GB2580904A

GB2580904A - An internal combustion engine

Info

Publication number: GB2580904A
Application number: GB1901011.5A
Authority: GB
Inventors: Jones Steve; Weall Adam; Gorman Cooper Brian
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2019-01-25
Filing date: 2019-01-25
Publication date: 2020-08-05
Anticipated expiration: 2039-01-25
Also published as: GB201901011D0; GB2580904B

Abstract

An internal combustion engine comprising a piston and a cylinder (13, fig.7) having an air intake (19, fig.7) positioned so that air entering the cylinder swirls (S) around longitudinal axis (A-A, fig.7). The piston comprises a body (2, fig.4) having a planar compression face (3, fig.4), a bowl (4, fig.4) open towards the plane of the compression face, and at least one pocket 5a-5f extending into the body from the plane of the compression face. The engine also comprises a fuel injector (16, fig.5,) including at least one jet 18a-18f, which is configured to inject fuel towards the compression face of the piston. The pockets are offset from the jet by a predetermined angle ß about the longitudinal axis so that fuel emitted from the jet into the swirling air is directed towards the pocket via arcuate path F. Also disclosed is a method of assembling the engine and a vehicle comprising the engine.

Description

AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to an internal combustion engine. Aspects of the invention relate to a vehicle comprising the internal combustion engine and to a method of assembling an internal combustion engine.

BACKGROUND

In an internal combustion engine, a piston compresses a charge of air within a combustion chamber in a cylinder prior to injection of fuel into the chamber at or near to a point at which the piston reaches top dead centre. A fuel injector has one or more jets from which fuel is injected into the combustion chamber in a radially outward and downward direction toward the cylinder walls and the piston bowl.

The highest combustion related temperatures within the combustion chamber are found in localised regions close to the fuel spray jet or jets. This can lead to a non-uniform distribution or transfer of heat to the compression face and bowl lip of the piston. Localised thermal stress caused by the non-uniform distribution of heat can reduce the performance of the piston material and lead to excessive heat loss which would otherwise be available for conversion into useful work.

By providing a piston with a bowl open towards its compression face and a pocket in radial alignment with a fuel jet and extending from the compression face into the piston body from the plane of the compression face, localised thermal stresses in the piston body can be mitigated as a result of fuel being delivered to the pocket from the jet.

In order to ensure thorough mixing of fuel and air in the cylinder, efficient combustion and to help prevent fuel droplets from settling on the surface of the cylinder, it is common for the air intake port to be positioned so that a swirl component is imparted to the air entering the combustion chamber. The term 'swirl' is used to describe a circulation of the combustion air about the longitudinal axis of the cylinder. Droplets of fuel emitted by the jet can become at least partially entrained in the circulating airflow and redirected. This results in less fuel being delivered to the pocket, or no fuel being delivered to the pocket.

It is an aim of the present invention to address one or more of the disadvantages associated

with the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide an internal combustion engine, a vehicle comprising the internal combustion engine and to a method of assembling an internal combustion engine, as claimed in the appended claims.

According to an aspect of the present invention there is provided an internal combustion engine comprising: a cylinder having a longitudinal axis and an air intake positioned so that a flow of air entering the cylinder through the air intake swirls about the longitudinal axis of the cylinder in a first direction; a piston received in the cylinder and configured to compress a charge of air, the piston comprising a body having a longitudinal axis parallel to a longitudinal axis of the cylinder, a planar compression face, a bowl open towards the plane of the compression face and formed in the body, and a pocket extending into the body from the plane of the compression face, and a fuel injector comprising a jet, the fuel injector being configured to inject fuel in a radially outward direction into the cylinder from the jet and towards the plane of the compression face of the piston; wherein the pocket is offset from the jet by a predetermined angle about the longitudinal axis in said first direction so that fuel emitted from the jet into the flow of air swirling about the longitudinal axis is directed towards the pocket.

By offsetting the pocket from the jet by a predetermined angle in an direction extending about the longitudinal axis of the cylinder, it is possible to compensate for the swirl component in the airflow which redirects the fuel emitted by the jet and as it travels towards the compression surface. This can result in a larger proportion of the fuel being delivered to the pocket and the dual advantages associated with the provision of a swirling airflow and a pocket in the compression face can be realised.

Optionally, the fuel injector comprises a plurality of jets, each jet being positioned to inject fuel into the cylinder, and the piston comprises a plurality of pockets arranged about the longitudinal axis of the cylinder, wherein at least two of the pockets each have a corresponding jet, said pockets being offset from their corresponding jet by a predetermined angle about the longitudinal axis in said first direction so that fuel emitted from a corresponding jet into the flow of air swirling about the longitudinal axis is directed towards its associated pocket.

The predetermined angle by which each pocket and its corresponding jet is offset may be the same. Alternatively, the predetermined angle by which each pocket and its corresponding jet is offset is different for at least some of the pockets and their corresponding jets.

Each pocket may have an opening that faces in a direction towards the longitudinal axis of the piston body, and said predetermined angle by which the or each pocket is offset may be measured from a radial centreline that extends from said longitudinal axis through a centre of the opening to a component of a line extending from the, or corresponding, jet to the compression face of the piston that lies in the same plane as the radial centreline of the opening.

Optionally, the or each jet comprises an opening having an axis, said predetermined angle being measured from said radial centreline extending through said centre of the opening of the pocket to said axis.

The predetermined angle by which a pocket and its corresponding jet is offset may be between 5 to 90 degrees. However, it is envisaged that a predetermined angle around about 15 degrees will be sufficient to ensure that the fuel spray is directed towards the pockets 5.

Optionally, at least some pockets comprises a first portion and a second portion, the first portion extending in a longitudinal direction into the body from the plane of the compression face at an angle of less than 90 degrees to the plane of the compression face, and the second portion extending from the first portion towards the bowl.

By providing an array of pockets in which the first portion extends at an angle of less than 90 degrees to the plane of the compression face, the squish area formed by the area between the plane of the compression face and a surface of the cylinder head, at locations where the highest thermal heat flux exists, is reduced. Consequently, local gas velocity and thermal loading on the compression face in this region is reduced so that the fuel-air mixture is more evenly spread across the compression face rather than being concentrated in those regions where the fuel spray interacts with the compression face The second portion may extend parallel to the plane of the compression face.

Alternatively, the second portion may extend at an angle to the plane of the compression face, said angle being different to the angle at which the first portion extends to the plane of the compression face.

The bowl may comprise a step extending annularly about the longitudinal axis of the body. Each pocket may then be in communication with said step.

A step further contributes to a reduction in gas velocity and an improvement in the thermal loading characteristics of the compression face.

The step may comprise an annular lip that extends from the second portion of the pockets that comprise a first portion and a second portion to a mouth of the bowl.

Optionally, the second portion extends from the first portion to meet said annular lip.

The second portion and said annular lip may both extend parallel to the plane of the compression face. Alternatively, the second portion and/or the annular lip each extend at an angle to the plane of the compression face.

Optionally, the second portion and the annular lip both extend at an angle to the plane of the compression face, and the angle at which the second portion extends to the plane of the compression face may be different to the angle at which the annular lip extends to the plane of the compression face.

The first portion of the pockets may comprise a surface that is curved in an angular direction extending about the longitudinal axis.

Optionally, at least two adjacent pockets comprise a first portion and a second portion, wherein the first portion of said at least two adjacent pockets merge.

Alternatively, at least two adjacent pockets comprise a first portion and a second portion, the first portion of said at least two adjacent pockets being spaced by an end face that extends between said at least two adjacent pockets in an angular direction about the longitudinal axis.

The end face may be arcuate and is coaxial with said longitudinal axis.

The bowl may have an axis coaxial with said longitudinal axis of the body of the piston.

The pockets can be arranged in a rotationally asymmetric pattern around the longitudinal axis of the body.

Alternatively, the fuel jets are arranged in a rotationally symmetric pattern around the longitudinal axis of the body.

According to another aspect, there is provided a vehicle comprising the internal combustion engine according to the invention.

According to yet another aspect of the invention, there is provided a method of assembling an internal combustion engine that comprises a cylinder having a longitudinal axis and an air intake positioned so that a flow of air entering the cylinder through the air intake swirls about the longitudinal axis of the cylinder in a first direction, a piston including a body having a longitudinal axis parallel to a longitudinal axis of the cylinder and a planar compression face, a bowl open towards the plane of the compression face and formed in the body, and a pocket extending into the body from the plane of the compression face, and a fuel injector comprising a jet, the fuel injector being configured to inject fuel in a radially outward direction into the cylinder from the jet and towards the compression face of the piston; wherein the method comprises inserting the piston into the cylinder and positioning the piston and fuel injector such that the pocket is offset from the jet by a predetermined angle about the longitudinal axis in said first direction so that fuel emitted from the jet into the flow of air swirling about the longitudinal axis is directed towards the pocket.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic plan view of a compression face of a piston body that forms part of the internal combustion engine according to an embodiment of the invention; Figure 2 shows a cross-section taken along the line X-X of the piston body shown in Figure 1; Figure 3 shows a cross-section taken along the line X-X of the piston body of Figure 1, according to a different embodiment; Figure 4 is a perspective view from above of a piston body forming part of the internal combustion engine according to an embodiment of the invention; Figure 5 is a perspective view from above in which the piston body of Figure 4 is received in a cylinder forming part of the internal combustion engine according to an embodiment of the invention, together with a fuel injector; Figure 6 is a schematic plan view of a compression face of a piston in accordance with another embodiment of the invention; Figure 7 shows a simplified perspective view showing the air inlet and exhaust outlet from the cylinder shown in Figure 5, and an arrow that indicates how the path of the air as it swirls around the longitudinal axis of the cylinder; Figure 8 is a similar plan view to Figure 1, but additionally shows the fuel jets and the path of travel of fuel from each jet towards a pocket that corresponds to each jet; Figure 9 shows a schematic view of a compression face of a body of a piston that forms part of the internal combustion engine in accordance with another embodiment of the invention; Figure 10 shows a cross-section taken along the line X-X of the body of the piston shown in Figure 9; Figure 11 is a cross-section of another embodiment, which is similar to that of Figure 10 but in which the annular lip of the step extends at an angle to the plane of the compression face; Figure 12 is a schematic view of an internal combustion engine according to an embodiment of the invention that has four cylinders; Figure 13 shows a vehicle fitted with the internal combustion engine of Figure 12, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

A schematic plan view illustration of a piston body 2 that forms part of an internal combustion engine (see Figure 12) in accordance with an embodiment of the invention for use with a vehicle (see Figure 13), is shown in Figure 1. Another embodiment of a piston body 2 is shown in the perspective view from above of Figure 4.

With reference to Figures 1 to 4, the piston body 2 has a compression face 3, which extends in a plane 3a (see Figure 2) across the top surface of the body 2, and a longitudinal axis A-A (see Figures 2 to 5). A re-entrant shaped bowl 4 is formed in the piston body 2 and is open in a direction towards the plane 3a of the compression face 3.

An array of pockets 5 extend from the plane 3a of the compression face 3 into the body 2. The pockets 5 are arranged so that they encircle the bowl 4. Each pocket 5 is open in the plane 3a of the compression face 3 and has a first wall portion 6 that extends in a longitudinal direction from the plane 3a of the compression face 3 at an angle of less than 90 degrees to the plane 3a of the compression face 3, and a second wall portion 7 that extends from the first wall portion 6 towards the mouth 8 of the bowl 4. The first and second wall portions 6, 7 may meet at a smooth curve or be rounded so that the first and second wall portions 6, 7 blend into each other. A sudden step-change between the first and second wall portions 6, 7 is thereby avoided. The shape of the pockets 5 according to an embodiment of the invention can be more clearly understood from the cross-sectional view of Figure 2, which is taken along line, X-X in Figure 1.

The second wall portion 7 extends parallel to the plane 3a of the compression face 3. However, as shown in an alternative cross-sectional view taken along line X-X of Figure 1 and shown in Figure 3, the second wall portion 7 may extend from the first wall portion 6 at an angle to the plane 3a of the compression face 3 so that the depth of the second wall portion 7 from the plane 3a of the compression face 3 increases in a direction extending away from the first wall portion 6. If the second wall portion 7 extends at an angle to the plane 3a of the compression face 3, the angle between the second wall portion 7 and the plane 3a of the compression face 3 may be different to the angle between the first wall portion 6 and the plane 3a of the compression face 3.

It will be appreciated that the pockets 5 need not have the shape referred to in the previous paragraph. In other embodiments, the pockets 5 could be formed from arcuate or part-spherically shaped depressions extending into the piston body 2 from the plane 3a of the compression face 3. The pockets 5 could also be of any other shape. Furthermore, the pockets 5 do not all need to be of the same size and/or shape and one or more pockets may differ in size and/or shape from one or more other pockets 5.

With reference to the piston body 2 shown in Figure 4, the first portion 6 of each pocket 5 has an arcuate shape in an angular direction extending about the longitudinal axis A-A of the piston body 2. In particular, the pockets 5 generally assume a 1D' shape when the compression face 3 is viewed from above in a direction along the longitudinal axis A-A of the piston body 2, as can be seen most clearly in Figure 1 and 4. The first portion 6 is formed by the curved portion of the 'D' shape.

As shown in Figure 1, the pockets 5 can be spaced from each other in an angular direction extending about the longitudinal axis A-A of the body 2. In such an embodiment, the first portion 6 of adjacent pockets 5 is spaced by an end face 11 that extends between the pockets 5 in an angular direction about the longitudinal axis A-A, as shown in Figure 1. The end face 11 is arcuate in shape and has an axis which is coaxial with the longitudinal axis A-A of the body 2.

As illustrated in Figure 4, the pockets 5 may also be closely arranged next to each other so that the first portion 6 of each pocket 5 smoothly merges with the first portion 5 of each adjacent pocket 5 to form a continuous wave-shaped edge. In this instance, the first portions 5 are separated by intermediate or curved joining regions 12 between each pocket 5 that extend from the first portions 6 and curve inwardly towards the longitudinal axis A-A. The first portions 6 and the curved regions 12 together form a continuous sinusoidal type waveform shape that follows a circular path around the bowl 4 when viewed from above in the direction of the longitudinal axis A-A.

The pockets 5 may be arranged asymmetrically about the longitudinal axis A-A. For example, in the embodiments of Figures 1 and 4, opposing pockets 5 are not diametrically aligned with each other but are offset in an angular direction extending about the longitudinal axis A-A by an angle a. Figure 6 shows a plan view of a compression face 3 according to another embodiment in which the pockets 5 are symmetrically arranged and so opposing pockets 5 are diametrically aligned with each other. A segment angle 0 is also illustrated in Figure 6, and represents the included angle of each pocket 5. In any embodiment, each pocket 5 may have a maximum segment angle 0 of 360 degrees divided by the number of fuel jets.

However, it will be appreciated that the the segment angle 0 may be less.

With reference to Figure 5, there is shown a piston body 2 according to Figure 4 received in a cylinder 13 of an internal combustion engine 14, shown in schematic form in Figure 12. The piston body 2 is shown in a top dead centre position and is mounted for reciprocal movement in a direction along the longitudinal axis A-A. The longitudinal axis A-A of the piston body 2 is parallel to the longitudinal axis of the cylinder 13. In the embodiment shown in Figure 5, the piston body 2 and the cylinder 13 are coaxially arranged. The piston body 2 is pivotally attached to one end of a piston rod 15 whose opposite end is attachable to a crankshaft (not shown), as is typical in internal combustion engines, so that force from the gas expanding in the cylinder 13 above the compression face 3 is transferred to the crankshaft via the piston body 2 and the piston rod 15.

Also shown is a fuel injection system 16 arranged to inject fuel into the cylinder 13 towards the compression face 3. The fuel injection system 16 includes a nozzle 17 that protrudes into the cylinder 13 and has a plurality of jets 18 arranged to spray fuel generally outwardly in a radial direction and towards the plane of the compression face 3, and more specifically towards the pockets 5, as represented by the lines emanating in different directions from the jets 18 in Figure 5.

Figure 7 shows an air intake 19 at an upper end of the cylinder 13 which is positioned so that the air entering the cylinder 13 is caused to swirl or circulate around the longitudinal axis A-A of the cylinder 13, as indicated by the arrow "S".

In the absence of swirl within the cylinder 13, the pockets 5 are aligned with the fuel jets 18 so that fuel eminating from a fuel jet 18 and following a radial path will be delivered directly to a corresponding pocket 5. However, for the reasons already indicated above, it is desirable for there to be a swirling flow of air within the cylinder 13.

A swirling airflow within the cylinder 13 at least partially diverts the path of the fuel from the jets 18 towards the compression face 3 of the cylinder 13. Therefore, to ensure that the fuel emitted by the jets 18 is delivered to a corresponding pocket 5 when there is a swirling airflow, each pocket 5 has a corresponding jet from which it is offset by a predetermined angle in a direction extending about the longitudinal axis A-A of the cylinder 13. The predetermined angle of offset of a pocket 5 from its corresponding jet 18 may be determined in advance by carrying out an assessment of how the fuel emitted by the jets 18 is affected by the air circulation within the cylinder 13. A preferred predetermined angle of offset may be in the range of between 5 and 90 degrees, or more preferably, in the region of 15 degrees. This angle may be measured between a line J-J extending from a corresponding jet 18 towards the compression face 3 of the piston body 2, and a radial centreline FI-R (see Figure 8) that extends from the longitudinal axis A-A of the cylinder 13 through a centre of the pocket 5 or, where the centreline Fl-F1 intersects a centre of an opening in the pocket 5 that faces the longitudinal axis A-A of the cylinder 13. The jet 18 may be a circular orifice in the nozzle 17 and the line J-J may extend from the centre of the orifice towards the compression face 3.

The arrangement of the jets 18 and their corresponding pockets 5 is illustrated in more detail with reference to the top plan view of the compression face of a piston body 2 of Figure 8. In the embodiment as shown, the nozzle 17 has six fuel jets 18a, 18b, 18c, 18d, 18e, 18f spaced evenly about the longitudinal axis A-A of the cylinder. Each pocket 5a, 5b, 5c, 5d, 5e, 5f is offset from its corresponding jet 18a, 18b, 18c, 18d, 18e, 18f by a predetermined angle B. Air enters the cylinder 13 through the inlet 19 (see Figure 7) to circulate around the longitudinal axis A-A in the direction indicated by arrow S (see Figures 7 and 8). The circulating airflow S at least partially entrains and diverts the path of the fuel emitted by each jet 18a, 18b, 18c, 18d, 18e, 18f, and causes it to follow a more arcuate path F from each jet 18a, 18b, 18c, 18d, 18e, 18f towards the compression face 3. More specifically, and as can been seen in Figure 8, pocket 5c is offset from jet 18c by the predetermined angle 8 so that fuel emitted from jet 18c and following an arcuate path F will be delivered to pocket 5c. Pocket 5b is offset from jet 18b by the same predetermined angle B so that fuel emitted from jet 18b and following an arcuate path F will be delivered to pocket 5b, and so on for each pocket 5 and its corresponding fuel jet 18.

Although reference is made to multiple jets 18, and a pockets 5 corresponding to each jet 18, it will be understood that there may be a single jet 18 and a single pocket 5. The number of jets 18 and pockets 5 may be the same so that each pocket 5 has a corresponding jet 18. Alternatively, there may be different numbers of pockets 5 relative to jets 18. Furthermore, if there are multiple pockets 5 and jets 18, only some of the jets 18 and corresponding pockets 5 may be offset by the predetermined angle B. Other pockets 5 may not be offset from jets 18 at all, or some jets and their corresponding pockets 5 may be offset by a different predetermined angle to other jets 18 and their corresponding pockets 5.

As shown in Figure 12, the internal combustion engine 14 comprises a cylinder block 20 having four cylinders 13, one of which is shown in Figures 5 and 7.

The piston body 2 may have other configurations. For example, as illustrated in Figures 9 to 11, the bowl 4 has a step, the extent of which is indicated with reference numeral 9. The step 9 extends annularly about the longitudinal axis A-A of the piston body 2. The pockets 5 are arranged so that each pocket 5 is in communication with the step 8, i.e. each pocket 5 is open towards the step 9 in a radial direction facing towards the longitudinal axis A-A. The step 9 has an annular lip 10 that faces the plane 3a of the compression face 3 and the second portion 7 meets the annular lip 10. The lip 10 extends in a radial direction between the second portion 7 and the mouth 8 of the bowl 4. The annular lip 10 may extend parallel to the plane of the compression face 3, as shown in Figure 10. However, in another configuration the annular lip may extend at an angle to the plane 3a of the compression face 3, as shown in Figure 11, so that the depth of the annular lip 10 from the plane 3a of the compression face 3 increases in a direction extending away from the second portion 7 in a direction towards the longitudinal axis A-A. If the annular lip 10 extends at an angle to the plane 3a of the compression face 3, the angle at which the annular lip 10 extends to the plane 3a of the compression face 3 may be different to the angle at which the second portion 7 extends to the plane 3a of the compression face 3. In another unillustrated embodiment, the first portion 6, the second portion 7, and the annular lip 10 all extend at angles relative to the plane of the compression face 3.

As indicated above in relation to previous embodiments, the pockets 5 of the piston body shown in Figures 9 to 11 may be of any desired shape and are not limited to having first and second portions 6, 7.

In the embodiments of Figures 9 to 11, the pockets 5 are offset from their corresponding jets in the same way as described above in relation to Figures 1 to 8.

With reference to the particular embodiment of Figure 9, when the bowl 4 includes a step 9, the end face 11 upstands from the annular lip 10. The end face 11 may extend at 90 degrees to the plane 3a of the compression face 3. Alternatively, the end face 11 may extend at an angle relative to the plane 3a of the compression face. The end face 11 may extend at an angle to the plane 3a of the compression face 3 which is the same as the angle that the first portion 6 extends to the plane 3a of the compression face 3.

Figure 13 shows an embodiment of a vehicle 19 that comprises the internal combustion engine 14 according to embodiments of the invention, and as shown in Figure 12. The internal combustion engine may be a light duty, direct injection, 4-stroke, 4-valve per cylinder diesel engine, although other types of engines, including petrol engines, are also within the scope of the invention.

To assemble an internal combustion engine 14 according to an embodiment of the invention, the piston body 2 is inserted into the cylinder 13 and positioned so that a pocket 5 formed in the compression face 3 is offset by a predetermined angle, in a direction extending about the longitudinal axis A-A, from a corresponding fuel jet 18 so that fuel emitted by the jet 18 will be delivered to the pocket 5.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

CLAIMS1. An internal combustion engine comprising: a cylinder having a longitudinal axis and an air intake positioned so that a flow of air entering the cylinder through the air intake swirls about the longitudinal axis of the cylinder in a first direction; a piston received in the cylinder and configured to compress a charge of air, the piston comprising: a body having a longitudinal axis parallel to a longitudinal axis of the cylinder, a planar compression face, a bowl open towards the plane of the compression face and formed in the body, and a pocket extending into the body from the plane of the compression face; and a fuel injector comprising a jet, the fuel injector being configured to inject fuel in a radially outward direction into the cylinder from the jet and towards the plane of the compression face of the body; wherein the pocket is offset from the jet by a predetermined angle about the longitudinal axis of the piston body in said first direction so that fuel emitted from the jet into the flow of air swirling about the longitudinal axis is directed towards the pocket.
2. An internal combustion engine according to claim 1, wherein the fuel injector comprises a plurality of jets, each jet being positioned to inject fuel into the cylinder toward the compression face in a different direction, and the piston body comprises a plurality of pockets arranged about the longitudinal axis of the cylinder, wherein at least two of the pockets each have a corresponding jet, said pockets being offset from their corresponding jet by a predetermined angle about the longitudinal axis in said first direction so that fuel emitted from a corresponding jet into the flow of air swirling about the longitudinal axis is directed towards its associated pocket.
3. An internal combustion engine according to claim 2, wherein the predetermined angle by which each pocket and its corresponding jet is offset is the same.
4. An internal combustion engine according to claim 2, wherein the predetermined angle by which each pocket and its corresponding jet is offset is different for at least some of the pockets and their corresponding jets.
5. An internal combustion engine according to any preceding claim, wherein the or each pocket has an opening that faces in a direction towards the longitudinal axis of the piston body, and said predetermined angle by which the or each pocket is offset is measured from a radial centreline that extends from said longitudinal axis through a centre of the opening to a component of a line extending from the, or corresponding, jet to the compression face of the piston body that lies in the same plane as the radial centreline of the opening.
6. An internal combustion engine according to claim 5, wherein the or each jet comprises an opening having an axis, said predetermined angle being measured from said radial centreline extending through said centre of the opening of the pocket to said axis.
7. An internal combustion engine according to any of claims 1 to 6, wherein the predetermined angle by which the pocket and the, or corresponding, jet is offset is between 5 and 90 degrees.
8. An internal combustion engine according to any preceding claim, wherein the, or at least some, pockets comprise a first portion and a second portion, the first portion extending in a longitudinal direction into the body from the plane of the compression face at an angle of less than 90 degrees to the plane of the compression face, and the second portion extending from the first portion towards the bowl.
9. An internal combustion engine according to claim 8, wherein the second portion extends parallel to the plane of the compression face.
10. An internal combustion engine according to claim 9, wherein the second portion extends at an angle to the plane of the compression face, said angle being different to the angle at which the first portion extends to the plane of the compression face.
11. An internal combustion engine according to claim 8, wherein the bowl comprises a step extending annularly about the longitudinal axis of the body and each pocket communicates with said step.
12. An internal combustion engine according to claim 11, wherein the step comprises an annular lip that extends from the second portion of the pockets that comprise a first portion and a second portion to a mouth of the bowl.
13. An internal combustion engine according to claim 12, wherein the second portion extends from the first portion to meet said annular lip.
14. An internal combustion engine according to claim 12 or 13, wherein the second portion and said annular lip both extend parallel to the plane of the compression face.
15. An internal combustion engine according to claim 12 or 13, wherein the second portion and/or the annular lip each extend at an angle to the plane of the compression face.
16. An internal combustion engine according to claim 15, wherein the second portion and the annular lip both extend at an angle to the plane of the compression face, the angle at which the second portion extends to the plane of the compression face being different to the angle at which the annular lip extends to the plane of the compression face.
17. An internal combustion engine according to any of claims 13 to 16, wherein the first portion of the pockets comprises a surface that is curved in an angular direction extending about the longitudinal axis.
18. An internal combustion engine according to claim 17, wherein at least two adjacent pockets comprise a first portion and a second portion, wherein the first portion of said at least two adjacent pockets merge.
19. An internal combustion engine according to claim 17, wherein at least two adjacent pockets comprise a first portion and a second portion, the first portion of said at least two adjacent pockets being spaced by an end face that extends between said at least two adjacent pockets in an angular direction about the longitudinal axis.
20. An internal combustion engine according to claim 19, wherein said end face is arcuate and is coaxial with said longitudinal axis.
21. An internal combustion engine according to any of claims 18 to 20, wherein the bowl has an axis coaxial with said longitudinal axis of the piston body.
22. An internal combustion engine according to any of claims 2 to 21, wherein the pockets are arranged in a rotationally asymmetric pattern around the longitudinal axis of the body.
23. An internal combustion engine according to any of claims 2 to 22, wherein the pockets are arranged in a rotationally symmetric pattern around the longitudinal axis of the body.
24. A vehicle comprising the internal combustion engine according to any preceding claim.
25. A method of assembling an internal combustion engine that comprises a cylinder having a longitudinal axis and an air intake positioned so that a flow of air entering the cylinder through the air intake swirls about the longitudinal axis of the cylinder in a first direction, a piston including a body having a longitudinal axis parallel to a longitudinal axis of the cylinder and a planar compression face, a bowl open towards the plane of the compression face and formed in the body, and a pocket extending into the body from the plane of the compression face, and a fuel injector comprising jet, the fuel injector being configured to inject fuel in a radially outward direction into the cylinder from the jet and towards the plane of the compression face of the piston body; wherein the method comprises inserting the piston body into the cylinder and positioning the piston body and fuel injector such that the pocket is offset from the jet by a predetermined angle about the longitudinal axis in said first direction so that fuel emitted from the jet into the flow of air swirling about the longitudinal axis is directed towards the pocket.