SE1950113A1 - Fuel system and method of preventing boiling of ethanol-based fuel at an internal combustion engine driven low pressure fuel pump of a fuel system - Google Patents

Abstract

The present invention relates to a fuel system (4) for an internal combustion engine (2) of a vehicle (1) adapted for a fuel having a boiling point below 90°C, the fuel system comprising a main fuel pipe (18) connecting an internal combustion engine driven low pressure fuel pump (12), a fuel tank (11) upstream of the low pressure pump (12), a fuel filter (17) downstream of the low pressure pump (12), and a high pressure pump (19) located downstream of the fuel filter (17), the high pressure pump (19) being configured to supply fuel to an injection system associated with the internal combustion engine. The fuel system (4) comprises a cooling flow recirculation line (15) associated with the main fuel pipe (18) and arranged to recirculate part of the fuel downstream of the low pressure pump (12) and upstream of the high pressure pump (19) back to the fuel tank (11), whereby cooling of the low pressure pump can be obtained especially during an engine brake mode of the vehicle.

Description

1Fuel system, a method of preventing boiling of a fuel having a boiling point below 90°C at aninternal combustion engine driven low pressure fuel pump of a fuel system and a vehicle comprising the fuel systemTECHNICAL FIELD The present disclosure relates to a fuel system for an internal combustion engine of a vehicleadapted for a fuel having a boiling point below 90°C. The present disclosure further relates toa method of preventing boiling of a fuel having a boiling point below 90°C at an internal com bustion engine driven low pressure fuel pump of the fuel system associated with the internal combustion engine of a vehicle.BACKGROUND ART Internal combustion engines, such as diesel engines, are used for example in trucks, buses,passenger cars, motor boats, vessels, ferries and ships. Internal combustion engines ofthedefined type are also used in industrial engines and/or engine driven industrial robots, powerplants such as e.g. electric power plants comprising a diesel generator, and in locomotives.Such internal combustion engines are associated with a fuel system adapted to transport fuelfrom one or more fuel tanks via an injection system to the internal combustion engine. Thefuel system comprises one or more fuel pumps, which may be driven mechanically by theinternal combustion engine. The fuel pumps create a fuel flow and pressure to transport thefuel to the injection system. The injection system then supplies fuel to the internal combustion engine.

Internal combustion engines may be driven by fuel which may be diesel, petrol, or ethanol orother types of biofuels. Ethanol and certain types of biofuels may have a low boiling point,normally below 90°C, which may lead to boiling ofthe fuel if the combustion enginetemperature becomes high, for example during engine braking ofthe vehicle when no fuel isinjected to the engine. lfthe fuel boils, the gaseous phase of the fuel cannot be pressurized bythe fuel pumps used to supply fuel from the fuel tank to a high pressure fuel pump associatedwith the combustion engine and arranged to supply fuel to the engine. Therefore, there is arisk for operational disturbances and vehicle off road "VOR". Thus, there is a need for a solution by which the risk for boiling of the fuel is reduced in the existing fuel systems.

SUMMARY OF THE INVENTION The objective of the present invention is thus to decrease the risk for operational disturbances in a fuel system adapted for a fuel having a boiling point of 90°C or less.

Especially, it is an objective to prevent operational disturbances when the engine temperatures are high, for example during engine braking of the vehicle.

A further objective is to provide a robust fuel system.

The objectives above are attained by a fuel system for an internal combustion engine of avehicle as defined in the appended claims. The fuel system is adapted for a fuel having aboiling point below 90 °C. The fuel system comprises a main fuel pipe connecting an internalcombustion engine driven low pressure fuel pump, a fuel tank upstream of the low pressurepump, a fuel filter downstream ofthe low pressure pump, and a high pressure pump locateddownstream ofthe fuel filter. The high pressure pump is configured to supply fuel to aninjection system associated with the internal combustion engine. The fuel system comprises acooling flow recirculation line associated with the main fuel pipe and arranged to recirculatepart of the fuel downstream of the low pressure pump and upstream ofthe high pressurepump back to the fuel tank. By returning a small part ofthe fuel back to the tank, the lowpressure pump may suck cool fuel from the tank and a flow of cool fuel through the pump ismaintained at a certain level. By the cooling flow is meant a flow having a flow rate, which issufficient to cool the low pressure pump, for example during an engine braking mode ofthevehicle. Thus, the low pressure pump is cooled and the fuel is prevented from boiling,especially during an engine braking mode ofthe vehicle, when no fuel is injected to the engine.

The cooling flow recirculation line may be associated with a bleeding orifice in the main fuelpipe. Thus, a simple construction is provided. The bleeding orifice may have a diameter ofmore than 0.5 mm. ln this way, the flow through the low pressure pump can be maintained at a desired level also during the engine braking mode.

The low pressure pump may be associated with an internal recirculation line provided with apressure regulating valve. Thus, any excess fuel produced by the low pressure pump may be recirculated back to an inlet ofthe low pressure pump. 3The fuel system may further comprise a main fuel return pipe arranged to return fuel back tothe fuel tank and comprising at least one of a fuel filter return pipe, a high pressure pumpreturn pipe and an accumulator return pipe, and wherein the cooling flow recirculation line isassociated with the main fuel return pipe. Therefore, existing fuel return pipes in the systems may be utilized for the cooling flow to be returned to the tank.

The cooling flow recirculation line may comprise a flow restriction valve and optionally a checkvalve. ln this way, the flow may be controlled more efficiently, and the check valve may prevent fuel from flowing back to the main fuel pipe.

The cooling flow recirculation line may have a capacity that is smaller than the capacity ofthe main fuel pipe. Thus, the risk for unsuccessful start ofthe engine is reduced.

The cooling flow return flow line may be associated with the main fuel pipe between the lowpressure pump and the fuel filter. Thus, the filter will not be charged with hot fuel which could deteriorate the fuel filter.

The cooling flow return line may alternatively or additionally be associated with the main fuelpipe between the fuel filter and the high pressure pump. Thus, the cooling flow may be returned to the tank before reaching the high pressure pump.The fuel system may be adapted for ethanol-based fuel.

The objectives above are also attained by a method of preventing boiling of a fuel having aboiling point below 90°C at an internal combustion engine driven low pressure fuel pump in afuel system associated with the internal combustion engine of a vehicle. The method isespecially suitable, when the vehicle is in an engine braking mode. The fuel system comprisesa main fuel pipe connecting an internal combustion engine driven low pressure fuel pump, afuel tank upstream ofthe low pressure pump, a fuel filter downstream ofthe low pressurepump, and a high pressure pump located downstream ofthe fuel filter. The high pressurepump is configured to supply fuel to an injection system associated with the internalcombustion engine. ln the method a cooling flow recirculating part ofthe fuel downstream ofthe low pressure pump and upstream of the high pressure pump back to the fuel tank isarranged. The flow rate of the cooling flow is arranged such that it may cool the low pressurepump during the engine braking mode of the vehicle. The fuel system may be of the kind described above. 4 The invention also relates to a vehicle comprising the above-mentioned fuel system.

Further features and advantages are described below in the detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically illustrates a vehicle comprising a fuel system ofthe presentdisclosure; Fig. 2 schematically illustrates a part of a powertrain of the vehicle in Fig. 1; Fig. 3 schematically illustrates a road section with an uphill and a downhill slope and atemperature curve for the fuel; Fig. 4 schematically shows an example coupling scheme for the fuel system of the present disclosure.DETAILED DESCRIPTION The invention will be described in more detail below with reference to exemplifyingembodiments and the accompanying drawings. The invention is however not limited to theexemplifying embodiments discussed and/or shown in the drawings, but may be varied withinthe scope of the appended claims. Furthermore, the drawings shall not be considered drawnto scale as some features may be exaggerated in order to more clearly illustrate the invention or features thereof.

Fig. fi schematically shows a side vlevv ef a lieavy vehicle 1, which is a truck, cornprlsirlg aninternal centhustioil erigihe Z, vvhich is associated with a fuel systern 4 comprising a fuel tahkill. ln the present disclosure the vehicle is a truck, but the vehicle could he anv other "type of aheavy vehicle, such as a bus. The vehicle fl. further comprises a gearbox 6 conhecqted to the driving wheels 1G of the vehicle i via a propeller shaft 8, Fig. 2 schematically shows parts of a powertrain for the vehicle 1. The powertrain comprisesthe internal combustion engine 2, which in this case is mechanically connected by a shaft to a first end of a gearbox 6 via a clutch device 3. The gearbox 6 has its second end mechanically 5connected by a propeller shaft 8 to a differential gear 5 associated with a driving axle. The driving axle comprises left and right drive shafts 7 which drive the powered driving wheels 10.

By this well-known arrangement, the mechanical work of the internal combustion engine 2 istransferred, via a number oftransmission devices such as the clutch device 3, gearbox 6,propeller shaft 8, differential gear 5 and drive shafts 7, to the powered driving wheels 10 forpropulsion of the vehicle 1. The gearbox 6 is a transmission device, which has a number offorward gears for propelling the vehicle 1 forwards and usually also one or more reversegears. The number of forward gears varies but twelve forward gears are for example usual in trucks. ln addition, the vehicle 1 may comprise or be connected to a control device 50 comprising oneor more electronic control units (ECUs). The purpose of said control device is tocontrol/regulate one or more functions in the vehicle 1, e.g. the speed, by means of one ormore actuators which may be related to various functions in the vehicle 1, such as enginecontrol, gear changing, cruise control, suspension configuration, etc. The control device 50may use a number of different parameters, e.g. current engine speed, current acceleratorpedal position, current engine torque, data from various sensors and map data to control the various functions of the vehicle 1. ln the present disclosure, the term ”powertrain” shall be considered to mean the combustion engine and the driveline of the vehicle.

The vehicle may be operated in an engine braking mode for example at downhill sections of aroad. By the ”engine braking mode” is meant an operating condition of a vehicle in which thevehicle powertrain is closed, i.e. the internal combustion engine is connected to the drivingwheels ofthe vehicle via the transmission devices, but there is no fuel injection to thecombustion engine. Thus, the gas actuator is not activated and the friction brakes of thevehicle are not necessarily activated. During the engine braking mode, the vehicle is moved byit's kinetic energy, which depends on e.g. weight ofthe vehicle, speed of the vehicle and slopeof the road. Since the powertrain is closed during the engine braking mode, the crankshaft ofthe combustion engine will be rotating and thus has a rotational speed. Thus, a component ordevice which in the present disclosure is described as being driven by the combustion engine may also be operational during the engine braking mode, unless explicitly disclosed otherwise. 6 According to the present disclosure, a method is provided for preventing boiling of a fuelhaving a boiling point below 90°C at a low pressure pump of a fuel system of a vehicle,especially when the vehicle is in an engine braking mode. Generally, the fuel system comprisesa fuel tank arranged upstream of a low pressure pump, which is arranged to suck fuel from thetank. The low pressure pump is arranged to supply and pressurize fuel further to a highpressure pump, which is arranged downstream ofthe low pressure pump and associated withthe internal combustion engine via an accumulator and an injection arrangement configuredto provide fuel to the internal combustion engine. The low pressure pump pressurizes the fuelto 9-14 bar, but is not limited thereto. The high pressure pump is associated with and locatedin close proximity of an engine block of the internal combustion engine and is arranged topressurize the fuel to a high pressure, e.g. to 500-2400 bar, but is not limited thereto. Thus,the low pressure pump pressurizes the fuel to a pressure, which is more than 10, or more than20 or more than 30 times smaller than the operating pressure ofthe high pressure pump.Further, the tank, the low pressure pump and the high pressure pump are connected by a main fuel pipe or conduit.

A fuel filter, also referred to as a pressure filter or a main fuel filter, is arranged in the mainfuel pipe between the low pressure pump and the high pressure pump, and thus downstreamof the low pressure pump and upstream ofthe high pressure pump. A furtherfuel filter maybe arranged at the suction side of the low pressure pump, i.e. between the tank and the low pressure pump.

The low pressure pump is associated with and driven by the internal combustion engine. Thus,the low pressure pump is operational also during the engine braking mode. However, duringthe engine braking mode, no fuel is injected into the combustion engine and an inlet meteringvalve of the high pressure pump is closed, whereby no fuel is fed to the high pressure pump.Since no new fuel is sucked into the fuel system and since the engine energy in the form ofheat propagates from the engine block via the high pressure pump to the low pressure pump,the temperature at the low pressure pump increases when the vehicle is in an engine brakingmode. Therefore the fuel may be easily heated up to the boiling point ofthe fuel, e.g. to about90°C. Thus, there is a risk that the fuel, which may be e.g. ethanol for example as marked”ED95”, will start to boil and evaporate, which leads to operational disturbances, since the gas phase ofthe fuel cannot be pressurized by the low pressure pump. Therefore, no fuel can be 7supplied in the fuel system further to the high pressure pump when the vehicle returns to anormal operational mode, in which fuel is injected to the engine, from the engine braking mode.

According to the present disclosure, boiling of the fuel having a boiling point below 90°C at alow pressure pump is prevented by arranging part ofthe fuel flow downstream of the lowpressure pump and upstream ofthe high pressure pump to circulate back to the fuel tank. Acooling flow recirculation line is thus associated with a main fuel pipe ofthe fuel system. Theflow rate in the cooling flow recirculation line may be adapted such that the flow can cool thelow pressure pump, especially during the engine braking mode of the vehicle. This can bemade for example by associating the cooling flow recirculation line with a bleeding orifice inthe main fuel pipe. Thus, a bleeding flow, which corresponds to the cooling flow, through theorifice will be continuous during the operation ofthe vehicle. The bleeding orifice diametermay be arranged such that the flow rate, which is sufficient to cool the low pressure pump andwhich may be pre-determined, is obtained. For example, the diameter may be more than 0.5mm, for example from 0.5 mm to 1 mm. Thus, part ofthe hot fuel is returned back to the fueltank, but the flow is still so small that no operational disturbances for example during the start of the vehicle are caused.

During the engine braking mode of the engine, fuel is sucked from the tank by the lowpressure pump in an amount corresponding to the cooling flow or bleeding flow. The lowpressure pump may be associated with an internal recirculation line provided with a pressureregulator or a pressure regulating valve. For example, an inlet ofthe recirculation line may bearranged adjacent to or connected with an outlet of the low pressure pump and an outlet ofthe recirculation line may be arranged in connection with the inlet of the low pressure pump.The pressure regulating valve opens to allow any excess fuel produced by the pump to berecirculated back to the inlet of the pump. During the engine braking mode of the vehicle,when no fuel is requested by the high pressure pump, but the low pressure pump is stilloperational, the pressure regulating valve aims to keep the flow over the pump constant.Thus, a fuel flow corresponding to the cooling flow is sucked from the tank through the lowpressure pump, thereby cooling the low pressure pump and reducing the risk that the fuelstarts to boil. The re-circulation may be arranged to be continuous bleeding flow during the operation of the low pressure pump. 8 Fig. 3 is provided to illustrate an example driving situation in which the engine braking mode isused. ln the drawing, a vehicle 1 is shown, which is travelling on a road having an uphill sectionUH and a downhill section DH. When the vehicle 1 travels uphill, high engine speeds are oftenused. Due to large demand of fuel in the engine, the temperature ofthe fuel at the lowpressure pump can be kept at a relatively constant level below the boiling point ofthe fuel,since the low pressure pump is cooled by new cool fuel sucked into the system from the fueltank. When the vehicle reaches a top HT of the hill and reaches a certain speed, e.g.corresponding to the speed limit ofthe road, the vehicle may be operated in the enginebraking mode. ln this way, the use of friction brakes may be reduced. ln the engine braki ngmode, there is no fuel injection to the internal combustion engine. Therefore, thetemperature of the low pressure pump rapidly rises from the initial engine brakingtemperature Teb, since the high pressure pump does not request fuel, and no fuel is injected tothe engine. Therefore, the heat from the engine block propagates to the low pressure pump,and thus, the fuel at the low pressure pump may be rapidly heated to a boiling point temperature Tbp.

By arranging the cooling flow recirculation line associated with the main fuel pipe andarranged to recirculate part ofthe fuel downstream ofthe low pressure pump and upstreamof the high pressure pump back to the fuel tank, the low pressure pump may use cool fuelfrom the tank, in an amount corresponding to the amount of the cooling flow returned back tothe tank. The cooling flow may be a continuous flow, and may be arranged as a continuousbleeding flow. The continuous bleeding flow may be arranged by associating the cooling flowrecirculation line with an orifice in the main fuel pipe. ln this way, the fuel is returned back tothe tank passively and continuously. Therefore, a small portion of the fuel flow from the mainfuel pipe bleeds continuously. Due to the over-capacity ofthe low pressure pump, thebleeding flow does not affect the normal operation of the fuel system, but provides sufficientcooling of the pump during the engine braking mode. The capacity of the cooling flowrecirculation line is smaller than the capacity ofthe main fuel pipe, and can be in the rangefrom about 1/20 to 1/10 of the capacity ofthe main fuel pipe. ln this way, a simple construction to the fuel system may be provided.

Fig. 4 illustrates an example of a fuel system 4 of the present disclosure. The fuel system 4 comprises a fuel tank 11 from which fuel is sucked by means of a low pressure pump 12 to a 9 high pressure pump 19, which supplies fuel at high pressure to an accumulator 20. The fuelsystem is further provided with a main fuel pipe 18, which connects the tank 11, the lowpressure pump 12 and the high pressure pump 19 ofthe fuel system 4. ln the shown examplein Fig. 4, the fuel system also comprises a fuel filter 17 arranged in the main fuel pipedownstream ofthe low pressure pump 12 and upstream of the high pressure tank 19, i.e. onthe pressurized side of the low pressure pump 12. A further fuel filter may be provided in thesuction side of the low pressure pump 12, i.e. upstream of the low pressure pump anddownstream ofthe tank 11. The high pressure pump 19 may be associated with a highpressure pump return pipe 25, which in turn may be associated with a main fuel return pipe 28 of the fuel system.

The accumulator 20, which can be of the type common rail, supplies fuel to fuel injectors 22,which in turn inject fuel to the internal combustion engine 2. To allow any excess fuel from theaccumulator 20 to be recirculated back to tank 11, an accumulator return flow pipe 24comprising a check valve 21 can be associated with the accumulator. ln this way, fuel from theaccumulator can be returned back to the fuel tank while the check valve 21 prevents flow backto the accumulator. The accumulator return flow pipe 24 may be associated with a main fuel return pipe 28 ofthe fuel system.

To decrease the risk for boiling ofthe fuel, especially when the vehicle is in an engine brakingmode, the fuel system 4 of the present disclosure is provided with a cooling flow recirculationline 15 associated with the main fuel pipe 18 and arranged to recirculate part ofthe fueldownstream ofthe low pressure pump 12 and upstream ofthe high pressure pump 19 back tothe fuel tank 11. The cooling flow recirculation line 15 is connected to the main fuel pipe 18 downstream ofthe low pressure pump 12.

The low pressure pump 12 may comprise an internal pressure regulating arrangement whichcomprises a recirculation line 14 and a check valve 13, which is arranged to open to allow anyexcess fuel produced by the low pressure pump 12 to be recirculated back to the low pressurepump 12. The inlet of the recirculation line 14 may be located at the outlet of the low pressurepump 12, and the outlet of the recirculation line 14 may be located at the inlet of the low pressure pump 12. The pressure regulating arrangement can be integrated with the low pressure pump 12. The cooling flow recirculation line 15 may locate downstream ofthe inlet of the recirculation line 14, which may be associated with the main fuel pipe 18.

The fuel filter 17 may also be associated with a fuel filter return pipe 27, which in turn may beassociated with the main fuel return pipe 28. The cooling flow recirculation line 15 may bearranged upstream ofthe fuel filter return pipe 27 in the main fuel pipe 18. The cooling flowrecirculation line may have a capacity that is smaller than the capacity of the main fuel pipe18, whereby the amount of fuel flowing through the return flow pipe may be easily andpassively controlled. As an example, but not limited thereto, the capacity may be for example from 1/20 to 1/10 of the flow capacity ofthe main fuel pipe.

The cooling flow recirculation line 15 may be associated with a bleeding orifice in the mainfuel pipe 18, which is illustrated by the reference sign 16. The orifice should have a diameterthat allows a flow, which is sufficiently large to provide cooling for the low pressure pump, butsmall enough to keep the flow at a level which does not cause operational disturbances, e.g.during the start ofthe engine. The diameter may be for example 0.5 mm or larger, such as 0.6mm. The main fuel pipe may have, for example, an inner diameter of about 9 mm and anouter diameter of 12 mm. Thus the diameter ofthe orifice may be from about 10-20 timessmaller than the inner diameter ofthe main fuel pipe. The cooling flow recirculation line 15may alternatively or additionally comprise a flow restriction valve and/or a check valve 16'. ln this way, the flow back to the main fuel pipe 18 is prevented. ln the embodiment of Fig. 4, the cooling flow recirculation line 15 is connected to the mainfuel pipe 18 upstream ofthe fuel filter 17, i.e. between the low pressure pump 12 and the fuelfilter 17. An existing main return flow pipe 28 may be at least partly utilized for the coolingflow in which the fuel from the low pressure pump 12 is returned back to the fuel tank 11. Thisleads to more compact and economical solution, since the existing return flow pipes may beutilized. lt should be noted that the cooling flow recirculation line 15 can be connected to orassociated with the main fuel pipe 18 alternatively or additionally between the fuel filter 17and the high pressure pump 19. Further, the cooling flow recirculation line 15 may beassociated with the main fuel return pipe 28, which may comprise at least one of the above-mentioned fuel filter return pipe 27, high pressure pump return pipe 25 and accumulator return pipe 24. 11 Although not illustrated in Fig. 4, the fuel system 4 may comprise more than one fuel tank.The fuel system may also comprise additional fuel pumps. For example, the fuel system 4 maycomprise an additional pump configured to transfer fuel from a second fuel tank to the fueltank 11 illustrated in Fig. 4. Alternatively, in case of a plurality of fuel tanks, these may have aself-regulating flow between each other via a connection conduit connecting the fuel tanks.I\/|oreover, the fuel system may comprise further fuel filters, for example a pre-filterarrangement arranged inside the fuel tank 11. Such pre-filter arrangement may comprise acoa rse mesh sieve for the purpose of filtering out particulate matter above a certain pre-determined size from the fuel. Alternatively or additionally, an additional filter referred to as asuction filter, may be arranged between the tank and the low pressure pump. The fuel filter,the low pressure pump and the high pressure pump with the accumulator and the injectorsare typically arranged on the combustion engine, whereas the fuel tank 11 may typically be arranged on the chassis of the vehicle.

Claims (13)

12CLAll\/IS

1. A fuel system (4) for an internal combustion engine (2) of a vehicle (1) adapted for a fuel having a boiling point below 90°C, the fuel system comprising a main fuel pipe (18)connecting an internal combustion engine driven low pressure fuel pump (12), a fueltank (11) upstream of the low pressure pump (12), a fuel filter (17) downstream of thelow pressure pump (12), and a high pressure pump (19) located downstream ofthefuel filter (17), the high pressure pump (19) being configured to supply fuel to aninjection system associated with the internal combustion engine, characterized in thatthe fuel system (4) comprises a cooling flow recirculation line (15) associated with themain fuel pipe (18) and arranged to recirculate part of the fuel downstream ofthe lowpressure pump (12) and upstream ofthe high pressure pump (19) back to the fuel tank(11).

2. Fuel system according to claim 1, characterized in that the cooling flow recirculation line (15) is associated with a bleeding orifice in the main fuel pipe (18).

3. Fuel system according to claim 2, characterized in that the bleeding orifice has a diameter of more than 0.5 mm.

4. Fuel system according to any one of the preceding claims, characterized in that the lowpressure pump (12) is associated with an internal recirculation line (14) provided with a pressure regulating valve (13).

5. Fuel system according to any one of the preceding claims, characterized in that the fuelsystem (4) further comprises a main fuel return pipe (28) arranged to return fuel backto the fuel tank (11) and comprising at least one of a fuel filter return pipe (27), a highpressure pump return pipe (25) and an accumulator return pipe (24), and wherein the cooling flow recirculation line (15) is associated with the main fuel return pipe (28).

6. Fuel system according to any one of the preceding claims, characterized in that the cooling flow recirculation line (15) comprises a flow restriction valve (16) and 10. 11. 13 optionally a check valve (16').

7. Fuel system according to any one of the preceding claims, characterized in that thecooling flow recirculation line (15) has a capacity that is smaller than the capacity of the main fuel pipe (18).

8. Fuel system according to any one of the preceding claims, characterized in that thecooling flow return flow line (15) is associated with the main fuel pipe (18) between the low pressure pump (12) and the fuel filter (17).

9. Fuel system according to any one of the preceding claims, characterized in that thecooling flow return line (15) is associated with the main fuel pipe (18) between the fuel filter (17) and the high pressure pump (19).

10. Fuel system according to any one of the preceding claims, characterized in that the fuel system is adapted for ethanol-based fuel.

11. Method of preventing boiling of a fuel having a boiling point below 90°C at an internalcombustion engine driven low pressure fuel pump (12) of a fuel system (4) associatedwith the internal combustion engine (2) of a vehicle (1), when the vehicle is in anengine braking mode, the fuel system comprising a main fuel pipe (18) connecting aninternal combustion engine driven low pressure fuel pump (12), a fuel tank (11)upstream ofthe low pressure pump (12), a fuel filter (17) downstream ofthe lowpressure pump (12), and a high pressure pump (19) located downstream ofthe fuelfilter (17), the high pressure pump (19) being configured to supply fuel to an injectionsystem associated with the internal combustion engine, characterized by arranging acooling flow recirculating part of the fuel downstream of the low pressure pump (12)and upstream ofthe high pressure pump (19) back to the fuel tank (11), and adaptingthe flow rate such that it cools the low pressure pump (12) during the engine braking mode of the vehicle.

12. 1412. Method according to claim 11, characterized by performing the method in a fuel system of any one of claims 1 to 10.

13. Vehicle (1) characterized in that it comprises the fuel system according to any of claims 1 to 10.