Method of switching from a liquefied gas fuel to a liquid fuel being provided to a direct injection combustion engine, and direct injection bi-fuel system for such an engine.

[0001] The present invention relates to a dual-fuel direct injection system for an internal combustion engine that is configured for separate fuel supply from two sources. In particular, the system is a dual-fuel direct injection system configured to separately supply two types of fuel, which are liquid fuel and liquefied gas fuel, as required, to an internal combustion engine.

[0002] Direct injection systems are configured to inject fuel directly into an internal combustion engine cylinder instead of pre-mixing the fuel with air in separate inlets. This configuration allows more accurate control of combustion and emissions, but requires more advanced engine management technologies. The higher torque provided by modern gasoline direct injection engines is a result of the synergy effect of direct injection, filling and variable valve timing. Combined, these aspects of direct injection technology provide greater flexibility in engine tuning. The result is a tendency to better charge the cylinders with a reduced knocking tendency.

[0003] In the automotive industry, gasoline direct injection technology has already been introduced for several engine types. This means that ordinary existing liquefied petroleum gas (LPG) technology must be changed or improved or completely redesigned to be used together with existing direct gasoline injection technology.

[0004] There are at least two options for using LPG for direct injection engines. First, providing the LPG pre-chamber by injection through the opening and second, providing direct LPG injection into the combustion chamber, see EP 2 143 916 A1. The LPG pre-chamber system mainly relies on existing master-slave sequential injection, which is also used in pre-chamber engines. The LPG direct injection system is a new system that is still being developed. When injection technologies are used

Direct from LPG, environmental benefits can be obtained by reducing carbon dioxide and particle emissions into the atmosphere.

In normal operation, the direct injection internal combustion engine uses a high pressure fuel pump, high pressure fuel rail and direct injectors for direct fuel injection into the combustion chamber. To reduce costs and overall system complexity, it is desirable to use high-pressure components for both types of fuel. To enable this, the system should be able to replace the first type of fuel with the second type of fuel and vice versa.

[0005] There are physical challenges that may arise when switching between two types of fuel. First, when replacing one fuel with another fuel, unwanted mixing may occur during engine operation. Secondly, when the system uses liquefied gas as one type of fuel and liquid fuel as the second type of fuel, depending on the gas composition and temperature, it is possible that the pressure in the liquefied gas system is higher than the pressure in the liquid fuel system.

[0006] An aspect of the present invention is to provide a dual-fuel direct injection system that can supply a liquid type of fuel and liquefied gas as a type of fuel as required to an internal combustion engine.

[0007] According to an embodiment of the present invention, a dual fuel direct injection system is provided that includes a liquid fuel subsystem and a liquefied gas fuel subsystem. The liquid fuel subsystem includes a liquid fuel tank configured to supply liquid fuel and a liquid fuel pump configured to pump liquid fuel from the liquid fuel tank. The liquefied gas fuel subsystem comprises a liquefied gas fuel tank configured to supply liquefied gas fuel and a liquefied gas fuel pump configured to pump liquefied gas fuel from a liquefied gas fuel tank. The dual-fuel direct injection system includes a connector configured to receive liquid fuel from the liquid fuel subsystem when the system is operating in liquid fuel use mode and to receive liquefied gas fuel from a liquefied gas fuel tank when the system is operating in a liquefied gas fuel mode,

The high pressure pump configured to receive fuel flowing through the connector and to pump fuel into the high pressure fuel tank of a direct injection internal combustion engine and may include means for increasing the pressure of liquid fuel configured to flush the liquefied gas fuel from the fuel supply to the high pressure pump in response for switching the system from the use mode of liquefied gas fuel to the mode of use of fuel liquid. The means for increasing the pressure may be in the form of a cleaning unit comprising a piston and configured to receive liquefied gas fuel on one side of the piston and liquid fuel on the other side of the piston. The pressure boosting means may alternatively be in the form of a pressure boosting pump configured to receive fuel from the liquid fuel pump and increase the pressure of the liquid fuel supplied to the connector to purge the fuel liquefied gas from the fuel supply to the high pressure pump in response to switching from the liquefied gas fuel for liquid fuel.

[0008] An aspect of the present invention is to provide a method for switching between a liquefied gas fuel such as liquefied gas and a liquid fuel such as gasoline or diesel in a direct injection internal combustion engine. According to an embodiment of the present invention, a method of switching is provided from supplying liquefied petrol fuel to a direct injection engine during a liquefied petrol fuel utilization mode to liquid fuel delivery to an engine during a liquid fuel utilization mode, the method comprising the steps of:

a) pumping liquefied gas fuel by means of a liquefied gas fuel pump to a high-pressure pump which is configured to pump liquefied gas fuel to a high-pressure direct injection engine rail in a liquefied gas fuel mode;

b) switching from the mode of using liquefied gas fuel to the mode of using liquid fuel;

c) pumping liquid fuel at a pressure at least equal to the vapor pressure of the liquefied gas fuel to a high-pressure pump by means of at least a first high-pressure pump, the fuel of the liquefied gas being flushed through the fuel return line between

EP 2 724 007 B1 high pressure pump and fuel tank;

d) stop pumping liquefied gas fuel to the high pressure pump;

e) stopping the purge of the liquefied gas fuel by closing the return valve in the fuel return line;

f) after the predetermined delay after step e) and in the liquid fuel mode, opening the return valve for a predetermined time to flush the liquid fuel containing any residual liquefied gas fuel through the fuel return line; and

g) reducing the pressure of the liquid fuel pumped to the high-pressure pump to a pressure lower than the vapor pressure of the liquefied gas fuel.

An advantage of the method of the present invention is that due to the temporary opening of the return valve again after stopping the pumping of the liquefied gas fuel and after closing the return valve, the liquid fuel containing the residual liquefied fuel fuel that could be present is washed out, i.e. removed from the fuel supply of the high-pressure pump, including the low-pressure area of ​​the high-pressure pump, through the fuel return line between the high-pressure pump and the fuel tank in a very efficient manner. If this method step were not implemented, there would still be some risk in practice of a gas stopper due to the residual vaporized gaseous fuel present in the system after flushing the liquefied gas fuel from the system. As a result, the reliability of the engine in which the method according to the invention is carried out is significantly increased, since the engine is prevented from stalling due to the gas plug, or the possibility of a gas plug occurring is at least significantly reduced.

[0010] When referring to the vapor pressure of the liquefied gas fuel in the context of the present invention, this should be understood as (local) vapor pressure of the liquefied gas fuel at the location of the high pressure pump. Due to the relatively high temperature at said location, it is important to keep the liquefied gas fuel in this particular place.

Preferably, step c) is carried out by supplying liquid fuel with

The first liquid fuel pump for pressure boosting means, by increasing the liquid fuel pressure by the first liquid fuel pump for pressure boosting means, to a pressure at least equal to the vapor pressure of the liquefied gas fuel and by supplying liquid fuel under elevated pressure to a high-pressure pump by means of pressure boosting. The means for increasing the pressure preferably consist of a pump for increasing the pressure of the liquid fuel.

[0012] Step f) may be carried out in an embodiment by deactivating the means for increasing the pressure to at least a degree sufficient to pump liquid fuel under reduced pressure to the high pressure pump.

Preferably, step g) is carried out simultaneously with the closing of the return valve at the end of step f). In an embodiment, step e) may be performed 1 to 30 seconds, preferably about 5 to 10 seconds, after step d). Preferably, the predetermined delay in step f) is in the range of 1 to 180 seconds. Preferably, the predefined delay in step f) is determined depending on the fuel consumption of the engine. The pre-set time of step f) can be in the range of 1 to 10 seconds. Preferably, the fuel return line is between the high pressure pump and the fuel tank for the liquefied gas fuel.

[0014] The invention further relates to a dual-fuel direct injection system that includes a liquid fuel subsystem and a liquefied gas fuel subsystem, the system being adapted to switch over from supplying liquefied gas fuel to a direct injection engine in a liquefied gas fuel supply mode for delivery liquid fuel for the engine in a mode of using liquid fuel, according to a method according to one of the preceding claims.

[0015] These and other aspects, properties and advantages of the invention will become clear from the following detailed description, the attached drawings and the appended claims.

[0016] Embodiments of the invention will now be described by way of example only, with reference to the accompanying schematic drawings, in which the corresponding references indicate the relevant parts, and in which:

EP 2 724 007 B1

Figure 1 shows an embodiment of a dual-fuel direct injection system for an internal combustion engine;

Figure 2 shows the dual-fuel direct injection system of Figure 1 in a mode of using liquid fuel;

Figure 3 shows the dual-fuel direct injection system of Figure 1 in a mode of using liquefied gas fuel;

Figure 4 shows another embodiment of a dual-fuel direct injection system for an internal combustion engine;

Figure 5 shows the dual-fuel direct injection system of Figure 4 in a mode of using liquid fuel;

Figure 6 shows the dual-fuel direct injection system of Figure 4 in a mode of using liquefied gas fuel; and

Figure 7 shows the dual fuel direct injection system of Figure 4 when the system is switched from the liquefied gas fuel mode of Figure 6 and the liquid fuel mode of Figure 5.

[0017] Figure 1 shows a dual fuel direct injection system 100 for an internal combustion engine according to an embodiment of the present invention. As described in more detail below, the system 100 is configured to switch between two types of fuel supplied to the engine. One fuel is liquid fuel, such as gasoline and diesel, and the other fuel is liquefied gas fuel, such as liquefied petroleum gas (LPG), which may contain propane or butane, or a mixture thereof.

[0018] As shown in Figure 1, the dual fuel direct injection system 100 includes the liquefied gas fuel subsystem 110 and the liquid fuel subsystem 150, as well as pressure components that are positioned between subsystems 110, 150 and the internal combustion engine as described in more detail below.

[0019] The liquefied gas fuel subsystem 110 includes a fuel tank 112 configured to hold a supply of liquefied gas or fuel vapors, such as LPG. In an embodiment, the fuel pressure of the liquefied gas in the fuel tank 112 may be about 2-16 bar. Fuel pump 114 is

EP 2 724 007 B1 mounted in the fuel tank 112. Fuel pump 114 may be any type of fuel pump that can be configured to remove liquefied gas from tank 112 by means of suction and can pump liquefied gas under elevated pressure, which is at least a pressure above the vapor pressure of the liquefied gas fuel, through a fuel supply line 117, through the safety shut-off valve 118, through the pressure-reducing check valve 120, through the shut-off valve 122, via connector 124 and to high pressure fuel pump 126. In another embodiment, fuel pump 114 may be mounted outside fuel tank 112.

[0020] The pressure limiting check valve 120 shown in Figure 1 includes a check valve 120a and a pressure limiting valve 120b. The check valve 120a and the pressure limiting valve 120b may be part of one integrated valve that performs the functions of a non-return valve and a pressure limiting valve and in this connection may be called a pressure limiting check valve 120. The check valve 120a is configured to prevent liquid fuel from entering the liquefied gas fuel subsystem 110, and the pressure relief valve 120b is configured to limit the differential pressure of the system between shutoff valve 122 and check valve 120a.

[0021] The shut-off valve 122 is configured to prevent liquefied gas fuel from entering the liquid fuel system 150 that could cause undesired mixing and fuel consumption. Connector 124 connects the liquefied gas fuel subsystem 110 and the liquid fuel subsystem 150, so that the liquefied gas fuel and liquid fuel can be supplied individually to the high pressure fuel pump 126. Between connector 124 and high pressure fuel pump 126 there is a pressure (temperature and) pressure sensor 128 that is configured to measure (temperature and) the fuel pressure supplied to high pressure fuel pump 126. In an embodiment, the second pressure (temperature and) sensor (not shown) may be provided on fuel tank 112 and be configured to measure fuel pressure (and temperature) in fuel tank 112.

[0022] The high pressure fuel pump 126 is connected to the high pressure fuel line 127 and is configured to pump fuel if the fuel is

The liquid fuel, or liquefied gas fuel, at elevated pressure, for the high pressure fuel container and fuel injectors, together designated 180 in Figure 1, of a direct injection internal combustion engine. The fuel pressure in the high-pressure tank may be in the range of 20 bar to about 200 bar or higher. Although Figure 1 schematically shows the configuration of a four-cylinder engine, the engine may include additional cylinders and / or high-pressure pumps. The illustrated embodiment should not be limiting in any way.

[0023] The liquefied gas fuel return subsystem 190 is connected to the high-pressure fuel reservoir and the high-pressure fuel pump 126 and is configured to provide a return path for the liquefied gas fuel to the fuel tank 112 when decompression in a high pressure fuel tank 180 or high pressure pump is required fuel 126 and / or if vapor bubbles must be removed from the fuel gas supply. The liquefied gas fuel return subsystem 190 includes a check valve 130 that is configured to prevent liquefied gas fuel from entering the high pressure fuel pump 126 through the fuel return line 129 and the return valve, in the present embodiment in the form of a shut-off valve 132 that is configured to prevent liquid fuel entering the liquefied gas 110 fuel subsystem when the liquid fuel is supplied to the internal combustion engine, which could cause undesirable mixing and fuel consumption. The pressure relief valve 134 is configured to limit differential pressure between the shut-off valve 132 and the check valve 130.

[0024] The liquefied gas fuel, which is returned from high pressure system components, such as high pressure fuel pump 126 and high pressure fuel tank, flows through the fuel return line 129, through the restriction 136, through the check valve to the fuel tank 112, as shown in Figure 1. The liquefied gas fuel pressure that is returned to the fuel tank is typically between the liquefied gas fuel pressure in the fuel tank 112 and the liquefied gas fuel pressure that is supplied from the high pressure fuel pump 126 to the high pressure fuel rail 180.

EP 2 724 007 B1

Check valve 138 is provided at the fuel tank 112 and is configured to prevent fuel leaks in the event of damage to the liquefied gas fuel subsystem 110. Restriction 136, which may be a fixed limitation or a variable limitation, is configured to control elevated system pressure by flowing through the fuel pump 114 The pressure increase relative to fuel tank 112 may be in the range between about 2 bars and about 10 bars.

[0025] The liquid fuel subsystem 150 comprises a fuel tank 152 configured to hold a supply of liquid fuel, such as gasoline or diesel. The fuel pump 154 ​​is mounted in the fuel tank 152 and is configured to remove liquid fuel from the fuel tank 152 by sucking and pumping liquid fuel through the shut-off valve 156. Any suitable pump, mounted inside or outside the fuel tank 152, can be used to pump liquid fuel from the fuel tank 152 through the shut-off valve 156. The shut-off valve 156 is configured to prevent liquid fuel from entering the connector 124 when the liquefied gas fuel is supplied to connector 124 through the liquefied gas fuel subsystem 110, as described above, and causing undesirable mixing and fuel consumption.

[0026] Means for increasing the pressure of the liquid fuel, preferably consisting of an additional fuel pump 158, or in other words pumps for increasing the pressure 158, can be used to increase the pressure of the liquid fuel before the liquid fuel enters the joint 124. It may be particularly advantageous, when the fuel consumption mode is switched from the liquefied gas fuel utilization mode to the liquid fuel utilization mode, as discussed in great detail below. The pressure increase provided by the additional fuel pump 158 relative to the base fuel pressure of the liquid liquid fuel supply may be in the range between about 2 bar and about 10 bar (or higher) or at least to a pressure above the vapor pressure of the liquefied gas fuel. The check valve 160 is configured to prevent liquefied petrol fuel from entering the liquid fuel subsystem 150 and causing unwanted mixing and fuel consumption.

[0027] As shown in Figure 1, the controller 170 is in communication with the liquefied gas fuel fuel pump 114, shut-off valves 118, 122, sensor

Pressure (temperature and) pressure 128 (and any pressure sensor (temperature and) provided on the fuel tank 112), shut-off valves 132, 156 and additional fuel pump 158 and is configured to control whether valves 118, 122, 132, 156 are in an open or closed configuration, and whether pumps 114, 158 are on or off. Controller 170 receives data from the pressure (temperature and) sensor 128 (and optional temperature / pressure sensor provided on the fuel tank 112) and uses the data to control the operation of the system by manipulating the various valves and pumps with which the controller 170 communicates. Fuel pump 154 ​​and high pressure fuel pump 126 may also be in communication with controller 170. The illustrated embodiment should not be limiting in any way. Switch 196 is also in communication with the controller 170 and is located in the vehicle cabin, so that the vehicle operator can use switch 196 to switch between the fuel utilization modes of the system 100, as discussed in more detail below. Alternatively or in combination with said switch 196, controller 170 may include a switch algorithm so as to autonomously switch between fuel use modes, i.e. based on e.g. measured values, such as fuel level in fuel tanks.

[0028] Figure 2 shows the situation when the internal combustion engine is operating on liquid fuel and the dual fuel direct injection system 100 is operating in a liquid fuel utilization mode. As shown in Figure 2, the fuel pump 154 ​​is turned on, so that liquid fuel can be pumped from the fuel tank 152. Shut-off valves 118, 122 and 132 are in a closed configuration, and the fuel pump 114 is turned off, as indicated by large "X" above these components of the 100 system. Check valve 160 is active to prevent any return flow from connector 124 back to the liquid fuel subsystem 150. Any retained liquefied gas or liquid fuel between shut-off valve 122 and check valve 120a will be released by pressure limiting valve 120b. Any retained liquefied gas or liquid fuel between the shut-off valve 132 and the check valve 130 will be released by the pressure relief valve 134.

[0029] Figure 3 shows the situation when the internal combustion engine operates on a liquefied gas fuel and the dual fuel direct injection system 100 operates in

In the mode of using liquefied gas fuel. As shown in Figure 3, the fuel pump 114 is turned on, such that the liquefied gas fuel can be pumped from the fuel tank 112. The shut-off valve 156 is in a closed configuration and the additional fuel pump 158 is turned off, as indicated by the large "X" above these elements system 100 components. Check valves 120, 130 and 138 are active. The controller 170 is configured to change the operating parameters of the system 100 based on such use of liquefied petroleum fuel so that approximately 10-35% more fuel is injected by the injectors into the internal combustion engine. This increase in volume leads to stable and efficient behavior of the internal combustion engine. Because the shut-off valve 132 is open in the mode of using liquefied gas fuel, the liquefied gas fuel circulates in the system.

[0030] When the internal combustion engine operates on liquid fuel and the dual-fuel direct injection system 100 operates in the liquid fuel mode of use shown in Figure 2, the vehicle operator may switch to the mode of use of the liquefied gas fuel shown in Figure 3. To this end, the vehicle operator may use a switch 196, which is located inside the vehicle cabin so that the signal is transmitted to the controller 170. The controller 170 will coordinate the switching procedure.

[0031] In particular, after using the fuel select switch 196 to select the mode of use of the liquefied gas fuel, the fuel pump 114 will be turned on and shutoff valves 118, 122 and 132 will open. In some situations, it may be necessary to activate the additional fuel pump 158 to reduce the pressure difference over the shut-off valve 122. After the delay, the shut-off valve 156 closes and the additional fuel pump 158 turns on. The flushing operation may consequently lead to the fact that a certain amount of liquid fuel will end up in fuel tank 112, which has been found to be acceptable. At this time, the fuel in high pressure line 127 and high pressure fuel rail 180 still consists of liquid fuel. The controller 170 is programmed to determine the decay factor for the value at which the controller 170 parameters are changed and the resulting control of the various system components that are in communication with the controller. The decay factor is a function of fuel consumption and physical system parameters. Upon completion of the decay, the fuel system 100 completes switching to fuel

Liquefied gas.

[0032] When the internal combustion engine operates on the liquefied gas fuel and the dual fuel direct injection system 100 operates in the liquefied gas fuel mode of use shown in Figure 3, the vehicle driver may switch to the liquid fuel mode of use shown in Figure 2. For this purpose the vehicle driver can use switch 196, which is located inside the vehicle cabin. Controller 170 will coordinate the switching procedure.

[0033] In particular, after using the fuel selection switch 196, the additional fuel pump 158 will turn on, the shut-off valve 156 will open, the shut-off valves 118, 122 will close (after a certain programmed delay) and the fuel pump 114 will turn off. Additional fuel pump 158 is used to increase the pressure of the liquid fuel approximately to the pressure of the liquefied gas fuel that was supplied to the high pressure pump 126, so that the liquefied gas fuel can be purged from the system 100 through the liquefied gas fuel return subsystem 190. After a delay, shut off valve 132 will close. The delay depends on the physical parameters of the system. After the second delay, the auxiliary fuel pump 158 will turn off. The second delay is a function of fuel consumption and physical system parameters. The fuel in the high-pressure fuel line 127 and in the high-pressure rail still consists of liquefied gas fuel. The controller 170 is programmed to determine the decay factor for the value at which the controller 170 parameters are changed and the resulting control of the various system components that are in communication with the controller. The decay factor is a function of fuel consumption and physical system parameters. Upon completion of the decay, the fuel system 100 will complete switching to liquid fuel use mode.

[0034] In practice, it seems that some residual fuel is still present in the system, i.e. in the high pressure pump fuel supply line, and the low pressure area of ​​the high pressure pump downstream of the shut-off valve 132 is closed as described above. After a predetermined delay, preferably in the range of about 10 to 180 seconds from the above closing step of the shut-off valve 132, and while the additional fuel pump 158 is still on, the shut-off valve is reopened for a predetermined time to flush out liquid fuel containing any residual liquefied fuel gas from fuel supply, to

EP 2 724 007 B1 high pressure pump through a fuel return line. This turns out to be an effective way to remove residual liquefied petroleum gas from the system in liquid fuel utilization mode. As a result, some fuel reaches the fuel tank 112, which has been found to be acceptable. The result of this method step is that any residual gaseous fuel is removed from the system in a very efficient manner and thus the chance of a gas plug arising during engine shutdown is significantly reduced.

At the same time or shortly after closing the shut-off valve 132 (return valve) again, the auxiliary fuel pump 158 is turned off as described above.

[0035] Since the high pressure fuel pump 126 and the high pressure fuel rail are used for liquid fuel as well as for liquefied gas fuel, the internal combustion engine will start on the last fuel used. In a hot engine, the conditions to run on liquefied petrol fuel may cause gas plug problems in some applications. In these applications, switching can occur when starting the engine.

Figure 4 shows a dual fuel direct injection system 200 for an internal combustion engine according to an embodiment of the invention. Similar to the dual-fuel direct injection system 100 described above, the dual-fuel direct injection system 200 of Figure 4 is configured to switch between two types of fuel supplied to the internal combustion engine. One fuel is liquid fuel, such as gasoline or diesel, and the other fuel is liquefied gas fuel, such as liquefied gas (LPG), which may contain propane or butane, or a mixture thereof.

[0036] As shown in Figure 4, the dual fuel direct injection system 200 includes the liquefied gas fuel subsystem 210 and the liquid fuel subsystem 250 as well as high pressure components that are located between subsystems 210, 250 and the internal combustion engine as described in more detail below . One of the differences between the dual-fuel direct injection system 200 described below and the dual-fuel direct injection system 100 described above is the presence of liquid fuel support means consisting of a cleaning unit 258 in place of additional fuel pump 158. As discussed in more detail below, the cleaning unit 258 is

EP 2 724 007 B1 placed in parallel with the liquefied gas fuel subsystem 210 and the liquid fuel subsystem 250 and is configured to replace the liquefied gas fuel in the fuel system 200 with liquid fuel by means of a cleaning operation.

[0037] As shown in Figure 4, the liquefied gas fuel subsystem 210 comprises a fuel tank 212 for holding a liquefied gas vapor fuel supply, such as LPG. In an embodiment, the fuel pressure of the liquefied gas in the fuel tank 212 may be about 2-16 bar. Fuel pump 214 is mounted in fuel tank 212. The fuel pump 214 can be any suitable type of fuel pump that can be configured to remove liquefied gas fuel from fuel tank 212 by suction and pumping liquefied gas fuel under elevated pressure, through the fuel supply line 217, through the safety shutoff valve 218, through the restrictor pressure check valve 220, through the shut-off valve 222, through the connection 224 and to the high-pressure pump 226.

[0038] A pressure limiting check valve 220 is shown in Figure 4 as comprising a check valve 220a and a pressure limiting valve 220b. The check valve 220a and the pressure limiting valve 220b may be part of one integrated valve that performs the functions of a non-return valve and a pressure limiting valve and therefore together may be called a pressure limiting check valve 220. The check valve 220a is configured to prevent liquid fuel from entering the liquefied gas fuel subsystem 210, and the pressure limiting valve 220b is configured to limit the differential pressure of the system between shutoff valve 222 and check valve 220a.

[0039] The shut-off valve 222 is configured to prevent liquefied gas fuel from entering the liquid fuel system 250, which could cause undesired mixing and fuel consumption. Connector 224 connects the liquefied gas fuel subsystem 210 and the liquid fuel subsystem 250, so that the liquefied gas fuel and liquid fuel can be supplied individually to the high pressure fuel pump 226. There is a pressure and temperature sensor 228 connected between the connector 224 and the high pressure fuel pump 226, which is configured to measure the temperature and pressure of the fuel supplied

EP 2 724 007 B1 to high pressure fuel pump 226.

[0040] The high pressure fuel pump 226 is connected to the high pressure fuel line 227 and is configured to pump fuel, whether the fuel is liquid fuel or liquefied gas fuel, at elevated pressure, to the high pressure fuel rail and fuel injectors, together designated as 280 in Figure 4, direct injection internal combustion engine. The fuel pressure in the high-pressure rail can be in the range of 20 bar to about 200 bar. Although Figure 4 schematically shows the configuration of a four-cylinder engine, the engine may include additional cylinders, high pressure pumps, electronic control units, etc. The illustrated embodiment should not be in any way limiting.

[0041] The liquefied gas fuel return subsystem 290 is connected to the high-pressure fuel rail and the high-pressure fuel pump 226 and is configured to provide a return path for the liquefied gas fuel to the fuel tank 212 when decompression in a high-pressure fuel rail 280 or in a high-pressure fuel rail is required fuel pump 226 to remove vapor bubbles as needed, and / or to lower the temperature of the liquefied gas fuel supply. The liquefied gas fuel return subsystem 290 includes a check valve 230 that is configured to prevent liquefied gas fuel from entering the high pressure fuel pump 226 through the fuel return line 229 and the return valve in the form of a shutoff valve 232 that is configured to prevent liquid fuel from entering to the liquefied gas fuel subsystem 210 when liquid fuel is supplied to the internal combustion engine, which could cause undesirable mixing and fuel consumption. The pressure limiting valve 234 is configured to limit the differential pressure of the system between the shutoff valve 232 and check valve 230.

[0042] Any liquefied gas fuel that is returned from high pressure system components, such as high pressure fuel pump 226 and high pressure reservoir, flows through fuel return line 229, through restriction 236, through check valve and into fuel tank 212 as shown in Figure 4. The fuel pressure of the liquefied gas that is returned to the fuel tank is typically between the fuel pressure of the liquefied gas in the tank

And fuel pressure 212 of liquefied gas, which is supplied from the high pressure fuel pump 226 to the high pressure fuel rail and injectors 280.

[0043] A check valve 238 is provided at the fuel tank 212 and is configured to prevent fuel leaks in the event of damage to the liquefied gas fuel subsystem 210. Restriction 236 is configured to control the elevated pressure of the system by flowing through the fuel pump 214. Pressure increase relative to the fuel tank 212 may be in the range between about 2 bars and about 10 bars.

[0044] The liquid fuel subsystem 250 includes a fuel tank 252 configured to hold a supply of liquid fuel, such as gasoline or diesel. The fuel pump unit 254 is mounted in the fuel tank 252 and is configured to remove liquid fuel from the fuel tank 252 by sucking and pumping liquid fuel through check valve 256 and to the cleaning unit 258. The check valve 256 is configured to prevent liquid fuel from returning back to the fuel tank 212 during the cleaning operation of the cleaning unit 258. The check valve 260 is configured to prevent liquefied gas fuel from entering the liquid fuel subsystem 250, which could cause undesired mixing and fuel consumption. Shut-off valve 262 is configured to prevent liquid fuel from entering the liquefied gas fuel subsystem 210, which could cause undesirable mixing and fuel consumption.

[0045] The cleaning unit 258 is disposed in parallel with the liquefied gas fuel subsystem 210 and the liquid fuel subsystem 250. The cleaning unit 258 includes a piston 258a that is configured to generate a pressure increase in the liquid fuel to produce a cleaning action from the fuel. The fuel side of the liquefied gas of the cleaning unit 258 is connected to the fuel supply line 217 via a shut-off valve 264. The second shut-off valve 266 is connected to the liquefied gas side of the cleaning unit 258 and is configured to slowly reduce the pressure of the cleaning unit 258 after the cleaning operation of the cleaning unit 258 has been completed. The released fuel of the liquefied gas may be flushed in the intake manifold or in the liquid fuel vent system through 265 in Figure 4.

[0046] The pressure increase provided by the cleaning unit 258 is related to the pressure in the liquefied gas fuel supply line 217 which is higher than the liquid fuel pressure downstream of the fuel pump 254 and with the physical parameters of the cleaning unit 258. The operation of the cleaning unit 258 is discussed in more detail below, with respect to switching the dual fuel direct injection system 200 from the use mode of liquefied gas fuel to the mode of use liquid fuel.

[0047] As shown in Figure 4, the controller 270 is in communication with the liquefied gas fuel pump 214, shut-off valves 218, 222, 232, 262, 264 and pressure sensor (temperature i) 228 and is configured to control whether valves 218 , 222, 232, 262, 264, 266 are in open configuration, whether in closed configuration and whether pump 214 is on or off. The controller 270 receives data from the pressure (temperature and) pressure sensor 228 and uses the data for system control operations by manipulating the various valves and pumps with which the controller 270 communicates. Fuel pump 254 and high pressure fuel pump 226 may also be in communication with controller 270. The illustrated embodiment should not be limiting in any way. The switch 296 is also in communication with the controller 270 and is located in the vehicle cabin, so that the vehicle operator can use the switch 296 to switch between the fuel use modes of the system 200, as discussed in more detail below.

[0048] Figure 5 shows the situation when the internal combustion engine is operating on liquid fuel and the dual fuel direct injection system 200 is operating in a liquid fuel utilization mode. As shown in Figure 5, the fuel pump 254 is turned on, the shut-off valves 218, 222, 264 and 232 are in a closed configuration, and the fuel pump 214 is turned off, as shown by the large "X" above these components of the system 200. Check valves 256 and 260 are active. Any liquefied gas or liquid fuel between shut-off valve 222 and check valve 220a is released by the pressure relief valve 220b. Any retained liquefied gas fuel or liquid fuel between the shut-off valve 232 and check valve 230 is released by the pressure limiting valve 234.

[0049] Figure 6 shows the situation when the internal combustion engine is operating on fuel

EP 2 724 007 B1, and the dual fuel direct injection system 200 operates in a liquefied gas fuel utilization mode. As shown in Figure 6, the fuel pump 214 is turned on, the shut-off valves 262, 264 and 266 are in a closed configuration. Check valves 220a, 230 and 238 are active. The controller 270 is configured to change the operating parameters of the system 200 based on the use of liquefied gas fuel in such a way that about 10 to 35% more fuel will be injected by the fuel injectors into the internal combustion engine. This increase in volume will lead to stable and efficient behavior of the internal combustion engine.

[0050] When the combustion engine runs on liquid fuel and the dual-fuel direct injection system 200 operates in the liquid fuel mode of use shown in Figure 5, the vehicle operator may switch to the liquefied gas mode of use shown in Figure 6 if desired . To this end, the vehicle operator may use a switch 296, which is located inside the vehicle cabin so that the signal is transmitted to the controller 270. The controller 270 will coordinate the switching procedure. Alternatively or in combination with said switch 296, controller 270 may include a switch algorithm so as to switch autonomously between fuel utilization modes, i.e. based on e.g. measured values ​​such as fuel level in fuel tanks.

[0051] In particular, after using the fuel selection switch 296 to select the mode of using the liquefied gas fuel, the fuel pump 114 will be turned on and the shut-off valves 218, 222 and 232 will be opened. In some situations, it may be necessary to temporarily activate the cleaning unit 258 by opening the shut-off valve 264 to reduce the pressure difference over the shut-off valve 222. After the delay, the shut-off valve 256 closes and optionally the cleaning unit 258 turns on by closing the shut-off valve 264. The cleaning operation may consequently lead to a certain amount of liquid fuel entering the fuel tank 212. The fuel in the high-pressure fuel rail 280 still consists from liquid fuel. The controller 270 is programmed to determine the decay factor for the value at which the controller 270 parameters are changed and the resulting control of various system components that are in communication with

EP 2 724 007 B1 controller. The decay factor is a function of fuel consumption and physical system parameters. After the decay, the fuel system 200 completed switching to liquefied gas fuel.

[0052] When the internal combustion engine operates on the liquefied gas fuel and the dual fuel direct injection system 200 operates in the liquefied gas fuel utilization mode shown in Figure 6, the vehicle operator may switch to the liquid fuel utilization mode illustrated in figure 5 if this is the case desirable. For this purpose, the vehicle operator can use the fuel selection switch 296, which is located inside the vehicle cabin so that the signal is transmitted to the controller 270. Controller 270 will coordinate the switching procedure.

[0053] As shown in Figure 7, after using the fuel selection switch 296 to select a mode for using liquid fuel, the shut-off valve 264 will open and the shut-off valve 266 will close so that in the cleaning unit 258 (with liquid fuel in the right chamber of the unit cleaning 258), the pressure may be increased by the higher pressure liquefied petroleum fuel. For example, the liquefied gas fuel may have a pressure of about 10-20 bar when it enters the cleaning unit 258. Since the fuel pump 254 is on, liquid fuel may be supplied to the cleaning unit 258 at a pressure of, for example, about 6 bar. The shut-off valve 222 will close and the shut-off valve 262 will open, starting the cleaning action. Shut-off valves 222, 262 close and open after a certain pre-determined delay. Because the pressure in the cleaning unit 258 is higher on the fuel side of the liquefied gas, piston 258a, the piston 258a will move towards the liquid fuel side of the cleaning unit and will increase the liquid fuel pressure to equal or higher than the steam pressure of the liquefied gas, e.g. 15 bar, in depending on the pressure and temperature of the liquefied gas fuel in storage unit 212, the chemical composition of the liquefied gas fuel. This increase in liquid fuel pressure allows liquid fuel to flush liquefied gas fuel from connector 224 and high pressure fuel pump 226.

[0054] After the delay, which depends on the physical parameters of the system and fuel consumption, the cleaning action has been completed. Shut-off valves 218, 264 and 232 will close and fuel pump 214 will be turned off. After a predetermined delay, preferably in the range of about 10 to 180 seconds from the above

At the closing stage of the shut-off valve 232 and while the cleaning unit is still active, the shut-off valve 232 is re-opened for a predetermined period of time, preferably about 1 to 10 seconds, to flush liquid fuel containing any residual fuel liquefied gas from the feed fuel to the high pressure pump through the fuel return line. Then, by opening the shut-off valve 266, the cleaning unit 258 can be reset to its initial configuration by allowing the fuel side of the liquefied gas piston 258a to slowly reduce its pressure to about 0 bar. The fuel side of the liquid piston 258a will reduce the pressure to the normal pressure of the liquid fuel, e.g. 6 bar.

[0055] Shortly after the rinsing operation, the fuel in the high pressure rail 280 still consists of liquefied gas fuel. The controller 270 is programmed to determine the decay factor for the value at which the controller 270 parameters are changed and the resulting control of various system components that are in communication with the controller. The decay factor is a function of fuel consumption and physical system parameters. Upon completion of the decay, the fuel system 200 completed switching to liquefied gas fuel. Controller

270 determines the decay factor for the value at which controller 270 parameters are changed. The decay factor is a function of fuel consumption and physical system parameters. After the end of the decay, when the liquid fuel completely replaced the fuel of the liquefied gas in the high-pressure container, the fuel system 200 completed switching.

[0056] Although specific embodiments of the invention have been described above, it should be understood that the invention may be used in a manner other than that described. The above descriptions are to be illustrative, not limiting. Therefore, it will be apparent to those skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims below.

EP 2 724 007 B1