System and method for supplying biofuel to an internal combustion engine

Abstract

System (1) for supplying of biofuel to an internal combustion engine (2) and presenting a main tank (5) containing biofuel an auxiliary tank (6) containing fuel from petroleum a fuel hydraulic circuit (13) configured to supply to the internal combustion engine (2) the biofuel contained in the main tank (5) or the fuel from petroleum contained in the auxiliary tank (6) a heating hydraulic circuit (7) within which a heating liquid flows intended to heat the biofuel and provided with a first heat exchanger (9) arranged inside the main tank (5) and a heating device (8) that is completely independent and separated from the internal combustion engine (2), connected to the heating hydraulic circuit (7) and configured to heat the heating liquid.

Description

[0001] SYSTEM AND METHOD FOR SUPPLYING BIOFUEL TO AN INTERNAL COMBUSTION ENGINE

[0002] Cross-Reference to Related Patent Applications

[0003] This application claims priority from Italian Patent Application No. 102024000026001 filed on November 19, 2024, the content of which is hereby incorporated by reference.

[0004] Technical Field

[0005] The present invention relates to a system and method for supplying biofuel to an internal combustion engine.

[0006] The present invention finds advantageous application to the use of biodiesel, to which the treatment will make explicit reference without thereby losing generality.

[0007] Prior Art

[0008] Biodiesel is used in a mixture with petroleum diesel (fossil) for supplying diesel engines. Despite the considerable advantages that would derive from the use of biodiesel, as it is obtained from biomass, the use of pure biodiesel (i.e., not mixed with petroleum diesel) is problematic.

[0009] First, biodiesel is subject to chemical and microbiological degradation much more so than petroleum diesel (fossil). This chemical reactivity contributes to its instability during storage and use, especially in the presence of moisture and contaminants.

[0010] Biodiesel exhibits phase transition characteristics different from petroleum diesel and dependent on the raw material from which the biodiesel originates. With reference to the transition from liquid to solid state in biodiesel, the cloud point varies between -5°C and +15°C (-17°C for petroleum diesel) and the pour point is generally 3-5°C lower than the cloud point (-26°C for petroleum diesel).

[0011] Finally, biodiesel, when used in internal combustion engines equipped with a particulate filter (FAP), is known to accentuate the "blowby" phenomenon (dilution of engine oil with fuel), especially during the regeneration operation of the particulate filter.

[0012] These properties of biodiesel now indicated make it so that the use of biodiesel in percentages higher than 10%, in cold or particularly harsh climates, or in winter seasons, can entail various complications.

[0013] Chemical and microbiological degradation of biodiesel leads to the formation of organic deposits, as well as to the proliferation of algae and bacteria, and concerns both the biodiesel contained in the tank and the residual biodiesel remaining in the fuel circuit once the engine has been shut down. Said deposits can cause obstructions, corrosion and adhesion phenomena and damage the components of the high- pressure system.

[0014] Patent application WO2022118352A1 describes a device for the use, in internal combustion engines with spontaneous ignition, of mixtures composed of petroleum diesel (fossil) and biodiesel with biodiesel percentages substantially higher than 7% (up to reaching 100% biodiesel).

[0015] Patent application DE102007020385A1 describes a vegetable oil supply system and an internal combustion engine operating according to the Diesel cycle; the supply system comprises a main tank containing vegetable oil, an auxiliary tank containing petroleum diesel, and a hydraulic supply circuit configured to supply to the internal combustion engine the vegetable oil contained in the main tank or the petroleum diesel contained in the auxiliary tank. Patent US10202950B2 describes a system for modifying an internal combustion engine so that it can use an alternative fuel that needs to be conditioned; in particular, the cooling liquid of the internal combustion engine is diverted from the radiator and used to heat or condition the alternative fuel both in the dedicated tank and in a special manifold that heats and circulates the fuel before sending it to the internal combustion engine. An electronic control unit monitors the temperature and pressure to ensure the correct viscosity and correct operation of the internal combustion engine.

[0016] Patent application CH696725A5 describes a device forthe controlled supply of various liquid fuels to a diesel engine; the device comprises at least two separate tanks for the storage of different types of fuels.

[0017] Patent application JP6385820B2 describes an internal combustion engine operating according to the Diesel cycle in which vegetable oil is used as fuel; based on the measurement of viscosity, the vegetable oil in a vegetable oil tank is heated and maintained at a predetermined viscosity.

[0018] Patent application W02006005930A2 describes a dual supply system for an internal combustion engine with compression ignition, arranged to operate using a fuel of vegetable origin, such as vegetable oil. The system comprises a first tank for vegetable oil, a second tank for petroleum diesel, an injection pump that supplies at least one injector, a fuel selection valve, a heat exchanger to heat the vegetable oil after it has left the tank and before being pumped to the injector and a recirculation circuit to return the fuel returned from the injection pump to the pump. The fuel selection valve is arranged to select the fuel supplied to the recirculation circuit based on the viscosity or temperature of the fuel in the circuit.

[0019] Patent application EP2840311A1 describes an ethanol / castor oil treatment system for the preparation of an ethanol / castor oil fuel to be used as fuel for an internal combustion engine.

[0020] Utility model DE202005007712U1 describes a supply system for the operation of a diesel engine with vegetable oil; a vegetable oil supply line from a vegetable oil tank and a petroleum diesel supply line from a petroleum diesel tank are provided.

[0021] Description of the Invention

[0022] The purpose of the present invention is to provide a system and method for supplying biofuel to an internal combustion engine that allow to increase the quantity of biofuel that is used under otherwise equal conditions and are at the same time simple and economical to implement.

[0023] According to the present invention, a system and method for supplying biofuel to an internal combustion engine are provided, as claimed by the appended claims.

[0024] The claims describe preferred forms of implementation of the present invention forming an integral part of the present description.

[0025] Brief Description of the Drawings

[0026] The present invention will now be described with reference to the attached drawings, which illustrate some non-limiting examples of implementation thereof, in which:

[0027] • Figure 1 is a schematic view of a biodiesel supply system for an internal combustion engine;

[0028] • Figures 2-5 and 9-13 show the supply system of Figure 1 with the paths followed by the fluids highlighted during various operating modes;

[0029] • Figure 6 is a schematic view of a variant of the supply system of Figure 1 ; and

[0030] • Figures 7 and 8 show the supply system of Figure 6 with the paths followed by the fluids highlighted during various operating modes. Preferred Embodiments of the Invention

[0031] In Figure 1 , with reference number 1 is indicated as a whole a fuel supply system to an engine 2 an internal combustion engine with spontaneous ignition of the mixture (i.e., operating according to the Diesel cycle) which is installed onboard a vehicle (typically, but not necessarily, a work vehicle) or is installed onboard machinery (for example a power generator).

[0032] The internal combustion engine 2 comprises a plurality of cylinders in which pistons slide alternately and in which combustion chambers are defined within which fuel is injected cyclically by injectors 3. The internal combustion engine 2 comprises a high-pressure fuel pump 4 that receives fuel from a low-pressure fuel pump and supplies fuel under pressure to the injectors 3, for example through a common channel ("common rail"). The internal combustion engine 2 comprises a fuel inlet at an intake of the high-pressure fuel pump 4 and an outlet of excess fuel (i.e., fuel pumped by the high-pressure fuel pump 4 and not injected by the injectors 3).

[0033] The supply system 1 comprises a main tank 5 intended to contain biodiesel and an auxiliary tank

[0034] 6 intended to contain petroleum diesel (fossil). According to alternative forms of implementation, the main tank 5 could be used to contain a mixture of biodiesel and petroleum diesel (fossil). If necessary, the main tank 5 can also be used to contain only petroleum diesel (fossil).

[0035] The supply system 1 further comprises a heating hydraulic circuit 7 within which a heating liquid (typically water-based to which antifreeze and anti-fouling additives are generally added) is circulated intended to heat the biodiesel. Along the heating hydraulic circuit 7 is arranged a heating device 8 configured to heat the heating liquid; for example, the heating device 8 could comprise a burner that is supplied with petroleum diesel (fossil) contained in the auxiliary tank 6 or could comprise electrical resistances. It is important to note that the heating device 8 is completely separate and independent from the internal combustion engine 2 (i.e., the heating device 8 is configured to generate heat autonomously and completely independent from the internal combustion engine 2) and therefore can be switched on and off independently from the starting of the internal combustion engine 2. Along the heating hydraulic circuit

[0036] 7 is also arranged a heat exchanger 9 that performs heat exchange between the heating liquid circulated within the heat exchanger 9 and the biofuel (i.e., biodiesel) located in the main tank 5 and surrounding the heat exchanger 9. By way of example, the heat exchanger 9 could comprise a coil of cylindrical shape arranged inside the main tank 5, or could comprise a tube within which the heating liquid flows and which is wound in a spiral. In particular, the heating hydraulic circuit 7 comprises a delivery duct 10 (illustrated with a dashed line) that connects an outlet of the heating device 8 to an inlet of the heat exchanger 9 and a return duct 11 (illustrated with a dashed line) that connects an outlet of the heat exchanger 9 to an inlet of the heating device 8. Along the delivery duct 10 is arranged a circulation pump 12, for example electrically actuated, that performs the circulation of the heating liquid along the heating hydraulic circuit 7.

[0037] The supply system 1 comprises a fuel hydraulic circuit 13 provided with an accumulation tank 14, in which a certain quantity of liquid biodiesel is accumulated ready to be supplied to the internal combustion engine 2 (i.e., to the inlet of the high-pressure fuel pump 4); the accumulation tank 14 essentially serves to absorb peaks in fuel demand when the internal combustion engine 2 is in operation and therefore is sized to contain a quantity of fuel sufficient to guarantee the operation at maximum power of the internal combustion engine 2 for a certain period of time (for example at least one minute of operation at maximum power). According to an alternative form of implementation not illustrated, the accumulation tank 14 is not present.

[0038] The fuel hydraulic circuit 13 comprises a delivery duct 15 that originates from the main tank 5 (i.e., draws from within the main tank 5) and ends in the accumulation tank 14. Along the delivery duct 15 is arranged a check valve 16 that permits flow of biodiesel only from the main tank 5 towards the accumulation tank 14 (and therefore not vice versa) and a filter 17. Along the delivery duct 15 is also arranged a circulation pump 18 electrically actuated that performs the circulation of biodiesel from the main tank 5 to the accumulation tank 14. Preferably, along the delivery duct 15 is also arranged a heat exchanger 19 that performs heat exchange between the heating liquid circulated within the heat exchanger and the biofuel (i.e., biodiesel) circulating in the delivery duct 15; that is, the heat exchanger 19 is arranged both along the delivery duct 15 in which biodiesel circulates, and along the return duct 11 of the heating hydraulic circuit 7 in which the heating liquid circulates. By way of example, the heat exchanger 19 could be plate-shaped, or could be a surface heat exchanger in which two fluid streams at different temperatures exchange their thermal content through embossed surfaces arranged one next to the other.

[0039] From the accumulation tank 14 a delivery duct 20 originates that ends in a first inlet of a three- way valve 21 controlled electrically. Along the delivery duct 20 is arranged a check valve 22 that permits flow of biodiesel only from the accumulation tank 14 towards the three-way valve 21 (and therefore not vice versa) and a filter 23.

[0040] The three-way valve 21 has an outlet that is connected to the high-pressure fuel pump 4 by means of a delivery duct 24 (possibly between the outlet of the three-way valve 21 and the high-pressure fuel pump 4 a low-pressure fuel pump could also be interposed).

[0041] From the auxiliary tank 6 a delivery duct 25 originates that ends in a second inlet of the three-way valve 21. Along the delivery duct 20 is arranged a check valve 26 that permits flow of petroleum diesel (fossil) only from the auxiliary tank 6 towards the three-way valve 21 (and therefore not vice versa) and a filter 27.

[0042] Therefore, the three-way valve 21 is controlled to alternately connect the delivery duct 24 that ends in the internal combustion engine 2 to the delivery duct 20 that originates from the accumulation tank 14 or the delivery duct 25 that originates from the auxiliary tank 6.

[0043] From the internal combustion engine 2 a return duct 28 originates that receives from the internal combustion engine 2 an excess of fuel which, after being pumped by the high-pressure fuel pump 4, has not been injected by the injectors 3. The return duct 28 ends in an inlet of a three-way valve 29 controlled electrically. From a first outlet of the three-way valve 29 a return duct 30 originates that flows into the main tank 5 and from a second outlet of the three-way valve 29 a return duct 31 originates that flows into the auxiliary tank 6. Therefore, the three-way valve 29 is controlled to alternately connect to the return duct 28 the return duct 30 that ends in the main tank 5 or the return duct 31 that ends in the auxiliary tank 6.

[0044] The fuel hydraulic circuit 13 comprises a return duct 33 that originates from the delivery duct 20 immediately upstream of the three-way valve 21 and ends in the main tank 5. Along the return duct 33 is arranged a check valve 34 that permits flow of biodiesel only from the delivery duct 20 towards the main tank 5 (and therefore not vice versa).

[0045] The fuel hydraulic circuit 13 comprises a delivery duct 35 that originates from the delivery duct 25 downstream of the check valve 26 and of the filter 27 (i.e., between the filter 27 and the three-way valve 21) and ends in the heating device 8 (obviously in the form of implementation in which the heating device 8 burns the petroleum diesel coming from the auxiliary tank 6). Preferably, along the delivery duct 35 is arranged a circulation pump 36, for example electrically actuated, that performs the circulation of petroleum diesel (fossil) from the auxiliary tank 6 to the heating device 8.

[0046] The fuel hydraulic circuit 13 comprises a bypass duct 37 that connects the delivery duct 15 to the return duct 33 and is provided with a two-way valve 38 controlled electrically. In particular, the bypass duct 37 originates from the delivery duct 15 between the filter 17 (i.e., downstream of the check valve 16) and the circulation pump 18 and ends in the return duct 33 upstream of the check valve 34. The two-way valve 38 is controllable to open or close the passage through the bypass duct 37, i.e., to permit or prevent flow of biodiesel along the bypass duct 37.

[0047] According to a preferred form of implementation, the fuel hydraulic circuit 13 comprises an interconnection duct 39 that connects the delivery duct 25 to the delivery duct 15 through a three-way valve 40 controlled electrically. In particular, a first inlet of the three-way valve 40 is connected to an initial part of the delivery duct 15, a second inlet of the three-way valve 40 is connected to the interconnection duct 39, and an outlet of the three-way valve 40 is connected to a final part of the delivery duct 15. In this way, the three-way valve 40 is controlled to alternately connect to the final part of the delivery duct 15 the initial part of the delivery duct 15 that originates from the main tank 5 or the interconnection duct 39 and therefore the delivery duct 25 that originates from the auxiliary tank 6. According to a preferred form of implementation, the interconnection duct 39 originates from the delivery duct 25 downstream of the filter 27 and of the check valve 26 and ends in the three-way valve 40 which is arranged along the delivery duct 15 downstream of the filter 17 and of the check valve 16 and in particular between the filter 17 and the origin of the bypass duct 37. That is, in the same area of the delivery duct 25 both the delivery duct 35 and the interconnection duct 39 originate.

[0048] A temperature sensor 41 is provided which is arranged inside the main tank 5 (preferably near the intake of the delivery duct 15) and is configured to measure a temperature of the biodiesel located inside the main tank 5. Furthermore, a temperature sensor 42 is provided which is arranged inside the accumulation tank 14 (if present) and is configured to measure a temperature of the biodiesel located inside the accumulation tank 14.

[0049] Finally, a control unit 43 is provided which oversees the operation of the fuel supply system 1 .

[0050] The operation of the fuel supply system 1 is described below.

[0051] With reference to what is illustrated in Figure 2, when the internal combustion engine 2 is started cold and the ambient temperature is lower than a solidification temperature of biodiesel (i.e., when the temperature detected by the temperature sensor 41 inside the main tank 5 is lower than the solidification temperature of biodiesel), it is necessary to previously heat the biodiesel to bring it back to the liquid state and therefore make it suitable for supply to the internal combustion engine 2. To heat the biodiesel the heating device 8 is started by supplying petroleum diesel (fossil) from the auxiliary tank 6 to the heating device 8 by activating the circulation pump 36 (therefore the petroleum diesel is drawn from the auxiliary tank 6 through the delivery duct 25 and subsequently through the delivery duct 35); it is important to note that the heating device 8 can be activated independently from the actual starting of the internal combustion engine 2 and therefore can be activated in advance (for example 2-10 minutes) compared to the actual starting of the internal combustion engine 2. In other words, the internal combustion engine 2 can indifferently be started right away (i.e., at the same time as the activation of the heating device 8) using petroleum diesel (fossil) from the auxiliary tank 6 (as illustrated in Figure 2), or the starting of the internal combustion engine 2 can be delayed compared to the activation of the heating device 8 to reduce the time of use of the internal combustion engine 2 with petroleum diesel (fossil). In particular, in Figure 2 the path followed by petroleum diesel (fossil) is illustrated with a thick solid line both for the activation of the heating device 8 and for the starting of the internal combustion engine 2.

[0052] At the same time as the activation of the heating device 8 the circulation pump 12 is started to circulate the heating liquid (progressively heated by the heating device 8) along the heating hydraulic circuit 7; in this way, the biodiesel contained in the main tank 5 is heated through the heat exchanger 9. In this regard it is important to note that the heat exchanger 9 is arranged inside the main tank 5 near the intake of the delivery duct 15 so as to liquefy the biodiesel initially around the intake of the delivery duct 15. In particular, in Figure 2 the path followed by the heating liquid is illustrated with a thick dashed line.

[0053] In Figure 2 the path of petroleum diesel (fossil) that is supplied from the auxiliary tank 6 to the heating device 8 (through the circulation pump 36) and is also supplied to the internal combustion engine 2 (through the high-pressure fuel pump 4) is also illustrated with a thick solid line if one wants to (optionally) start the internal combustion engine 2 during the heating of the biodiesel contained in the main tank 5.

[0054] When the temperature of the biodiesel inside the accumulation tank 14 measured by the temperature sensor 42 exceeds a first predetermined threshold value, then the control unit 43 activates the circulation pump 18 keeping the three-way valve 21 in the position in which it connects to the delivery duct 24 that ends in the internal combustion engine 2 the delivery duct 25 coming from the auxiliary tank 6 (i.e., in the position in which the delivery duct 20 coming from the accumulation tank 14 is isolated from the delivery duct 24 that ends in the internal combustion engine 2) and opening the two-way valve 38. In this way and as illustrated in Figure 3 (in which for clarity the supply of petroleum diesel from the auxiliary tank 6 to the internal combustion engine 2 is no longer illustrated), the biodiesel begins to circulate along the delivery duct 15 to the accumulation tank 14 passing through the heat exchanger 19 where it is heated by the heating liquid and therefore from the accumulation tank 14 it returns (at a higher temperature following the heating in the heat exchanger 19) in the delivery duct 15 along the return duct 33 and therefore along the bypass duct 37 (because the two-way valve 38 is open) without reaching the tank 5. The fact that the circulation pump 18 is activated with a certain delay compared to the beginning of the heating of the biodiesel in the main tank 5 (i.e., the circulation pump 18 is activated only when the temperature of the biodiesel inside the accumulation tank 14 measured by the temperature sensor 42 exceeds the first predetermined threshold value) reduces the mechanical stresses on the circulation pump 18 as it allows the circulation pump 18 to operate right away with biodiesel in the liquid state (or at least for the most part in the liquid state). Through the heat exchanger 19, the heating of the biodiesel is particularly effective and rapid thanks to the high efficiency of the heat exchange.

[0055] When the temperature of the biodiesel inside the main tank 5 measured by the temperature sensor 41 exceeds a second predetermined threshold value (or, alternatively, when the temperature of the biodiesel inside the accumulation tank 14 measured by the temperature sensor 42 exceeds the second predetermined threshold value) then the control unit 43 closes the two-way valve 38 allowing the flow of biodiesel towards the main tank 5. In this way and as illustrated in Figure 4 (in which for clarity the supply of petroleum diesel from the auxiliary tank 6 to the internal combustion engine 2 is no longer illustrated), the biodiesel begins to circulate from the main tank 5 along the delivery duct 15 to the accumulation tank 14 passing through the heat exchanger 19 where it is heated by the heating liquid and therefore from the accumulation tank 14 it returns (at a higher temperature following the heating in the heat exchanger 19) in the main tank 5 along the return duct 33. Through the heat exchanger 19, the heating of the biodiesel is particularly effective and rapid thanks to the high efficiency of the heat exchange.

[0056] The biodiesel that returns to the main tank 5 along the return duct 33 and has been heated in the heat exchanger 19 performs two functions: it further heats the biodiesel present in the main tank 5 (in addition to the heating action of the heat exchanger 9) and having a certain velocity it is able to move the biodiesel in the tank to increase the convective heat exchange of the heat exchanger 9 accelerating the heating of the biodiesel in the main tank 5.

[0057] When the temperature of the biodiesel inside the main tank 5 measured by the temperature sensor 41 exceeds a third predetermined threshold value (greater than the first predetermined threshold value) and / or when the temperature of the biodiesel inside the accumulation tank 14 measured by the temperature sensor 42 exceeds a fourth predetermined threshold value (greater than the second predetermined threshold value), then the control unit 43 (as illustrated in Figure 5) operates the three-way valve 21 to connect to the delivery duct 24 that ends in the internal combustion engine 2 the delivery duct 20 coming from the accumulation tank 14 in place of the delivery duct 25 coming from the auxiliary tank 6. In this way, "hot" biodiesel (i.e., hotterthan the solidification temperature) coming from the accumulation tank 14 is supplied to the internal combustion engine 2. Obviously, the control unit 43 also operates the three-way valve 29 in a way consistent with the three-way valve 21 so that the excess petroleum diesel (fossil) from the internal combustion engine 2 returns to the auxiliary tank 6 and the excess biodiesel from the internal combustion engine 2 returns to the main tank 5.

[0058] When the temperature of the biodiesel inside the main tank 5 measured by the temperature sensor 41 exceeds a fifth predetermined threshold value (greater than the third predetermined threshold value) and / or when the temperature of the biodiesel inside the accumulation tank 14 measured by the temperature sensor 42 exceeds a sixth predetermined threshold value (greater than the fourth predetermined threshold value and the fifth predetermined threshold value), then the control unit 43 switches off the heating device 8 and optionally (but not necessarily) stops the circulation pump 12; similarly, when the temperature of the biodiesel inside the main tank 5 measured by the temperature sensor 41 is again lower (with a certain hysteresis) than the fifth predetermined threshold value and / or when the temperature of the biodiesel inside the accumulation tank 14 measured by the temperature sensor 42 is again lower (with a certain hysteresis) than the sixth predetermined threshold value, then the control unit 43 restarts the circulation pump 12 (if stopped previously) and, if after a certain amount of time, the thresholds have still not been reached, it switches the heating device 8 back on.

[0059] Figure 6 illustrates a variant of the fuel supply system 1 , in which the heating hydraulic circuit 7 is connected to a cooling hydraulic circuit of the internal combustion engine 2. In particular, the heating hydraulic circuit 7 comprises a delivery duct 44 that originates from a port made in the cooling hydraulic circuit of the internal combustion engine 2 to receive (tap) cooling liquid that circulates in the cooling hydraulic circuit of the internal combustion engine 2 and a return duct 45 that ends in a port made in the cooling hydraulic circuit of the internal combustion engine 2 to introduce cooling liquid into the cooling hydraulic circuit of the internal combustion engine 2.

[0060] The heating hydraulic circuit 7 comprises a delivery duct 46 that ends in the heating device 8 and a bypass duct 47 that ends in the delivery duct 10 downstream of the heating device 8 (i.e., between the heating device 8 and the circulation pump 12). The heating hydraulic circuit 7 comprises a three-way valve 48 having an inlet connected to the delivery duct 44 and two outlets connected respectively to the delivery duct 46 and the bypass duct 47. Therefore, the three-way valve 48 is controlled to alternately connect to the delivery duct 44 coming from the internal combustion engine 2 the delivery duct 46 that ends in the heating device 8 or the bypass duct 47 that ends in the delivery duct 10 downstream of the heating device 8, or the three-way valve 48 is controlled to isolate the delivery duct 44 coming from the internal combustion engine 2 both from the delivery duct 46 that ends in the heating device 8 and from the bypass duct 47 that ends in the delivery duct 10 downstream of the heating device 8. The heating hydraulic circuit 7 comprises a three-way valve 49 having an inlet connected to an initial part of the return duct 11 and two outlets connected respectively to a final part of the return duct 11 and to the return duct 45. Therefore, the three-way valve 49 is controlled to alternately connect the initial part of the return duct 11 coming from the heat exchanger 9 to the final part of the return duct 11 that ends in the heating device 8 or to the return duct 45 that ends in the internal combustion engine 2.

[0061] Preferably, the delivery duct 44 is inserted into the cooling hydraulic circuit of the internal combustion engine 2 upstream of a bypass circuit that is controlled by a thermostatic valve and is configured to exclude a radiator when the temperature of the cooling liquid is below a predetermined threshold value. In this way, the delivery duct 44 can receive the cooling liquid progressively heated by the internal combustion engine 2 from the first instants of operation of the internal combustion engine 2.

[0062] Obviously, in the fuel supply system 1 illustrated in Figure 6 the heating liquid that circulates in the heating hydraulic circuit 7 is completely identical to the cooling liquid that circulates in the cooling hydraulic circuit of the internal combustion engine 2 (i.e., it is the same liquid that depending on where it is circulated performs two different and opposite functions); therefore the heating liquid that circulates in the heating hydraulic circuit 7 can be mixed without problems with the cooling liquid that circulates in the cooling hydraulic circuit of the internal combustion engine.

[0063] The fuel supply system 1 illustrated in Figure 6 can operate like the fuel supply system 1 illustrated in Figure 1 by excluding the cooling hydraulic circuit of the internal combustion engine 2, i.e., by operating the two three-way valves 48 and 49 to prevent any exchange between the heating liquid that circulates in the heating hydraulic circuit 7 and the cooling liquid that circulates in the cooling hydraulic circuit of the internal combustion engine 2. In this operating mode, the three-way valve 48 is controlled to isolate the delivery duct 44 coming from the internal combustion engine 2 both from the delivery duct 46 that ends in the heating device 8 and from the bypass duct 47 that ends in the delivery duct 10 downstream of the heating device 8 and the three-way valve 49 is controlled to connect the initial part of the return duct 11 coming from the heat exchanger 9 to the final part of the return duct 11 that ends in the heating device 8.

[0064] Alternatively and according to what is illustrated in Figure 7, the fuel supply system 1 illustrated in Figure 6 allows, by suitably operating the two three-way valves 48 and 49, to pass the heating liquid that circulates in the heating hydraulic circuit 7 also through the internal combustion engine 2. In this operating mode, the three-way valve 48 is controlled to connect the delivery duct 44 coming from the internal combustion engine 2 to the delivery duct 46 that ends in the heating device 8 and the three-way valve 49 is controlled to connect the initial part of the return duct 11 coming from the heat exchanger 9 to the return duct 45 that ends in the internal combustion engine 2. In this operating mode, the heat generated by the heating device 8 is also used to accelerate the heating of the internal combustion engine 2 (and, if necessary, also of a cab of the vehicle in which the internal combustion engine 2 is installed).

[0065] The operating mode illustrated in Figure 7 is indicated for comfort and the reduction of polluting emissions in very cold climates (in which the achievement of the optimal working temperature of the internal combustion engine 2 and the achievement of a comfortable temperature in the cab require a lot of time). Obviously, if part of the heat generated by the heating device 8 is used for heating the internal combustion engine 2 this will inevitably slow down the heating of the biodiesel; to reduce the impact of this slowdown, one can initially keep the heating hydraulic circuit 7 isolated from the cooling hydraulic circuit of the internal combustion engine 2 and therefore enable the connection between the heating hydraulic circuit 7 and the cooling hydraulic circuit of the internal combustion engine 2 only after a certain time interval or only when the temperature of the biodiesel inside the main tank 5 measured by the temperature sensor 41 and / or the temperature of the biodiesel inside the accumulation tank 14 measured by the temperature sensor 42 exceed respective threshold values.

[0066] Alternatively and according to what is illustrated in Figure 8, the fuel supply system 1 illustrated in Figure 6 allows, by suitably operating the two three-way valves 48 and 49 and after the cooling liquid that circulates in the cooling hydraulic circuit of the internal combustion engine 2 has reached a minimum working temperature, to exclude the heating device 8 and therefore to use only the heat generated by the internal combustion engine 2 to heat the biodiesel. In this operating mode, the three-way valve 48 is controlled to connect the delivery duct 44 coming from the internal combustion engine 2 to the bypass duct 47 that ends in the delivery duct 10 and the three-way valve 49 is controlled to connect the initial part of the return duct 11 coming from the heat exchanger 9 to the return duct 45 that ends in the internal combustion engine 2. This operating mode allows to eliminate part of the consumption of the heating device 8 which is used only until the internal combustion engine 2 is up to temperature.

[0067] According to a possible form of implementation, the heating liquid that circulates in the heating hydraulic circuit could be the engine oil of the internal combustion engine 2. Engine oil has, compared to other water-based liquids, a much lower specific heat, which accelerates heating at equal thermal power supplied by the heating device 8. Also in this form of implementation, which can be realized with a circuit similar to that of Figure 8 (as valves and ducts), heating of the internal combustion engine 2 is achieved even when the internal combustion engine 2 is stopped.

[0068] In other words, the heating hydraulic circuit 7, instead of being connected to the cooling hydraulic circuit of the internal combustion engine 2 to exchange water with the cooling hydraulic circuit, is connected to a hydraulic lubrication circuit of the internal combustion engine 2 to exchange lubricating oil with the hydraulic lubrication circuit. In this case, the delivery duct 44 originates from a port made in the hydraulic lubrication circuit of the internal combustion engine 2 to receive (tap) lubricating oil that circulates in the hydraulic lubrication circuit of the internal combustion engine 2 and the return duct 45 ends in a port made in the hydraulic lubrication circuit of the internal combustion engine 2 to introduce lubricating oil into the hydraulic lubrication circuit of the internal combustion engine 2.

[0069] It is known that in harsh climates, one of the main causes of wear on the sliding surfaces of internal combustion engines is oil that, when the internal combustion engine is cold, is too viscous. In this form of implementation, by heating the engine oil preferably before starting the internal combustion engine 2 (in order to use it as heating liquid to heat the biodiesel), this problem is solved.

[0070] In this form of implementation, the increase in engine oil volume (necessary for filling all the components of the heating hydraulic circuit in which the heating liquid circulates) reduces the risk of damage caused by dilution of engine oil with fuel (the "blowby" phenomenon). Indeed, having a greater quantity of engine oil, it will take longer before the concentration of fuel in oil is such as to create lubrication problems.

[0071] According to a possible form of implementation not illustrated, the fuel hydraulic circuit 13 comprises a bypass duct controlled by a solenoid valve that is arranged in parallel to the heat exchanger 19 and can be used to prevent the circulation of biodiesel through the heat exchanger 19 when it is not necessary to heat the biodiesel and it is desired to avoid the pressure drops caused by the circulation of biodiesel through the heat exchanger 19. The control unit 43 operates the solenoid valve of the bypass duct of the heat exchanger 19 based on the temperature of the biodiesel inside the main tank 5 measured by the temperature sensor 41 and / or the temperature of the biodiesel inside the accumulation tank 14 measured by the temperature sensor 42.

[0072] According to an alternative form of implementation not illustrated, the heating device 8 can be initially supplied with petroleum diesel (fossil) from the auxiliary tank 6 and subsequently (i.e., when the biodiesel in the accumulation tank 14 has reached an adequate temperature) is supplied with biodiesel from the accumulation tank 14 (if present); in this way, the use of petroleum diesel (fossil) is further reduced thereby increasing the use of biodiesel. If in this form of implementation the supply duct 35 of the heating device 8 is inserted downstream of the three-way valve 21 , it is possible to perform the cleaning process also in the heating device 8.

[0073] According to a possible form of implementation not illustrated, the main tank 5 could also be heated using the hot exhaust gases emitted by the internal combustion engine 2; in this case, the hot exhaust gases emitted by the internal combustion engine 2 can directly heat the walls of the main tank 5 by being circulated in contact with the walls of the main tank 5 or the hot exhaust gases emitted by the internal combustion engine 2 can heat the heating liquid that circulates in the heating hydraulic circuit 7 through a special heat exchanger (possibly bypassable by means of a solenoid valve).

[0074] According to a possible form of implementation not illustrated, the fuel supply system 1 comprises a thermally insulated container (i.e., provided with walls coupled to a thermally insulating material) that contains the components of the heating hydraulic circuit 7 (included or excluded the heating device 8) and the components of the fuel hydraulic circuit 13. The presence of the thermally insulated container allows to reduce heat losses to the external environment thereby increasing the efficiency and rapidity of heating the biodiesel.

[0075] According to a preferred form of implementation, the four valves 21 , 29, 38 and 40 are integrated in a single common body (in particular a metal block and for example an aluminum block) in which the hydraulic ducts are made.

[0076] When the internal combustion engine 2 is stopped and it is expected that the internal combustion engine 2 will remain off for a relatively long time (for example longer than 30-60 minutes when the ambient temperature is lower than the solidification temperature of biodiesel or longer than 24 hours when the ambient temperature is higher than the solidification temperature of biodiesel), the control unit 43 can perform a cleaning (washing) cycle (operation) to remove biodiesel from the internal combustion engine 2 and (if necessary) to also remove biodiesel from at least part of the fuel hydraulic circuit 13 by replacing the biodiesel with petroleum diesel (fossil). This cleaning (washing) cycle guarantees that the internal combustion engine 2 can be restarted after a long time (several days or several weeks) from the previous starting (especially when the ambient temperature is lowerthan the solidification temperature of biodiesel), allows to increase the time intervals of maintenance, and makes the restart much faster (when the ambient temperature is lowerthan the solidification temperature of biodiesel). Indeed, this cleaning (washing) cycle allows to avoid formation of algae, polymers and other harmful components that derive from the degradation of biodiesel and damage the components of the internal combustion engine 2, in particular those subjected to high pressure (for example the high-pressure fuel pump 4 and the injectors 3).

[0077] According to what is illustrated in Figures 9 and 10, the control unit 43 can perform a partial cleaning (washing) cycle that provides for the circulation of petroleum diesel (fossil) from the auxiliary tank 6 only through the delivery duct 25 and therefore directly from the delivery duct 25 to the delivery duct 24 that ends in the internal combustion engine 2 through the three-way valve 21. In this partial cleaning (washing) cycle, the circulation of petroleum diesel (fossil) occurs due to the pumping performed by the high-pressure fuel pump 4 of the internal combustion engine 2 (or alternatively by a low-pressure fuel pump of the internal combustion engine 2) and concerns the delivery duct 24, the return duct 28 and the internal combustion engine 2 (the delivery duct 25 and the return duct 31 are never traversed in any condition by biodiesel and therefore are always filled only with petroleum diesel). To perform the partial cleaning (washing) cycle, the control unit 43 operates the three-way valve 21 to connect to the delivery duct 24 that ends in the internal combustion engine 2 the delivery duct 25 that originates from the auxiliary tank 6.

[0078] Initially, and as illustrated in Figure 9, the control unit 43 operates the three-way valve 29 to connect to the return duct 28 the return duct 30 that ends in the main tank 5, so that (initially, i.e., in the initial part of the partial cleaning cycle) the mixture of petroleum diesel (fossil) and biodiesel (predominantly composed of biodiesel) is introduced into the main tank 5 instead of into the auxiliary tank 6; subsequently, and as illustrated in Figure 10, the control unit 43 operates the three-way valve 29 to connect to the return duct 28 the return duct 31 that ends in the auxiliary tank 6, so that (subsequently, i.e., in the final part of the partial cleaning cycle) the mixture of petroleum diesel (fossil) and biodiesel (predominantly composed of petroleum diesel) is introduced into the auxiliary tank 6 instead of into the main tank 5.

[0079] According to what is illustrated in Figures 11 and 12, the control unit 43 can perform, alternatively to the above-described partial cleaning (washing) cycle, a complete cleaning (washing) cycle. In the complete cleaning (washing) cycle, the control unit 43 operates the three-way valve 21 to connect to the delivery duct 24 that ends in the internal combustion engine 2 the delivery duct 20 that originates from the accumulation tank 14 and operates the three-way valve 40 to connect to a final part of the delivery duct 15 the interconnection duct 39 and therefore the delivery duct 25 that originates from the auxiliary tank 6. Operating as described above and thanks to the pumping action generated by the circulation pump 18, the petroleum diesel (fossil) is circulated from the auxiliary tank 6 along the final part of the delivery duct 15, through the circulation pump 18, through the heat exchanger 19, through the accumulation tank 14, along the delivery duct 20, along the delivery duct 24, through the internal combustion engine 2, and along the return duct 28. Consequently, after a certain time interval, all these parts will be substantially free of biodiesel and filled (washed) with petroleum diesel (fossil).

[0080] Initially, and as illustrated in Figure 11 , the control unit 43 operates the three-way valve 29 to connect to the return duct 28 the return duct 30 that ends in the main tank 5, so that (initially, i.e., in the initial part of the complete cleaning cycle) the mixture of petroleum diesel (fossil) and biodiesel (predominantly composed of biodiesel) is introduced into the main tank 5 instead of into the auxiliary tank 6; subsequently, and as illustrated in Figure 12, the control unit 43 operates the three-way valve 29 to connect to the return duct 28 the return duct 31 that ends in the auxiliary tank 6, so that (subsequently, i.e., in the final part of the complete cleaning cycle) the mixture of petroleum diesel (fossil) and biodiesel (predominantly composed of petroleum diesel) is introduced into the auxiliary tank 6 instead of into the main tank 5.

[0081] Preferably, during the complete cleaning (washing) cycle, the control unit 43 operates the two- way valve 38 to open the passage through the bypass duct 37, i.e., to allow flow of petroleum diesel (fossil) along the bypass duct 37. In this way, the recirculation of the excess flow of the circulation pump 18 occurs through the bypass duct 37 without passing through the main tank 5 thereby avoiding the washing with petroleum diesel (fossil) concerning the main tank 5 (also due to the presence of the check valve 34 along the final part of the return duct 33 that ends in the main tank 5). According to a preferred form of implementation, initially the two-way valve 38 is kept closed allowing the biodiesel contained in the accumulation tank 14 and in the filters to return to the main tank 5; only after a certain time interval the two-way valve 38 is opened allowing the bypass and preventing the petroleum diesel from going into the main tank 5.

[0082] According to a possible form of implementation, a cleaning (washing) cycle that is indifferently partial or complete can be controlled as a function of time, i.e., can last for a preset time interval (which is shorter for the partial cleaning cycle and longer for the complete cleaning cycle). In particular, also the change in the position of the three-way valve 29 is controlled as a function of time: initially for a first preset time interval (which is shorter for the partial cleaning cycle and longer for the complete cleaning cycle) the three-way valve 29 connects the return duct 28 to the return duct 30 that ends in the main tank 5, while subsequently and for a second preset time interval (which is shorter for the partial cleaning cycle and longer for the complete cleaning cycle) the three-way valve 29 connects the return duct 28 to the return duct 31 that ends in the auxiliary tank 6.

[0083] According to what is illustrated in Figure 13, also possible is a standby cleaning (washing) cycle that is performed when the internal combustion engine 2 is stopped and does not concern the internal combustion engine 2 (i.e., does not circulate fuel through the internal combustion engine 2). In this case, the control unit 43 operates the three-way valve 21 to connect to the delivery duct 24 that ends in the internal combustion engine 2 the delivery duct 25, operates the three-way valve 40 to connect to the final part of the delivery duct 15 the interconnection duct 39 and therefore the delivery duct 25 that originates from the auxiliary tank 6, and activates the circulation pump 18. Operating as described above and thanks to the pumping action generated by the circulation pump 18, the petroleum diesel (fossil) is circulated from the auxiliary tank 6 along the final part of the delivery duct 15, through the circulation pump 18, through the heat exchanger 19, through the accumulation tank 14, along the delivery duct 20, and along the return duct 33 that originates from the delivery duct 20 immediately upstream of the three-way valve 21 and ends in the main tank 5 (as the three-way valve 21 isolates the delivery duct 20 from the delivery duct 24). Consequently, after a certain time interval, all these parts will be substantially free of biodiesel and filled (washed) with petroleum diesel (fossil).

[0084] In other words, the control unit 43 is configured to perform, during a stop of the internal combustion engine 2 and before the internal combustion engine 2 stops, a first cleaning cycle (partial as illustrated in Figures 9 and 10 or complete as illustrated in Figures 11 and 12) during which petroleum fuel from the auxiliary tank 6 is supplied to the internal combustion engine 2 to reduce the presence of biofuel in the internal combustion engine 2; in the first cleaning cycle the function of the high-pressure fuel pump 4 of the internal combustion engine 2 is essential. Furthermore, the control unit 43 is configured to perform, only after the internal combustion engine 2 has stopped, a second cleaning cycle (as illustrated in Figure 13) which is subsequent to the first cleaning cycle and during which petroleum fuel from the auxiliary tank 6 is supplied to the fuel hydraulic circuit 13 only and excluding the internal combustion engine 2 to reduce the presence of biofuel in the fuel hydraulic circuit 13. For example, the control unit 43 is configured to perform the first cleaning cycle at each shutdown of the internal combustion engine 2 and the control unit 43 is configured to perform the second cleaning cycle only after a predetermined time interval has passed from the last first cleaning cycle, i.e., from the last shutdown of the internal combustion engine 2. According to a possible form of implementation, the control unit 43 is configured to perform the second cleaning cycle only if a temperature of the biodiesel present in the fuel hydraulic circuit 13 (measured by the temperature sensor 42) or in the main tank 5 (measured by the temperature sensor 41) is lower than a predetermined threshold value.

[0085] According to a possible form of implementation, the partial cleaning (washing) cycle is first performed which allows a rapid shutdown of the internal combustion engine 2 and subsequently, immediately or after a certain time depending on the environmental and operational conditions of the vehicle, also the complete cleaning (washing) cycle is performed with the internal combustion engine 2 stopped (as illustrated in Figure 13); in this way the cleaning time in which the internal combustion engine 2 is running is minimized and therefore minimal disturbance to business processes and operators. To perform this operation without excessive mixing, it could be indicated, but not obligatory, the addition of valves and ducts between the three-way valve 21 and the internal combustion engine 2, so as to convey the biodiesel to the main tank 5 and the petroleum diesel (fossil) to the auxiliary tank 6.

[0086] According to an alternative form of implementation, along the return duct 28 (or, less frequently, along the return duct 31) is installed a concentration sensor 50 that is configured to determine the composition of the fuel flowing along the return duct 28 and in particular is configured to determine the percentage (concentration) of biodiesel, i.e., to determine the percentage (concentration) of biodiesel and, consequently, the percentage (concentration) of petroleum diesel (fossil). In this form of implementation, a cleaning (washing) cycle that is indifferently partial or complete can be controlled as a function of the composition of the fuel flowing along the return duct 28; that is, the cleaning (washing) cycle is stopped when the percentage (fraction) of biodiesel in the fuel flowing along the return duct 28 drops below a predetermined threshold value.

[0087] Obviously, in this form of implementation, the measurement provided by the concentration sensor 50 is also used to control the three-way valve 29, i.e., also the change in the position of the three-way valve 29 is controlled as a function of the measurement provided by the concentration sensor 50: initially and as long as the measurement provided by the concentration sensor 50 indicates a prevalence of biodiesel the three-way valve 29 connects the return duct 28 to the return duct 30 that ends in the main tank 5, while subsequently and from when the measurement provided by the concentration sensor 50 indicates a prevalence of petroleum diesel (fossil) the three-way valve 29 connects the return duct 28 to the return duct 31 that ends in the auxiliary tank 6.

[0088] Thanks to the use of the concentration sensor 50, the cleaning (washing) cycle is much more effective (i.e., it is guaranteed to always achieve the desired result in terms of biodiesel residue) and much more efficient (i.e., the duration of the cleaning cycle is always the minimum necessary to achieve the desired result in terms of biodiesel residue regardless of the random variation of background conditions).

[0089] The control unit 43 can implement control strategies that determine when to perform a partial cleaning (washing) cycle (always with the internal combustion engine 2 running) and when to perform a complete cleaning (washing) cycle (with the internal combustion engine 2 running or stopped); these strategies can take into account the ambient temperature (the colder it is and the more necessary it is to perform a cleaning cycle), the time elapsed from shutdown, the temperature of the biodiesel inside the main tank 5 measured by the temperature sensor 41 , the temperature of the biodiesel inside the accumulation tank 14 measured by the temperature sensor 42, the position of the vehicle (detected in a known manner by a GPS system), the history of vehicle use, and / or the forecast of vehicle use as well as all the data available on the network of the vehicle 2 or machinery that can be read by the control unit 43. Alternatively, a cleaning (washing) cycle can be performed at the request of the driver who is trained to request the execution of the cleaning (washing) cycle at the end of his working shift or at the request of a remote operator such as, for example, a fleet manager in a logistics company, who monitors vehicles from the company headquarters.

[0090] It is important to note that a cleaning (washing) cycle entails the progressive replacement of biodiesel with petroleum diesel (fossil) and therefore entails the inevitable mixing of biodiesel and petroleum diesel (fossil) in the auxiliary tank 6; the presence of some biodiesel in the auxiliary tank 6 does not cause problems if the percentage of biodiesel remains contained (indicatively lower than 10%). Therefore, cleaning (washing) operations should not be too frequent to avoid introducing too much biodiesel into the auxiliary tank 6.

[0091] As explained previously, during a partial or complete cleaning (washing) cycle with the internal combustion engine 2 running, the control unit 43 controls (at least initially but could also be for the entire cleaning cycle) the three-way valve 29 to connect to the return duct 28 the return duct 30 that ends in the main tank 5 instead of the return duct 31 that ends in the auxiliary tank 6, so that the mixture of petroleum diesel (fossil) and biodiesel is introduced into the main tank 5 instead of into the auxiliary tank 6. The control unit 43 could also control the three-way valve 29 to connect to the return duct 28 the return duct 30 that ends in the main tank 5 in the initial part of a cleaning (washing) cycle in which the fuel exiting from the internal combustion engine 2 has a prevalence of biodiesel and subsequently to connect to the return duct 28 the return duct 31 that ends in the auxiliary tank 6 in the final part of the cleaning (washing) cycle in which the fuel exiting from the internal combustion engine 2 has a prevalence of petroleum diesel (fossil). The switching of the three-way valve 29 can be decided as a function of the time elapsed or can be decided, more effectively, as a function of the reading performed by the concentration sensor 50 (installed along the return duct 28).

[0092] The concentration sensor 50 allows to characterize mixtures composed of biodiesel and petroleum diesel (fossil), i.e., allows to know in a mixture composed of biodiesel and petroleum diesel (fossil) what is the concentration (percentage) of biodiesel and, consequently, what is the concentration (percentage) of petroleum diesel (fossil). In the form of implementation illustrated in the attached figures, the concentration sensor 50 is arranged along the return duct 28 but according to other forms of implementation the concentration sensor 50 could be arranged in other areas or there could be two or more concentration sensors 50.

[0093] According to a possible form of implementation, a concentration sensor 50 installed in the main tank 5 allows to verify (certify) that the main tank 5 actually contains only biodiesel, i.e., is filled only with biodiesel, thereby avoiding possible fraud related to economic incentives granted for the use of biodiesel or permits granted for the use of biodiesel. A concentration sensor 50 installed in the main tank 5 also allows to recognize the type of fuel located inside the main tank 5 and therefore allows to identify the composition of mixtures of FAME biodiesel, dimethyl ether DME, Renewable Diesel (HVO), petroleum diesel (fossil). The concentration sensor 50 also allows to recognize the origin of FAME biodiesel (triglyceride starting material before transesterification, for example palm oil, waste cooking oil, animal fat...).

[0094] The concentration sensor 50 reads temperature values, viscosity, density, dielectric constant and other fuel properties (in particular biodiesel). The values read by the concentration sensor 50 for each property are processed by the control unit 43. The control unit 43 can use the values read by the concentration sensor 50 directly in the operation strategies of the fuel supply system 1 or the values read by the concentration sensor 50 can be further processed in order to obtain correlations. By way of example, the correlations identified could be compared with a database populated with correlations between the properties read by the concentration sensor 50. For example, in the database all values of the properties of interest can be saved as the temperature varies for all fuels of interest (for example all mixtures of FAME biodiesel and petroleum diesel or FAME biodiesel and renewable diesel HVO). Furthermore, since the properties of FAME biodiesel also vary based on the raw material from which the biodiesel was produced, one can also have all values of the properties of interest as the origin and percentage of mixture with other fuels vary. A more complex but nevertheless feasible thing is the monitoring of the quality of FAME biodiesel, which as it degrades varies its properties.

[0095] According to a possible form of implementation, a concentration sensor 50 installed along the delivery duct 24 (or installed inside the internal combustion engine 2) can be used to measure (certify) the quantity of biodiesel that is actually used (consumed) by the internal combustion engine 2; this information can be used to demonstrate the actual use of biodiesel to be entitled to environmental certifications and / or economic incentives.

[0096] The concentration sensor 50, in addition to providing information on the concentration of biodiesel, also provides a reliable measure of the viscosity and temperature of the fuel. According to a possible form of implementation, the concentration sensor 50 is installed in the accumulation tank 14 to replace the temperature sensor 42 (which becomes unnecessary as the concentration sensor 50 also measures the temperature of the fuel). In this way, the heating process of the biodiesel is not controlled as a function of the temperature of the biodiesel in the accumulation tank 14 but is controlled as a function of the viscosity of the biodiesel in the accumulation tank 14; consequently, the control of the heating process becomes more precise as the ultimate purpose of heating the biodiesel is not to increase the temperature of the biodiesel but to make the biodiesel sufficiently fluid to be able to be used in the internal combustion engine 2.

[0097] In other words, the ultimate purpose of heating the biodiesel is the lowering of its viscosity: the curve of variation of the viscosity of biodiesel as the temperature varies is known in the literature for all types of biodiesel, however it is not known for all possible mixtures of petroleum diesel (fossil) and biodiesel that can form over time in the main tank 5. Normally, the control unit 43 considers the biodiesel located in the accumulation tank 14 ready when the biodiesel reaches a certain temperature, to which it is believed corresponds a certain viscosity; however, having available in the accumulation tank 14 the concentration sensor 50 it is possible to measure the viscosity of the biodiesel directly by stopping the heating process exactly at the desired viscosity thereby avoiding excessive heating of the biodiesel (with the risk of degradation of the biodiesel and excessive energy consumption) or too little heating of the biodiesel (putting stress on the pumps and other components provided with moving parts).

[0098] Consequently, according to a possible form of implementation, the viscosity sensor 50 is configured to determine a viscosity of the biofuel in the main tank 5 and the control unit 43 is configured to activate the intake from the main tank 5 only when the viscosity of the biofuel in the main tank 5 drops below a predetermined threshold value.

[0099] According to a preferred form of implementation, the concentration sensor 50 is a capacitive sensor provided with compensation means to reduce the effect of parasitic capacitances that manifest themselves in printed circuits, so that the accuracy of the measurements performed by the capacitive sensor device is not significantly affected by parasitic capacitances. By way of example, the concentration sensor 50 can be of the type described in patent application EP4296621A1 or in patent application EP2009434A2.

[0100] According to a preferred form of implementation, the heating hydraulic circuit 7 is provided with a temperature sensor configured to detect the temperature of the heating liquid; this temperature sensor is preferably positioned on the return duct 11 upstream of the heat exchanger 19. The control unit 43 is configured to prevent heating liquid that is too hot (i.e., at too high a temperature) from circulating in the heat exchangers 9 and 19, risking bringing the biodiesel to excessively high temperatures that would accelerate its degradation. In particular, if the temperature read by this temperature sensor exceeds a threshold value when also one of the two temperature sensors 41 or 42 has exceeded a threshold value, the control unit 43 switches off the heating device 8 or, in the case in which the heating hydraulic circuit 7 is also connected to the cooling hydraulic circuit of the internal combustion engine 2, the control unit 43 switches the valves 48 and 49 in order to guarantee continuity of heating in the heat exchangers 9 and 19 by keeping the temperature of the heating liquid controlled to prevent the biodiesel from degrading due to overheating. For example, starting from the condition illustrated in Figure 8 in which the valves 48 and 49 are controlled to bypass the heating device 8 and put the heating circuit 7 in communication with the cooling hydraulic circuit of the internal combustion engine 2, one could have in the heating hydraulic circuit 7 a heating liquid that is too hot; in this case a configuration is used in which the cooling hydraulic circuit of the internal combustion engine 2 is excluded and the heating device 8 is switched off, so that the heating liquid present in the heating hydraulic circuit 7 cools down, ceasing to receive thermal power from the internal combustion engine 2.

[0101] Preferably, the heating device 8 is also provided with its own "thermal protection" temperature sensor, which performs the shutdown in case the heating liquid reaches a maximum temperature.

[0102] According to a preferred form of implementation, the control unit 43 is connected with external systems to the vehicle 2 or machinery (for example company computer systems, for example through an FMS module or "Fleet Management System"), so as to communicate information regarding the internal combustion engine 2 (both read from the CAN bus network of the vehicle or machinery on which the internal combustion engine 2 is installed, and read from the sensors part of the fuel supply system 1) and to possibly receive information from external systems. For example, the control unit 43 can receive preset commands on the strategies to adopt for the cleaning operation or on the heating strategies based for example on timetables or distance kilometres between arrival and vehicle position. In case of installation of the fuel supply system 1 on a vehicle, the control unit 43 could also be configured to connect with the control systems of law enforcement agencies or cities or other entities; a non-limiting example of this configuration occurs when a city wants to limit access to polluting vehicles: if the vehicle is powered by biodiesel (low-polluting), the concentration sensor 50 reads the information on the fuel in use and communicates it to the entity. In this way, entities can control vehicle circulation and allow companies to certify that their vehicles are low-polluting.

[0103] According to a preferred form of implementation, the main tank 5 contains biodiesel (or another biofuel), but it could also happen that a mixture of biodiesel and petroleum diesel (fossil diesel) or only petroleum diesel (fossil diesel) is supplied to the main tank 5 if biodiesel is not available; in other words, if in a refuelling area biodiesel is not available rather than keeping the vehicle stationary one can refuel with a mixture of biodiesel and petroleum diesel (fossil diesel) or only with petroleum diesel (fossil diesel) to allow continued use of the vehicle. If a concentration sensor installed in the main tank 5 is configured to determine the composition of the fuel present in the main tank 5, the control unit 43 will adapt the control strategies to optimize the use of the fuel present in the main tank 5.

[0104] According to a possible form of implementation, in vehicles equipped with a particulate filter, the control unit 43 is aware of the occurrence of the filter regeneration conditions (through communication with the control unit dedicated to such operation). Knowing the characteristics of the fuel being supplied to the internal combustion engine 2, the control unit 43 can optimize the regeneration strategies. By way of example, it can inhibit regeneration for a certain time in order to allow the transition to petroleum diesel (drawn from the auxiliary tank 6), or it can allow regeneration with a mixture of petroleum diesel and biodiesel from the main tank 5 if this has a sufficiently low biodiesel concentration. In the case in which the heating liquid circulating in the heating hydraulic circuit is engine oil, regeneration can be allowed with a higher biodiesel concentration.

[0105] The check valves 16, 22, 26 and 34 are not essential for the operation of the fuel hydraulic circuit 13 but are useful for preventing unwanted emptying of the fuel hydraulic circuit 13. According to other forms of implementation not illustrated, the position of the check valves 16, 22, 26 and 34 could be different or one or more of the check valves 16, 22, 26 and 34 could not be present.

[0106] The filters 17, 23 and 27 are useful but not essential for the operation of the fuel hydraulic circuit 13. According to other forms of implementation not illustrated, the position of the filters 17, 23 and 27 could be different or one or more of the filters 17, 23 and 27 could not be present.

[0107] The foregoing description has made explicit reference to the use of biodiesel, but the fuel supply system 1 described above can also be used for the use of a biofuel different from biodiesel. The forms of implementation described here can be combined with each other.

[0108] The fuel supply system 1 described above has numerous advantages.

[0109] First, the fuel supply system 1 described above allows to considerably increase the quantity of biodiesel that is used under otherwise equal conditions. This result is achieved thanks to the extreme controllability of the biodiesel heating process which can therefore be in all environmental conditions rapid, effective and efficient (the sooner liquid biodiesel is obtained, the sooner it can replace petroleum diesel in the fuel supply to the internal combustion engine 2); that is, rapid, effective and efficient heating of the biodiesel allows a lower use of petroleum diesel (fossil), increasing the environmental benefits derived from the use of biodiesel.

[0110] Furthermore, the fuel supply system 1 described above is relatively simple and economical to implement.

[0111] LIST OF REFERENCE NUMBERS

[0112] 1 - fuel supply system

[0113] 2 - internal combustion engine

[0114] 3 - injectors

[0115] 4 - high-pressure fuel pump

[0116] 5 - main tank

[0117] 6 - auxiliary tank

[0118] 7 - heating hydraulic circuit

[0119] 8 - heating device

[0120] 9 - heat exchanger

[0121] 10 - delivery duct

[0122] 11 - return duct

[0123] 12 - circulation pump

[0124] 13 - fuel hydraulic circuit

[0125] 14 - accumulation tank

[0126] 15 - delivery duct

[0127] 16 - check valve 17 - filter

[0128] 18 - circulation pump

[0129] 19 - heat exchanger

[0130] 20 - delivery duct

[0131] 21 - three-way valve

[0132] 22 - check valve

[0133] 23 - filter

[0134] 24 - delivery duct

[0135] 25 - delivery duct

[0136] 26 - check valve

[0137] 27 - filter

[0138] 28 - return duct

[0139] 29 - three-way valve 30 - return duct

[0140] 31 - return duct

[0141] 32 - bypass duct

[0142] 33 - return duct

[0143] 34 - check valve

[0144] 35 - delivery duct

[0145] 36 - circulation pump

[0146] 37 - bypass duct

[0147] 38 - two-way valve

[0148] 39 - interconnection duct

[0149] 40 - three-way valve

[0150] 41 - temperature sensor

[0151] 42 - temperature sensor

[0152] 43 - control unit

[0153] 44 - delivery duct

[0154] 45 - return duct

[0155] 46 - delivery duct

[0156] 47 - bypass duct

[0157] 48 - three-way valve

[0158] 49 - three-way valve

[0159] 50 - concentration sensor

Claims

CLAIMS1. A supply system (1) for supplying biofuel to an internal combustion engine (2), in particular of a vehicle; the supply system (1) comprises: a main tank (5) containing biofuel; an auxiliary tank (6) containing petroleum fuel; a fuel hydraulic circuit (13) configured to supply to the internal combustion engine (2) the biofuel contained in the main tank (5) or the petroleum fuel contained in the auxiliary tank (6); a heating hydraulic circuit (7) within which a heating liquid flows intended to heat the biofuel and provided with a first heat exchanger (9); and a heating device (8) which is configured to generate heat autonomously and completely independently from the internal combustion engine (2), is connected to the heating hydraulic circuit (7), and is configured to heat the heating liquid flowing in the heating hydraulic circuit (7); the supply system (1) is characterized in that: the first heat exchanger (9) is arranged inside the main tank (5); the fuel hydraulic circuit (13) comprises a first delivery duct (15) that originates from the main tank (5) and is preferably provided with a first check valve (16) that permits flow of biofuel only out of the main tank (5); the fuel hydraulic circuit (13) comprises an accumulation tank (14) into which the first delivery duct (15) flows and which is configured to accumulate a certain quantity of biofuel; the fuel hydraulic circuit (13) comprises a second delivery duct (20) that originates from the accumulation tank (14) and is configured to supply the biofuel toward the internal combustion engine (2); and the fuel hydraulic circuit (13) comprises a first circulation pump (18) arranged along the first delivery duct (15) and configured to circulate the biofuel from the main tank (5) to the accumulation tank (14).

2. The supply system (1) according to claim 1 , wherein the fuel hydraulic circuit (13) comprises a second heat exchanger (19) that is arranged along the first delivery duct (15), is connected to the heating hydraulic circuit (7), and is configured to perform heat exchange between the heating liquid and the biofuel.

3. The supply system (1) according to claim 2, wherein the fuel hydraulic circuit (13) comprises a first return duct (33) that originates from the second delivery duct (20) and ends in the main tank (5) and is preferably provided with a second check valve (34) that permits flow of biofuel only toward the main tank (5).

4. The supply system (1) according to claim 3, wherein the fuel hydraulic circuit (13) comprises: a bypass duct (37) that connects the first delivery duct (15) to the first return duct (33); and a two-way valve (38) controllable to open or close the passage through the bypass duct (37).

5. The supply system (1) according to one of claims 1 to 4, wherein the fuel hydraulic circuit (13) comprises: a third delivery duct (25) that originates from the auxiliary tank (6) and is preferably provided with a third check valve (26) that permits flow of petroleum fuel only out of the auxiliary tank (6); and a first three-way valve (21) configured to connect to the internal combustion engine (2)alternatively the second delivery duct (20) or the third delivery duct (25).

6. The supply system (1) according to claim 5, wherein the fuel hydraulic circuit (13) comprises: a second return duct (30) that flows into the main tank (5); a third return duct (31) that flows into the auxiliary tank (6); and a second three-way valve (29) controllable to connect to the internal combustion engine (2) alternatively the second return duct (30) or the third return duct (31).

7. The supply system (1) according to claim 6, wherein the fuel hydraulic circuit (13) comprises: a fourth return duct (28) that connects the internal combustion engine (2) to the second three-way valve (29); and a concentration sensor (50) that is arranged along the fourth return duct (28) and is configured to determine the concentration of biofuel.

8. The supply system (1) according to claim 5, 6 or 7, wherein the fuel hydraulic circuit (13) comprises an interconnection duct (39) that connects the third delivery duct (25) to the first delivery duct (15) through a third three-way valve (40) controllable to connect to a final part of the delivery duct (15) alternatively an initial part of the delivery duct (15) or the interconnection duct (39).

9. The supply system (1) according to one of claims 5 to 8, wherein: the heating device (8) uses diesel; and the fuel hydraulic circuit (13) comprises a fourth delivery duct (35) that originates from the third delivery duct (25) and ends in the heating device (8) and preferably comprises a second circulation pump (36) that is arranged along the fourth delivery duct (35) and is configured to circulate the petroleum fuel from the auxiliary tank (6) to the heating device (8).

10. The supply system (1) according to one of claims 1 to 9 and comprising: a temperature sensor (42) configured to determine a temperature of the biofuel in the accumulation tank (14); and a control unit (43) configured to activate the first circulation pump (18) only when the temperature of the biofuel in the accumulation tank (14) exceeds a predetermined threshold value.11 . The supply system (1) according to one of claims 1 to 10 and comprising: a first viscosity sensor (50) configured to determine a viscosity of the biofuel in the main tank (5); and a control unit (43) configured to activate intake from the main tank (5) only when the viscosity of the biofuel in the main tank (5) drops below a predetermined threshold value.

12. The supply system (1) according to one of claims 1 to 11 and comprising: a temperature sensor (42) configured to determine a temperature of the biofuel in the accumulation tank (14); and a control unit (43) configured to supply to the internal combustion engine (2) the biofuel contained in the main tank (5) orthe petroleum fuel contained in the auxiliary tank (6) as a function of the temperature of the biofuel in the accumulation tank (14).

13. The supply system (1) according to one of claims 1 to 12 and comprising: a second viscosity sensor (50) configured to determine a viscosity of the biofuel in the accumulation tank (14); and a control unit (43) configured to supply to the internal combustion engine (2) the biofuel containedin the main tank (5) or the petroleum fuel contained in the auxiliary tank (6) as a function of the viscosity of the biofuel in the accumulation tank (14).

14. The supply system (1) according to one of claims 1 to 13, wherein the heating hydraulic circuit(7) can be connected to a cooling hydraulic circuit of the internal combustion engine (2) and comprises: a fifth delivery duct (44) that originates from a port made in the cooling hydraulic circuit of the internal combustion engine (2) to receive cooling liquid that circulates in the cooling hydraulic circuit of the internal combustion engine (2); a fifth return duct (45) that ends in a port made in the cooling hydraulic circuit of the internal combustion engine (2) to introduce cooling liquid into the cooling hydraulic circuit of the internal combustion engine (2); a sixth delivery duct (10) that originates from the heating device (8) and ends in the first heat exchanger (9); a sixth return duct (11) that connects an outlet of the first heat exchanger (9) to the heating device(8); a fourth three-way valve (48) controllable to connect to the fifth delivery duct (44) alternatively the heating device (8) or the sixth delivery duct (10) or to isolate the fifth delivery duct (44); and a sixth three-way valve (49) controllable to connect to an initial part of the sixth return duct (11) alternatively a final part of the sixth return duct (11) or the fifth return duct (45).

15. The supply system (1) according to one of claims 1 to 14, wherein the accumulation tank (14) is completely free of filtering elements and of filtering capacity, is arranged downstream of a filter (17) interposed along the first delivery duct (15), and is sized to contain a quantity of fuel sufficient to guarantee the operation at maximum power of the internal combustion engine (2) for a certain period of time, preferably at least one minute of operation at maximum power.

16. A supply method for supplying biofuel to an internal combustion engine (2), in particular of a vehicle; the supply method comprises the steps of: filling a main tank (5) with biofuel; filling an auxiliary tank (6) with petroleum fuel; supplying to the internal combustion engine (2), by means of a fuel hydraulic circuit (13), the biofuel contained in the main tank (5) or the petroleum fuel contained in the auxiliary tank (6); heating the biofuel by means of a heating hydraulic circuit (7) within which a heating liquid flows and provided with a heat exchanger (9); and heating the heating liquid by means of a heating device (8) which is configured to generate heat autonomously and completely independently from the internal combustion engine (2) and is connected to the heating hydraulic circuit (7); the supply method is characterized in that: the heat exchanger (9) is arranged inside the main tank (5); the fuel hydraulic circuit (13) comprises a first delivery duct (15) that originates from the main tank (5) and is preferably provided with a check valve (16) that permits flow of biofuel only out of the main tank (5); the fuel hydraulic circuit (13) comprises an accumulation tank (14) into which the first delivery duct (15) flows and which is configured to accumulate a certain quantity of biofuel;the fuel hydraulic circuit (13) comprises a second delivery duct (20) that originates from the accumulation tank (14) and is configured to supply the biofuel toward the internal combustion engine (2); and the fuel hydraulic circuit (13) comprises a circulation pump (18) arranged along the first delivery duct (15) and configured to circulate the biofuel from the main tank (5) to the accumulation tank (14).

17. A supply system (1) for supplying biofuel to an internal combustion engine (2), in particular of a vehicle; the supply system (1) comprises: a main tank (5) containing biofuel; an auxiliary tank (6) containing petroleum fuel; a fuel hydraulic circuit (13) configured to supply to the internal combustion engine (2) the biofuel contained in the main tank (5) or the petroleum fuel contained in the auxiliary tank (6); and a heating hydraulic circuit (7) within which a heating liquid flows intended to heat the biofuel and provided with a first heat exchanger (9) arranged inside the main tank (5); wherein the fuel hydraulic circuit (13) comprises a first delivery duct (15) that originates from the main tank (5) and at least one second heat exchanger (19) that is arranged outside the main tank (5) and along the first delivery duct (15), is connected to the heating hydraulic circuit (7), and is configured to perform heat exchange between the heating liquid and the biofuel that circulates in the first delivery duct (15); the supply system (1) is characterized in that the fuel hydraulic circuit (13) comprises: an accumulation tank (14) that preferably is completely free of filtering elements and of filtering capacity, is configured to accumulate a certain quantity of biofuel, and into which the first delivery duct (15) flows and which; a second delivery duct (20) that originates from the accumulation tank (14) and is configured to supply the biofuel toward the internal combustion engine (2); and a first circulation pump (18) arranged along the first delivery duct (15) and configured to circulate the biofuel from the main tank (5) to the accumulation tank (14).

18. The supply system (1) according to claim 17, wherein the accumulation tank (14) is sized to contain a quantity of fuel sufficient to guarantee the operation at maximum power of the internal combustion engine (2) for a certain period of time, preferably at least one minute of operation at maximum power.

19. The supply system (1) according to claim 17 or 18, wherein the fuel hydraulic circuit (13) comprises a filter (17) interposed along the first delivery duct (15) upstream of the accumulation tank (14).

20. The supply system (1) according to claim 17, 18 or 19 and comprising a heating device (8) which is completely independent and separate from the internal combustion engine (2), is connected to the heating hydraulic circuit (7) and is configured to heat the heating liquid.

21. The supply system (1) according to one of claims 17 to 20, wherein the fuel hydraulic circuit (13) comprises a first return duct (33) that originates from the second delivery duct (20) and ends in the main tank (5) and is preferably provided with a second check valve (34) that permits flow of biofuel only toward the main tank (5).

22. The supply system (1) according to claim 21 , wherein the fuel hydraulic circuit (13) comprises: a bypass duct (37) that connects the first delivery duct (15) to the first return duct (33); anda first two-way valve (38) controllable to open or close the passage through the bypass duct (37).

23. The supply system (1) according to claim 20, 21 or 22, wherein the fuel hydraulic circuit (13) comprises: a third delivery duct (25) that originates from the auxiliary tank (6) and is preferably provided with a third check valve (26) that permits flow of biofuel only out of the auxiliary tank (6); and a first three-way valve (21) configured to connect to the internal combustion engine (2) alternatively the second delivery duct (20) or the third delivery duct (25).

24. The supply system (1) according to claim 23, wherein the fuel hydraulic circuit (13) comprises: a second return duct (30) that flows into the main tank (5); a third return duct (31) that flows into the auxiliary tank (6); and a second three-way valve (29) controllable to connect to the internal combustion engine (2) alternatively the second return duct (30) or the third return duct (31).

25. The supply system (1) according to claim 23 or 24, wherein the fuel hydraulic circuit (13) comprises an interconnection duct (39) that connects the third delivery duct (25) to the first delivery duct (15) through a third three-way valve (40) controllable to connect to a final part of the delivery duct (15) alternatively an initial part of the delivery duct (15) or the interconnection duct (39).

26. The supply system (1) according to claim 23, 24 or 25, wherein: the heating device (8) uses diesel; and the fuel hydraulic circuit (13) comprises a fourth delivery duct (35) that originates from the third delivery duct (25) and ends in the heating device (8) and preferably also comprises a second circulation pump (36) that is arranged along the fourth delivery duct (35) and is configured to circulate the petroleum fuel from the auxiliary tank (6) to the heating device (8).

27. The supply system (1) according to one of claims 17 to 26, wherein the heating hydraulic circuit (7) can be connected to a cooling hydraulic circuit of the internal combustion engine (2) and comprises: a fifth delivery duct (44) that originates from a port made in the cooling hydraulic circuit of the internal combustion engine (2) to receive cooling liquid that circulates in the cooling hydraulic circuit of the internal combustion engine (2); and a fifth return duct (45) that ends in a port made in the cooling hydraulic circuit of the internal combustion engine (2) to introduce cooling liquid into the cooling hydraulic circuit of the internal combustion engine (2).

28. The supply system (1) according to claim 27, wherein the heating hydraulic circuit (7) comprises: a sixth delivery duct (10) that originates from the heating device (8) and ends in the first heat exchanger (9); a sixth return duct (11) that connects an outlet of the first heat exchanger (9) to the heating device (8); a third three-way valve (48) controllable to connect to the fifth delivery duct (44) alternatively the heating device (8) or the sixth delivery duct (10) or to isolate the fifth delivery duct (44); and a sixth three-way valve (49) controllable to connect to an initial part of the sixth return duct (11) alternatively a final part of the sixth return duct (11) or the fifth return duct (45).

29. The supply system (1) according to one of claims 17 to 26, wherein: the cooling liquid consists of lubricating oil; and the heating hydraulic circuit (7) can be connected to a hydraulic lubrication circuit of the internal combustion engine (2) to exchange lubricating oil with the hydraulic lubrication circuit.

30. A supply method for supplying biofuel to an internal combustion engine (2), in particular of a vehicle; the supply method comprises the steps of: filling a main tank (5) with biofuel; filling an auxiliary tank (6) with petroleum fuel; supplying to the internal combustion engine (2), by means of a fuel hydraulic circuit (13), the biofuel contained in the main tank (5) or the petroleum fuel contained in the auxiliary tank (6); heating the biofuel by means of a heating hydraulic circuit (7) within which a heating liquid flows and provided with a first heat exchanger (9) arranged inside the main tank (5); wherein the fuel hydraulic circuit (13) comprises a delivery duct (15) that originates from the main tank (5); wherein the fuel hydraulic circuit (13) comprises at least one second heat exchanger (19) that is arranged outside the main tank (5) and along the delivery duct (15), is connected to the heating hydraulic circuit (7), and is configured to perform heat exchange between the heating liquid and the biofuel that circulates in the delivery duct (15); the supply method is characterized in that the fuel hydraulic circuit (13) comprises: an accumulation tank (14) that preferably is completely free of filtering elements and of filtering capacity, is configured to accumulate a certain quantity of biofuel, and into which the first delivery duct (15) flows and which; a second delivery duct (20) that originates from the accumulation tank (14) and is configured to supply the biofuel toward the internal combustion engine (2); and a circulation pump (18) arranged along the first delivery duct (15) and configured to circulate the biofuel from the main tank (5) to the accumulation tank (14).31 . A supply system (1) for supplying biofuel to an internal combustion engine (2), in particular of a vehicle; the supply system (1) comprises: a main tank (5) containing biofuel; an auxiliary tank (6) containing petroleum fuel; a fuel hydraulic circuit (13) configured to supply to the internal combustion engine (2) the biofuel contained in the main tank (5) or the petroleum fuel contained in the auxiliary tank (6); and a heating hydraulic circuit (7) within which a heating liquid flows intended to heat the biofuel and provided with a first heat exchanger (9) arranged inside the main tank (5); the supply system (1) is characterized by the fact of comprising: at least one viscosity sensor (50) to determine a viscosity of the biofuel; and a control unit (43) configured to supply to the internal combustion engine (2) the biofuel contained in the main tank (5) or the petroleum fuel contained in the auxiliary tank (6) as a function of the viscosity of the biofuel measured by the viscosity sensor (50).

32. The supply system (1) according to claim 31 , wherein the viscosity sensor (50) is arranged inside the main tank (5).

33. The supply system (1) according to claim 31 or 32, wherein the fuel hydraulic circuit (13) comprises: a first delivery duct (15) that originates from the main tank (5) and is preferably provided with a first check valve (16) that permits flow of biofuel only out of the main tank (5); and an accumulation tank (14) into which the first delivery duct (15) flows and which is configured to accumulate a certain quantity of biofuel; a second delivery duct (20) that originates from the accumulation tank (14) and is configured to supply the biofuel toward the internal combustion engine (2); and a first circulation pump (18) arranged along the first delivery duct (15) and configured to circulate the biofuel from the main tank (5) to the accumulation tank (14).

34. The supply system (1) according to claim 33, wherein the viscosity sensor (50) is arranged inside the accumulation tank (14).

35. The supply system (1) according to claim 33 or 34, wherein the fuel hydraulic circuit (13) comprises a first return duct (33) that originates from the second delivery duct (20) and ends in the main tank (5) and is preferably provided with a second check valve (34) that permits flow of biofuel only toward the main tank (5).

36. The supply system (1) according to claim 33, 34 or 35, wherein the fuel hydraulic circuit (13) comprises: a third delivery duct (25) that originates from the auxiliary tank (6) and is preferably provided with a third check valve (26) that permits flow of petroleum fuel only out of the auxiliary tank (6); and a first three-way valve (21) which is configured to connect to the internal combustion engine (2) alternatively the second delivery duct (20) or the third delivery duct (25) and is controlled by the control unit (43) as a function of the viscosity of the biofuel.

37. The supply system (1) according to claim 36, wherein the fuel hydraulic circuit (13) comprises: a second return duct (30) that flows into the main tank (5); a third return duct (31) that flows into the auxiliary tank (6); and a second three-way valve (29) which is controllable to connect to the internal combustion engine (2) alternatively the second return duct (30) or the third return duct (31) and is controlled by the control unit (43) as a function of the viscosity of the biofuel.

38. The supply system (1) according to one of claims 31 to 37, wherein the control unit (43) is configured to supply to the internal combustion engine (2) the biofuel contained in the main tank (5) when the viscosity measured by the viscosity sensor (50) is lower than a threshold value and to supply to the internal combustion engine (2) the petroleum fuel contained in the auxiliary tank (6) when the viscosity measured by the viscosity sensor (50) is higher than the threshold value.

39. A supply method for supplying biofuel to an internal combustion engine (2), in particular of a vehicle; the supply method comprises the steps of: filling a main tank (5) with biofuel; filling an auxiliary tank (6) with petroleum fuel; supplying to the internal combustion engine (2), by means of a fuel hydraulic circuit (13), the biofuel contained in the main tank (5) or the petroleum fuel contained in the auxiliary tank (6); and heating the biofuel by means of a heating hydraulic circuit (7) within which a heating liquid flowsand provided with a first heat exchanger (9) arranged inside the main tank (5); the supply method is characterized by comprising the steps of: determining a viscosity of the biofuel by means of at least one viscosity sensor (50); and supplying to the internal combustion engine (2) the biofuel contained in the main tank (5) or the petroleum fuel contained in the auxiliary tank (6) as a function of the viscosity of the biofuel measured by the viscosity sensor (50).

40. A supply system (1) for supplying biofuel to an internal combustion engine (2); the supply system (1) comprises: a main tank (5) containing biofuel; an auxiliary tank (6) containing petroleum fuel; a fuel hydraulic circuit (13) configured to supply to the internal combustion engine (2) the biofuel contained in the main tank (5) or the petroleum fuel contained in the auxiliary tank (6); and a control unit (43) configured to perform, during a shutdown of the internal combustion engine (2) and before the internal combustion engine (2) stops, a first cleaning cycle during which petroleum fuel contained in the auxiliary tank (6) is supplied to the internal combustion engine (2) to reduce in the internal combustion engine (2) the presence of biofuel; the supply system (1) is characterized in that the control unit (43) is configured to perform, only after the internal combustion engine (2) has stopped, a second cleaning cycle which is subsequent to the first cleaning cycle and during which petroleum fuel contained in the auxiliary tank (6) is supplied to the fuel hydraulic circuit (13) only and excluding the internal combustion engine (2) to reduce in the fuel hydraulic circuit (13) the presence of biofuel.

41. The supply system (1) according to claim 40, wherein the control unit (43) is configured to perform the first cleaning cycle at each shutdown of the internal combustion engine (2).

42. The supply system (1) according to claim 40 or 41 , wherein the control unit (43) is configured to perform the second cleaning cycle only after a predetermined time interval has passed from the last first cleaning cycle, that is, from the last shutdown of the internal combustion engine (2).

43. The supply system (1) according to claim 40, 41 or 42, wherein the control unit (43) is configured to perform the second cleaning cycle only if a temperature of the biodiesel present in the fuel hydraulic circuit (13) or in the main tank (5) is lower than a predetermined threshold value.

44. The supply system (1) according to one of claims 40 to 43, wherein the fuel hydraulic circuit (13) comprises: a first return duct (28) that originates from the internal combustion engine (2); a second return duct (30) that flows into the main tank (5); a third return duct (31) that flows into the auxiliary tank (6); and a first three-way valve (29) controllable to connect to the first return duct (28) alternatively the second return duct (30) or the third return duct (31).

45. The supply system (1) according to claim 44, wherein the control unit (43) controls the first three-way valve (29) to connect to the first return duct (28) the second return duct (30) during an initial phase of the first cleaning cycle and to connect to the first return duct (28) the third return duct (31) during a final phase of the first cleaning cycle.

46. The supply system (1) according to one of claims 40 to 45, wherein the control unit (43) isconfigured to control each cleaning cycle as a function of time and therefore to terminate the cleaning cycle after a predetermined time interval has elapsed.

47. The supply system (1) according to one of claims 40 to 45, wherein: a concentration sensor (50) is provided configured to determine the concentration of biofuel in a fuel exiting from the internal combustion engine (2); and the control unit (43) is configured to control the first cleaning cycle as a function of the concentration of biofuel determined by the concentration sensor (50) and therefore to terminate the first cleaning cycle when the concentration of biofuel is lower than a predetermined threshold value.

48. The supply system (1) according to claim 47, wherein the fuel hydraulic circuit (13) comprises: a first return duct (28) that originates from the internal combustion engine (2) and along which the concentration sensor (50) is arranged; a second return duct (30) that flows into the main tank (5); a third return duct (31) that flows into the auxiliary tank (6); and a first three-way valve (29) controllable to connect to the first return duct (28) alternatively the second return duct (30) or the third return duct (31).

49. The supply system (1) according to one of claims 40 to 48 wherein: the fuel hydraulic circuit (13) comprises a first delivery duct (15) that originates from the main tank (5); and the control unit (43) is configured to circulate, during each cleaning cycle, the petroleum fuel contained in the auxiliary tank (6) also along a final part of the first delivery duct (15) to reduce in the final part of the first delivery duct (15) the presence of biofuel.

50. The supply system (1) according to claim 49, wherein: the fuel hydraulic circuit (13) comprises: an accumulation tank (14) into which the first delivery duct (15) flows and which is configured to accumulate a certain quantity of biofuel; and a second delivery duct (20) that originates from the accumulation tank (14) and is configured to supply the biofuel toward the internal combustion engine (2); and the control unit (43) is configured to circulate, during each cleaning cycle, the petroleum fuel contained in the auxiliary tank (6) also through the accumulation tank (14) and along the second delivery duct (20) to reduce in the accumulation tank (14) and in the second delivery duct (20) the presence of biofuel.51 . The supply system (1) according to claim 50, wherein the fuel hydraulic circuit (13) comprises: a third delivery duct (25) that originates from the auxiliary tank (6) and is preferably provided with a third check valve (26) that permits flow of biofuel only out of the auxiliary tank (6); a second three-way valve (21) configured to connect to the internal combustion engine (2) alternatively the second delivery duct (20) or the third delivery duct (25); and an interconnection duct (39) that connects the third delivery duct (25) to the first delivery duct (15) through a third three-way valve (40) controllable to connect to a final part of the delivery duct (15) alternatively an initial part of the delivery duct (15) or the interconnection duct (39).

52. The supply system (1) according to one of claims 1 to 51 , wherein the control unit (43) is configured to perform, during a shutdown of the internal combustion engine (2), the first cleaning cycle only if it is foreseen that the internal combustion engine (2) will remain stopped for a long time andpreferably longer than 30 minutes when the ambient temperature is lower than the solidification temperature of the biofuel and preferably longer than 24 hours when the ambient temperature is higher than the solidification temperature of the biofuel.

53. The supply system (1) according to one of claims 1 to 52, wherein the fuel hydraulic circuit (13) comprises: a first delivery duct (15) that originates from the main tank (5) and is preferably provided with a first check valve (16) that permits flow of biofuel only out of the main tank (5); an accumulation tank (14) into which the first delivery duct (15) flows and which is configured to accumulate a certain quantity of biofuel; a second delivery duct (20) that originates from the accumulation tank (14) and is configured to supply the biofuel toward the internal combustion engine (2); a third delivery duct (25) that originates from the auxiliary tank (6) and is preferably provided with a third check valve (26) that permits flow of petroleum fuel only out of the auxiliary tank (6); a circulation pump (18) arranged along the first delivery duct (15) and configured to circulate the biofuel from the main tank (5) to the accumulation tank (14); a first return duct (33) that originates from the second delivery duct (20) and ends in the main tank (5) and is preferably provided with a second check valve (34) that permits flow of biofuel only toward the main tank (5); a second return duct (30) that flows into the main tank (5); a third return duct (31) that flows into the auxiliary tank (6); an interconnection duct (39) that connects the third delivery duct (25) to the first delivery duct (15); a first three-way valve (21) configured to connect to the internal combustion engine (2) alternatively the second delivery duct (20) or the third delivery duct (25); a second three-way valve (29) controllable to connect to the internal combustion engine (2) alternatively the second return duct (30) or the third return duct (31); and a third three-way valve (40) controllable to connect to a final part of the delivery duct (15) alternatively an initial part of the delivery duct (15) or the interconnection duct (39).

54. The supply system (1) according to claim 53, wherein the fuel hydraulic circuit (13) comprises: a bypass duct (37) that connects the first delivery duct (15) to the first return duct (33); and a two-way valve (38) controllable to open or close the passage through the bypass duct (37).

55. The supply system (1) according to claim 53 or 54, wherein: to perform the first cleaning cycle, the control unit (43) is configured to control the first three-way valve (21) to connect to the internal combustion engine (2) the third delivery duct (25) that originates from the auxiliary tank (6); or to perform the first cleaning cycle, the control unit (43) is configured to control the first three-way valve (21) to connect to the internal combustion engine (2) the second delivery duct (20) and to control the third three-way valve (40) to connect to the final part of the delivery duct (15) the interconnection duct (39) and therefore the third delivery duct (25).

56. The supply system (1) according to claim 53, 54 or 55, wherein, to perform the second cleaning cycle, the control unit (43) is configured to control the first three-way valve (21) to connect to the internal combustion engine (2) the third delivery duct (25), to control the third three-way valve (40) to connect tothe final part of the delivery duct (15) the interconnection duct (39) and therefore the third delivery duct (25), and to actuate the circulation pump (18).

57. A supply method for supplying biofuel to an internal combustion engine (2); the supply method comprises the steps of: filling a main tank (5) with biofuel; filling an auxiliary tank (6) with petroleum fuel; supplying to the internal combustion engine (2), by means of a fuel hydraulic circuit (13), the biofuel contained in the main tank (5) or the petroleum fuel contained in the auxiliary tank (6); and performing, during a shutdown of the internal combustion engine (2) and before the internal combustion engine (2) stops, a first cleaning cycle during which petroleum fuel contained in the auxiliary tank (6) is supplied to the internal combustion engine (2) to reduce in the internal combustion engine (2) the presence of biofuel; the supply method is characterized by comprising the step of performing, only after the internal combustion engine (2) has stopped, a second cleaning cycle which is subsequent to the first cleaning cycle and during which petroleum fuel contained in the auxiliary tank (6) is supplied to the fuel hydraulic circuit (13) only and excluding the internal combustion engine (2) to reduce in the fuel hydraulic circuit (13) the presence of biofuel.

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