LPG has a vapour pressure of about 7 bar at ambient temperature). This low pressure control system essentially comprises a restriction 202 installed in the low pressure return line 200, which in this embodiment connects the low pressure chamber 97 and the tank by means of an outlet 201 , which need not be in the uppermost part of the low pressure chamber 97, but may be located at any point in it. This restriction may be realized in different ways such as by means of a check valve with a cracking pressure of 8 bar, or by means of a variable area valve actively controlled based on the actual pressure in chamber 97 read by an ad hoc pressure sensor.

According to the invention, the ECU 13 is configured to activate the operation of the low pressure pump 1 1 before the engine is started (for instance, upon opening a vehicle door if the engine is installed in a vehicle or upon activating a remote control). The low pressure pump 1 1 is activated to its maximum flow so as to circulate through the outlet 201 ' to the tank 12 any possible LPG bubbles that may be present in the low pressure circuit (line 10, chamber 97 and line 200).

Additionally, and also before the engine is started, the variable area valve is activated, so as to increase the pressure in the low pressure line to its maximum value of 8 bar above the tank pressure, such that any existing LPG bubbles will collapse and become liquid.

As shown in Figure 2, the efficacy of the low pressure circuit is further improved by designing the low pressure chamber 97 to have its inlet 101 located in front of the flow control valve 96-93, such that the cold LPG coming from the tank directly contacts the flow control valve.

In an third preferred embodiment of the direct injection engine invention depicted in Figure 4, the low pressure circuit can be pressurized to 45 bar absolute pressure during the start phase of the engine. 45 bar absolute is the highest pressure that the LPG retained in the high pressure chamber 91 may be expected to reach after having stopped the engine. In this case, all the elements of the low pressure circuit must be designed to withstand 45 bar. The pressurization may be realised by means of a special low pressure pump 1 1 able to provide the LPG at a pressure of at least 45 bar in the low pressure fuel supply line 10, or by means of an ad hoc pump 102 installed in series with the pump 1 1 and able to raise the pressure provided by the pump 1 1 to the 45 bar needed to overcome the maximum pressure in the chamber 91 .

In this preferred embodiment, the ECU 13 is configured to activate the flow control valve (solenoid 96 plus first check valve 93) before the engine is started (for instance, upon opening a vehicle door if the engine is installed in a vehicle or upon activating a remote control). Since the pressure in the chamber 97 is higher than in the chamber 91 , cold LPG flows from the chamber 97 to the chamber 91 and fills it with liquid LPG. Also, if the pressure in rail 7 is lower than in the high pressure chamber 91 , liquid LPG flows from the high pressure chamber 91 to the rail 7. When the engine is cranked, the high pressure circuit is filled with liquid LPG and the pump 9 can pressurize it to the required level. Therefore, the engine starts normally. In order to eliminate any remaining bubbles after the engine has started, the low pressure circuit may be kept at 45 bar absolute pressure during a few seconds (from 1 to 5 seconds) after the engine has started.

In other preferred embodiments of the invention, a return path from the high pressure chamber 91 to the low pressure circuit is provided so as to release pressure. There are three possibilities: either the flow control valve (solenoid 96 plus first check valve 93) is used and designed to operate against a counter-pressure of at least 45 bar (absolute pressure);

or as shown in Figure 5 an additional solenoid valve 230 is installed in the high pressure chamber 91 and connected to the low pressure chamber 97;

- or as shown in Figure 6 an additional solenoid valve 21 1 is installed in the high pressure chamber 91 and connected to the tank 12 via its own return path 210 or sharing the return path 200 from the low pressure chamber 97.

The objective of these three embodiments is the same. When LPG is trapped inside the high pressure chamber 91 after the engine has stopped, its temperature raises and, consequently, the pressure inside the high pressure chamber 91 raises. If this pressure is not released, the outward movement of the plunger 92 will not be able to fill the chamber 91 with liquid LPG from the low pressure chamber 97 because the higher pressure in the high pressure chamber 91 impedes the flow. In the first two cases the objective is achieved by decreasing the pressure in the high pressure chamber 91 to 15 bar (pressure in the low pressure chamber 97), and in the third embodiment the pressure in the high pressure chamber 91 is decreased to 7 bar (pressure in the tank 12).

In these three embodiments, the ECU 13 is configured to operate the flow control valve (93, 96), or valve 21 1 or valve 230 before the engine is started (for instance, upon opening a vehicle door if the engine is installed in a vehicle or upon activating a remote control). This action balances the pressure between the high pressure chamber 91 and the low pressure circuit (chamber 97 or tank 12). This, in turn, enables the filling of the chamber 91 with liquid LPG as soon as the plunger 92 starts moving outward when the engine is cranked. Once the chamber 91 is filled with liquid LPG, the pump 9 can pressurize it to the required level. Therefore, the engine starts normally.

As a precaution and in order to eliminate any remaining bubbles, the flow control valve (93, 96), or valve 21 1 or valve 230 may be kept open during the first pump strokes (one to four strokes) of the pump 9. In a further preferred embodiment of the invention as shown in Figure 7, a solenoid operated valve 221 is provided in the high pressure rail 7 which provides a return path 220 of LPG to the tank 12, thereby releasing pressure in the rail 7 which in turn decreases the pressure in the high pressure chamber 91 .

The solenoid operated valve 221 can be specifically mounted in the high pressure rail 7 and operated by the electronic control unit 13, or if the high pressure rail 7 already includes a safety valve, this existing safety valve may be modified to be actively actuated and set to operate against a counter-pressure of at least 200 or 250 bar (absolute pressure), depending on the maximum pressure of the injection system.

In this embodiment, the ECU 13 is configured to operate the solenoid valve 221 or the modified safety valve before the engine is started (for instance, upon opening a vehicle door if the engine is installed in a vehicle or upon activating a remote control). This action balances the pressure between the high pressure rail 7 and the tank 12. Consequently, the LPG in the chamber 91 is at a higher pressure than the rail 7 and it starts flowing from the chamber 91 to the rail 7 through the check valve 94. This, in turn, releases the pressure in the chamber 91 and enables the filling of the chamber 91 with liquid LPG as soon as the plunger 92 starts moving outward when the engine is cranked. Once the chamber 91 is filled with liquid LPG, the pump 9 can pressurize it to the required level. Therefore, the engine starts normally.

As a precaution and in order to eliminate any remaining bubbles, the solenoid valve 221 or the modified safety valve may be kept open during the first pump strokes (one to four strokes) of the pump 9.

In still another preferred embodiment, a shell surrounding the high pressure rail 7 for cooling any fuel contained therein is provided. This shell is fed with coolant at a controlled temperature, typically in the range of 20 to 40 °C, thereby keeping the LPG contained within at temperatures below the start of bubble formation. During normal operation of the engine, coolant is circulating permanently.

As it is evident from the description, the different aspects and embodiments of the invention defined in this section can be combined with one another, as long as they are compatible with each other.

In this text, the term "comprises" and its derivations (such as "comprising", etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc. On the other hand, the invention is obviously not limited to the specific embodiments described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.

Claims

1 . Direct injection engine (100) which comprises a fuel supply system having:

a low-pressure circuit comprising a low pressure fuel supply line (10) connecting a low pressure pump (1 1 ) submerged in fuel tank (12) to a low pressure chamber (97) which is part of a pump (9); and,

a high-pressure circuit comprising a high pressure fuel supply line (15) connecting a high pressure chamber (91 ) of the pump (9) to a high pressure rail (7);

the high and low pressure chambers being connected by a flow control valve (96, 93);

wherein the direct injection engine (100) comprises:

means for balancing pressure between the high-pressure circuit and the low-pressure circuit;

the direct injection engine further comprising control means (13) for operating the means for balancing pressure between the high-pressure circuit and the low-pressure circuit and the means for eliminating any remaining LPG in gas phase in the low- or high- pressure circuits at least before the engine is started or during start of the engine.

2. Direct injection engine (100) according to claim 1 , wherein the means for balancing pressure between the high-pressure circuit and the low-pressure circuit comprises means for pressurizing the low pressure circuit to 45 bar absolute pressure.

3. Direct injection engine (100) according to claim 2, wherein the means for pressurizing the low pressure circuit to 45 bar absolute pressure include a low pressure pump (1 1 ) being able to provide a pressure of at least 45 bar in the low pressure fuel supply line (10), or providing an additional pump (102) in series with the low pressure pump (1 1 ) and able to raise the pressure provided by the low pressure pump (1 1 ) to at least 45 bar in the low pressure fuel supply line (10).

4. Direct injection engine (100) according to any of claims 2-3, wherein the control means (13) are configured to keep the low pressure circuit at 45 bar absolute pressure also during a few seconds after the direct injection engine is started.

5. Direct injection engine (100) according to claim 1 , wherein the means for balancing pressure between the high-pressure circuit and the low-pressure circuit comprises providing a return path for releasing pressure from the high-pressure circuit to the low-pressure circuit.

6. Direct injection engine (100) according to claim 5, wherein the flow control valve (96, 93) is designed to operate against a counter-pressure of at least 45 bar,

7. Direct injection engine (100) according to claim 5, wherein the return path is provided between the high pressure chamber (91 ) and the low pressure chamber (97) by means of an operated valve (230).

8. Direct injection engine (100) according to claim 5, wherein the return path is a return path (210) provided between the high pressure chamber (91 ) and the tank (12) by means of an operated valve (21 1 ).

9. Direct injection engine (100) according to any of claims 6-8, wherein the control means (13) are configured to operate the flow control valve (96, 93) and/or the operated valve (230, 21 1 ) also during the first strokes of the pump (9).

10. Direct injection engine (100) according to claim 5, wherein the means for balancing pressure between the high-pressure circuit and the low-pressure circuit comprises providing a return path (220) from the high pressure rail (7) to the tank (12) by means of an operated valve (221 ).

1 1 . Direct injection engine (100) according to claim 10, wherein the control means (13) are configured to activate the operated valve (221 ) during the first strokes of the pump (9).

12. Direct injection engine (100) according to any of claims 1 -1 1 , wherein the means for eliminating any remaining LPG in gas phase in the low-pressure circuit (10, 97, 200, 210) comprise providing an outlet (201 , 201 ') in the low pressure chamber (97), the outlet (201 ) being connected to the tank (12) by means of a return path (200).

13. Direct injection engine (100) according to claim 12, wherein the outlet (201 ) is in an uppermost part of the low pressure chamber (97).

14. Direct injection engine (100) according to claim 12, wherein the means for eliminating any remaining LPG in gas phase in the low-pressure circuit further comprise:

a low pressure pump (1 1 ) being able to provide sufficient flow so as to make LPG bubbles flow to the tank (12) and working against sufficient counter-pressure above the pressure inside the tank (12) so as to provoke the collapse of LPG bubbles; and

- a restriction (202) in the return path (200) for guaranteeing that the pressure in the low pressure line (10) is at least 8 bar above the pressure of the tank (12).

15. Direct injection engine (100) according to any of claims 1 -13, wherein the low pressure fuel supply line (10) is connected to the low pressure chamber (97) through an inlet (101 ) which is located in front of the flow control valve (96, 93).