Arrangement and method for bi-fuel combustion engines
The invention relates to an arrangement for a combustion engine, such as a combustion engine with direct injection. The invention also relates a method for the alternate injection of two types of fuel in a combustion engine. The invention further concerns a controller for a bi-fuel combustion engine.
A bi-fuel system for direct injection is known from WO 09/110792 from the same applicant and incorporated by reference. The known bi-fuel system provides a system that can be circulated and provides a system that allows
expanding the liquefied vapor fuel in fuel lines during switching from liquefied vapor fuel to liquid fuel. A further example showing the use of a circulation pump when switching from LPG to liquid fuel is known from
Further a bi-fuel system is known from EP 2 143 916. Figure 5 discloses a system having a return line connected to a return line node in the liquid fuel line forming a sub-circuit. The sub-circuit comprises a
Although the known system and method operates satisfactory under normal operating conditions, it was found that in hot summer conditions igniting a warm engine could be troublesome.
It is therefore a goal to improve the prior art method and system, specifically preventing ignition problems during summer conditions.
According to a first aspect a bi-fuel arrangement for combustion engines is provided. Preferably a bi-fuel arrangement for direct injection of fuel in the combustion chamber is provided. The arrangement, installed in an motor
vehicle, can comprise at least one high-pressure fuel pump connectable to the internal combustion engine for the direct injection of fuel. The high-pressure fuel pump can be connected to the high-pressure rail of the motor block.
In an embodiment the arrangement comprises at least a first fuel storage for a liquefied vapor fuel, such as LPG, and a second fuel storage for liquid fuel such as gasoline or petrol, both fuel storages connected by fuel lines to an inlet of the high-pressure fuel pump for
supplying fuel to said high-pressure fuel pump. In an embodiment the respective fuel lines have a connecting node upstream from the high-pressure pump or the high-pressure pump has two inlets.
In this application fuel line refers to lines used for fuel for supplying fuel to high pressure pump and subsequently to the engine. The fuel lines are the lines used for supplying fuel in a normal operating mode of the system. E.g the liquid fuel line is the fuel line running from the petrol/gasoline storage to the high pressure pump.
At least a liquid fuel line has a non-return valve preventing fuel from re-entering fuel lines and the fuel storage and/or for defining a flow direction of the fuel in a downstream direction. Multiple non-return valve can be present in the fuel lines. The non-return valve is
positioned directly upstream from the connecting node, connecting the respective fuel lines.
In an embodiment the high-pressure fuel pump has a return line connected to at least one of the fuel supply lines and/or fuel storages. This allows supplying extra fuel to the high-pressure fuel pump, while the volume of fuel pressurized is controlled. The extra fuel is allowed to return. This could also have a cooling effect. Preferably liquefied vapor fuel is returned to the storage. Suitable
control valves can be part of the return line for opening or closing the return line.
In an embodiment a control valve connects the return line to the liquid fuel line at a return line node. The return line node is a position in the liquid fuel line. This return line node is positioned upstream from the non¬ return valve. This allows returning fuel in an upstream part of the liquid fuel lines and allows expanding the volume of fuel lines, as described in more detail in WO 09/110792. Further details are also disclosed in WO 11/059316. All embodiments, features and advantages of these prior art references are explicitly incorporated by reference. Further non-return valve can be positioned upstream from the node.
The control valve is closed in default operation. The control valve is arranged to be opened when the operator of the arrangement switches from liquefied vapor fuel supply to liquid fuel supply. As a result liquefied vapor fuel is allowed to expand in (part of) the liquid fuel lines.
The inventor discovered that in hot conditions, e.g. summer conditions in combination with a warm engine, engine ignition using liquid fuel is hindered as a result of high vapor pressure of liquefied vapor gas present in the return lines when the engine was running on liquefied vapor fuel before stopping the engine. The inventor solved this problem by supplying small amounts of pressurized liquid fuel in the LPG/liquid fuel mixture, present in the sub- circuit, using an auxiliary liquid fuel pump. The auxiliary liquid fuel pump allows the supply of liquid fuel in the fuel line sub-circuit formed by the return line connected to the liquid fuel line, both connected to the high-pressure pump. The auxiliary liquid fuel pump is positioned upstream from the return line node in order to allow liquid fuel from the storage to be supplied to the sub-circuit. Without the
auxiliary liquid fuel pump, the fuel line sub-circuit would run dry. A 'normal' or standard liquid fuel pump can supply liquid fuel up to pressures of about 5 bar. In the fuel line sub-circuit pressures can remain higher than 5 bar, as a result of liquefied vapor fuel vaporizing and expanding.
Prior art disclosures WO09/110792, WO2009/098728 and EP 2 143 916 disclose a sub-circuit having, what in this application is called, a circulation pump only.
In an embodiment the arrangement comprises a suitable control arranged to operate the liquid fuel pump and auxiliary pump simultaneously for a time period when switching from liquefied to liquid fuel.
In an embodiment the arrangement comprises a liquid fuel pump upstream from the auxiliary liquid fuel pump. This is the 'normal' liquid fuel pump, e.g. the liquid fuel pump for liquid fuel supply before the one-fuel system was fitted with a bi-fuel system, usually placed inside the liquid fuel container. This normal liquid fuel pump is able to provide a pressure head of about 5 bars. The auxiliary pump is placed serially and can therefore increase the pressure of the supplied fuel.
In an embodiment the auxiliary liquid fuel pump is a low volume, high-pressure gain pump. It was found that - in said conditions - only small amounts of liquid fuel are necessary to overcome the problem of the invention. This allows fitting a small pump with a low debit but with an pressure head of at least 5 to 7 bars, resulting in a total liquid fuel pressure, when the 'normal' and auxiliary liquid fuel pump are positioned in series, of 10-12 bars at the outlet of the auxiliary pump.
In an embodiment the liquid fuel line, and in particular the part of the liquid fuel line that is a part of the fuel line sub-circuit, has a fuel volume for
collecting an amount of fuel downstream from the return line node. When switching from LPG to liquid fuel and forming the fuel line sub-circuit, an amount of liquid fuel is already present in the fuel line sub-circuit. The expansion of the LPG and mixture with the liquid fuel lowers the vapor pressure in the fuel line sub-circuit preventing
evaporation. The fuel volume is positioned slightly
downstream or at the return line node in the liquid fuel line .
Preferably the fuel volume has a volume of at least 3x, more preferably at least 6x and even more
preferably at least 9x, a volume of the liquid fuel line downstream from the return line node. More liquid fuel present in the fuel line sub-circuit will lower the vapor pressure .
Although in some embodiments the high-pressure fuel pump can provide a driving force for fuel flowing in a fuel line sub-circuit formed by the liquid fuel line and return fuel line when connected after switching from LPG to liquid fuel, in an embodiment the sub-circuit comprises a circulation pump arranged to circulate fuel towards the high-pressure pump. This further increases the mixing of the fuels .
In an embodiment the non return valve and the return line node are received in a single housing unit connected by fuel lines to the first and second fuel storages and the high-pressure fuel pump. This reduces the complexity of fitting a bi-fuel system in a single fuel engine .
In an embodiment the circulation pump is received in the single housing. In an embodiment the single housing unit also comprises the fuel volume. In an embodiment the single housing unit also comprises the auxiliary liquid fuel
pump Again complexity is reduced. The housing only needs fuel connections.
The arrangement can comprise a controller arranged to, when switching from the first fuel to the second fuel, open the control valve, to activate the circulation pump and activate the auxiliary liquid fuel pump for at least one minute, in an embodiment for at least three minutes. This extended period allow mixing and prevents the evaporation of liquefied vapor fuel in the fuel system.
According to a further aspect a kit for fitting a bi-fuel system in a car is provided, preferably a car having a high pressure direct injection combustion engine.
According to an embodiment the kit comprises a fuel storage for a liquefied vapor fuel, fuel lines connectable to an inlet of the high-pressure fuel pump, a non-return valve to be incorporated in a fuel line from the fuel storage for liquid fuel, a return line connectable to the return of the high-pressure fuel pump and to the fuel storage for
liquefied vapor fuel, a control valve for connecting the return line with the liquid fuel line at a return line node upstream from the non-return valve, and comprising an auxiliary liquid fuel pump to be incorporated in the liquid fuel line upstream from the return line node. This kit allows to form a bi-fuel system in a single fuel engine and reducing the problem of switching from LPG to a liquid fuel in warm conditions.
The kit comprises a suitable controller arranged to operate the auxiliary liquid fuel pump when switching from liquefied to liquid fuel.
In an embodiment the auxiliary liquid fuel pump of the kit is a low volume, high-pressure gain pump. In an embodiment the kit comprises a fuel volume for collecting an amount of fuel to be fitted in the liquid fuel line
downstream from the return line node. The fuel volume has a volume of at least 3x, 6x or 9x, a volume of the liquid fuel line downstream from the return line node.
In an embodiment the kit further comprises a circulation pump to be fitted in the liquid fuel line downstream from the return valve node arranged to circulate fuel towards the high-pressure pump. The circulation pump allows and support fuel mixture in the fuel line sub-circuit during and after switching from LPG to liquid fuel.
Preferably the kit comprises a single housing or
FSU. The single housing is connected by fuel lines to the respective fuel storages and high-pressure fuel pump. This allows easy fitting of the kit in the one-fuel system. The return line node is part of the single housing unit. The control valve is received in the single housing. The non¬ return valve (s) is/are received or part of the single housing. The auxiliary pump is part of/received in the single housing. The circulation pump is preferably also received in the single housing as well as the fuel volume.
According to a further aspect of the invention a method for the alternate injection of two types of fuel in a combustion engine is provided. According to the method two fuel supplies are provided: a first liquefied vapor fuel storage and a second liquid fuel storage. The method allows switching between the two supplies. Fuel from either supply is directed into a high-pressure fuel pump. Fuel lines can connect the storage with the high-pressure pump. In the fuel lines the fuel will pass a non return valve. The high- pressure pump increases the pressure of the supplied fuel, and the pressure fuel is subsequently injected into a combustion engine.
In an embodiment switching from the liquefied vapor fuel to the liquid fuel comprises forming a fuel line
sub-circuit by returning fuel from the high-pressure fuel pump to a return fuel node upstream from the non-return valve in a liquid fuel line. Fuel can circulated in the liquid fuel line to the high-pressure and can partially return to return fuel node. This sub-circuit allows mixing of the liquid fuel and liquefied vapor fuel present in the high-pressure pump and return lines just before switching or present in the fuel lines because the engine was running on LPG and was stopped, while the engine is ignited using liquid fuel.
A further improvement of the bi-fuel method is obtained by providing auxiliary pumping of liquid fuel into the fuel line sub-circuit formed by the opened return line during switching. The auxiliary pump in series with the 'normal' pump can supply liquid fuel at relatively higher pressures such as more than 10 bar, or even more than 12 bars, to the fuel line sub-circuit, which will improve the mixture of the present LPG with the liquid fuel allowing to switch fuels also in warm conditions.
In an embodiment the method comprises circulating fuel in the fuel line sub-circuit. This improves mixing and prevents evaporation of the liquefied vapor fuel after switching, by further lowering the vapor pressure in the sub-circuit .
In an embodiment the fuel line sub-circuit is formed during at least one minute, in an embodiment at least three minutes, where after returning the fuel is interrupted closing the sub-circuit. This longer time period allows sufficient mixture. After this prolonged period all or close to all LPG present in the sub-circuit is used.
In an embodiment the method comprises accumulating liquid fuel in the fuel line sub-circuit. The fuel is accumulated prior to switching to the liquefied vapor
operation mode. This ensures the presence of an amount of liquid fuel in the fuel line sub-circuit when switching fuel/operation mode. The liquefied vapor fuel can mix with the excess amount of liquid fuel present in the fuel line sub-circuit.
In an embodiment the method comprises pumping the liquid fuel when operating in the liquid fuel mode and auxiliary pumping the liquid fuel when switching from liquefied vapor fuel to liquid fuel. The auxiliary pumping is switch on only for a limited period of e.g. 30 seconds - 10 minutes.
In an embodiment the auxiliary pumping comprises low volume high pressure pumping. The auxiliary pumping allows supply of liquid fuel to the fuel line sub-circuit with a pressure of at least 3 bars, 5 bars, preferably 7 bars. To lower the vapor pressure of the liquefied vapor fuel in the fuel line sub-circuit only a limited amount of xfresh' liquid fuel is needed, lowering the debit
requirements of the auxiliary pump.
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 subject of divisional patent applications .
The invention will now be described with reference to the drawing showing a single embodiment of method and device according to the invention, in which:
Figure 1 shows an embodiment of an bi-fuel arrangement according to the invention;
Figure 2 shows a graph showing the fuel pressure in the fuel line sub-circuit;
Figure 3 shows an embodiment of a controller.
Figure 1 shows schematically an embodiment of an arrangement according to the invention. The arrangement shown schematically represents the bi-fuel system in a vehicle. The vehicle could originally be have one-fuel system, such as a petrol/gasoline system. The original system comprises a gasoline storage 1 having an internal gasoline pump 2 that allows the supply of the liquid fuel to gasoline fuel line 3. Originally the gasoline fuel line 3 is connected to the vehicle's high-pressure fuel pump 4. The high-pressure fuel pump 4 has an entry side 5. The high pressure exit 6 is connected to a high-pressure rail 7in turn connected to direct injectors and cylinders of the engine 8.
The other part of the bi-fuel arrangement 10 according to figure 1 can be parts of kit of part for fitting a bi-fuel system in a single fuel engine.
The kit of parts can comprise: a liquefied vapor fuel storage 11 having a liquefied vapor fuel pump 12. A liquefied vapor fuel line 13 having a control valve 14 and a non-return valve 15. Further a fuel return line 16 can comprise a liquefied vapor fuel return line 17 having a control valve 18. The fuel return line 16 can have a further control valve 19 arranged to open and close a connection with a return line node 20. The fuel return line 16 has a node allowing both connections.
In this embodiment the return line node 20 is located at the position of a fuel volume 21. Both the fuel volume 21 and the return line node 20 are part of the liquid fuel line. In normal operation, during liquid fuel supply to the engine, liquid fuel will pass both the return line node
21 and the fuel volume 21. In another embodiment the fuel volume 21 can be positioned downstream from return line node 20 (closer to pump 25) or the fuel volume 21 can be
positioned in the return line 16, closer to valve 19.
In an embodiment the fuel volume 21 is positioned in the fuel line parallel with a control valve: if the control valve is opened, fuel is supplied through the control valve, bypassing the fuel volume, to be supplied to pump 25 and high pressure pump 4. Bypassing the fuel volume lowers the resistance. The control valve can be closed to allow supply of liquid fuel to the fuel volume.
In this embodiment, the fuel volume 21 connects a part of liquid fuel line 3 located upstream from the node 20 and a further part of the liquid fuel line 22 connected with connecting node 23 with the liquefied vapor fuel line 13.
Connecting node 23 is connected by fuel line 24 with the entry 5. The liquid fuel line 22 downstream from liquid fuel volume 21 comprises a circulation pump 25 and a non return-valve 26. Further the upstream part 3 comprises an auxiliary liquid fuel pump 27 in parallel with a nonreturn valve 28.
A further non-return valve 40 is positioned directly upstream from the return line node 20 in the liquid fuel line. This non-return valve 40 is arranged to prevent entry of fuel, specifically liquefied fuel in all liquid fuel lines parts upstream from the return line node 20, specifically in the auxiliary liquid fuel pump 27 and/or the storage 1.
Many of the parts of the kit (including the control valves 15, 26,28,40; the pumps 25,27; control valves 14,18,19) can be part of a pre-assembled single housing 30. Single housing 30 can be connected by fuel lines with the respective storages 1,11 and the high-pressure pump 4.
All control valve 14,18,19 can be controlled by a central controller (not shown in the figures) . Electronic connections could connect the respective parts, including the pump 27,25 with the controller. The controller can be connected to a operator controlled switch for switching between fuels. The controller can also have switches for automatically switching fuels, such as during ignition or when one of the fuel storages 1,11 runs empty.
In normal operation the controller arranged the control valve to run in either a liquid fuel operation mode or a liquefied vapor operation mode.
In the liquid fuel operation mode pump 2 supplies fuel to fuel volume 21, passing non-return valve 28 and by¬ passing auxiliary pump 27. Control valve 19 is closed. In turn fuel is supplied to the circulation pump 25, in some embodiments by-passing the circulation pump 25 (similar to the auxiliary pump bypass) to reach non-return valve 26 and node 23. In liquid fuel operation mode, pump 12 is switched off and control valve 14 is closed. Fuel is only supplied to node 23 from liquid fuel line 22. Only gasoline reaches high-pressure pump 4 and is pressurized when it enters high pressure rail 7. Control valve 18 is closed. The amount of fuel provide at entry 5 is generally equal to the amount of fuel supplied to the high-pressure rail 7.
In liquefied vapor operation mode, control valve
14 and 18 are opened, while control valve 19 is closed. Node 41 in the return line 16 connects the return line to either the storage 11 or to the return line node 20. Pump 12 supplies liquefied vapor fuel to node 23 and high-pressure pump 4 passing non-return valve 15. An excess of liquefied fuel can be supplied to the high-pressure pump, wherein a part of the supplied fuel is returned via return line 16 and opened valve 18 to the liquefied vapor fuel storage.
When switching from liquefied vapor fuel to liquid fuel the controller initiated a method for controlling the valves and pumps as illustrated in Figure 3. A high signal shows 'open' or 'on' , while a low signal indicates 'closed' or Off .
At T = 0 pump 12 is on, control valve 14 and 18 are opened, while the other pump and control valves are off/closed. At T = tl, a fuel switch is initiated. The pump 2 is switch on, while pump 12 is stopped. Control valves 14 and 18 are closed, while control valve 19 is opened. Opening valve 19 results in expansion of the present liquefied vapor in the fuel lines to expand into the fuel lines downstream from non-return valve 28. This lowers the vapor pressure of the liquefied vapor gas, preventing evaporation.
By opening control valve 19 a fuel line sub- circuit is formed: fuel volume 21, circulation pump 25, fuel line 22, one-way valve 26, node 23, high-pressure pump 3, return line 16 and control valve 19 are all interconnected. One way valve 26 fixes the flow direction of the sub-circuit indicated by arrow 31.
The liquefied vapor gas is present in the fuel lines at a relative high pressure B, e.g. between 5-20 bar as illustrated in figure 2. At T=tl control valve 19 is opened and immediately the pressure drops.
Pump 2 is capable of pressurizing the liquid fuel to about 3-5 bars. Although the pressure drops by opening the control valve 19, the resulting pressure is still not below 5 bars in extreme hot conditions and fuel cannot be supplied to the sub-circuit by pump 2 alone.
Auxiliary liquid fuel pump 27, having a small debit and a relatively high pressure rise, is cable of inserting small amounts of fuel into the sub-circuit.
A relatively large volume of fuel is present in the fuel volume 21 in the sub-circuit when switching from liquefied vapor to liquid fuel mode. The liquefied vapor can mix with this liquid. The mixing of the fuels when switching from liquefied fuel supply to liquid fuel supply will take advantage of the Raoult effect, lowering the vapor pressure of the resultant fuel mix, preventing evaporation.
Circulation pump 25 can circulate the fuel mixture in the circuit according to arrow 31, while fresh liquid fuel is supplied by pump 4 to the high-pressure rail 7.
If the conditions in which the bi-fuel arrangement operates are very warm, the inventor discovered that even a large volume of fuel present in the fuel volume 21 would have to be consumed in the engine before the pressure drops to a pressure level that can be achieved with guarantees by the 'normal' gasoline pump 2. Dotted line 40 in Figure 2 shows the pressure in the sub-circuit as a function of time. At t3 the pressure is still more than 5 bars and the normal pump 2 would still not be able to supply fuel to the sub- circuit as a result of a too high pressure difference.
Accordingly the kit of parts and bi-fuel system according to the invention comprises an auxiliary pump 27 to be received in the fuel system upstream from the fuel line sub-circuit formed by opening control valve 19. The
auxiliary pump 27 is able to supply, even though only a limited amount, fresh and cool liquid fuel to the sub- circuit, in turn lowering the prevailing pressure according to solid line 41 in figure 2, such that after t3 pump 2 is capable of providing fresh fuel to the sub circuit and in time to the fuel lines with control valve 19 closed.
Quite surprisingly feeding additional fuel to the sub-circuit will result in quicker lowering of the pressure difference to be overcome by the 'normal' fuel pump 2.
Further the additional supply will lower the vapor pressure of the circulated fuel as a result of the Raoult effect .
After the pressure drops in the fuel line sub- circuit, the auxiliary pump can be stopped. This can be immediately but sometime only after several minutes .
Circulating can be stopped and the control valve 19 can be closed after suitable mixing of the liquefied vapor fuel present in the fuel lines with the liquid fuel. This can be after several minutes, At. This can be later than the stopping of auxiliary pump 27 as indicated in
After At the arrangement is operating in a normal liquid fuel mode.
After switching from liquid fuel to liquefied vapor fuel at t2, the method can open valves 14 and 18 and switch on pump 12. Prior to opening valves 14 + 18 pump 25 and valve 19 can be switched on for several seconds in order to ensure that the fuel volume 21 is filled with liquid fuel in order to ensure suitable mixing and expansion of the liquefied vapor gas if switch to liquid fuel again. In another embodiment liquid fuel is supplied to the fuel volume for several seconds after switching to liquefied vapor fuel.
The volume of the fuel volume 21 can be 5x more than the volume of fuel lines in the fuel line sub-circuit. This ensures that an access of liquid fuel is present when switching to the liquid fuel operating mode.