A fuel system for an engine and an engine system comprising such a fuel system

Abstract

A fuel system for an engine 2 comprising a source of liquid ammonia 14; a fuel injector 13; an ammonia fuel line 15 for transferring ammonia from the source of liquid ammonia to the fuel injector; and

Description

The present invention relates to a fuel system for an engine. More particularly, but not exclusively, the present invention relates to a fuel system for an engine, the fuel system comprising an ammonia pump arranged in series in an ammonia fuel line extending between a source of liquid ammonia and a fuel injector, and a pressure reducing valve and a cooling jacket arranged in series in an ammonia cracker line between a source of liquid ammonia and an ammonia cracker, the cooling jacket extending through or at least partially surrounding the ammonia pump and being in thermal contact therewith. The present invention also relates to an engine system. More particularly, but not exclusively the present invention relates to an engine system comprising an engine and such a fuel system for an engine connected thereto. Engine systems which use ammonia as fuel are known. It is well known however that ammonia tends to change phase from liquid to gas. This problem becomes more pronounced as temperature increases. Such engine systems typically include high pressure ammonia pumps which provide ammonia to a common fuel rail and then to ammonia injectors. Such pumps typically comprise a cylinder which contains a piston. If ammonia vapour is present in the cylinder of the pump then the increase in pressure in the cylinder during a stroke of the piston is unlikely to be sufficient to liquify the ammonia vapour. This means that ammonia vapour is transferred to the common fuel rail and hence to the fuel injectors which can prevent the fuel injectors from operating. The present invention seeks to overcome the problems of the prior art. Accordingly, in a first aspect, the present invention provides a fuel system for an engine comprising a source of liquid ammonia; a fuel injector; an ammonia fuel line extending between the source of liquid ammonia and fuel injector for transferring ammonia from the source of liquid ammonia to the fuel injector; an ammonia pump arranged in series in the ammonia fuel line; an ammonia cracker; an ammonia cracker line extending between the source of liquid ammonia and ammonia cracker for the transfer of ammonia from the source of liquid ammonia to the ammonia cracker; a cooling jacket arranged in series in the ammonia cracker line; and, a pressure reducing valve arranged in series in the ammonia cracker line between the source of liquid ammonia and the cooling jacket; the cooling jacket extending through or at least partially surrounding the ammonia pump and being in thermal contact therewith. The fuel system for an engine according to the invention uses ammonia as a fuel. However, is also uses the cooling of ammonia as it passes through the pressure reducing valve and then cooling jacket on its way to the ammonia cracker to cool the ammonia pump, so ensuring the ammonia in the ammonia pump is in the liquid state and so increasing the efficiency of the engine. Preferably the cooling jacket at least partially surrounds the ammonia pump. Preferably the cooling jacket comprises a jacket wall defining a jacket volume. Preferably the cooling jacket comprises a cooling block which defines at least one cooling tube extending therethrough, the at least one cooling tube being connected in series in the ammonia cracker line. Alternatively, the cooling jacket extends through the ammonia pump. Preferably the cooling jacket comprises a cooling block defining at least one cooling tube. Preferably the pressure reducing valve is attached to the ammonia pump so as to produce thermal contact between the two. Preferably the ammonia fuel line and the ammonia cracker line comprise a common branch portion extending from the source of liquid ammonia. Preferably the fuel system for an engine further comprises an ammonia lift pump arranged in the common branch portion. Alternatively, the source of liquid ammonia comprises a primary source of liquid ammonia and a secondary source of liquid ammonia, the primary source of liquid ammonia being connected to the ammonia fuel line and the secondary source of liquid ammonia being connected to the ammonia cracker line. Preferably the portion of the ammonia fuel line between the ammonia pump and the fuel injector is termed the common fuel rail; the fuel system further comprising a heat exchanger, the heat exchanger comprising first and second heat exchange paths extending therethrough, the first heat exchange path being arranged in series in the common fuel rail and the second heat exchange path being arranged in series in the ammonia cracker line between the cooling jacket and cracker. Preferably the fuel system for an engine further comprises at least one of a vaporiser and a preheater arranged in series in the ammonia cracker line between the heat exchanger and ammonia cracker. Preferably the fuel system for an engine further comprises an ammonia pressure sensor configured to measure the pressure of ammonia in the common fuel rail; and, a pressure control unit connected to the pressure sensor and ammonia pump and configured to control the ammonia pump in response to the pressure measured by the ammonia pressure sensor. Preferably the ammonia pump comprises a piston in fluid communication with the ammonia fuel line. In a further aspect of the invention there is provided an engine system comprising a fuel system for an engine as claimed in any one of claims 1 to 9; and, an engine, the engine comprising at least one cylinder, the cylinder comprising a cylinder wall which defines a cylinder volume; and, an inlet manifold connected to the cylinder for providing an inlet gas to the cylinder volume; the fuel injector extending through the cylinder wall. Preferably the engine system further comprises a hydrogen injector and a hydrogen line extending from the hydrogen injector to the ammonia cracker for providing hydrogen from the ammonia cracker to the hydrogen injector; the hydrogen injector being configured provide hydrogen to the cylinder volume. Preferably the hydrogen injector extends through the cylinder wall. Preferably the engine system further comprises a piston arranged within the cylinder, the hydrogen injector being arranged such that it is covered by the piston during a compression phase of the engine. Alternatively, the hydrogen injector is configured to inject hydrogen into the inlet manifold. The present invention will now be described by way of example only and not in any limitative sense with reference to the accompanying drawings in which Figure 1 shows, in schematic form, an engine system according to the invention; Figure 2 shows, in schematic form, the ammonia pump of the engine system of figure 1; Figure 3 shows, in schematic form, a further embodiment of an engine system according to the invention; Figure 4 shows, in schematic form, a further embodiment of an engine system according to the invention; and, Figure 5 shows, in schematic form. A further embodiment of an engine system according to the invention. Shown in figure 1, in schematic form, is a first embodiment of an engine system 1 according to the invention. The engine system 1 comprises an engine 2 which comprises a plurality of cylinders 3, only one of which is shown. The cylinder 3 comprises a cylinder wall 4 which defines a cylinder volume 5. Arranged in the cylinder volume 5 is a piston 6 which in use is reciprocally displaced along a piston axis 7 as the engine 2 performs a two or four stroke cycle. The engine 2 further comprises an inlet manifold 8 which is connected to the cylinder 3 by an inlet valve 9. An exhaust manifold 10 is connected to the cylinder 3 by an exhaust valve 11. As is known in the art, during an intake phase of the engine 2 the inlet valve 9 opens to allow an intake gas to be drawn from the inlet manifold 8 into the cylinder volume 5. During an exhaust phase of the engine 2 the exhaust valve 11 opens to allow exhaust gasses in the cylinder volume 5 to be expelled to the exhaust manifold 10. The engine system 1 further comprises a fuel system 12. The fuel system 12 comprises a fuel injector 13 which extends through the cylinder wall 4 which in use injects liquid ammonia into the cylinder volume 5 at the appropriate point in the two or four stroke cycle. The fuel system 12 further comprises a source of liquid ammonia 14. In this embodiment the source of liquid ammonia 14 is a pressurised cylinder containing liquid ammonia at a pressure of around 5 to 15 bar. Extending between the source of liquid ammonia 14 and the fuel injector 13 is an ammonia fuel line 15 for transferring liquid ammonia from the source of liquid ammonia 14 to the fuel injector 13. Arranged in series in the ammonia fuel line 15 such that ammonia flows through it is an ammonia pump 16. The portion of the ammonia fuel line 15 between the ammonia pump 16 and the fuel injector 13 is termed the common fuel rail 17. Connected to the common fuel rail 17 is an ammonia pressure sensor 18 for measuring the pressure of ammonia in the common fuel rail 17. Connected between the ammonia pump 16 and the ammonia pressure sensor 18 is a pressure control unit 19 which receives the pressure measured by the ammonia pressure sensor 18 and controls the ammonia pump 16 in response thereto to control the pressure in the common fuel rail 17. Typically, the pressure control unit 19 is configured to maintain the pressure in the common fuel rail 17 within a pre-defined range. Typically, the pre-defined range is around 50 to 500 bar. The ammonia pump 16 is shown in more detail in figure 2. The ammonia pump 16 comprises a first control valve 20 and a one way valve 21 arranged in series in the ammonia fuel line 15. Arranged between these two valves 20,21 and in fluid communication with the ammonia fuel line 15 is an ammonia pump cylinder 22 which defines an ammonia pump cylinder volume 23. The ammonia pump cylinder volume 23 contains an ammonia pump piston 24 as shown. In use in an intake phase the first control valve 20 is open. The piston 24 is displaced so as to increase the ammonia pump cylinder volume 23 and draw liquid ammonia into the ammonia pump cylinder volume 23. In an expulsion phase the ammonia pump piston 24 is then displaced in the opposite direction so decreasing the ammonia pump cylinder volume 23 and increasing the pressure of the liquid ammonia therein. At this point the first control valve 20 is closed and the liquid ammonia in the ammonia pump cylinder volume 23 is expelled through the one way valve 21 into the common fuel rail 15 so increasing the pressure of liquid ammonia in the common fuel rail 17. The ammonia pump 16 works well provided that is pumping solely liquid ammonia. If ammonia vapour is present in the ammonia pump cylinder volume 23 and common fuel rail 17 then the increase in pressure in the expulsion phase is minimal which prevents the pressure in the common fuel rail 17 from being increased to the desired level. Further, the increase in pressure is unlikely to be sufficient to re-liquify any ammonia vapour in the ammonia pump cylinder volume 23 and common fuel rail 17. The increase in temperature of the ammonia pump 16 during operation tends to exacerbate this problem. Returning to figure 1, the fuel system 12 further comprises an ammonia cracker 25 which cracks ammonia into nitrogen and hydrogen. Extending between the ammonia cracker 25 and source of liquid ammonia 14 is an ammonia cracker line 26 for transferring ammonia from the source of liquid ammonia 14 to the ammonia cracker 25. The ammonia cracker line 26 and ammonia fuel line 15 comprise a common branch portion 27 which extends from the source of liquid ammonia 14. The common branch portion 27 comprises a shut off valve 28 for isolating the source of liquid ammonia 14 from the remainder of the fuel system 12. It also comprises an ammonia lift pump 29 for providing liquid ammonia from the source of liquid ammonia 14 to the ammonia pump 16 and ammonia cracker 25. Arranged in series in the ammonia cracker line 26 between the source of liquid ammonia 14 and the cracker 25 is a cooling jacket 30. The cooling jacket 30 comprises a jacket wall 30a which defines a jacket volume 30b. The cooling jacket 30 abuts and partially surrounds the ammonia pump 16 and is in good thermal contact with the ammonia pump 16. Also connected in series in the ammonia cracker line 26 between the source of liquid ammonia 14 and the cooling jacket 30 is a pressure reducing valve 31 which reduces the pressure in the ammonia cracker line 26 before it reaches the cooling jacket 30. The fuel system 12 further comprises a heat exchanger 32 comprising first and second heat exchange paths 33,34 extending therethrough. The first and second heat exchange paths 33,34 are in good thermal contact. In this embodiment the heat exchanger 32 is a solid metal block. The first heat exchange path 33 comprises a tube extending through the block. The second heat exchange path 34 also comprises a tube extending through the block. The diameter of the second heat exchange path 34 is larger, typically two to three times larger, than the diameter of the first heat exchange path 33. The first heat exchange path 33 is arranged in series in the common fuel rail 17 such that ammonia travelling along the common fuel rail 17 passes along the first heat exchange path 33. The second heat exchange path 34 is connected in series in the ammonia cracker line 26 between the cooling jacket 30 and ammonia cracker 25 such that ammonia leaving the cooling jacket 30 flows through the second heat exchange path 34. Also connected in series in the ammonia cracker line 26 in series between the second heat exchange path 34 and ammonia cracker 25 is a vaporiser 35 and pre-heater 36 as shown. The engine system 12 further comprises a hydrogen line 37 extending between the ammonia cracker 25 and inlet manifold 8 for transferring hydrogen produced by the cracker 25 to the inlet manifold 8. In use liquid ammonia is provided from the source of liquid ammonia 14, through the shut off valve 28 to the lift pump 29. The lift pump 29 provides the liquid ammonia to the ammonia pump 16. The ammonia pump 16 pumps the ammonia into the common fuel rail 17, so increasing the pressure of liquid ammonia in the common fuel rail 17. The ammonia pressure sensor 18 repeatedly measures the pressure in the common fuel rail 17. The pressure control unit 19 reads the pressure measured by the ammonia pressure sensor 18 and in response controls the ammonia pump 16 to maintain the pressure of liquid ammonia in the common fuel rail 17 within a predetermined range. The ammonia lift pump 29 also provides liquid ammonia to the pressure reducing valve 31 in the ammonia cracker line 26. The pressure reducing valve 31 reduces the pressure of the liquid ammonia to typically around 1 to 2 bar. This drop in pressure creates a cooling effect, cooling the pressure reducing valve 31 and also the ammonia. It may also cause an at least partial phase change of the ammonia from liquid to gas. The temperature of the ammonia at this point is typically around -30 to -35 deg C. After exiting the pressure reducing valve 31 the ammonia flows along the ammonia cracker line 26 to the cooling jacket 30. The ammonia flows through the cooling jacket volume 30b so cooling the cooling jacket 30. The cooling jacket 30 is in good thermal contact with the ammonia pump 16 and so cools the ammonia pump 16. This may cause the ammonia in the cooling jacket 30 to boil, further changing its state from liquid to gas. Cooling of the ammonia pump 16 ensures that the ammonia in the ammonia pump cylinder volume 23 is in the liquid state which is important for the efficient operation of the ammonia pump 16 and engine system 1 as a whole as described above. The ammonia that leaves the cooling jacket 30, and which is now a mixture of ammonia gas and liquid, flows further along the ammonia cracker line 26 to the heat exchanger 32 and flows along the second heat exchange path 34. This is in good thermal contact with the first heat exchange path 33 which is in series in the common fuel rail 17 and so cools the ammonia in the common fuel rail 17, ensuring it remains in the liquid state. Passing through the heat exchanger causes further conversion of ammonia in the ammonia cracker line 26 from liquid to gas. After exiting the second heat exchange path 34 of the heat exchanger the ammonia travels further along the ammonia cracker line 26 passing through a vaporiser 35 and pre-heater 36 before reaching the ammonia cracker 25. The vaporiser 35 and pre-heater 36 ensure complete conversion of the ammonia in the ammonia cracker line 26 from liquid to gas before it reaches the cracker 25. The cracker 25 cracks the ammonia into nitrogen and hydrogen which then flows along the hydrogen line 37 to the inlet manifold 8. A hydrogen injector 38 injects hydrogen from the hydrogen line 37 into the inlet manifold 8 at the appropriate point in the operation of the engine system 1. Simultaneously with the above, the piston 6 is reciprocally displaced along the piston axis 7 as the engine 2 performs a two or four stroke cycle. During an intake phase the piston 6 moves away from the intake manifold 8. The intake valve 9 is open and exhaust valve 11 is closed. As the piston 6 moves away from the inlet manifold 8 the hydrogen in the inlet manifold 8 from the hydrogen line 37 combines with air to from an inlet gas which is drawn into the cylinder 4. During a compression phase of the engine 2 liquid ammonia is drawn from the common fuel rail 17 and injected into the cylinder volume 5 by the fuel injector 13. As the ammonia in the common fuel rail 17 has been cooled it is substantially, if not completely liquid, so increasing the efficiency of the engine 2. Typically the liquid ammonia is injected at high pressure, typically in the range 50 to 500 Bar. This improves fuel stratification, cooling the charge in the cylinder to prevent pre-ignition allowing higher compression ratios, which significantly improves engine efficiency and power output. Shown in figure 3 is an alternative embodiment of an engine system 1 according to the invention. This is similar to the embodiment of figure 1 but the fuel system 12 lacks the heat exchanger 32. In this embodiment the cooling of the ammonia pump 16 by the cooling jacket 30 is sufficient to maintain the ammonia in the ammonia fuel line 15 in a liquid state. Further, in this embodiment the source of liquid ammonia 14 comprises primary and secondary sources 39,40 of liquid ammonia as shown. The primary source 39 of liquid ammonia is connected to the ammonia fuel line 15. The secondary source 40 of liquid ammonia is connected to the ammonia cracker line 26. In a further embodiment of the invention shown in figure 4, the cooling jacket 30 comprises a cooling block 30c which extends partly around the ammonia pump 16. The cooling block 30c defines a plurality of cooling tubes 30d extending therethrough, the cooling tubes 30d being connected in series in the ammonia cracker line 26. In use the ammonia flows through the cooling tubes 30d so cooling the cooling jacket 30. In an alternative embodiment of the invention the cooling block 30c extends through the ammonia pump 16, typically through the ammonia pump cylinder volume 23. The cooling block 30c defines a plurality of cooling tubes 30d extending therethrough. Shown in figure 5 is a further embodiment of an engine system 1 according to the invention. This embodiment is similar to that of figure 1 except the hydrogen injector 38 extends through the cylinder wall 4 in order to inject hydrogen into the cylinder volume 5. An electronic control unit (not shown) controls the hydrogen injector 38 to inject hydrogen during or just after the closing of the inlet valve 9. The hydrogen injector 38 is arranged such that during the compression phase it is covered by the piston 6 so protecting it from high combustion pressures and temperatures. Further, in contrast to the embodiment of figure 1, the pressure reducing valve 31 is in thermal contact with the ammonia pump 16 so that in use the ammonia pump is cooled by both the pressure reducing valve 31 and cooling jacket 30.

Claims

1. A fuel system for an engine comprisinga source of liquid ammonia;a fuel injector;an ammonia fuel line extending between the source of liquid ammonia and fuel injector for transferring ammonia from the source of liquid ammonia to the fuel injector;an ammonia pump arranged in series in the ammonia fuel line;an ammonia cracker;an ammonia cracker line extending between the source of liquid ammonia and ammonia cracker for the transfer of ammonia from the source of liquid ammonia to the ammonia cracker;a cooling jacket arranged in series in the ammonia cracker line; and,a pressure reducing valve arranged in series in the ammonia cracker line between the source of liquid ammonia and the cooling jacket;the cooling jacket extending through or at least partially surrounding the ammonia pump and being in thermal contact therewith.

2. A fuel system as claimed in claim 1, wherein the cooling jacket at least partially surrounds the ammonia pump.

3. A fuel system as claimed in claim 2, wherein the cooling jacket comprises a jacket wall defining a jacket volume.

4. A fuel system as claimed in claim 2, wherein the cooling jacket comprises a cooling block which defines at least one cooling tube extending therethrough, the at least one cooling tube being connected in series in the ammonia cracker line.

5. A fuel system as claimed in claim 1, wherein the cooling jacket extends through the ammonia pump.

6. A fuel system as claimed in claim 5, wherein the cooling jacket comprises a cooling block defining at least one cooling tube.

7. A fuel system for an engine as claimed in any one of claims 1 to 6, wherein the pressure reducing valve is attached to the ammonia pump so as to produce thermal contact between the two.

8. A fuel system for an engine as claimed in any one of claims 1 to 7, wherein the ammonia fuel line and the ammonia cracker line comprise a common branch portion extending from the source of liquid ammonia.

9. A fuel system for an engine as claimed in claim 8, further comprising an ammonia lift pump arranged in the common branch portion.

10. A fuel system for an engine as claimed in claim 1, wherein the source of liquid ammonia comprises a primary source of liquid ammonia and a secondary source of liquid ammonia, the primary source of liquid ammonia being connected to the ammonia fuel line and the secondary source of liquid ammonia being connected to the ammonia cracker line.

11. A fuel system for an engine as claimed in any one of claims 1 to 10, wherein the portion of the ammonia fuel line between the ammonia pump and the fuel injector is termed the common fuel rail;the fuel system further comprising a heat exchanger, the heat exchanger comprising first and second heat exchange paths extending therethrough, the first heat exchange path beingarranged in series in the common fuel rail and the second heat exchange path being arranged in series in the ammonia cracker line between the cooling jacket and cracker.

12. A fuel system for an engine as claimed in claim 11, further comprising at least one of a vaporiser and a preheater arranged in series in the ammonia cracker line between the heat exchanger and ammonia cracker.

13. A fuel system for an engine as claimed in either of claims 11 or 12, further comprisingan ammonia pressure sensor configured to measure the pressure of ammonia in the common fuel rail; and,a pressure control unit connected to the pressure sensor and ammonia pump and configured to control the ammonia pump in response to the pressure measured by the ammonia pressure sensor.

14. A fuel system for an engine as claimed in any one of claims 1 to 13, wherein the ammonia pump comprises a piston in fluid communication with the ammonia fuel line.

15. An engine system comprisinga fuel system for an engine as claimed in any one of claims 1 to 14; and,an engine, the engine comprisingat least one cylinder, the cylinder comprising a cylinder wall which defines a cylinder volume; and,an inlet manifold connected to the cylinder for providing an inlet gas to the cylinder volume;the fuel injector extending through the cylinder wall.

16. An engine system as claimed in claim 15, further comprising a hydrogen injector and a hydrogen line extending from the hydrogen injector to the ammonia cracker for providing hydrogen from the ammonia cracker to the hydrogen injector;the hydrogen injector being configured provide hydrogen to the cylinder volume.

17. An engine system as claimed in claim 16, wherein the hydrogen injector extends through the cylinder wall.

18. An engine system as claimed in in claim 17, further comprising a piston arranged within the cylinder, the hydrogen injector being arranged such that it is covered by the piston during a compression phase of the engine.

19. An engine system as claimed in claim 16, wherein the hydrogen injector is configured to inject hydrogen into the inlet manifold.IntellectualPropertyOfficeApplication GB2413657.4Search report under Section 17 of the Patents Act 1977Date search completed: 16 May 2025Claims searched: 1-19International classificationSubclass and subgroup Valid from F02M21 / 02 01 / 01 / 2006 F02M43 / 00 01 / 01 / 2006 F02M43 / 02 01 / 01 / 2006Field of searchWorldwide search of patent documents classified in the following areas of the IPC:F02B, F02D, F02MDatabases used in the preparation of this search report:SEARCH-PATENTDocuments considered to be relevantPatent literatureCategory Relevant Document of relevanceclaimsA - KR 1020210145031 A (DAEWOO SHIPBUILDING &MARINE), See figures and paragraph 50. Disclosing an ammonia and hydrogen fuel system comprising a temperature controller C1 (which may be a cooler) positioned between a liquid ammonia pump HP and the engine E. No specific pump cooling is disclosed. A - US 2012 / 0004831 A1 (MIYAGAWA et al.), see figure 5 and paragraphs 28 and 36. Disclosing a ammonia and hydrogen fuel system comprising a liquid ammonia pump (paragraph 28). No specific pump cooling is disclosed. A - CN 114810433 B (FOSHAN XIANHU LABORATORY), See whole document, disclosing a liquid ammonia and hydrogen gas fuel injection system, wherein the liquid ammonia is pressurised buy a high-pressure pump 5. No cooling of the pump is disclosed. A - CN 114458444 B (QINGDAO DOUBLE RUI MARINE ENVIRONMENTAL ENGINEERING STOCK LTD COMPANY), See whole document. Disclosing an ammonia and hydrogen fuel system, wherein there are two liquid ammonia pumps 8 &10, and a downstream heat exchanger 12. No pump cooling is disclosed.Non-patent literatureCategory Relevant claims Document of relevanceCategoriesLetter or DescriptionsymbolLetter or symbol Description X Document indicating lack of novelty or inventive step.Y Document indicating lack of inventive step, if combined with another document of the same category. & Member of the same patent family. A Document indicating technological background. P Document published on or after the priority date but before the fling date of the present application. E Earlier application published on or after the filing date of the present application.

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