FIELD OF THE INVENTION

The present invention relates to the field of gaseous fuelled internal combustion engines, and in particular, to an internal combustion engine operated with a fuel offering including hydrogen and/or ammonia.

BACKGROUND TO THE INVENTION

A gaseous fuel as described herein should be understood to be a fuel which is in the gaseous phase at atmospheric pressure and temperature.

Gaseous fuelled internal combustion engines have the potential to substantially reduce the amount of pollutant emissions produced during internal combustion engine operation when compared to operation with liquid fossil fuels such as gasoline or diesel. Substituting some or all of the liquid fuel for a gaseous fuel such as natural gas, pure methane, ethane, liquefied petroleum gas, lighter flammable hydrocarbon derivatives, hydrogen or mixtures thereof, can potentially lower certain emissions whilst preserving the efficiency and performance of the engine depending on the gaseous fuel mixture used.

However, replacing liquid fuels with gaseous fuels in a conventional internal combustion engine presents several challenges.

In a reciprocating piston internal combustion engine, the time available for fuel injection is short, particularly when operating at high engine speeds. This can be challenging for injecting gaseous fuels into internal combustion engines, as the fuel mass flow rate of injectors for gaseous fuels is significantly reduced compared to liquid fuels. For example, commercially available gasoline injectors can deliver approximately 140 g/s of fuel at 7 bar of fuel pressure, whilst a hydrogen injector can only deliver approximately 10 g/s despite running on a fuel pressure of 40 bar.

In addition to the short duration of an engine cycle, injection of gaseous fuel in the air path (indirect injection) or in the combustion chamber (direct injection) during the intake stroke, displaces air, thereby reducing engine performance. Consequently, the bulk of gaseous injection is preferentially performed directly into the combustion chamber (direct injection) after intake valve closure and/or intake port closure, reducing the period of main injection to the compression stroke.

A known solution to increasing the amount of gaseous fuel which can be injected into a combustion chamber at a given time is to increase the number of direct injection injectors per combustion chamber. Other solutions include modifying conventional gaseous fuel injectors, however this adds complexity to the engine.

For premixed spark-ignited combustion, a key aspect for complete, efficient, and low- emission conversion of fuel, is a homogeneous air/fuel mixture. Late direct injection (i.e. when the bulk of injection occurs after intake valve closure and/or intake port closure) can be detrimental to fluid homogeneity as the available time for air and fuel mixing is very short.

Additionally, gaseous fuelled internal combustion engines suffer from inefficient air/fuel mixing compared to liquid fuelled internal combustion engines, owing to the lack of droplet break-up and fuel evaporation. Also, gaseous fuel injectors tend to create a directive fuel stream that can be detrimental to air/fuel mixing. Directive fuel streaming is a known consequence of injecting fuel into a combustion chamber, often via a single fuel injector. The single fuel jet created by the single injector impinges on the wall of the combustion chamber, which localises the mixing of air/fuel around the point of impingement, and results in a non-uniform mixing of air/fuel across the combustion chamber.

Whilst non-carbonaceous fuels such as hydrogen and ammonia are particularly attractive fuel offerings because of their potential to reduce pollutant emissions, the low density of the fuels makes achieving a suitable flow rate and air/fuel mixture particularly challenging.

Therefore, there is a requirement for a reciprocating piston internal combustion engine which can simply and effectively achieve suitable flow rates and efficient air/fuel mixing, even when operated with low density gaseous fuels and late injection timing.

It is against this background that the present invention has arisen. SUMMARY OF THE INVENTION

According to the present invention, there is provided a reciprocating piston internal combustion engine which operates with a fuel offering including hydrogen and/or ammonia, the internal combustion engine comprising: a combustion chamber containing air; and a plurality of injectors configured to inject one or more gaseous fuels directly into the combustion chamber simultaneously; wherein the plurality of injectors are further configured to enhance the mixing of the gaseous fuels with the air inside the combustion chamber.

In some embodiments, there may be provided a reciprocating piston internal combustion engine which operates with a fuel offering including hydrogen and/or ammonia, the internal combustion engine comprising: a combustion chamber containing air; and a plurality of injectors configured to inject one or more gaseous fuels directly into the combustion chamber; wherein the plurality of injectors are further configured to enhance the mixing of the gaseous fuels with the air inside the combustion chamber.

The present invention aims to maximise the efficiency with which a fuel offering including hydrogen and/or ammonia can be injected into a reciprocating piston internal combustion engine whilst also enhancing air/fuel mixing. In some embodiments, the simultaneous injection of one or more gaseous fuels by the plurality of injectors, forces a conversion of jet primary momentum into secondary momentum, thereby increasing the fraction of the combustion chamber volume fed with fuel during the injection process, and enhancing air/fuel mixing.

In some embodiments, the internal combustion engine comprises a plurality of direct injection injectors. In some embodiments, the internal combustion engine may preferably comprise two injectors. In some embodiments, the internal combustion engine may comprise two or more injectors. In some embodiments, the plurality of direct injection injectors increases the amount of fuel which can be injected into the combustion chamber during the short space of time available for fuel injection with minimal air displacement in a reciprocating piston internal combustion engine.

In some embodiments, the plurality of injectors are configured to enhance the mixing of the gaseous fuel and air within the combustion chamber. In some embodiments, the plurality of injectors can be configured such that the injection paths from each of the plurality of injectors interact to enhance gas motion and air/fuel mixing. In some embodiments, this prevents the internal combustion engine from suffering from the detrimental effects of directive fuel streaming.

In some embodiments, by configuring the plurality of injectors to enhance the gaseous air/fuel mixing within the combustion chamber, the present invention may utilise standard gaseous fuel injectors to achieve high enough flow rates and sufficient mixing, even when the fuel offering includes low density gaseous fuels such as hydrogen and/or ammonia. Therefore, the present invention may provide a simple and straightforward solution to a common problem, utilising widely available gas injectors without requiring any further modification.

In some embodiments, the plurality of injectors can be configured such that the gas jets resulting from injection of gas through the injectors interact to create a distinctive flow pattern. In some embodiments, simultaneous operation of the multiple injection devices per combustion chamber creates a momentum field that cannot be attained with a single injection device.

In some embodiments, the plurality of injectors may be configured to be substantially facing each other. Within the context of the present invention, the term "facing" or "substantially facing" should be understood to not be limited to injector arrangements in which the injectors are located strictly along the same horizontal and/or vertical line. It should be understood that the term "facing" or "substantially facing" can include injector arrangements in which the injectors are offset by some angle but yet are still substantially opposite one another. The key characteristic of the substantially facing plurality of injectors is that they are configured such that the gas jets resulting from injection of gas through the injectors converge at a focal point and have a direct, straight-on interaction.

Within the context of the present invention, a "focal point" as described herein should be understood to be a small volume and not limited to a single point.

In some embodiments, the plurality of injectors being configured to be substantially facing may result in a reduction of jet momentum along the injection paths whilst inducing momentum transverse to the injection paths. In some embodiments, the substantially facing arrangement and simultaneous injection, facilitates a straight-on interaction of the primary jet momentum resulting from the gas guided by each injection device. In some embodiments, the primary jet momentum is converted into transverse momentum, and this enables the injected gas to reach the largest possible fraction of the combustion chamber volume. In some embodiments, this can improve air/fuel mixing.

In some embodiments, the "substantially facing" arrangement is defined by the orientation of the primary injection axis. In some embodiments, when the plurality of injectors are substantially facing, each primary jet axis crosses the chamber mid-plane at a radius inferior to a quarter of the combustion chamber radius. In some embodiments, the interaction of the gas jets at the mid-plane of the combustion chamber, contrasts the directive fuel streaming effect typical of single injector internal combustion engines.

In some embodiments, when the plurality of injectors are substantially facing each other, each primary jet axis may have, in the plane defined by the primary jet axes and the piston motion axis, an orientation with ± 45 degrees of the plane perpendicular to the piston motion axis. In some embodiments, the creation of transverse momentum in all directions is only possible if the orientation of the injection axes of the plurality of injectors, are within 45° of the plane perpendicular to the piston motion axis (generally referred to as the head gasket plane). Beyond 45°, momentum along the axis of piston motion would be exclusively upwards (along the compression direction) or downwards (along the expansion direction).

In some embodiments, the plurality of injectors may be configured to be substantially offset from each other. In some embodiments, the plurality of injectors may be configured to be offset from each other.

Within the context of the present invention, the term "substantially offset" should be understood to mean when the plurality of injectors are configured such that each primary jet axis crosses the chamber mid-plane at a distance superior to a quarter of the combustion chamber radius. The distance is taken with respect to the centre of gravity of all such primary jet axis crossing points.

In some embodiments, the plurality of injectors configured to be offset, or substantially offset from each other may result in conversion/distortion of the momentum of the gas jets created by injection of gas through the injectors, and in an induced rotational gas movement in the combustion chamber, which could not be obtained whilst using a single injector.

In some embodiments, the resultant gas motion may have rotational movement in a horizontal plane. In some embodiments, the resultant gas motion may have rotational movement in a vertical plane. In some embodiments, the resultant gas motion may have a rotational movement in both the horizontal and vertical planes. In some embodiments, the plurality of injectors configured to be offset from each other creates a whirling flow motion in the resultant gas flow within the combustion chamber which improves air/fuel mixing. In some embodiments, the plurality of injectors may be configured to create a tumble or swirl motion in the resultant gas flow within the combustion chamber which improves air/fuel mixing.

In some embodiments, one or more of the plurality of injectors may be configured to inject one or more gaseous fuels into the combustion chamber at an angle which is offset from the axis of the injector.

In some embodiments, one or more of the plurality of injectors may further comprise a nozzle which may inject the gaseous fuel into the combustion chamber at an angle which is offset from the axis of the injector. In some embodiments, one or more of the plurality of injectors may comprise a cap which directs the gaseous fuel into the combustion chamber at an angle which is offset from the axis of the injector.

In some embodiments, the combustion chamber may further comprise a baffle which deflects the injection path of the gaseous fuel such that it is injected into the combustion chamber at an angle which is offset from the axis of the injector.

In some embodiments, the one or more gaseous fuels may comprise hydrogen, ammonia and/or methane. In some embodiments, each of the plurality of injectors may inject substantially the same gaseous fuel directly into the combustion chamber. In some embodiments, the internal combustion engine may be operated with a pure hydrogen fuel offering or a pure ammonia fuel offering. In some embodiments, the internal combustion engine may be operated with a fuel offering which is a mixture of hydrogen and ammonia. In some embodiments, the internal combustion engine may be operated with a fuel offering mixture which includes methane. In some embodiments, it may be preferable for the fuel offering to not comprise carbon containing gaseous fuels in order for the reduction of greenhouse emissions to be maximised.

In some embodiments, at least one of the plurality of injectors may inject a substantially different gaseous fuel directly into the combustion chamber. For example, one of the plurality of injectors may inject hydrogen into the combustion chamber whilst another of the plurality of injectors may inject ammonia into the combustion chamber.

In some embodiments, the plurality of injectors may be configured to inject one or more gaseous fuels directly into the combustion chamber simultaneously.

In some embodiments, the plurality of injectors may be configured to inject one or more gaseous fuels directly into the combustion chamber independently of each other. In some embodiments, the internal combustion engine may comprise a plurality of injectors but may only use a single injector at a certain operating point of the engine. In some embodiments, there may be a plurality of injectors in the combustion chamber but only one may be active in certain conditions. In some embodiments, the plurality of injectors may be configured to inject one or more gaseous fuels directly into the combustion chamber independently of each other under conditions requiring considerably reduced fuel supply, such as when idling.

In some embodiments, the internal combustion engine may further comprise at least one intake valve. In some embodiments, the internal combustion engine may have more than one intake valve. In some embodiments, the intake valve may be an air inlet valve. In some embodiments, the intake valve or air inlet valve may control the flow of air into the combustion chamber. In some embodiments, the internal combustion engine may have no intake valves and the opening and closing of the air path towards the combustion chamber may be controlled by the piston position.

In some embodiments, the plurality of injectors may be configured to inject one or more gaseous fuels directly into the combustion chamber when the at least one intake valve is closed. In some embodiments, the majority of the one or more gaseous fuels may be injected directly into the combustion chamber when the air inlet valve is closed. Therefore, in some embodiments, the internal combustion engine may be configured for late injection timing. In some embodiments, the gaseous fuel may be injected into the combustion chamber as the piston closes the combustion chamber volume. In some embodiments, this may increase the safety and engine performance when injecting fuel offerings comprising hydrogen.

In some embodiments, the internal combustion engine may be a 2-stroke engine. In some embodiments, the internal combustion engine may be a 4-stroke engine.

FIGURES

The present invention will now be described, by way of example only, with reference to the accompanying figures in which:

Figure 1 shows a cylinder head model with two injectors in a dual facing position;

Figure 2 shows the cylinder head model of Figure 1 with a schematic of gas flow when both injectors are simultaneously activated;

Figure 3 shows a top view for a dual facing configuration;

Figures 4A and 4B show the directive, straight-on fuel stream created by an individual injector;

Figures 4C and 4D compare the fuel stream from the dual facing configuration of the present invention; and

Figure 5 shows a top view for a dual offset configuration and purely vertical mixing; and

Figure 6 shows a top view for a dual offset configuration and purely horizontal mixing.

DETAILED DESCRIPTION

The present invention relates to a reciprocating piston internal combustion engine 10 which comprises a cylinder head 11 with a plurality of injectors 12 which can achieve suitable flow rates and air/fuel mixing, even when operated with low density gaseous fuel offerings including hydrogen and/or ammonia.

By way of example, Figure 1 illustrates a 4-stroke reciprocating piston internal combustion engine 10. However it should be understood that the invention is also suitable for use with 2-stroke internal combustion engines. The cylinder head 11 of the internal combustion engine 10, comprises a combustion chamber 14. The cylinder head 11 comprises a plurality of injectors 12 which are configured to inject one or more gaseous fuels directly into the combustion chamber 14. Figure 1 shows two injectors 12 injecting into one combustion chamber 14, however it should be understood that the present invention may comprise two or more injectors 12. The plurality of injectors 12 increases the amount of fuel which can be injected into the combustion chamber 14 during the short space of time available for fuel injection during operation of the reciprocating piston internal combustion engine 10. The plurality of injectors 12 may be standard gaseous fuel injectors without requiring any modification. The gaseous fuel offering may be a single fuel offering such as pure hydrogen or pure ammonia, or may be a fuel mixture such as hydrogen/ammonia or hydrogen/methane for example. The plurality of injectors 12 may inject substantially the same fuel, or may inject different fuels into the combustion chamber 14 through each of the injectors 12.

The cylinder head 11 of the internal combustion engine 10 may further comprise at least one intake valve (not shown). Alternatively, the cylinder head 11 of the internal combustion engine 10 may not have an intake valve and the air flow towards the combustion chamber 14 may be controlled by piston motion. The plurality of injectors 12 are operated such that most of the gaseous fuel is injected directly into the combustion chamber 14 when the volume of the combustion chamber is closed. The plurality of injectors 12 are configured to inject one or more gaseous fuels directly into the combustion chamber 14 such that the mixing of the gaseous fuel with the air inside the combustion chamber 14 is enhanced.

As shown in Figure 2, when in operation, each of the injectors 12 creates a gas jet 16 extending from the injector 12 into the combustion chamber 14. It should be noted that although Figure 2 shows two injectors 12 in operation simultaneously, the injectors 12 may also be operated independently of one another. The mixing of gaseous fuel and air can be enhanced within the combustion chamber 14 by configuring the plurality of injectors 12 such that when operated simultaneously, the resultant gas jets 16 interact with each other and a distinctive flow pattern is created.

As shown in Figures 1, 2 and 3, the plurality of injectors 12 may be configured such that they are substantially facing each other. This results in gas jets 16 converging at a focal point.

Referring to Figure 3, the injectors 12 configured to be substantially facing one another result in gas jets 16 having a direct, straight on interaction at a focal point. The converging of the gas jets 16 results in a reduction of jet momentum along the injection paths and induces momentum transverse to the injection paths. The induced flow motion is illustrated by the arrows 18a in Figure 3. This induced flow motion improves the gaseous air/fuel mixing within the combustion chamber 14.

Referring to Figure 4, a comparison between the injection path and induced flow motion of the gas jets 16 from a single injector 20 (Figures 4A and 4B) and a dual facing injector arrangement (Figures 4C and D) is shown. Figures 4A and 4B show a single injector 20 producing the gas jet 16 and the induced flow motion, illustrated by the arrows 18b. The single injector has an injection path directed substantially to one side of the combustion chamber 14, where it impinges on the combustion chamber wall. The air/fuel mixing within the combustion chamber 14 is limited in this arrangement, as the fuel reaches a comparatively small volume of the combustion chamber. This is an example of the detrimental directive fuel streaming effect.

As shown in Figures 4C and 4D, the dual facing arrangement of the plurality of injectors 12 improves the air/fuel mixing. The gas jets 16 are directed substantially towards the midplane 22 of the combustion chamber, when viewed in a plane perpendicular to the piston motion axis. The chamber mid-plane 22 is defined by the piston motion axis and the chamber diameter perpendicular to the line joining the combustion chamber centre to the centre of the injection orifice on the injection device. The gas jets 16 each cross the midplane 22 of the combustion chamber at a radius inferior or equal to a quarter of the combustion chamber radius. The induced flow motion/ transverse momentum indicated by arrows 18a reaches the largest possible fraction of the combustion chamber volume, and results in an enhanced air/fuel mixing over a short time period.

As shown in Figure 4D, in order for the induced flow motion/ transverse momentum indicated by arrows 18a to reach the maximum volume of the combustion chamber 14, the plurality of injectors 12 must be arranged in a dual facing arrangement, within 45° of the plane perpendicular to the piston motion axis (generally referred to as the head gasket plane). If the injectors are arranged beyond 45°, momentum along the axis of piston motion would be exclusively upwards (along compression direction) or downwards (along expansion direction).

As shown in Figure 5 and 6, the plurality of injectors 12 may be configured such that they are offset from each other, which can induce a rotational flow motion as illustrated by the arrows 18c and 18d.

Figure 5 shows a top view of a combustion chamber 14 with a plurality of injectors 12 configured in a vertically offset arrangement. As shown in Figure 5, this can induce a vertical rotational motion in the combustion chamber 14, with the induced flow motion illustrated by the arrows 18c. The offset injectors 12 may result in an induced tumble motion about the axis indicated by the dashed line 21.

Figure 6 shows a top view of a combustion chamber 14 with a plurality of injectors 12 configured in a horizontal offset arrangement. As shown in Figure 6, this can induce a horizontal rotational motion in the combustion chamber 14 as indicated by the arrows 18d. The offset injectors 12 may result in an induced swirl motion in the combustion chamber 14.

Whilst Figure 5 shows a purely vertical induced rotational movement and Figure 6 shows a purely horizontal induced rotational movement, a mixture of both horizontal and vertical rotational movement within the combustion chamber 14 is likely to occur in an internal combustion engine 10 and is preferable for optimised gas air/fuel mixing through selection of orientation of each injector 12. The detailed optimisation of the injector orientation gives detailed control of the flow motion of the mixed fluids in the chamber 14.

It should be noted that whilst Figures 2 to 6 show gas jets 16 extending from injectors 12 along the same axis as the injectors 12, one or more of the injectors 12 may be configured such that the gas jet 16 extends from the injector 12 into the combustion chamber 14 at an angle which is offset from the axis of the injector 12. This may occur when the injector 12 further comprises a nozzle or a baffle, for example.

Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

"and/or" where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example "A and/or B" is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.

Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described.

It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments. It is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims.