Spark-ignited direct-injection engine combustion systems

Abstract

Direct injection stratified charge combustion engine, including: a combustion cylinder (14) to receive an air-fuel mixture; an air intake channel to allow air into the combustion cylinder (14); a fuel injector (22) configured to deliver fuel within the cylinder in a spray pattern (24) that is substantially aligned with a cylinder central axis (26) to produce the air-fuel mixture; a spark igniter located within a path of the spray pattern to ignite the combustion of the air-fuel mixture; and a movable piston (12) defining a lower boundary of the combustion cylinder (14) to contain the combustion of the air-fuel mixture, wherein the piston (12) includes a bowl section (36) with an angled re-entrant edge and a centrally arranged convex bulge in the direction of the cylinder central axis (26), which is arranged on an inlet opening side of the combustion cylinder (14) to deflect the fluid flow to a vortex in fluid association with a combustion site near the cylinder central axis (26), characterized in that the movable piston (12) further comprises an extension wall (542) which is defined by a top surface (242) on the inlet channel side.

Description

TECHNICAL AREA

[0001] The present disclosure relates to a combustion management system for spark-ignition direct injection combustion engines. INTRODUCTION

[0002] Fuel injectors regulate the fuel supply to internal combustion engines, directing it either into an intake manifold upstream of a combustion chamber or directly into the combustion chamber. The atomization of the fuel spray enhances vaporization and mixing with air to achieve optimal combustion and thus engine power generation. Additionally, atomization can promote more complete combustion of the air-fuel mixture, minimize the formation of unwanted combustion byproducts, and prevent uncontrolled combustion events.

[0003] Spark-ignition direct injection (SIDI) engines can operate using a combination of stratified charge and homogeneous charge strategies, depending on power requirements and other engine operating conditions. Under high-load conditions, vertical eddies, also known as tumble fluid flows, can improve the air-fuel mixture and promote enhanced combustion. However, a SIDI engine can operate at low loads using a lean air-fuel ratio and stratified charge, and tumble fluid flows can present unique challenges in maintaining optimal combustion conditions.US Patent 7 055 490 B2 describes a cylinder-injected, spark-ignited internal combustion engine with a fuel injector that atomizes fuel essentially in a sector of relatively small thickness and essentially vertically to achieve homogeneous combustion.

[0004] DE 102 38 317 A1 describes an engine with direct injection and spark ignition, with a combustion chamber formed between a lower surface of a cylinder head and an upper surface of a piston, an inlet valve and an exhaust valve arranged in an inlet opening and an exhaust opening respectively, which are arranged on opposite sides of the cylinder head, and a spark plug arranged in the cylinder head.

[0005] JP 4 155 184 B2 describes a movable piston with a bowl section. DE 101 45 956 A1 describes an engine with direct fuel injection in which the sloping surface formed on the top of the piston and the opposite roof surface of the cylinder head are different relative to a plane perpendicular to the longitudinal axis of the cylinder, so that the intake air trapped between the sloping surfaces of the piston and the opposite roof surface is slowly forced out of the gap between these surfaces and is prevented from flowing directly into the bowl at high speed. SUMMARY

[0006] A direct-injection stratified-charge internal combustion engine includes a combustion cylinder to hold an air-fuel mixture and an air intake to draw air into the combustion cylinder. The direct-injection engine also features a fuel injector configured to deliver fuel within the cylinder in a spray pattern essentially aligned with a cylinder centerline to create the air-fuel mixture. A spark plug is positioned within the path of the spray pattern to ignite the combustion of the air-fuel mixture. The direct-injection engine further includes a moving piston that defines a lower boundary of the combustion cylinder to contain the combustion of the air-fuel mixture.The piston is configured to include a bowl section with an angled re-entrant edge and a centrally located convex bulge in the direction of the cylinder's central axis, which is arranged on an inlet port side of the combustion cylinder to deflect the fluid flow in the direction of a vortex in fluid association with a combustion site near the cylinder's central axis, wherein the movable piston further comprises an extension wall extending circumferentially on a top side of the piston near an outer edge of the bowl section.

[0007] A moving piston is arranged to move within the combustion chamber of a direct-injection engine according to a combustion cycle. The moving piston includes a side section configured to seal against one side of the combustion chamber and a top section that defines a lower boundary of the combustion cylinder to contain an air-fuel mixture during the combustion cycle. The moving piston also includes a piston bowl formed in the top section to receive a fuel injection, which is generally delivered at a point along a central cylinder axis. The piston bowl is configured to define a bottom section that extends laterally in a first direction toward the side section at a distance from the central cylinder axis that is greater than in a second direction opposite to the central cylinder axis.

[0008] A direct-injection stratified-charge internal combustion engine includes a combustion cylinder to hold an air-fuel mixture and an air intake to draw air into the combustion cylinder. The direct-injection engine also features a fuel injector configured to deliver a fuel spray pattern within the cylinder at a point substantially close to the cylinder's centerline to create the air-fuel mixture. A spark plug is positioned along the path of the fuel spray pattern to ignite the combustion of the air-fuel mixture. The direct-injection engine further includes a moving piston that defines a lower boundary within the combustion cylinder to contain the combustion of the air-fuel mixture.The movable piston includes a piston recess that defines a bottom section extending in a first direction from the central cylinder axis by a lateral distance to the side section that is greater than a distance in an opposite second direction from the central cylinder axis. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial cross-section of a combustion chamber along line 1-1 of Fig. 3. Fig. 2 is a partial cross-section of a combustion chamber along line 2-2 of Fig. 3. Fig. Figure 3 is a schematic top view of a combustion chamber. Fig. 4A-4E are computer simulation results showing air-fuel ratio contours and fluid flow vectors. Fig. Figure 5 is a perspective view of a piston head according to one embodiment. Fig. 6 is a cross-section of a piston head along the line 6-6 according to a first alternative embodiment. Fig. Figure 7 is a cross-section of a piston head along line 6-6 according to a second alternative embodiment. Fig. Figure 8 is a cross-section of a piston head along line 6-6 according to a third alternative embodiment. Fig. Figure 9 is a cross-section of a piston head along line 6-6 according to a fourth alternative embodiment. DETAILED DESCRIPTION

[0009] Embodiments of the present disclosure are described herein. It is understood, however, that the disclosed embodiments are merely examples and that other embodiments may take different and alternative forms. The figures are not necessarily to scale; some features may be shown larger or smaller to illustrate the details of certain components. Consequently, the structural and functional details disclosed herein are not to be understood as limiting, but merely as a representative basis to convey to those skilled in the art the various ways in which the present invention may be used.As those skilled in the art understand, various features illustrated and described with reference to any of the figures can be combined with features illustrated in one or more other figures to create embodiments not explicitly illustrated or described. The illustrated combinations of features provide representative embodiments for typical applications. However, arbitrary combinations and modifications of the features consistent with the teachings of this disclosure may be desirable for certain applications and implementations.

[0010] Split-charge direct injection (SIDI) combustion engines can reduce the overall fuel consumption of gasoline engines. However, even in SIDI engines, incomplete combustion under certain conditions limits efficiency and leads to increased emissions of byproducts. Incomplete combustion can result from the inability to maintain a proper air-fuel mixture near the spark plug, leading to undermixing or overmixing of the fuel with the air. These undermixed and overmixed mixtures are associated with increased fuel consumption as well as hydrocarbon and carbon monoxide emissions.

[0011] Several different design strategies can be used to control fuel injection and ignition timing for SIDI engines. For example, wall-guided combustion systems largely utilize swirl fluid flows (i.e., horizontal flow corners) induced by the injector nozzle and intake ports, in combination with one or more combustion chamber walls and the top surface of a piston, to deflect the fuel jet toward the spark plug. To avoid excessive spray impact on the piston surface at high back pressures (i.e., high pressure in the combustion chamber) and to allow sufficient time for the fuel to return from the piston to the ignition point, these systems require a relatively early injection timing.The increased fuel path of wall-mounted systems, from a side-mounted injector to the top of the piston and back to the spark plug, creates ample opportunity for overmixing, resulting in less than all of the fuel being burned. Additionally, during operation in stratified charge mode, a significant amount of fuel can impact the piston surface, leading to smoke and hydrocarbon emissions. To improve combustion stability at low loads (approximately less than 2 bar BMEP), an air intake may need to be throttled to reduce air intake, resulting in increased pumping losses and reduced efficiency.

[0012] In a second example, spray-guided combustion systems often use fuel spray dynamics to form the air-fuel mixture. In this case, the fuel injector and spark plug can be positioned closer together within the cylinder to ignite the fuel delivered by the injector more quickly. Due to this spatial proximity, these systems may require tight timing of ignition and fuel injection, leaving only a small window near the end of the injection for spark plug ignition. This shorter timing limits flexibility and allows less time for fuel droplets to vaporize. This can lead to droplet combustion and very fuel-rich mixtures, resulting in smoke emissions. Also, due to the proximity of the fuel injector and spark plug, such systems may be less tolerant of tumble fluid flows (i.e.,vertical vortices) of the air-fuel mixture.

[0013] With reference to the Fig. Figures 1 to 3 show a combustion chamber of an exemplary SIDI engine. A piston 12 is movable within a closed end cylinder 14 and interacts with the cylinder 14 to define a variable-volume combustion chamber 16. The piston 12 incorporates a shaped recess 18 oriented in the direction of primary fuel injection. The combustion chamber 16 is configured with a spark plug 20 and a fuel injector 22, which are arranged cooperatively to control the air-fuel mixture and the timing of combustion. A fuel spray pattern 24 distributes fuel for combustion throughout the chamber 16. The fuel spray pattern 24 from the injector 22 is arranged such that the spark plug 20 ignition occurs within a path of the spray pattern. With particular reference to the cross-sectional view of Fig. 2 The spray tip of the fuel injector 22 is located at a substantially central position within the cylinder 14. The spray pattern 24 is also substantially aligned with a cylinder center axis 26 to produce the air-fuel mixture. The spark plug 20 is offset relative to the fuel injector 22, but is, in the view of Fig. 2 is also aligned with the central axis 26. The fuel injector 22 and the spark plug 20 are arranged longitudinally such that the intake ports 28 lie on a first side of an axis defined by a line through the fuel injector and the spark plug, and the exhaust ports 30 are located on an opposite second side of the line through the injector and the spark plug. In some embodiments, due to engine design, packaging, and other considerations, there may be an offset between the spray head position of the fuel injector and the central cylinder axis 26. Notwithstanding any necessary offset values, according to aspects of the present disclosure, the fuel injection point is arranged in the most central location possible to create a combustion zone close to the center of the combustion chamber.

[0014] With specific reference to the cross-sectional view of Fig. 1 is an alignment axis 32 of the fuel injector 22 inclined with respect to the cylinder central axis 26, defining an angle θ. While the example of Fig. Since 1 represents a positive value for θ, it should be recognized that some examples may include a fuel injector oriented essentially parallel to the central axis 26 in each of two views that are orthogonal to each other (i.e., θ essentially zero). According to one example, θ is approximately 5 degrees. The location and orientation of each of the fuel injector 22 and the spark plug 20 may take into account considerations such as the housing, injector spray pattern, spark gap projection, spark gap-to-injector spray tip distance, etc. Regardless of the injection angle, the injection point is generally located near the central cylinder axis 26.

[0015] In the example of the Fig. 1 and Fig. 2. Combustion is controlled by the design of the fuel spray pattern. That is, the top 34 of the piston 12 defines a lower section of the combustion chamber. And the top 34 contains a bowl section 36 as part of the recess 18, which is used to receive the fuel-air mixture during a compression stroke. According to some examples, the volume of the bowl section 36 is about 50 percent of the total chamber volume when the piston is at top dead center (TDC). The spark plug activation is set so that a trailing end of the fuel spray is ignited by the spark plug. To influence the overall distribution of fuel density over the combustion chamber and to avoid undesirable saturation, the fuel spray can be divided into several smaller fuel pulses, with the ignition spark being timed according to a subsequent fuel pulse.

[0016] To meet full-load torque and power requirements, combustion can benefit from intake ports positioned to create high tumble, or vertical eddies in the fluid flow. Under moderate and low load conditions, the SIDI engine is configured to operate using a lean air-fuel ratio. In these cases, high tumble may be less desirable for lean stratified combustion performance during moderate and low loads because it can disrupt the stratification process and prevent adequate containment of the air-fuel charge within the piston bowl.

[0017] With reference to Fig. 4A to Fig. Figure 4E shows computer-predicted fuel density and airflow vectors for an exemplary lean stratified part-load operating condition. Each figure represents a time increment during one piston compression stroke. The view of each simulation result corresponds to the cross-sectional view of Fig. 2. The relative timing of each increment is represented by the crankshaft rotation angle in degrees of crankshaft rotation (CAD). CAD refers to the position of the engine's crankshaft relative to the piston as it moves within the combustion cylinder. Each CAD value corresponds to a position of the piston head relative to the TDC position. Fig. 4A to Fig. 4E, the piston head advances towards the TDC position (e.g., CAD = 720 degrees) during the compression stroke of the combustion cycle.

[0018] With reference to Fig. 4A, an initial fuel spray pattern 124 is emitted from a fuel injection point 100 near a central cylinder axis at a time approximately CAD 690 degrees. Near a trailing end of the initial fuel spray pattern 124, the fuel is ignited by the spark plug.

[0019] Fig. Figure 4B shows the predicted fluid flow vectors and the fuel density of the air-fuel mixture, which corresponds to approximately CAD 692 degrees. Arrow 110 indicates the presence of a predicted tumble vortex due to the flow operating conditions. The location of the vortex, represented by arrow 110, is near a fuel-denser region and thus contributes to the mixing of fuel and air within the cylinder by drawing fuel-dense areas of the mixture back toward the central section where combustion was initiated.

[0020] With reference to Fig. At 4C, which corresponds to approximately CAD 696 degrees, it is evident that the areas with higher fuel content begin to spread laterally across the cylinder, away from the center. It should be noted that the tumble vortex, represented by arrow 110, is generally in the same position but helps to push portions of the higher fuel content areas away from the central combustion area.

[0021] Referring to Fig. 4D, which corresponds approximately to CAD 700 degrees, a subsequent fuel pulse with a fuel spray pattern 134 is injected into the piston bowl later in the compression stroke, so that it can be contained in the bowl when it mixes with the air remaining in the cylinder. In the example of the Fig. 4A to Fig. 4E has a residence time of 1 millisecond between the initial fuel pulse at CAD 690 degrees and the subsequent second pulse at approximately CAD 700 degrees. The spray pattern 134 of the subsequent fuel injection further influences both the fluid flow of the air-fuel mixture and the fuel density distribution across the combustion cylinder.

[0022] With reference to Fig. At 4E, which corresponds to approximately CAD 704 degrees, the central portion of the combustion chamber exhibits a higher fuel density, which is related to the subsequent fuel pulse. The combination of the subsequent fuel pulse and the corresponding late-cycle combustion near the center of the bowl can actually push earlier unburned fuels on the intake port side further away from the combustion chamber. As shown by Fig. As can be seen in Figure 4E, the position of the high tumble vortex, represented by arrow 110 on the intake port side, shifts closer to the center of the bowl and is less effective at pulling the high-fuel-density sections back towards the center as combustion progresses. A separation gap 120 can be induced when there is little or no fuel density between the combustion area towards the center of the cylinder and a higher-fuel-density area 130 near an edge of the piston bowl. In other words, the higher-fuel-density area 130 is separated from the combustion area, allowing some of the air-fuel charge to remain unburned.Furthermore, parts of the air-fuel charge area 130 begin to leak out of the piston bowl overall, resulting in suboptimal combustion efficiency, which leads to high fuel consumption, high hydrocarbon and carbon monoxide emissions and high combustion instability.

[0023] According to aspects of the present disclosure, the piston bowl geometry can be configured to exploit tumble vortices under a wider range of load conditions. That is, the shape can be conducive to better retaining the air-fuel mixture during low-load situations with a high degree of tumble flow, which is normally undesirable for lean stratified combustion conditions. The bowl shape can be configured to coincide with the tumble effects to maximize combustion efficiency under these low-load conditions. The remaining high-fuel-density flow sections can be forced to remain in better contact with tumble vortices to largely reduce or eliminate the amount of fuel escaping from the combustion zone near the center of the piston bowl.

[0024] The present disclosure provides a number of different piston bowl designs, each of which helps to retain the air-fuel charge within the piston bowl during the combustion process, even in the presence of high tumble eddies. Each of the bowl designs helps to prevent overflow into the squish area of ​​the unburned air-fuel mixture. By containing the air-fuel charge within the bowl, the flame can reach the entire air-fuel mixture in the piston bowl. Combustion efficiency is improved, resulting in reduced fuel consumption, lower hydrocarbon and carbon monoxide emissions, and improved combustion stability. Furthermore, the various bowl shapes do not impede the function of high tumble flows during higher loads, thus maintaining full-load torque and power requirements.

[0025] Fig. Figure 5 is a perspective view of a piston head 212 arranged to maximize the combustion efficiency of high tumble flows within the combustion cylinder for both high-load and low-load conditions. The piston 212 may include a pair of recesses 214 corresponding to the air intake valves. The piston head 212 may also include a pair of recesses 216 corresponding to the exhaust valves of the combustion cylinder. A central bowl section 236 is configured to enhance combustion near the center of the cylinder with multiple fuel pulses and tumble flow swirls. More specifically, a wall 138 on the intake side of the combustion chamber is uniquely configured to retain outer portions of the air-fuel mixture in conjunction with the combustion area near the center of the bowl 236.The Wall 138 can incorporate a combination of any number of enhancements to promote complete combustion during low-load operating conditions where tumble fluid flows are present.

[0026] With reference to Fig. In section 6, the piston 212 is improved to maximize combustion efficiency. A bottom section of the piston bowl extends toward the intake ports, allowing the air-fuel mixture to travel a longer path within the bowl. The result is a greater volume of the air-fuel mixture remaining in the piston bowl, as opposed to escaping the bowl and leaving the combustion zone. Because the mixture remains in contact with other parts of the mixture that undergo combustion, it allows the flame to catch up with the unburned mixture and achieve more complete combustion. A first improved wall 338 is displaced radially outward toward an edge of the cylinder head 212 relative to the baseline wall 238 on the intake port side to enhance combustion, as described immediately before.The result is a piston bowl 338 extended in one direction, which improves the connection between the outer sections of the fuel-air mixture and the combustion sections of the mixture. According to some examples, the bowl 336 is asymmetrical with respect to a vertical axis, so that a radial clearance on the intake port side is increased from a value of r1 to a value of r1+Δr. In one particular example, the radial clearance is increased by about 15 to 35 percent (i.e., 0.15*r1 < Δr < 0.35*r1). In another specific example, the bowl 336 defines an asymmetrical shape relative to the cylinder center axis 26. As discussed above, offsets may exist between a center axis of the bowl and a center axis of the combustion chamber.

[0027] In Fig. In Figure 7, the piston 212 is improved in another way to enhance combustion efficiency. The baseline wall 238 can be reoriented to influence the flow direction of the fuel-air mixture passing over it. The result is reduced fluid flow crossing the edge of the bowl 436 and improved continuity between the outer sections of the fuel-air mixture and the combustion sections of the mixture near the center of the bowl. A second improved wall 438 is angled by α degrees on the intake port side of the cylinder to improve the re-entry of fluid flow back toward the center of the bowl. According to some examples, 20 degrees ≤ α ≤ 40 degrees. According to one specific example, the angle α is approximately 28 degrees.

[0028] With reference to Fig. In 8, the wall 538 of the piston bowl 536 is extended laterally in the direction of the intake ports, as described above, but the bottom section 540 is also designed to be deeper in order to increase the volume of the air-fuel mixture enclosed in the piston bowl 536. The bottom section 540 is deepened by approximately h1 dimension. In some examples, the bowl is deepened by an amount of approximately 1 millimeter to 5 millimeters. According to one specific example, h1 can be approximately 3.2 millimeters. Containing more fuel-air mixture in the bowl also allows the flame to reach the unburned mixture and achieve more complete combustion. A second depth improvement, which in the example of Fig. As provided in Figure 8, this involves raising the height of the baseline top surface 242. An increased height can help resist fluid flow over the edge of the piston bowl 536 as the piston 212 approaches top dead center. The top surface 242 defines an extension wall 542 on the intake port side to further prevent fuel and air from crossing the piston bowl edge due to vertical tumble of the fluid flow in the combustion cylinder. The baseline top surface 242 is raised by a dimension h2 to aid in the intake of the fuel-air mixture. In some examples, the top surface is raised by approximately 3 to 7 millimeters. According to one specific example, h2 can be approximately 4.8 millimeters.It should be noted that the height h2 may be limited by the design gap between the top of the piston at top dead center and the underside of a (not shown) cylinder cap, which may be the upper boundary of the cylinder volume. In some examples, the baseline top 242 of the piston 212 is raised on both the intake and exhaust sides of the cylinder. Furthermore, the additional mass of the extension wall 542 may be configured to modify the cylinder volume, thereby affecting the overall compression ratio of the combustion cycle.

[0029] Increasing the volume of the air-fuel mixture enclosed in the piston bowl improves combustion under moderate and low load conditions, but may have some disadvantages under high load operating conditions.

[0030] For example, there may be a higher risk of trapping unburned or unmixed air or fuel at the base of the bowl during wide-open throttle conditions, which operate using the highest fuel masses during the combustion cycle. Adding more volume to a local area of ​​the bowl can result in insufficient time to burn the increased fuel and / or air mass.

[0031] With reference to Fig. 9. A combination of each of the combustion improvement features can be implemented in a single-piston design. That is, each of the flow path enhancement Δr, reentry enhancement α, local bowl depth enhancement h1, and topside height enhancement h2 can be used together to achieve an additive benefit relative to each individual feature. Overall, the collective improvements help to reduce the separation of high air-fuel ratio regions such that, when a subsequent fuel pulse and corresponding fuel combustion occur, no gap regions escape from the piston bowl due to the fuel-air mixture. It should be recognized that, while the example of Fig.9 includes a combination of four types of piston geometry improvements, any number or combination of the improvements disclosed herein may be used according to aspects of the present disclosure.

[0032] Although exemplary embodiments are described above, these embodiments are in no way intended to describe all possible forms encompassed by the claims. Rather, the words used in the specification serve to describe, not to limit, and it is understood that various modifications can be made without deviating from the inventive concept and the scope of the disclosure. As previously described, the features of different embodiments can be combined to form further embodiments of the invention that are not explicitly described or illustrated.Although various embodiments may have been described to offer advantages or to be preferred over other embodiments or implementations of the prior art with respect to one or more desired features, those skilled in the field will recognize that one or more features or characteristics may be compromised to achieve the desired overall system properties, which depend on the specific application and implementation. These properties may include, but are not limited to, cost, strength, durability, life-cycle costs, marketability, appearance, packaging, size, usability, weight, manufacturability, ease of assembly, etc.Therefore, embodiments that are described as less desirable with respect to one or more features compared to other embodiments or implementations of the prior art are not outside the scope of disclosure and may be desirable for certain applications.

Claims

[1] Direct injection stratified charge internal combustion engine, comprising: a combustion cylinder (14) to receive an air-fuel mixture; an air intake channel to allow air into the combustion cylinder (14); a fuel injector (22) configured to deliver fuel within the cylinder in a spray pattern (24) that is substantially aligned with a cylinder central axis (26) to produce the air-fuel mixture; a spark igniter located within a path of the spray pattern to ignite the combustion of the air-fuel mixture; and a movable piston (12) defining a lower boundary of the combustion cylinder (14) to contain the combustion of the air-fuel mixture, wherein the piston (12) includes a bowl section (36) with an angled re-entrant edge and a centrally arranged convex bulge in the direction of the cylinder central axis (26), which is arranged on an inlet opening side of the combustion cylinder (14) to deflect the fluid flow to a vortex in fluid association with a combustion site near the cylinder central axis (26), characterized by , that the movable piston (12) further comprises an extension wall (542) defined by a top surface (242) on the inlet channel side. [2] Direct injection engine according to claim 1, wherein the bowl section (36) is asymmetrical with respect to the cylinder central axis (26), wherein the bowl section (36) defines a first opening edge on the intake port side of the combustion cylinder (14), which extends further towards an outer edge of the piston head relative to an opposing second opening edge on an exhaust port side of the combustion cylinder (14). [3] Direct injection engine according to claim 2, wherein the bowl section (36) defines a radius r1 with respect to the cylinder central axis (26) and the first opening edge is extended by Δr, wherein 0.15*r1 ≤ Δr ≤ 0.35*r1. [4] Direct injection engine according to claim 1, wherein the bowl section (36) defines a first depth on the inlet channel side of the combustion chamber which is deeper than a second depth on an opposite outlet channel side of the combustion chamber. [5] Direct injection engine according to claim 1, wherein the angled re-entrant edge is aligned at an angle α relative to the cylinder central axis and 20 degrees ≤ α ≤ 40 degrees. [6] Direct injection engine according to claim 1, wherein the extension wall (542) is arranged on the inlet port side of the combustion cylinder. [7] Movable piston (212) arranged to move within a combustion chamber of a direct injection engine according to a combustion cycle, comprising a movable piston (212): a side section configured to seal against one side of the combustion chamber; a top surface defining a lower boundary of the combustion cylinder (14) to contain an air-fuel mixture during the combustion cycle; and a piston bowl (536) formed in the upper surface to deliver fuel injection at a location generally along a cylinder central axis (26), wherein the piston bowl defines a bottom section (540) extending laterally in a first direction to the side section at a distance from the cylinder central axis (26) that is greater than in an opposite second direction from the cylinder central axis (26), wherein the bottom section (540) has a central convex bulge projecting out of the upper surface in the direction of a cylinder central axis (26) of the movable piston, characterized by , that the movable piston further comprises an extension wall (542) defined by a top surface (242) on the inlet channel side. [8] Movable piston (212) according to claim 7, wherein the first direction is directed from the cylinder central axis (26) towards an inlet port side of the combustion cylinder. [9] Movable piston (212) according to claim 7, wherein the piston recess (536) defines a deeper depth on an inlet port side of the cylinder relative to an opposite outlet port side of the combustion cylinder.

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