Internal combustion engine

Abstract

To restrain blow-out of electric discharge at the time of ignition.SOLUTION: An internal combustion engine comprises: an ignition plug having a center electrode and a ground electrode faced to a combustion chamber, and arranged between an intake value and an exhaust valve; and a cylinder injection valve arranged on an intake valve side to the ignition plug and injecting fuel to the combustion chamber, wherein the ground electrode and the center electrode form a discharge gap opposite to an axial direction of the ignition plug. The internal combustion engine comprises a wall part provided between the center electrode and the cylinder injection valve inside the combustion engine, and extending to a predetermined position from a ceiling side of the combustion chamber along the axial direction of the ignition plug. The predetermined position is included in a range between a tip position of the center electrode and a bottom position of the ground electrode in the axial direction of the ignition plug, and the ignition plug is arranged so that a base end of the ground electrode is positioned on an exhaust valve side to the center electrode.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an internal combustion engine. [Background technology]

[0002] Patent Document 1 discloses that in an internal combustion engine equipped with an in-cylinder injection valve and an ignition plug, the ignition plug is disposed so that the ground electrode is located on the exhaust valve side with respect to the center electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-132833 A Summary of the Invention [Problem to be solved by the invention]

[0004] In an internal combustion engine, if the flow speed of air passing through the discharge gap of the spark plug becomes fast, there is a risk that the discharge will be blown out at the time of ignition, resulting in a decrease in ignition quality.

[0005] The present invention has been made in consideration of the above circumstances, and has an object to provide an internal combustion engine that can suppress the blowing out of discharge at the time of ignition. [Means for solving the problem]

[0006] The present invention provides an internal combustion engine comprising: a spark plug having a center electrode and a ground electrode facing a combustion chamber, the spark plug being arranged between an intake valve and an exhaust valve; and an in-cylinder injection valve arranged on the intake valve side of the spark plug and injecting fuel into the combustion chamber, the ground electrode and the central electrode facing each other in the axial direction of the spark plug to form a discharge gap, the internal combustion engine further comprising: a wall portion arranged inside the combustion chamber between the center electrode and the in-cylinder injection valve and extending from a ceiling side of the combustion chamber to a predetermined position along the axial direction of the spark plug, the predetermined position being included in the range between a tip position of the center electrode and a bottom position of the ground electrode in the axial direction of the spark plug, and the spark plug being arranged such that a base end of the ground electrode is located on the exhaust valve side of the center electrode. Effect of the Invention

[0007] In the present invention, since a wall portion is provided on the intake valve side of the center electrode, the airflow flowing from the intake valve side to the exhaust valve side toward the discharge gap of the ignition plug collides with the wall portion, suppressing the flow rate of the airflow around the discharge gap, and suppressing the discharge from being blown out at the time of ignition. Also, since the base end of the ground electrode is disposed on the exhaust valve side, it is easy to keep the spray around the discharge gap. These features improve the ignition performance of the internal combustion engine. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating an internal combustion engine according to an embodiment; [Diagram 2] FIG. 2 is a diagram for explaining an ignition plug. [Diagram 3] FIG. 13 is a diagram showing an airflow colliding with a wall when a discharge occurs in a discharge gap. [Figure 4] FIG. 4 is a diagram for explaining an equivalence ratio in the vicinity of a discharge gap. [Diagram 5] FIG. 4 is a graph for explaining the air excess ratio and the air flow velocity around the discharge gap. [Figure 6]11 is a graph for explaining the difference in the maximum rich value, the maintenance time for an appropriate air excess ratio, and the flow velocity of the air current due to the difference in the tip position of the wall portion. FIG. [Figure 7] FIG. 2A is a diagram showing a schematic diagram of an internal combustion engine of Comparative Example 1, and FIG. 2B is a diagram for explaining an equivalence ratio in the vicinity of a discharge gap in Comparative Example 1. [Figure 8] 10(a) is a diagram for explaining the equivalence ratio in the vicinity of the discharge gap in Comparative Example 2, and FIG. 10(b) is a diagram for explaining the equivalence ratio in the vicinity of the discharge gap in Comparative Example 3. FIG. [Figure 9] FIG. 4 is a graph showing the flow speed of air currents around the discharge gap in the example and comparative examples 1 to 3. [Figure 10] FIG. 2 is a graph showing excess air ratios in an example and comparative examples 1 to 3. [Figure 11] 13 is a diagram for explaining that the tip position of the wall portion is set within a predetermined range. FIG. [Figure 12] 12 is a graph for explaining the effect obtained by including the tip position of the wall portion within the range shown in FIG. 11. [Figure 13] 11 is a diagram for explaining a structure in which a wall portion is formed so as to cover the radial outside of a center electrode. FIG. [Figure 14] FIG. 14 is an explanatory diagram including a cross section along line CC in FIG. [Figure 15] FIG. 1 is a diagram illustrating an internal combustion engine having a structure in which a wall portion is provided on a cylinder head. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An internal combustion engine according to an embodiment of the present invention will be specifically described below, however, the present invention is not limited to the embodiment described below.

[0010] 1 is a schematic diagram of an internal combustion engine according to an embodiment. The internal combustion engine 1 is a spark ignition type direct injection engine. The internal combustion engine 1 is a lean burn engine or an EGR engine, and is an engine in which an air-fuel mixture can flow at high speed inside a cylinder of the internal combustion engine 1. The internal combustion engine 1 includes an ignition plug 2, a direct injection valve 3, and a wall portion 4.

[0011] The spark plug 2 has a center electrode 21 and a ground electrode 22 as electrodes provided so as to face the inside of the combustion chamber 5, and is disposed between the intake valve and the exhaust valve. The combustion chamber 5 is partitioned by a cylinder head 6, a cylinder block, and a piston. The in-cylinder injection valve 3 is a fuel injection valve disposed on the intake valve side of the spark plug 2. The in-cylinder injection valve 3 is attached to the cylinder head 6 and provided on the ceiling side of the combustion chamber 5. The housing 23 of the spark plug 2 is attached to the cylinder head 6, and the center electrode 21 and the ground electrode 22 are provided on the ceiling side of the combustion chamber 5. The tip of the spark plug 2 including the center electrode 21 and the ground electrode 22 serves as an ignition part. The spark plug 2 can generate a discharge spark in an axial gap (hereinafter referred to as a discharge gap) between the center electrode 21 and the ground electrode 22 by applying a high voltage to the center electrode 21. In this description, the axial direction of the spark plug 2 may be simply referred to as the axial direction.

[0012] 2, the center electrode 21 is provided on the central axis CL of the spark plug 2 and protrudes forward beyond the front end surface 23a of the housing 23. The housing 23 is formed in a cylindrical shape around the central axis CL and extends in the axial direction of the spark plug 2. The front end surface 23a of the housing 23 is an annular surface centered on the central axis CL and is a flat surface formed in a direction perpendicular to the axial direction of the spark plug 2.

[0013] The ground electrode 22 extends from the housing 23 to the tip side of the spark plug 2 so as to form a discharge gap between itself and the center electrode 21. The ground electrode 22 has a facing portion 22a that faces the center electrode 21 in the axial direction of the spark plug 2, and a connecting portion 22b that connects the facing portion 22a to the housing 23.

[0014] The opposing portion 22a is a tip (ground electrode tip) on the ground electrode 22 side provided on the central axis CL of the spark plug 2. The opposing portion 22a is made of a precious metal or the like, and is connected to the base material of the ground electrode 22. This opposing portion 22a faces the center electrode 21 in the axial direction of the spark plug 2 to form a discharge gap.

[0015] The connecting portion 22b is formed in an arm shape extending from the housing 23 so as to pass through a position intersecting the central axis CL. The base end side of the connecting portion 22b is connected to the tip surface 23a of the housing 23 and extends along the axial direction, and the tip side extends along a direction perpendicular to the axial direction. That is, the connecting portion 22b is curved between the base end side and the tip side. As shown in FIG. 1, the base end side of the connecting portion 22b is disposed on the exhaust valve side with respect to the center electrode 21. The curvature between the base end side and the tip side of the connecting portion 22b may be a bend having an R portion.

[0016] Further, a tip base end surface 22c on which the opposing portion 22a is provided, and a bottom surface 22d on the opposite side to the tip base end surface 22c are provided on the tip side of the connecting portion 22b. Both the tip base end surface 22c and the bottom surface 22d are formed by surfaces perpendicular to the axial direction of the spark plug 2. The tip base end surface 22c is a surface facing the center electrode 21 in the axial direction. The bottom surface 22d is the bottom surface of the connecting portion 22b and the bottom surface of the ground electrode 22.

[0017] The wall portion 4 is disposed on the intake valve side of the central electrode 21 inside the combustion chamber 5. The wall portion 4 is a structural portion that functions to suppress the flow speed of the air flow passing through the discharge gap of the spark plug 2. The wall portion 4 is configured on the intake valve side of the central electrode 21 and functions as an airflow suppressing portion.

[0018] In detail, the wall portion 4 is provided between the center electrode 21 and the in-cylinder injection valve 3 inside the combustion chamber 5, and extends from the ceiling side of the combustion chamber 5 in the axial direction of the spark plug 2. The wall portion 4 is integrally formed with the housing 23 by welding or the like. The wall portion 4 is a plate-shaped member, and is formed to have a thickness approximately equal to that of the ground electrode 22. The wall portion 4 extends along the axial direction of the spark plug 2 from the tip surface 23a of the housing 23 to the same axial position as the tip base end surface 22c of the ground electrode 22. For example, the tip position of the wall portion 4 is set to a position P1 where the distance from the tip surface 23a of the housing 23 is 5.1 mm. In other words, the axial length of the wall portion 4 is formed to be 5.1 mm.

[0019] As shown in FIG. 3, the wall 4 has a wall surface 41 against which the airflow flowing from the intake valve side toward the exhaust valve side toward the discharge gap of the spark plug 2 collides. The wall surface 41 is a surface facing the intake valve side with respect to the center electrode 21. When an airflow (tumble flow) flows from the intake valve side toward the exhaust valve side inside the combustion chamber 5 of the internal combustion engine 1, the airflow collides with the wall surface 41 of the wall 4, thereby suppressing the flow rate of the airflow flowing into the discharge gap near the ignition timing, and it is possible to prevent the discharge between the center electrode 21 and the ground electrode 22 from being blown out. In this way, in the internal combustion engine 1, the wall 4 is provided on the intake valve side of the discharge gap of the spark plug 2, so that the flow rate in the discharge gap can be significantly suppressed. This optimizes the flow of the mixture in the discharge gap, thereby realizing an appropriate discharge length.

[0020] In this way, the wall 4 on the intake valve side and the ground electrode 22 on the exhaust valve side can suppress the flow rate of the fluid around the center electrode 21 of the spark plug 2 and rectify the airflow. This prevents the discharge from being blown out and allows the discharge to be extended stably.

[0021] Furthermore, in the spark plug 2, the connection portion 22b of the ground electrode 22 is curved from the opposing portion 22a toward the exhaust valve side. Therefore, the ground electrode 22 functions as an airflow suppression portion on the exhaust valve side relative to the center electrode 21. In the internal combustion engine 1, the airflow that has passed through the discharge gap collides with the connection portion 22b on the exhaust valve side. In the internal combustion engine 1, the wall portion 4 serves as the airflow suppression portion on the intake valve side, and the ground electrode 22 serves as the airflow suppression portion on the exhaust valve side, so that the wall portion 4 and the ground electrode 22 can form an airflow stagnation portion near the discharge gap. As a result, as shown in FIG. 4, it is possible to hold the spray from the in-cylinder injection valve 3 around the center electrode 21 for a long time. This allows an appropriate mixture to be formed around the center electrode 21 for a long time even under conditions of high-speed in-cylinder flow, thereby enabling stable ignition of the internal combustion engine 1. In addition, it is possible to expand the lean limit and EGR limit, particularly on the high rotation side, during the operating state of the internal combustion engine 1, thereby contributing to improving the thermal efficiency of the internal combustion engine 1.

[0022] FIG. 5 is a graph for explaining the air excess ratio and the flow velocity of the air flow around the discharge gap. As shown in FIG. 5, in the internal combustion engine 1, at the ignition timing IT, the flow velocity of the air flow around the discharge gap of the spark plug 2 can be suppressed, and the air excess ratio λ around the discharge gap of the spark plug 2 becomes the richest side. The larger the value of the air excess ratio λ, the leaner the air excess ratio becomes, and the smaller the value, the richer the air excess ratio becomes. When the air excess ratio λ around the discharge gap becomes richer than the threshold value A, it becomes an appropriate air excess ratio that allows stable ignition. The threshold value A is set to an air excess ratio that allows stable ignition. Therefore, the time when the air excess ratio λ becomes richer than the threshold value A is the maintenance time T1 of the appropriate air excess ratio that allows stable ignition. In the internal combustion engine 1, the maintenance time T1 is configured to include the ignition timing IT. The air excess ratio λ that becomes the richest side within this maintenance time T1 becomes the richest value B. The internal combustion engine 1 is configured so that at or close to the ignition timing IT, the excess air ratio λ around the discharge gap becomes the richest value B. In this way, the internal combustion engine 1 can suppress the flow velocity around the discharge gap at the ignition timing IT and make the excess air ratio λ become an appropriate value.

[0023] FIG. 6 is a graph for explaining the difference between the richest value, the maintenance time of the appropriate excess air ratio, and the flow velocity of the airflow due to the difference in the tip position of the wall portion. In order to realize stable ignition, it is preferable that the richest value B is on the rich side, the maintenance time T1 is long, and the flow velocity of the airflow is low. As shown in FIG. 6, in the internal combustion engine 1, the tip position of the wall portion 4 is a position P1 at a distance of 5.1 mm from the tip surface 23a of the housing 23. A comparison is made based on the difference in the tip position of the wall portion 4. For example, when the tip position of the wall portion 4 changes from 3.5 mm to 5.1 mm, the richest value B gradually changes to the rich side, the maintenance time T1 gradually changes to be longer, and the flow velocity of the airflow gradually changes to the low speed side. Also, when the tip position of the wall portion 4 changes from 5.1 mm to 6.5 mm, the richest value B gradually changes to the lean side, the maintenance time T1 gradually changes to the short side, and the flow velocity of the airflow remains on the low speed side. Thus, in the internal combustion engine 1, by positioning the tip end of the wall portion 4 at position P1, where the distance from the tip end surface 23a of the housing 23 is 5.1 mm, the performance of the maximum rich value B, the performance of the maintenance time T1, and the performance of the airflow velocity are optimal. This makes it possible to suppress the airflow in the combustion chamber 5 and form an appropriate flow around the discharge gap. In addition, the spray is maintained around the discharge gap, and the air-fuel mixture required for stable ignition can be formed around the discharge gap.

[0024] Next, the internal combustion engine 1 will be compared with a comparative example with reference to Figures 7 to 10. Note that Figures 7(b), 8(a), and 8(b) show the equivalence ratio around the discharge gap near the ignition timing, similar to Figure 4.

[0025] The embodiment is configured by an internal combustion engine 1 including a wall portion 4. Comparative examples 1 to 3 are internal combustion engines 100, 200, and 300 having a structure in which the wall portion 4 is not provided. Comparative example 1 is an internal combustion engine 100 including an ignition plug 102 arranged so that a connection portion 101 is located on the front side as shown in FIG. 7(a). Comparative example 2 is an internal combustion engine 200 including an ignition plug 202 arranged so that a connection portion 201 is located on the intake valve side as shown in FIG. Comparative example 3 is an internal combustion engine 300 including an ignition plug 302 arranged so that a connection portion 301 is located on the exhaust valve side as shown in FIG. 8(b). The internal combustion engines 100, 200, and 300 of comparative examples 1 to 3 are spark ignition type direct injection engines and are lean burn engines.

[0026] As shown in FIG. 9, the flow velocity around the discharge gap in Comparative Example 1 is on the high-speed side compared to Comparative Examples 2 to 3 and the Example. In Comparative Example 1, as shown in FIG. 7(a), the discharge is blown out. The flow velocity around the discharge gap in Comparative Example 3 is improved to the low-speed side compared to Comparative Example 1, but is on the high-speed side compared to Comparative Example 2 and the Example. In contrast, the flow velocity around the discharge gap in the Example is significantly improved to the low-speed side compared to Comparative Example 1 and Comparative Example 3. In the Example, as shown in FIG. 1, the wall portion 4 is arranged on the intake valve side, so that the flow velocity around the discharge gap is significantly suppressed. In addition, the flow velocity around the discharge gap in Comparative Example 2 is significantly improved to the low-speed side compared to Comparative Example 1 and Comparative Example 3. In Comparative Example 2, the flow velocity around the discharge gap is significantly suppressed by the connection portion 201 of the ground electrode located on the intake valve side. The flow velocity in Comparative Example 2 is suppressed to the same extent as the flow velocity in the Example. However, in the internal combustion engine 200 of Comparative Example 2, as shown in FIG. 8(a), the connection portion 201 of the ground electrode hinders the spray, and the area around the discharge gap becomes lean.

[0027] As shown in FIG. 10, the air excess ratio λ around the discharge gap in Comparative Example 2 has a maximum rich value that is leaner than those in Comparative Examples 1 and 3 and the Example. In contrast, the air excess ratio λ around the discharge gap in the Example has a maximum rich value that is significantly shifted to the rich side compared to Comparative Example 2. In Comparative Example 1 and Comparative Example 3, the air excess ratio λ around the discharge gap has a maximum rich value that is shifted to the rich side compared to Comparative Example 2. However, in Comparative Example 1 and Comparative Example 3, the maintenance time T1 at which the appropriate air excess ratio is obtained is short. In Comparative Example 1, as shown in FIG. 7(b), the spray around the discharge gap is easily swept away in a short time. In contrast, in the Example, the maintenance time T1 at which the appropriate air excess ratio is obtained is longer than those in Comparative Example 1 and Comparative Example 3. In addition, the maximum rich value of the air excess ratio λ in Comparative Example 2 is leaner than the appropriate air excess ratio at which stable ignition is possible, so that the maintenance time T1 does not exist in Comparative Example 2. In the Example, as shown in FIG. 4, the wall portion 4 is arranged on the intake valve side and the connection portion 22b of the ground electrode 22 is arranged on the exhaust valve side, so that the spray can be maintained around the discharge gap for a long time. Thus, according to the embodiment, compared to the comparative examples 1 to 3, it is possible to suppress the flow rate of the air current around the discharge gap and to maintain the spray around the discharge gap for a long period of time.

[0028] It is possible to configure a modified version of the internal combustion engine 1. For example, in the modified version, the tip position of the wall portion 4 is not limited to the same position P1 as the tip base end surface 22c, but may be any position included in the valid range according to the structures of the center electrode 21 and the ground electrode 22. As shown in FIG. 11, in the internal combustion engine 1 in the modified version, the tip position of the wall portion 4 is set in the axial direction of the spark plug 2 within a range (validation range) between a position P2 that is the same as the tip position of the center electrode 21 and a position P3 that is the same as the bottom surface position of the ground electrode 22. The position P2 that is the same as the tip position of the center electrode 21 is 3.5 mm away from the position P0 of the tip surface 23a of the housing 23. The position P3 that is the same as the bottom surface position of the ground electrode 22 is 6.5 mm away from the position P0 of the tip surface 23a of the housing 23. The validity range is a distance from the tip surface 23a of the housing 23 of 3.5 to 6.5 mm. As shown in FIG. 12, in the internal combustion engine 1 of this modified example, the tip position of the wall portion 4 is set within the valid range between the positions P2 and P3, so that the richest value B, the maintenance time T1, and the flow velocity of the airflow are improved compared to those of the comparative examples 1 to 3. If the tip position of the wall portion 4 is shorter than the position P2, which is the same as the tip position of the center electrode 21 (less than 3.5 mm), the flow velocity of the airflow becomes high, which is not preferable. On the other hand, if the tip position of the wall portion 4 is longer than the bottom surface 22d of the ground electrode 22 (more than 6.5 mm), the richest value B becomes lean and the maintenance time T1 becomes short, which is not preferable. In addition, the longer the wall portion 4, the more likely it is that pre-ignition (early ignition) will occur due to the high temperature of the wall portion 4. Therefore, by keeping the tip position of the wall portion 4 within the valid range, the high temperature of the wall portion 4 due to excessive lengthening is prevented. As a result, pre-ignition due to the high temperature of the wall portion 4 can be prevented, and knocking can be suppressed. According to this modification, it is possible to improve ignition performance and pre-ignition resistance. The distance of the tip of the center electrode 21 from the tip surface 23a of the housing 23 is not limited to 3.5 mm, and may be about 3.5 mm. Similarly, the distance of the bottom of the ground electrode 22 from the tip surface 23a of the housing 23 is not limited to 6.5 mm, and may be about 6.5 mm.In other words, the lower limit of the valid range is not limited to 3.5 mm, and the upper limit of the valid range is not limited to 6.5 mm.

[0029] As another modified example, the shape of the wall portion 4 may be expanded in the circumferential direction of the center axis CL of the spark plug 2. As shown in FIG. 13 and FIG. 14, in the internal combustion engine 1 in another modified example, the wall portion 4 is expanded in the circumferential direction of the spark plug 2, and the end face 42 is set within a range of ±90 degrees from the intake side reference line L1. For example, the wall portion 4 has one end face 42 formed at a position −90 degrees from the intake side reference line L1 and the other end face 42 formed at a position +90 degrees from the intake side reference line L1. The wall portion 4 is formed in an arc shape in the circumferential direction of the center axis CL of the spark plug 2. The tip position of this wall portion 4 is set at the same position P1 as the tip base end face 22c of the ground electrode 22. According to this other modified example, the wall portion 4 is formed so as to extend in the circumferential direction so as to cover the radial outside of the center electrode 21 and to cover the intake valve side, thereby improving the robustness of the flow velocity suppression effect when the position of the wall portion 4 is misaligned from the intake side reference line L1 when the spark plug 2 is attached. In addition, since the positional misalignment when the spark plug 2 is attached varies greatly depending on the internal combustion engine 1 and the thread configuration of the spark plug 2, the amount of expansion from the intake side reference line L1 is not limited to ±90 degrees and can be set to a predetermined position. In addition, in this other modified example, the tip position of the wall portion 4 is not limited to position P1 and can be set to a predetermined position within the valid range.

[0030] As another modified example, the wall 4 may be provided not only in the housing 23 but also in the cylinder head 6. As shown in FIG. 15, the wall 7 is provided in a portion of the cylinder head 6 between the spark plug 2 and the in-cylinder injection valve 3. The wall 7 is formed integrally with the cylinder head 6. The wall 7 is formed integrally with the ceiling of the combustion chamber 5. Like the wall 4, the wall 7 also extends along the axial direction of the spark plug 2, and its tip position is set within the valid range. According to this modified example, it is possible to obtain the same effect as the wall 4 formed integrally with the housing 23 of the spark plug 2. In addition, since the wall 4 is grounded to the cylinder head 6 side, it is not necessary to align the position of the wall 4 with the intake valve side when installing the spark plug 2. [Explanation of symbols]

[0031] 1. Internal combustion engine 2 Spark plugs 3. In-cylinder injection valve 4 Wall section 5. Combustion chamber 6. Cylinder head 21 Center electrode 22 Ground electrode 22a Opposite part 22b Connection 22c Tip base face 22d bottom 23 Housing 23a Tip surface

Claims

1. a spark plug having a center electrode and a ground electrode provided so as to face a combustion chamber, the spark plug being disposed between an intake valve and an exhaust valve; an in-cylinder injection valve that is disposed on the intake valve side with respect to the spark plug and injects fuel into the combustion chamber; an internal combustion engine including: a wall portion provided inside the combustion chamber between the center electrode and the in-cylinder injection valve, the wall portion extending from a ceiling side of the combustion chamber to a predetermined position along an axial direction of the ignition plug, the predetermined position is included in a range between a tip position of the center electrode and a bottom surface position of the ground electrode in an axial direction of the spark plug, The spark plug is disposed such that a base end of the ground electrode is located on the exhaust valve side with respect to the center electrode. An internal combustion engine characterized by:

2. The wall portion has a wall surface against which an airflow flowing from the intake valve side toward the exhaust valve side and toward the discharge gap collides.

2. The internal combustion engine according to claim 1 .

3. The predetermined position is set at the same position as the tip base end surface of the ground electrode in the axial direction of the spark plug.

3. An internal combustion engine according to claim 2.

4. The wall portion is formed in an arc shape in the circumferential direction of the central axis of the ignition plug.

4. An internal combustion engine according to claim 3.

5. The wall portion is integrally formed with the housing of the ignition plug or with the ceiling portion of the combustion chamber.

5. An internal combustion engine according to claim 1 ,

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