WO2024228009A1

WO2024228009A1 - A method of operating an engine system

Info

Publication number: WO2024228009A1
Application number: PCT/GB2024/051051
Authority: WO
Inventors: Paul QUICKENDEN; Ronald HODKINSON
Original assignee: Individual
Current assignee: Individual
Priority date: 2023-04-29
Filing date: 2024-04-23
Publication date: 2024-11-07
Anticipated expiration: 2025-10-29

Abstract

A method of operating an engine system comprising the steps of • (a) providing an engine system (1); • (b) providing an inlet gas to the cylinder volume (4) of a cylinder (2) of the engine system, the inlet gas comprising hydrogen and air; • (c) injecting unignited fuel into the cylinder volume during the compression phase of the cylinder to produce an unignited cylinder volume mixture, the unignited fuel comprising liquid ammonia; and, • (d) igniting the unignited cylinder volume mixture to initiate a combustion phase

Description

A method of operating an engine system

The present invention relates to a method of operating an engine system. More particularly, but not exclusively, the present invention relates to a method of operating an engine system comprising the steps of (a) providing an engine system, (b) providing an inlet gas to the cylinder volume of a cylinder of the engine system, the inlet gas comprising hydrogen and air, (c) injecting unignited fuel into the cylinder volume during the compression phase of the cylinder to produce an unignited cylinder volume mixture, the unignited fuel comprising liquid ammonia, and (d) igniting the unignited cylinder volume mixture to initiate a combustion phase.

Engine systems which use ammonia as fuel are known. It is known that ammonia can be difficult to burn and so hydrogen is added to aid combustion.

CN114810433A (Foshan Xianhu Laboratory) discloses a method of operating an engine system both in a start up phase and a running phase. In the start up phase hydrogen and air along with a small amount of ammonia are drawn into the cylinder volume during an intake phase. A mixture of ammonia and hydrogen is then ignited and injected into the cylinder volume. This process results in uneven burning within the cylinder volume and hence low efficiency.

US8,904,994B2 (Toyota Jidosha Kabushiki Kaisha) discloses an ammonia burning internal combustion engine. The engine comprises a liquid ammonia injector which injects ammonia into an inlet manifold which is connected to a cylinder volume. A hydrogen injector injects hydrogen directly into the cylinder volume. As ammonia is drawn from the inlet manifold into the cylinder volume during an intake phase the amount of air in the cylinder volume is reduced. This reduces engine power. Further, there is poor mixing with the hydrogen injected into the cylinder volume. This results in uneven and inefficient burning. Further, the hydrogen injector is exposed to the high temperatures and pressures in the cylinder volume during the compression and combustion phases which is undesirable. The present invention seeks to overcome the problems of the prior art.

Accordingly, the present invention provides a method of operating an engine system, the method comprising the steps of

(a) providing an engine system, the engine system comprising at least one cylinder, the cylinder comprising a cylinder wall which defines a cylinder volume and a piston arranged within the cylinder volume the piston configured to be reciprocally displaced within the cylinder volume as the cylinder performs a two stroke or four stroke cycle, the two stroke or four stroke cycle comprising intake, compression, combustion and exhaust phases; an inlet manifold connected to the cylinder and in fluid communication with the cylinder volume for providing an inlet gas to the cylinder volume; an exhaust manifold connected to the cylinder and in fluid communication with the cylinder volume for receiving an exhaust gas from the cylinder volume; a fuel injector extending through the cylinder wall and configured to inject fuel into the cylinder volume; and, a fuel source connected to the fuel injector;

(b) providing an inlet gas to the cylinder volume via the inlet manifold during the intake phase of the cylinder, the inlet gas comprising hydrogen and air;

(c) controlling the fuel injector to inject unignited fuel from the fuel source into the cylinder volume during the compression phase of the cylinder where it mixes with the inlet gas to produce an unignited cylinder volume mixture, the fuel comprising liquid ammonia; and

(d) igniting the unignited cylinder volume mixture at the end of the compression phase to initiate the combustion phase. In the method according to the invention an inlet gas comprising hydrogen and air is drawn into the cylinder volume during an intake phase of the cylinder. Liquid ammonia is then injected in to the cylinder volume during a compression phase of the cylinder where it mixes with the inlet gas to form a cylinder volume mixture. At the end of the compression phase the cylinder volume mixture is ignited. Injecting the ammonia into the cylinder volume during the compression phase ensures extensive mixing with the inlet gas which results in even and efficient burning. Further, since the air is drawn into the cylinder volume in one phase and the ammonia is injected into the cylinder volume in a subsequent phase this maximises the amount of air in the cylinder volume so maximising engine power. Further, as the source of hydrogen is connected to the inlet manifold it is protected from the high pressures and temperatures in the cylinder volume. Further, since the source of hydrogen is not exposed to high pressures it can comprise an ammonia cracker. The cracking of ammonia is more efficient at low pressures.

Preferably the cylinder volume mixture is ignited when the distance between the piston and the top dead center position of the piston is less than 10% of the range of motion of the piston, more preferably less than 5% of the range of motion of the piston.

Preferably the engine system further comprises a phase sensor, the phase sensor comprising a crankshaft position sensor and a camshaft position sensor, the phase of the cylinder being determined during the method by means of the phase sensor.

Preferably the inlet gas comprises less than 5% by mass of ammonia, preferably less than 1%.

Preferably the fuel comprises at least 95% by mass of ammonia, preferably at least 98% by mass. Preferably the engine system further comprises an intake valve arranged between the inlet manifold and cylinder volume configured to control the flow of inlet gas from the inlet manifold to the cylinder volume; the method further comprising the step of closing the intake valve at the start of the compression phase.

Preferably the engine system further comprises a spark plug extending through the cylinder wall, the step of igniting the cylinder volume mixture comprising the step of igniting the cylinder volume mixture by means of the spark plug.

Preferably the fuel source comprises a fuel tank, a fuel line extending from the fuel tank to the fuel injector and a fuel pump connected in series in the fuel line; the portion of the fuel line between the fuel pump and the fuel injector being termed the common fuel rail; the method further comprising the step of measuring the pressure in the common fuel rail and controlling the fuel pump in response to the measured common fuel rail pressure.

Preferably the step of controlling the fuel injector depends upon the measured common rail fuel pressure.

Preferably the method further comprises the step of measuring the engine speed and wherein the step of controlling the fuel injector depends upon the measured engine speed.

Preferably the engine system further comprises an ammonia cracker and wherein the step of providing an inlet gas to the cylinder volume via the inlet manifold comprises the steps of cracking ammonia into nitrogen and hydrogen by means of the ammonia cracker and providing the cracked hydrogen to the inlet manifold. Preferably the engine system further comprises a hydrogen line extending from the ammonia cracker to the inlet manifold and a hydrogen flow limiter valve arranged within the hydrogen line; the step of providing the inlet gas to the cylinder volume via the inlet manifold further comprising the steps of

(i) measuring the pressure in the hydrogen line; and,

(i) controlling the hydrogen flow limiter valve in response to the measured pressure to control the flow of hydrogen along the hydrogen line from the ammonia cracker to the inlet manifold.

Preferably the step of providing an inlet gas to the cylinder volume further comprises the step of measuring the engine speed and controlling the hydrogen flow limiter valve in response to the measured engine speed.

Preferably the engine system further comprises a catalyst connected to the exhaust manifold, the method further comprising the step of expelling exhaust gases from the cylinder volume into the exhaust manifold and then through the catalyst during the exhaust phase.

Preferably the engine system comprises a plurality of cylinders and a plurality of fuel injectors.

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 Figures 1(a) to 1(d) show, in schematic form, a first embodiment of an engine system which employs the method according to the invention with the cylinder in different phases during a four stroke cycle;

Figure 2 shows a further embodiment of an engine system which employs a method according to the invention; and,

Figure 3 shows the ammonia pump of figure 2 in vertical cross section.

Shown in figure 1(a) in schematic form is an engine system 1 which employs a method according to the invention. The engine system 1 comprises a cylinder 2 which comprises a cylinder wall 3 which defines a cylinder volume 4. The cylinder 2 further comprises a piston 5 arranged within the cylinder volume 4 and configured to be reciprocally displaced along a cylinder axis 6 as the cylinder 2 performs a four stroke cycle. The piston 5 is connected to a crankshaft 7 which in turn drives a camshaft (not shown) as is known in the art.

The engine system 1 further comprises an inlet manifold 8 which is connected to the cylinder 2 for providing an inlet gas to the cylinder volume 4. The inlet gas comprises hydrogen and air. The inlet gas typically comprises less than 5% by mass of ammonia, more preferably less than 1%. An intake valve 9 is arranged between the inlet manifold 8 and cylinder volume 4 and controls the flow of inlet gas from the inlet manifold 8 into the cylinder volume 4.

The engine system 1 further comprises an exhaust manifold 10 which is connected to the cylinder 2 and receives exhaust gas from the cylinder volume 4. An exhaust valve 11 is arranged between the cylinder volume 4 and exhaust manifold 10 to control the flow of exhaust gas between the cylinder volume 4 and exhaust manifold 10. The engine system 1 further comprises a spark plug 12 which extends through the cylinder 2 and into the cylinder volume 4 as shown.

The engine system 1 comprises a fuel injector 13 which extends through the cylinder wall and is configured so as to directly inject fuel into the cylinder volume 4. The engine system 1 further comprises a fuel source 14 connected to the fuel injector 13 and air and hydrogen sources 15,16 connected to the inlet manifold 8. The engine system 1 further comprises an injection control unit 17 connected to the fuel injector 13 and configured to control the injector 13 to inject fuel from the fuel source 14 into the cylinder volume 4. The fuel is liquid ammonia or substantially liquid ammonia. Preferably it typically comprises at least 95% by mass of liquid ammonia, more preferably at least 98% by mass.

In use the cylinder 2 performs a well-known four stroke cycle. As is known in the art, when performing the cycle the cylinder 2 passes through four phases - intake, compression, combustion, and exhaust. In figure 1(a) the cylinder 2 is shown in the intake phase. In this phase the intake valve 9 is open, and the piston 5 is moving away from the intake valve 9. Hydrogen and air mix in the inlet manifold 8 to produce the inlet gas. The motion of the piston 5 draws the inlet gas into the cylinder volume 4.

Figure 1(b) shows the cylinder 2 in the compression phase. In this phase the intake valve 9 and exhaust valve 11 are both closed. The piston 5 moves towards the intake and exhaust valves 9,11 so increasing the pressure of the inlet gas in the cylinder volume 4. The engine system 1 further comprises a phase sensor 18 for measuring the phase of the cylinder 2. The injection control unit 17 is connected to the phase sensor 18. The injection control unit 17 determines from the phase sensor 18 that the cylinder 2 is in the compression phase and controls the fuel injector 13 so injecting the fuel into the cylinder volume 4. The fuel injector 13 typically injects the fuel into the cylinder volume 4 at a pressure of around 100 to 500 Bar. At these high pressures the fuel diffuses rapidly through the inlet gas in the cylinder volume 4 to produce an unignited cylinder volume mixture. Shortly before the piston 5 reaches top dead center the spark plug 12 ignites the cylinder volume mixture in the cylinder volume 4. This causes this mixture to expand, so driving the piston 5 away from the inlet manifold 8 and driving the crankshaft 7 as shown in figure 1(c). At this point the cylinder 2 is in the combustion phase. As the fuel has diffused throughout the inlet gas before ignition the combustion process is quick and complete so increasing the power generated in the combustion phase and the efficiency of the engine system 1.

Finally in an exhaust phase of the cylinder 2 as shown in figure 1(d) the exhaust valve 11 is opened, and the piston 5 displaced towards the exhaust manifold 10. This expels the exhaust gas from the cylinder volume 4 into the exhaust manifold 10, so completing the four-stroke cycle. The four-stroke cycle then repeats, starting again with the cylinder 2 in the intake phase. The exhaust gas is the gas which remains in the cylinder volume 4 after combustion and typically comprises unburnt ammonia and NO_X. The exhaust manifold 10 is connected to an SCR catalyst which substantially eliminates the ammonia and NO_X in the exchange gas flowing along the exhaust manifold 10 before it reaches the surrounding air.

Over the course of the four stroke cycle the piston 5 moves along the cylinder axis 6 between the top dead center position and a point maximally distant from the top dead center position. The distance between this point and the top dead center position is the range of motion R of the piston 5. Preferably the cylinder volume mixture is ignited when the distance between the piston 5 and the top dead center position of the piston 5 is less than 10% of R, preferably less than 5% of R.

The method of operation of the engine system 1 has been described with reference to the cylinder 2 performing a four-stroke cycle. Over the four-stroke cycle the cylinder 2 passes through four phases. As is well known in the art, by changing the timings of opening and closing of the intake valve 9 and exhaust valve 11 the engine system 1 can operate with the cylinder 2 performing a two-stroke cycle. In the two stroke cycle the cylinder 2 still passes through four phases - intake, compression, combustion, and exhaust.

Shown in figure 2 is a further embodiment of an engine system 1 which operates according to the method of the invention. The engine system 1 comprises six cylinders 2, each of which comprises a piston 5. The cylinders 2 are connected to a common inlet manifold 8 and a common exhaust manifold 10. For clarity, only the inlet manifold 8 is shown. The pistons 5 are connected to a crankshaft 7 which in turn is connected to a camshaft 19.

The engine system 1 comprises a plurality of fuel injectors 13, each connected to a common fuel source 14. Each fuel injector 13 is connected to an associated cylinder 2 and configured to inject liquid fuel from the fuel source 14 into the cylinder volume 4 of that cylinder 2. As before, the fuel is essentially liquid ammonia, comprising at least 95% by mass of ammonia, more preferably at least 98% by mass. The engine system 1 further comprises a phase sensor 18. The phase sensor 18 comprises a crankshaft position sensor 20 connected to the crankshaft 7 and a camshaft position sensor 21 connected to the camshaft 19. Connected to the phase sensor 18 and to the fuel injectors 13 is an injection control unit 17. In use, for each cylinder 2 and fuel injector 13 connected thereto, the injection control unit 19 determines the phase of the cylinder 2 from the camshaft position sensor 21 and crankshaft position sensor 20 and opens and closes the fuel injectors 13 so as to inject liquid fuel into each cylinder volume 4 during the compression phase of the cylinder 2.

The fuel source 14 connected to the fuel injectors 13 comprises a fuel tank 22 containing liquid ammonia and a fuel line 23 which extends from the fuel tank 22 to each fuel injector 13. Connected in series in the fuel line 23 (ie such that the fuel flows through it) is a shut off valve 24 which can be closed to isolate the fuel tank 22 if necessary. Also connected in the fuel line 23 is a fuel pump 25. The portion of the fuel line 23 between the fuel pump 25 and the injectors 13 is termed the common fuel rail 26. Arranged in the common fuel rail 26 is a fuel pressure sensor 27 which measures the fuel pressure in the common fuel rail 26. A pressure control unit 28 is connected to the fuel pressure sensor 27 and the fuel pump 25. In use the pressure control unit 28 reads the pressure measured by the fuel pressure sensor 27 and operates the fuel pump 25 in response thereto to keep the fuel pressure in the common fuel rail 26 within a predetermined range.

The fuel pump 25 of this embodiment of the invention is shown in figure 3 in vertical cross section. The fuel pump 25 comprises a pump control valve 29 arranged in series in the fuel line 23 and a piston 30 driven by the camshaft 19 by means of a cam follower 31 as shown. In use the pressure control unit 28 closes the pump control valve 29 during a pumping stroke of the piston 30 to maintain the correct pressure in the common fuel rail 26. The fuel pump 25 further comprises a non-return valve 32 for transferring fuel from the common fuel rail 26 back to the fuel tank 22 in the event of over pressuring the common fuel rail 26.

In an alternative embodiment of the invention the fuel pump 25 is electrically driven. In a further alternative embodiment of the invention the fuel pump 25 is driven by an auxiliary drive system. In further alternative embodiments the fuel pump 25 is a gear pump or a metering piston type of pump.

The injection control unit 17 is also connected to the fuel pressure sensor 27 and is configured to control the fuel injectors 13 in response to the pressure in the common fuel rail 26. If the pressure in the common fuel rail 26 drops, then the fuel injectors 13 are held open for longer so that the correct amount of fuel is injected into each cylinder volume 4. The injection control unit 17 is further configured to determine the engine speed from the crankshaft position sensor 20 and camshaft position sensor 21 and control the fuel injectors 13 in response to the determined speed. As the speed increases the amount of fuel injected into each cylinder volume 4 also increases.

Returning to figure 2, the engine system 1 further comprises a hydrogen gas source 16 connected to the inlet manifold 8 and an air source 15 also connected to the inlet manifold 8. During operation, in the intake phase, hydrogen from the hydrogen source 16 and air from the air source 15 mix in the inlet manifold 8 to form the inlet gas which is drawn into the cylinder volume 4.

In this embodiment the air source 15 is a conduit which is connected to the inlet manifold 8 and which is open at its end remote from the inlet manifold 8 to the surrounding air. Arranged within the conduit is a filter. In this embodiment the air source 15 is normally aspirated. In alternative embodiments is may be turbocharged or supercharged. In this embodiment the air source 15 is connected to the inlet manifold 8 via a throttle body 33.

As to the hydrogen gas source 16 this comprises an ammonia tank 22 containing liquid ammonia. It further comprises an ammonia cracker 34 which receives ammonia from the ammonia tank 22 by means of a cracker ammonia line 35. In this embodiment the ammonia tank 22 of the hydrogen gas source 16 and the fuel tank 22 of the fuel source 14 are a common tank 22. The cracker ammonia line 35 and fuel line 23 share a common branch portion 36 as shown. Arranged in series in the branch portion 36 is an ammonia lift pump 37 for circulating liquid ammonia to the fuel pump 25 and back to the ammonia tank 22.

Arranged in series in the cracker ammonia line 35 is a pressure regulator 38, a vaporiser 39 and a preheater 40 as shown which together provide warmed ammonia gas at a regulated pressure to the cracker 34.

The hydrogen gas source 16 further comprises a hydrogen line 41 which extends from the ammonia cracker 34 to the inlet manifold 8. In use ammonia is provided to the ammonia cracker 34. The ammonia is cracked to produce cracked ammonia which is essentially nitrogen and hydrogen along with a trace amount (typically less than 1% by mass) of ammonia. The nitrogen and hydrogen flow along the hydrogen line 41 to the inlet manifold 8 where they mix with air to form the inlet gas. Arranged in series in the hydrogen line 41 is a hydrogen flow limiter valve 42. Connected to the hydrogen line 41 proximate to the hydrogen flow limiter valve 42 and between the hydrogen flow limiter valve 42 and cracker 34 is a hydrogen pressure sensor 43 which is configured to measure the pressure in the hydrogen line 41. Connected to the hydrogen flow limiter valve 42 and the hydrogen pressure sensor 43 is a hydrogen flow control unit 44. In use the hydrogen flow control unit 44 controls the hydrogen flow limiter valve 42 in response to the pressure measured by the hydrogen pressure sensor 43 so ensuring the correct amount of hydrogen is provided to the inlet manifold 8.

The hydrogen flow control unit 44 is also connected to the crankshaft position sensor 20 and camshaft position sensor 21. The hydrogen flow control unit 44 is further configured to determine the engine speed from the crankshaft position sensor 20 and camshaft position sensor 21 and to control the hydrogen flow limiter valve 42 in response to the engine speed so varying the amount of hydrogen provided to the cylinders 2 as engine speed changes.

The engine system 1 further comprises an inlet manifold pressure sensor 45 which is configured to measure the pressure in the inlet manifold 8. It further comprises a mass flow sensor 46 configured to measure the mass flow rate of air into the inlet manifold 8. The hydrogen flow control unit 44 is connected to both of these sensors 45,46 and also to the throttle body 33 and is configured to control the hydrogen flow limiter valve 42 in response to the position of the throttle body 33, the pressure measured by the inlet manifold pressure sensor 45 and the measured mass flow rate. Similarly, the injector control unit 17 is also connected to both of these sensors 45,46 and also to the throttle body 33 and is configured to control the fuel injectors 13 in response to the position of the throttle body 33, the pressure measured by the inlet manifold pressure sensor 45 and the measured mass flow rate.

The injector control unit 17 and hydrogen flow control unit 44 together control the flow of fuel and hydrogen into the cylinders 2. Typically, the flows are controlled such that at the point of ignition the mass of hydrogen in the cylinder volume 4 is around 1.5% to 3% of the mass of the ammonia in the cylinder volume 4. If the engine load increases then the hydrogen flow control unit 44 and injector control unit 17 will detect this, for example from the engine speed, by the position of the throttle body 33 or from the inlet manifold pressure sensor 45 or mass flow sensor 46 and will adjust the amount of hydrogen and/or ammonia provided to the cylinder volume 4.

The injection control unit 17, pressure control unit 28 and hydrogen flow control unit 44 may be separate units. This is particularly the case for large engine systems. In practice, and as is the case in the current embodiment, a single engine control unit 47 simultaneously performs the functions of all of the injection control unit 17, pressure control unit 28 and hydrogen flow control unit 44. The engine control unit 47 may also perform other engine management tasks as is known in the art. In this embodiment the engine control unit 47 controls the power supply 48 to the cracker 34 and also the ammonia lift pump 37.

Claims

1. A method of operating an engine system, the method comprising the steps of

(d) igniting the unignited cylinder volume mixture at the end of the compression phase to initiate the combustion phase.

2. A method as claimed in claim 1, wherein the cylinder volume mixture is ignited when the distance between the piston and the top dead center position of the piston is less than 10% of the range of motion of the piston, more preferably less than 5% of the range of motion of the piston.

3. A method as claimed in either of claims 1 or 2, wherein the engine system further comprises a phase sensor, the phase sensor comprising a crankshaft position sensor and a camshaft position sensor, the phase of the cylinder being determined during the method by means of the phase sensor.

4. A method as claimed in any one of claims 1 to 3, wherein the inlet gas comprises less than 5% by mass of ammonia, preferably less than 1%.

5. A method as claimed in any one of claims 1 to 4, wherein the fuel comprises at least 95% by mass of ammonia, preferably at least 98% by mass.

6. A method as claimed in any one of claims 1 to 5, wherein the engine system further comprises an intake valve arranged between the inlet manifold and cylinder volume configured to control the flow of inlet gas from the inlet manifold to the cylinder volume; the method further comprising the step of closing the intake valve at the start of the compression phase.

7. A method as claimed in any one of claims 1 to 6, wherein the engine system further comprises a spark plug extending through the cylinder wall, the step of igniting the cylinder volume mixture comprising the step of igniting the cylinder volume mixture by means of the spark plug.

8. A method as claimed in any one of claims 1 to 7, wherein the fuel source comprises a fuel tank, a fuel line extending from the fuel tank to the fuel injector and a fuel pump connected in series in the fuel line; the portion of the fuel line between the fuel pump and the fuel injector being termed the common fuel rail; the method further comprising the step of measuring the pressure in the common fuel rail and controlling the fuel pump in response to the measured common fuel rail pressure.

9. A method as claimed in claim 8, wherein the step of controlling the fuel injector depends upon the measured common rail fuel pressure.

10. A method as claimed in any one of claims 1 to 9, further comprising the step of measuring the engine speed and wherein the step of controlling the fuel injector depends upon the measured engine speed.

11. A method as claimed in any one of claims 1 to 10, wherein the engine system further comprises an ammonia cracker and wherein the step of providing an inlet gas to the cylinder volume via the inlet manifold comprises the steps of cracking ammonia into nitrogen and hydrogen by means of the ammonia cracker and providing the cracked hydrogen to the inlet manifold.

12. A method as claimed in claim 11, wherein the engine system further comprises a hydrogen line extending from the ammonia cracker to the inlet manifold and a hydrogen flow limiter valve arranged within the hydrogen line; the step of providing the inlet gas to the cylinder volume via the inlet manifold further comprising the steps of (i) measuring the pressure in the hydrogen line; and,

13. A method as claimed in claim 12, wherein the step of providing an inlet gas to the cylinder volume further comprises the step of measuring the engine speed and controlling the hydrogen flow limiter valve in response to the measured engine speed.

14. A method as claimed in any one of claims 1 to 13, wherein the engine system further comprises a catalyst connected to the exhaust manifold, the method further comprising the step of expelling exhaust gases from the cylinder volume into the exhaust manifold and then through the catalyst during the exhaust phase.

15. A method as claimed in any one of claims 1 to 14, wherein the engine system comprises a plurality of cylinders and a plurality of fuel injectors.