WO2013167753A1

WO2013167753A1 - Fuel system, kit and method for directly injecting a fuel in a combustion engine

Info

Publication number: WO2013167753A1
Application number: PCT/EP2013/059832
Authority: WO
Inventors: Servatius Alfons Maria Jaasma
Original assignee: Vialle Alternative Fuel Systems B.V.
Priority date: 2012-05-11
Filing date: 2013-05-13
Publication date: 2013-11-14
Also published as: NL2008803C2

Abstract

The invention relates to a fuel system and method for a combustion engine with direct injection. The system comprises at least one high pressure fuel line connected to an injection device of the combustion engine for the direct injection of fuel. A first fuel is supplied to the node by a first fuel supply unit. The first fuel supply unit comprises at least a high-pressure fuel pump having an inlet connected to a first fuel storage for a liquid fuel, such as gasoline, and having an outlet connected to the node of the high pressure fuel line. A second fuel supply unit supplies a different fuel to the node in the high pressure fuel line, the second fuel supply comprising at least a second fuel storage for liquefied vapor fuel, such as liquid petrol gas (LPG), and a liquefied vapor fuel pump.

Description

FUEL SYSTEM, KIT AND METHOD FOR DIRECTLY INJECTING A FUEL IN A COMBUSTION ENGINE

The invention relates to a fuel system for a

combustion engine with direct injection. The invention further relates to a kit for a fuel system and to a method for directly injecting a fuel in a combustion engine.

Direct injection increases the efficiency of

combustion in in combustion engines. Diesel can be

pressurized to pressures over 1000 bar. Gasoline can be pressurized to 100-200 bars. Suitable high pressure pumps are used to supply the fuel to a high pressure fuel line connected e.g. to a common rail allowing the direct

injection of the fuel into the combustion chambers.

In this application any pressure above 35 bars is a high pressure.

Bi-fuel systems using a liquid fuel, such as petrol or diesel, and a liquefied vapor fuel such as liquefied

petroleum gas (LPG) are known. Such a system is e.g.

disclosed in PCT2009/110792. The high pressure pump is supplied, at the low pressure end, with either fuel and used to pressurize the fuel.

The liquefied vapor fuel is supplied in a liquid state from the liquefied vapor fuel storage. In a liquid state, the liquefied vapor fuel will be pressurized. Especially during the switching LPG to petrol the pressure at the low pressure end/inlet of the high pressure pump can drop, resulting in evaporation of the LPG present in the fuel lines upstream from the high pressure pump.

This application relates both to fuel systems arranged to supply fuel alternately as to fuel systems for supplying the fuel in mixed form. This application also relates to systems operating on a single fuel in which a extra fuel system is to be fitted, using a kit .

A problem with the known fuel systems and methods is warm starting the combustion engine . As a result of the heat present in the high pressure pump, liquefied vapor fuel can vaporize forming bubbles . This can result in vapor -lock and failure to start the engine . A well known problem in dual fuel systems is the change over from LPG to gasoline as a result of the relative high pressure of LPG . A further known problem according to prior art is the necessity of a return line for the LPG . Such a return line has the risk of

gasoline entering into LPG- storage .

It is a goal to improve at least one aspect of the known system and method .

In accordance with a first aspect of the invention a fuel system for a combustion engine with direct inj ection is provided comprising at least one high pressure fuel line . In an embodiment the high pressure fuel line is connected to an injection device of the combustion engine for the direct inj ection of fuel . The high pressure fuel line can comprise or is connected to a (downstream) common rail .

In an embodiment the high pressure fuel line comprises a node . The node connects to the downstream inj ection device with two upstream separate supply units for fuel . This allows supplying the two fuels from separated supply units .

In an embodiment the high pressure fuel line is connected to a first supply unit . The first supply unit will supply a liquid fuel to the high pressure fuel line . In an embodiment the first supply unit comprises at least a high- pressure fuel pump having an inlet connected to a first fuel storage for a liquid fuel , such as gasoline . The high pressure pump outlet is connected to the node of the high pressure fuel line . In an embodiment the fuel system comprises a second supply unit for supplying a second, different fuel to the node in the high pressure fuel line . This second supply unit can comprise at least a second fuel storage for liquefied vapor fuel , such as liquefied petrol gasoline (LPG) . The second supply allows feeding a second, different fuel to the high pressure fuel line for inj ecting into the combustion engine . The second supply can comprise a liquefied vapor fuel pump for supplying that second fuel from the storage to the fuel system. The liquefied vapor fuel pump can be a liquid LPG pump .

In this embodiment the second fuel is fed to the high pressure fuel line using a fuel supply separate from the first fuel supply . This separate system can be completely adapted to the demands of supplying a liquefied petrol gas preventing the vaporization and thereby preventing the known problems . Feeding a liquefied vapor fuel , such as liquid LPG, to the low pressure area of the first fuel supply is prevented . At the low pressure area for liquid fuel the pressure is below critical pressure of e.g. LPG, and the LPG could evaporate . Further specifically the second supply system can be without a return line for returning fuel that was fed from the storage back to that storage .

In prior art arrangements , such as W02009/110792 , DE 10 2008 043930 and WO 2011/059316 (explicitly completely incorporated by reference if allowed under national law) the two fuels were or could be mixed upstream from the high pressure line .

In an embodiment the most upstream node arranged to receive fuel from both supply units is the node in the high pressure fuel line . That node is arranged downstream from the high pressure pump connected to the first fuel storage . The first and second supply units are completely separated fuel supply units up until the node in the high pressure fuel line . In the high pressure fuel 1 ine however, the pressure is maintained above the critical pressure of the liquefied vapour fuel , preventing evaporation . Therefore this arrangement overcomes some of the problems indicated with respect to the prior art .

As the node is inter alia downstream from the high pressure pump, the liquefied vapor fuel can be supplied at pressures above the critical pressure and the evaporation issue is overcome . The LPG has a sufficient high pressure before the LPG is mixed with the liquid fuel .

In an embodiment second LPG fuel supply is arranged to by-pass the high pressure pump in the first supply unit . The LPG is pressurized in the second supply unit , e.g. using a dedicated LPG high pressure pump .

In an embodiment the first supply unit comprises a high pressure pump arranged exclusively to supply liquid fuel . This prevents mixing of the second fuel with the first fuel at pressures below at least 42 bars , further preventing evaporation of the liquefied vapor fuel .

In a further embodiment the first supply unit , the second supply unit or both supply units comprise a nonreturn valve positioned directly upstream from the node . This prevents the fuel from the high pressure fuel line at the node to reach upstream parts of fuel systems , operating at lower pressures that could result in evaporation

problems .

In embodiment the one-way valve in the first supply unit is a one-way valve in the high pressure pump .

A fuel line connects the second fuel storage over the one-way valve to the node . In an embodiment the high

pressure fuel line is arranged to operate at 30 , preferably at 38 bars and more preferably at 42 bars or more . At a pressure of 42 bars or more the LPG is above its critical pressure, preventing evaporation . Any evaporation issues are limited to the second supply unit , that can be equipped in order to prevent any problems arising from evaporation .

In an embodiment the second supply unit is arranged to supply the second fuel to the node at at least 42 bars . In an embodiment the second supply unit is arranged to supply liquefied vapor fuel in a super critical state . Such a second supply unit is arranged to supply the LPG fuel at a pressure above the critical pressure of LPG for the high pressure fuel line and other downstream features of the combustion engine . The evaporation issue is solved for LPG if operated above the critical pressure .

In an embodiment the pressure throughout the fuel line is over at least 42 bars . A high pressure pump for liquefied vapor fuels is positioned upstream from the fuel line preventing evaporation problems in the fuel line .

The fuel system according to the invention allows operating all features downstream from the high pressure fuel line at sufficient high pressure to prevent evaporation issues .

In an embodiment the fuel system is arranged to maintain a pressure of at least 30 , preferably at least 38 bars and more preferably higher than the critical pressure of the most volatile material in the LPG (e.g. propane) , for example, at least 42 bars in the high pressure fuel line , since 42 bars is the critical pressure for propane . If , using non-return valve and leak- free fuel lines , pressure in the high pressure fuel lines is maintained above 42 bars , bubble forming is prevented .

In an embodiment starting the engine is controlled by a controller arranged to first pressurize the fuel present in the high pressure fuel line to a pressure above 20 bar, preferably 30 and more preferably 40 bars before ignition is attempted .

It is advantageous to arrange the liquefied fuel pump in the liquefied fuel storage . This allows good priming of the pump . Further fitting the LPG storage as an extra fuel supply system is more easily.

In an embodiment the liquefied vapor fuel storage in the second supply unit comprises an opening sealed by an accessory plate . Such an accessory plate can be used to seal of the opening and provides several functions for allowing the LPG to be supplied from the storage .

In an embodiment of the second supply unit the most downstream pump for supplying the second fuel to the node is positioned at the accessory plate or more upstream.

Preferably the most downstream pump is positioned upstream, that is inside the liquefied vapor fuel storage . This allows supplying the liquefied fuel to fuel lines outside the storage at pressures above the critical pressure, preventing evaporation . Further by providing and supplying the second fuel at pressures over the critical pressure, return lines for returning liquefied fuel to the storage are not needed anymore .

In an embodiment the fuel system comprises a

controller arranged to control the first and second supply units . This allows alternating the fuel supply or mixing the fuel . In an embodiment the controller is arranged , when starting the combustion engine , to allow supply of fuel from the first supply unit only. Only liquid fuel is supplied .

In an embodiment a non- return valve is arranged downstream from a pump chamber of the high pressure pump .

This prevents entering of the LPG fuel into the low pressure area of the high pressure pump or other low pressure areas of the system . In an embodiment a non-return valve is arranged near a downstream end of the second supply. Preferably this nonreturn valve is arranged just upstream from the connection node . This prevents the first fuel from entering the second supply unit .

In embodiment the high pressure pump in the first supply unit can be free of any return lines (or leak line) for returning fuel to the storage . Contrary to the

PCT2009/110792 prior art a return line from the high

pressure line is not needed as a result of the separated supply units to the node in the high pressure line .

In an embodiment the second supply unit can be free of any return lines (or leak line) for returning fuel to the second storage . By providing the two different fuels to a node in the high pressure line from two separated supply units , the fuel system can be arranged without return lines .

In an embodiment the high pressure pump comprises a pump chamber having a controlled inlet valve for controlling the amount of fuel supplied to the pump chamber and thereby controlling the amount of fuel to be pressurized . Preferably a controller, such as an ECU, is arranged to control the controlled inlet valve .

According to another aspect a fuel system for a combustion engine with direct inj ection is provided . The fuel system comprises at least one high pressure fuel line connected to an inj ection device of the combustion engine for the direct inj ection of fuel .

In an embodiment a LPG supply unit is connected to the high pressure line for supplying a liquefied fuel vapor fuel , such as liquid petrol gas (LPG) , to that high pressure fuel line . The LPG supply unit can comprise at least a LPG fuel storage for liquefied petrol gas (LPG) and one or more LPG pumps . The LPG pump can be arranged to supply LPG in liquid state or super critical state . At least one LPG pump is preferably positioned in the LPG fuel storage .

The LPG pump and LPG storage are connected to the high pressure line over a fuel line . The LPG fuel is supplied from the storage in liquid or super critical state to the fuel system, in particular to the high pressure line of the fuel system.

In an embodiment the LPG supply unit , and in

particular one of the liquid LPG pumps of the LPG supply unit , is arranged to supply the LPG at a pressure above the critical pressure of propane in the LPG, e.g. 42 bar pressure . The LPG supply unit is arranged to supply the LPG in a super critical state .

A suitable high pressure pump is used in the second supply unit to provide the LPG at the desired high

pressures . According to the so-called phase diagram, when the temperature and pressure is sufficiently high (i.e. above the critical temperature and the critical pressure) , the liquid and gaseous phases become indistinguishable , in what is known as a supercritical fluid . In other words , regardless the temperature, where a pressure is higher than the critical pressure , a material can be either in a normal liquid phase or in a supercritical fluid phase , but not in gaseous phase . This means that even the temperature might change after the inj ection, evaporation is still prevented as long as the pressure is maintained above the critical pressure .

Further the high pressure pump in the LPG supply unit for providing the LPG at the pressure of at least 42 bars to the high pressure line is arranged to pump LPG only . The LPG supply unit has a LPG dedicated high pressure pump . By providing a dedicated LPG high pressure pump the high pressure pump can be configured operate most efficiently with LPG.

In an embodiment a first supply unit is also connected to the high pressure line for providing a liquid fuel to the high pressure line . The LPG supply unit is a second supply unit , supplying a different second fuel . Throughout the fuel line in the second supply unit the pressure of the LPG is at least 42 bars .

Although in prior bi-fuel systems it was preferred to use the existing high pressure pump, the inventor now developed a fuel system wherein the second supply of

liquefied vapor fuel is separated from the first fuel supply unit , that prevents (LPG) evaporation problems .

In an embodiment the LPG-only high pressure pump is the LPG fuel pump positioned in the storage . The LPG fuel pump is arranged to operate at at least 42 bars .

In an embodiment the dedicated LPG high pressure pump is a pump positioned at or upstream from an accessory plate sealing off an opening of the LPG storage . Any downstream parts are supplied with LPG at at least pressures over 42 bars , preventing evaporation issues and allowing the LPG unit to be provided without return lines to the LPG storage .

According to a further aspect a kit for fitting a bi- fuel system in a high pressure direct inj ection combustion engine is provided . The internal combustion engine having direct inj ection comprises a high pressure fuel line . A first fuel supply unit , such as a liquid fuel , provides fuel to that high pressure line .

In an embodiment the kit comprises a second supply unit for supplying a second liquefied vapor fuel , such as LPG, wherein the second supply unit is arranged to supply the liquefied vapor fuel in a super critical state . By providing the liquefied vapor fuel in a super critical state, evaporation issues are prevented .

In an embodiment the kit comprises a second supply- unit for supplying a second liquefied vapor fuel , such as liquefied petrol gas , to the high pressure fuel line . The second supply unit comprises a second fuel storage for a liquefied vapor fuel such as liquid petrol gasoline (LPG) , a liquefied fuel pump , and a connecting device for connecting the second supply unit to the high pressure fuel line . The connection device can comprise any generally known leak free connector, including fuel lines .

In an embodiment the connection device replaces the existing high pressure fuel line . The connection device can be formed as a T-high pressure fuel line comprising a node allowing to connect two supply units to the the combustion engine . The first and second supply units are connected to downstream sides of the node, while the high pressure line and inj ection device of the engine is connected to a

downstream side of the node . The first supply unit , the original supply unit is held separated from the second supply (provided by the kit) up to the node in the high pressure line .

The kit provides a dedicated LPG high pressure pump to supply the LPG from the storage to the high pressure line .

In an embodiment the connecting device comprises a high pressure fuel line and a non-return valve to be

connected to that high pressure fuel line .

In an embodiment the kit comprises a controller arranged for controlling an amount of fuel supplied from the second fuel supply and for controlling an amount of fuel supplied from a first fuel supply formed by the first fuel storage and high pressure pump . The controller can override or replace the already present ECU. Any of the other features discussed in relation to the fuel system as discussed in this application can be part of the kit .

According to a yet another aspect a method for

inj ecting two different fuels in a combustion engine is provided . The method comprises supplying pressurized (high pressure) fuels to a node in a high pressure fuel line .

Subsequently the pressurized fuel from the high pressure fuel line is inj ected into the cylinders of the engine .

In an embodiment a first , liquid fuel is supplied using a first supply unit comprising a first , liquid fuel storage to the high pressure fuel line over a high pressure pump to the node .

In an embodiment of the method a second, different fuel , i.e. a liquefied vapor fuel , is supplied to the high pressure fuel line from a second fuel storage . According to this method a separate ( second) fuel supply unit is

provided, separate from the first fuel supply, and the second supply unit is connected to the node in the high pressure fuel line . The node in the high pressure line connects the two separated fuel supplies . By supplying the second fuel , preferably a liquefied vapor fuel such as liquefied petroleum gas (LPG) , to the node in the high pressure fuel line , the fuel can be supplied at a pressure above the critical pressure of the liquefied vapor fuel , preventing evaporation that would result in the formation of bubbles .

The node connects the two separated supply units with the downstream inj ection .

In an embodiment the second supply unit supplies the liquefied vapor fuel in super critical state to the node . In an embodiment the second fuel is pressurized inside the second fuel storage . This evaporation issue, if any- remaining , is thereby limited to inside the storage .

Preferably the fuel system and method is return line free . This prevents mixing of fuel and reduces the

complexity of the fuel system and method .

In an embodiment the second fuel is pressurized to at least 30 , preferably at least 38 bars and more preferably at least 42 bars . At these pressures in combination with higher operating temperatures of the combustion engines ,

evaporation of the LPG is prevent as these pressures are above the vapor pressure, or even above the critical pressure .

In an embodiment the node in the high pressure fuel line is a most upstream node receiving the two or more fuels . The two different fuels are supplied to the high pressure line or high pressure fuel rail separated,

preventing mixing and specifically preventing feeding of liquefied vapor fuels to low pressure areas of the fuel system.

In an embodiment the two fuels pass one-way valves directly upstream from the node . This prevents the liquefied fuel reaching low pressure areas , whereas mixing of the liquid fuel with the second supply is prevented .

In an embodiment the first fuel is supplied using a high pressure pump exclusively supplying the first fuel . This can be a dedicated liquid fuel pump . Whereas earlier methods were directed at configuring a single high pressure pump to operate with two different fuels , this invention is directed at using dedicated pumps and separating the

different fuel flows until the pressure is above critical pressures of the fuels used . In an embodiment both fuels are supplied at at least 42 bars to the node in the high pressure fuel line . In the high pressure fuel line the pressure is at least above the critical pressure, preventing evaporation .

In an embodiment supplying the second fuel comprises operating a liquefied vapor fuel pump in a liquefied vapor fuel storage . In an embodiment the liquefied vapor pump delivers the second fuel at at least 42 bars . In any fuel line downstream from the storage, the pressure in the fuel lines , throughout the entire fuel lines downstream from the storage, is above the critical pressure, preventing

evaporation .

In an embodiment the second fuel storage is a

liquefied vapor fuel storage having an accessory plate sealed onto an opening of the liquefied vapor fuel storage . In an embodiment of the method supplying the second fuel comprises pumping using one or more liquefied fuel pumps , wherein the most downstream liquefied fuel pump is at most at the accessory plate .

In an embodiment the supply of the first and second fuel is controlled . In an embodiment starting the combustion engine comprises supplying first fuel only.

In an embodiment the method comprises switching between respective fuels for alternating fuel supply or comprises controlling the supply of fuels to mix fuel from fuel supplies .

In an embodiment the method is free from returning fuels to the respective fuel storages .

In any embodiment of the method the two different fuels can be supplied simultaneously, allowing mixing, to the high pressure pump, or at separated intervals .

Various embodiments are possible within the scope of the invention . The scope of protection is in no means limited by the illustrated embodiments . Although the invention will now be described with reference to the drawing and the claims , other (partial ) aspects of the embodiments illustrated or explicitly or implicitly

disclosed herein could be the subj ect of divisional patent applications .

The invention will now be described with reference to the drawing showing embodiments of methods and fuel systems according to the invention, in which :

Figure 1 shows an embodiment of a fuel system

according to the invention

Figure 2 shows a further embodiment of a fuel system according to the invention .

A fuel system 1 comprises a schematically illustrated engine 21 having four cylinders . A schematically illustrated common rail 20 will allow direct inj ection of the fuel into the cylinders . Common rail 20 is a part of an inj ection device for direct inj ection .

Fuel is supplied via the high pressure fuel line 8. Fuel is supplied to the high pressure fuel line from the (first) liquid fuel supply unit 9 and/or from liquefied vapor fuel supply unit 10. Both are fuel supply units connected directly to a node 16 in the high pressure fuel line 8. The two supply units 9,10 are separated units . The supply units 9,10 are upstream connections to the node 16. A downstream side of the node 16 is connected to the common rail 20

In a prior art combustion engine the liquid fuel supply unit 9 is present . The liquid fuel supply unit 9 comprises a liquid fuel storage 2 having a inlet line 3 and a pump 4. Pump 4 can be located inside or outside the storage 2. A fuel line 5 connects the storage and fuel pump 4 with a high pressure pump 6 , here a controlled high pressure pump connected to controller 7. The controller can be an ECU . In the embodiment of the invention , as shown, high pressure pump 6 is a dedicated pump connected to the liquid fuel storage 2 only. The high pressure pump 6 will have non-return valve preventing fuel from the high pressure line 8 to flow back into the low pressure area 5.

The high pressure pump 6 allows increasing the

pressure in the fuel to pressures at least above 30 bars , preferably 100-200 bars . The high-pressurized fuel is provided to the high pressure fuel line 8 and supplied to the engine . The controlled high pressure pump 6 allows supplying the exact needed amount of fuel .

A kit can be provided to allow fitting a second fuel supply in the already present fuel system. The kit provides a second supply unit for supplying a different , liquefied vapor fuel to the high pressure line 8 at node 16. The second supply unit 10 supplies the second fuel in super critical state . The second supply unit 10 supplies the liquefied vapor fuel at at least 42 bars .

The kit can comprise a second fuel storage 11 , a fuel line 18 having a first fuel pump 12 , preferably located inside the storage 11 and optionally a second pump 14. Fuel line 18 connects the storage 11 with high pressure fuel line 8 at node 16. A non/return valve 15 is part of fuel line 18 and is provided close to node 16.

In an embodiment the kit provides a T-connector, including node 16 and high pressure line 8. The T-connector can replacing the existing high pressure line of the first supply unit 9.

The first fuel supply unit 9 and/or second fuel supply unit 10 supply fuel to the high pressure fuel line 8 and thereby to the common rail for direct inj ection . The node 16 connects to the two separate supply units . The node 16 is the most upstream node connecting the supply units for the two fuels . The node 16 is fed with the two fuels from two separated supplies 9,10.

Storage 11 can be a liquefied vapor fuel storage, preferably arranged for storing liquefied petroleum gas . A safety valve 13 can close the supply of fuel from storage 11.

Pump 12 is preferably a high pressure pump allowing to supply liquefied vapor fuels at at least 42 bars and/or in super critical state . In LPG storages 11 LPG is held at a pressure of about 8 - 12 bars .

Pump 12 , and in an embodiment in combination with auxiliary pump 14 , is arranged to supply the second fuel from storage 11 at a pressure of at least 30 , preferably at least 38 , and more preferably higher than the critical pressure of LPG, e.g. at least 42 bars in fuel line 18. The pump 12 (or in combination with pump 14 ) will provide a pressure increase of about 20 , preferably at least 34 bars . This will prevent evaporation of liquefied petroleum gas at all times .

The pumps 12 , 14 in the second fuel supply unit 10 are dedicated pumps , arranged to pump the second fuel only. Such pumps can be configured optimally for the properties of the second fuel . Mixing of fuels in the high pressure pump according to prior art arrangements is prevented .

Node 16 is shown schematically. In an embodiment a suitable connector connects fuel line 18 and fuel line 8. As the high pressure line 8 (and node 16 ) are connected to supply units 9,10 supplying fuels at pressures of at least 42 bars , such pressures can be maintained in the high pressure fuel line 8 and downstream common rail 20 ,

independent of the operation or switching off of the engine . As the liquefied vapour fuel enters the high pressure line 8 in super critical state, evaporation is prevented .

In some embodiments two fuels are supplied

simultaneously to node 16, allowing the mixing of fuels in the high pressure line 8. The mixing will lower the vapor pressure, further preventing evaporation .

In an embodiment a controller (not shown) is connected to the supply units 9,10. The controller can be arranged to control the respective supply of fuels . The controller can be arranged to allow switching between the supply of the respective fuels . In an embodiment the controller is

arranged to supply liquid fuel only when the engine 21 is started / ignited .

Figure 2 shows another embodiment . Similar parts are indicated with similar reference numerals .

LPG storage 11 comprises an opening 112. This can be a cylindrical opening or any other opening . Onto the opening a accessory plate 113 , shown schematically only, is gas- sealed . Reference is made to similar prior art arrangements .

The auxiliary pump 114 can be positioned in the storage 11. Figure 2 shows the auxiliary pump 114 positioned on the accessory plate 113. This allows the auxiliary pump 114 to be directly connected with the inside of the storage 11. If auxiliary pump 114 is equipped with a return line, the return line is directly connected with the storage 11.

Claims

1. Fuel system for a combustion engine with direct inj ection, comprising at least one high pressure fuel line having a node , the node ( 16 ) connecting at least :

• a downstream inj ection device of the combustion engine for the direct inj ection of fuel ,

• an upstream first supply unit for supplying a fuel to the node in the high pressure fuel line , the first supply comprising at least :

o a first fuel storage for a liquid fuel , such as gasoline, and

o a high-pressure fuel pump having an inlet connected to the first fuel storage and having an outlet connected to the high pressure fuel line ; and

• an upstream second supply unit for supplying a second different fuel to the node in the high pressure fuel line, the second high pressure line supply comprising at least :

o a second fuel storage for liquefied vapor fuel , such as liquefied petrol gas (LPG) , and o a liquefied vapor fuel pump .

2. Fuel system according to claim 1 , wherein the node in the high pressure fuel line is a most upstream node arranged to receive fuel from both supply units .

3. Fuel system according to claim 1 or 2 , wherein one of or both supply units comprise a one-way valve directly upstream from the node .

4. Fuel system according to any of the previous claims , wherein the high pressure pump in the first supply is exclusively arranged to supply liquid fuel .

5. Fuel system according to any of the previous claims , wherein the high pressure fuel line is arranged to operate at 42 bars or more and the supply units are arranged to supply the fuel at at least 42 bars , and/or wherein the second supply unit is arranged to supply the liquefied vapor fuel in super critical state to the node .

6. Fuel system according to claim 5 , wherein the fuel system is arranged to maintain a pressure of at least 42 bars in the high pressure fuel line .

7. Fuel system according to any of the previous claims , wherein the liquefied vapor fuel pump is arranged in the liquefied vapor fuel storage .

8. Fuel system according to any of the previous claims wherein liquefied vapor fuel storage comprises an accessory plate sealed onto an opening of the liquefied vapor fuel storage, wherein the second supply unit comprises one or more liquefied fuel pumps , wherein the most

downstream liquefied fuel pump is at most at the accessory plate .

9. Fuel system according to any of the previous claims , wherein the second supply unit comprises one or more pumps positioned inside the storage for liquefied vapour fuel only and arranged to supply the second fuel from the storage at a pressure above at least 42 bars .

10. Fuel system according to any of the previous claims , also comprising a controller arranged to control the first and second supply units .

11. Fuel system according to claim 10 , wherein the controller is arranged, when starting the combustion engine, to allow supply of fuel from the first supply unit only.

12. Fuel system according to claim 10 or 11 , wherein the controller is arranged to switch between respective fuel supplies for alternating fuel supply or wherein the controller is arranged to mix fuel from fuel supplies .

13. Fuel system according to any of the previous claims , wherein the high pressure pump in the first supply unit is free from a return line for returning fuel to the fuel storage .

14. Fuel system according to any of the previous claims , wherein the high pressure pump comprises a

controlled inlet valve for controlling an amount of fuel supplied to a pump chamber of the high pressure pump .

15. Fuel system according to any of the previous claims , wherein the fuel system is free of a return line for returning liquefied vapor fuel from the fuel system to the liquefied vapor fuel storage .

16. Fuel system for a combustion engine with direct inj ection, comprising :

- at least one high pressure fuel line connected to an inj ection device of the combustion engine for the direct inj ection of fuel ; and

a LPG supply unit (10) for supplying liquefied petrol gas (LPG) to the high pressure fuel line , the LPG supply unit comprising at least :

• a LPG fuel storage for liquefied petrol gas ;

· one or more LPG pumps , wherein one of the LPG pumps is positioned in the LPG fuel storage ; and

• a fuel line connecting the LPG fuel storage to the high pressure fuel line ,

wherein one of the most downstream LPG pump in the LPG supply unit is a high pressure pump arranged to supply the LPG in super critical state and/or at at least 42 bar pressure , and wherein the high pressure pump ( 12 , 14 ) in the LPG supply unit (10) is arranged as an LPG-only pump .

17. Fuel system according to claim 16 , wherein the LPG supply unit is arranged to operate at least 42 bar throughout the entire fuel line .

18. Fuel system according to claim 16 or 17 , wherein the LPG only high pressure pump is the LPG pump positioned in the LPG fuel storage .

19. Fuel system according to any of the previous claims , wherein the LPG fuel pump is arranged to operate at at least 42 bars .

20. Kit for fitting a bi - fuel system in a high pressure direct inj ection combustion engine having a high pressure fuel line , the kit comprising a second supply unit for supplying a second, liquefied vapor fuel to the high pressure fuel line , the second supply unit (10) arranged to supply the second liquefied vapor fuel in a super critical state .

21. Kit for fitting a bi - fuel system in a high pressure direct inj ection combustion engine having a high pressure fuel line , the kit comprising a second supply unit for supplying a second fuel to the high pressure fuel line, the second supply unit having

• a second fuel storage for a liquefied vapor fuel such as liquid petrol gas (LPG) ,

• a liquefied vapor fuel pump, and

· a connecting device for connecting the second fuel

supply to the high pressure fuel line,

wherein the kit further comprises a node to be positioned in the high pressure fuel line , the node to be connected with at least :

· a downstream inj ection device of the combustion engine for the direct inj ection of fuel ,

• an upstream first supply unit for supplying the

original fuel , and • the upstream second supply unit .

22. Kit according to claim 21 , wherein the connecting device comprises a high pressure fuel line and a non-return valve to be incorporated in that high pressure fuel line .

23. Kit according to claims 21 or 22 , wherein the kit comprises a controller arranged for controlling an amount of fuel supplied from the second fuel supply and for controlling an amount of fuel supplied from a first fuel supply formed by the first fuel storage and high pressure pump .

24. Kit according to any of the claims 20 - 23 , wherein the second supply unit further comprises a dedicated LPG high pressure pump for supplying the LPG to the high pressure line at at least 42 bars .

25. Method for inj ecting two fuels in a combustion engine , the method comprising :

- supplying pressurized fuels to a node in a high

pressure fuel line and

- inj ecting the pressurized fuel from the node in the high pressure fuel line into the combustion engine , wherein supplying the pressurized fuels to the node

comprises feeding two fuels to the node from two separated supplies , wherein a first , liquid fuel is supplied from a first fuel storage to the node over a high pressure pump and wherein a second, different , liquefied vapor fuel is supplied to the node from a second fuel storage .

26. Method according to claim 25 , wherein the second fuel is pressurized inside the second fuel storage .

27. Method according to claim 25 or 26, wherein the second fuel is supplied to the node at a pressure of at least 42 bars and/or in super critical state .

28. Method according to any of the claims 25 - 27 , wherein the node in the high pressure fuel line is a most upstream node receiving the two or more fuels .

29. Method according to any of the claims 25 - 28 , wherein the two fuels pass one-way valves directly upstream from the node .

30. Method according to any of the claims 25 -

29 , wherein the first fuel is supplied using a high pressure pump exclusively supplying the first fuel .

31. Method according to any of the claims 25 -

30 , wherein both fuels are supplied at at least 42 bars to the node in the high pressure fuel line .

32. Method according to any of the claims 25 -

31 , wherein supplying the second fuel comprises operating a liquefied vapor fuel pump in a liquefied vapor fuel storage and wherein the liquefied vapor pump delivers the second fuel at at least 42 bars .

33. Method according to any of the claims 25 - 32 , wherein the second fuel storage is a liquefied vapor fuel storage having an accessory plate sealed onto an opening of the liquefied vapor fuel storage, wherein supplying the second fuel comprises pumping using one or more liquefied fuel pumps , wherein the most downstream liquefied fuel pump is at most at the accessory plate .

34. Method according to any of the claims 25 -

33 , comprising controlling the supply of the first and second fuel , wherein starting the combustion engine

comprises supplying first fuel only.

35. Method according to any of the claims 25 - 34 , the method comprises switching between respective fuels for alternating fuel supply or comprises controlling the supply of fuels to mix fuel from fuel supplies .

36. Method according to any of the claims 25 - 35 , wherein the method is free from returning fuels to the respective fuel storages .